This has only been tested on the UV-5R and UV-S9Plus. This may also work with other models.
Programming the channels of Baofeng radios is straightforward using CHIRP. That’s great, but it seems to me that a radio that requires a computer and a special cable to program is pretty useless in the field.
The general belief is that manual programming of these radios is difficult. I can understand why. I spent several hours fiddling around. I studied various tutorials and followed step by step instructions without success. Putting together bits I’ve learned with some experimentation, I have the following sequences that work without fail for me.
Programming these radios isn’t difficult, just a little odd in comparison to my Yaesu FT-60. The main difference is that to program a duplex channel on the Yaesu, you set everything up in VFO mode, transmit and receive frequencies, CTCSS, etc. Then in one step you transfer all of it into a memory channel.
With the Baofeng, you start out the same way, setting up everything in the VFO, but storing it is a two step process. The receive and transmit parameters are stored in two steps by storing to the same memory channel twice. This can be tricky but I found a straightforward way to do it that’s easy to remember. At the end I include a little “theory of operation” that might help you visualize what’s happening.
Before following either the SIMPLEX or DUPLEX procedures below, erase the contents of the memory channel you want to program. Let’s say you want to erase memory channel 5.
MENU (to enter menu mode) DEL-CH (select the DEL-CH function, use arrows or enter 28) MENU (to enter the delete channel function) Select the channel with arrows or numeric entry MENU (to perform the memory delete operation) EXIT (to exit menu mode)
Note that the DEL-CH and MEM-CH functions display a 3-digit channel number. If the number is preceded by CH, like CH005, then the memory is in use. If the channel number is plain like 005, the channel is empty and can be programmed.
Switch to VFO mode and the upper display (A), and enter the frequency you want to store. Then perform the following steps.
MENU (To enter menu mode) MEM-CH (select the MEM-CH function, use arrows or enter 27) MENU (to select the MEM-CH function) Select the channel using arrows or numeric entry MENU (to perform the memory store operation) EXIT (to exit menu mode)
Now switch from VFO to memory mode (VFO/MR), select your new channel and test it.
Remember to delete the channel you want to program, described in the first step above.
Switch to VFO mode and the upper display (A). Since we’re talking duplex, you’re probably trying to set up a channel for a repeater and will need to program offset and CTCSS. I’ll show all of the steps below.
First, enter the downlink frequency (the frequency you listen to). Let’s say it’s 146.685. Enter 146685 and it should display on the upper (A) VFO.
Let’s say the repeater has a negative offset of 600 kHz (input is at 146.085) and an input PL tone or CTCSS of 103.5 Hz, no downlink PL, no DCS. So your radio must transmit a 103.5 Hz tone to break the squelch on the repeater.
MENU (to enter menu mode) R-DCS (select R-DCS function using arrows or enter 10) MENU (to select the function) Use arrow keys to turn this off MENU (to perform the operation)
R-CTCS (select R-CTCS function using arrows or enter 11) MENU (to select the function) Use arrow keys to turn this off. (If your repeater has downlink PL and you want to try using it, then set this to the right frequency. I would leave it off for now and experiment later.) MENU (to perform the operation)
T-DCS (select T-DCS function using arrows or enter 12) MENU (to select the function) Use arrow keys to turn this off. MENU (to perform the operation)
T-CTCS (select T-CTCS function using arrows or enter 13) MENU (to select the function) Use arrow keys to select 103.5 Hz (or your repeater’s CTCSS tone frequency) MENU (to perform the operation)
SFT-D (select the shift direction function using arrows or enter 25) MENU (to select the function) Use arrow keys to select + or – shift/offset. Our example repeater is minus. MENU (to perform the operation)
OFFSET (select the offset function using arrows or enter 26) Enter the six digit offset. Note that the display is in Mhz! So the 600 kHz offset of our example repeater is 000600. MENU (to perform the operation) EXIT (exit menu mode)
Once you’ve become accustomed to programming the radio, some of the parameters above will already be set and can be skipped or just checked.
At this point you can test your VFO settings and make sure you can use the repeater. If all is working properly, the next steps will program the channel. (which you have previously erased as described in the first step above.) Let’s say channel 5 is your target. Do not skip any steps below.
MENU (enter menu mode) MEM-CH (select the MEM-CH function using arrow keys or enter 27) Select channel 5. It should display 005 not CH005. If it shows the latter, you failed to delete the channel as instructed in the first step above. You must delete the channel before attempting to program it. You can probably delete it now using the DEL-CH function, 28, but this has not been tested throughly.) MENU (to perform the store to receive memory operation) EXIT (to exit menu mode)
Momentarily press the *SCAN key. This engages “reverse mode” that will flip the transmit and receive frequencies in the VFO so that the transmit frequency is now displayed in A.
MENU (enter menu mode) MEM-CH (should already be selected and since it already has a receive frequency but no transmit frequency, will display CH005. This is correct.) MENU (to perform the transmit memory store operation) EXIT
Switch to memory/channel mode VFO/MR and test your new channel.
The above is the “magic sequence” that makes it easy. If you have everything set up in the VFO, and the target channel is already deleted, the sequence is:
MENU MEM-CH Select channel MENU EXIT *SCAN MENU MENU EXIT
Once accustomed to it, you can delete the channel, set up the frequency, PL tone, offset, offset direction, and program the channel in well under a minute.
Theory of Operation
Each memory channel has space for a receive frequency with its associated parameters, and a transmit frequency with its associated parameters. When you delete a channel, it clears both.
When you store a frequency and its parameters into an empty channel, the information gets stored in the receive space. When you store a frequency and parameters a second time to the same memory channel, that information gets stored in the transmit space. So it takes two steps to program a duplex channel because they have different transmit and receive frequencies.
Storing a simplex channel only requires the first step. You store the frequency and parameters once and they reside in the receive space. If you transmit on a channel that only has the receive space programmed, the radio will transmit on the receive frequency, and you have simplex.
In other words, if only the receive space of a channel is programmed and the transmit space is blank, then the channel is treated as simplex. It will transmit and receive on the receive frequency. If both receive and transmit spaces of a memory channel are programmed, the radio will operate duplex on the two different frequencies.
As one might guess, I love radio. I grew up surrounded by vacuum tube equipment and I love old vacuum tube radios. When my friend, Todd, mentioned that a 1925 vintage RCA Radiola 20 was coming into his possession, and he wanted to restore it, I was more than a little interested. Todd had known this radio since childhood, but had never seen it in operation.
Todd is a broadcast engineer with decades of experience operating, repairing, installing, and upgrading AM and FM broadcast radio transmitters. Radio is in his blood.
From 1973 to 1978, I ran a Hammond Organ repair business in Los Angeles, which found me constantly working on vacuum tube equipment, sometimes dating back to the mid-1930s. The Radiola 20 is ten years older than that. Technology improved very quickly in those days. The tubes used in the Radiola in 1925 were already obsolete by 1931. Since the Radiola operated on primary batteries (dry cells), it was designed for minimum power consumption. This radio will not help warm your sitting room, it runs cold. There was much to be learned here and we were both very excited.
While we were waiting for the radio to ship and arrive, we did research on every aspect of the radio we could find. It took a lot of digging on the Internet and we assembled pretty much everything there is to know and every bit of documentation and literature ever published about the Radiola 20. We found the owners manual and setup guide, RCA’s schematics, technical notes, service notes, and troubleshooting guide for radio repairmen, plus more service notes published by Gernsback. We also drew a modern style schematic using KiCAD. When the radio arrived, Todd found it to be in near pristine condition, like new, and all the original paperwork that came with it was there, including the warranty card. This was a museum quality radio perfect for taking modern color photos of the internals.
With all this information we collected on our hands, we decided to share it here in one place for others to use. A blog is not the ideal medium for this but it has the advantage of stability and permanance. While researching this information, we often ran into items that had been published on personal web sites many years before that no longer existed, dead links, and photos that were no longer hosted. It’s sad when that happens. Publishing on Blogger and a private blog should avoid this problem for as long as possible. With luck, one of them will be captured in the Internet Archive.
Part 2 – The Radiola 20 is Special
Lots of different kinds of radios were being made in 1924, 1925. The RCA Radiola 20 is special because it was the first radio that was both reasonably priced and easy to use. Early radios were difficult to tune and wouldn’t stay on frequency. They required constant fiddling with the controls. At this time, the first superheterodyne radios were appearing. They were easy to use but were large, required a lot of parts, a lot of power, and were priced from $500 to $700 — the price of a new automobile. That’s $7,300 to $10,220 in today’s dollars. Only the wealthy could afford that kind of money for a radio. The Radiola 20 sold for about $100 or $1,460 in today’s dollars. Still, a sizeable purchase, but a lot less than ten grand.
The Radiola 20 is a major engineering achievement and results from the melding of several aspects of radio technology. To appreciate this radio requires a basic grasp of those technologies. This understanding does not require technical knowledge, nor math. Since I don’t know the reader’s knowledge of these things, I will delve briefly into all the background and history leading up to radio, without getting too technical. I’ll also discuss some of the fascinating personalities involved in the development of radio — the birthing ground and foundation of modern electronics.
If you already know the history and different radio design types, you can skip the rest of this section and go to Part 3. If you don’t know, I will cover more detail here than is absolutely necessary, but it will give you a more complete picture.
What I find interesting is how quickly technology develops when consumer demand appears. This is easily seen in the development of radio. Since practical radio and the birth of modern electronics are really the same thing, and both depend on the vacuum tube, I’ll begin with that.
Vacuum tubes are based on a phenomenon called thermionic emission. When an object is heated to incandescence (glowing hot), electrons become free to move and easily leave the surface of the material. This effect becomes noticeable above 1,300 degrees Fahrenheit and was first noted by Bequerel in 1853. If you put an electric charge on an object in dry air, it will hold the charge for a long time. If you then heat the object to 1,300F, it loses the charge. Bequerel observed this but didn’t know why it happened.
Over the next 30 years, the thermionic effect was repeatedly forgotten and rediscovered by different researchers. It was rediscovered again by Edison in 1880 when he was trying to discover why his incandescent lamps seemed sensitive to polarity when run on direct current. When they failed, the positive end of the filament was darkened more than the negative end. The answer was that not all of the current was traveling through the entire filament. Some of the current was somehow traveling through the vacuum in the light bulb and striking the most positive end of the filament. He made special bulbs with an extra electrode inside to measure the effect and it’s named after him: the Edison Effect. He filed a patent for a voltage regulator that used the effect. Edison didn’t see any practical use for it, nor did he understand why it happened. By the way, this was the very first US patent for an electronic (not electrical) device.
Some experimentation with thermionic emission took place over the next 20 years, but not much. The next step was taken by Ambrose Fleming. Since the Edison Effect resulted in conduction in just one direction, a diode, he surmised this might be useful for the detection of radio waves. He was right. It worked better than a crystal, and vastly better than the mechanical cohering detectors used to detect spark transmitter signals in the early 1900s. He patented the diode in 1904. It consisted of a small heated filament, as in a light bulb, and a plate electrode. The device looked liked a small light bulb.
It’s interesting that thermionic emission was not understood until the advent of quantum physics. It was the subject of the 1928 Nobel Prize in physics. Even today, in 2018, physicists still argue over certain fine points that underlie thermionic emission.
At this time, around 1904, the only way to transmit radio waves was with high-voltage spark transmitters or large high-frequency mechanical alternators. These could only be used with Morse Code. There was no speech or music, no audio. Radio was used by the military, by ships at sea, and by radio amateurs (hams). Transmissions were noisy and broad so often only one transmitter in a region could operate at a time because of interference, and there was deliberate jamming. It was chaos.
The next step was a giant one. Lee De Forest was a great promoter of radio with a long and tumultuous career that began in the 1890s. In 1905 and 1906, he was desperately trying to come up with a radio detector that worked well and that didn’t run afoul of the multitude of patents that already existed. He was working with Fleming type diode tubes and wondered what would happen if he inserted a grid of wires between the cathode and anode, and connected the antenna signal to the grid. It worked and he was granted a patent for his invention in 1908. De Forest wasn’t much of a scientist and didn’t understand how it worked, but he had invented the first electronic amplifying device. A small voltage on the control grid could control a much larger current flowing from the filament to the plate electrode.
It is impossible to overstate the importance of this invention — a device capable of power gain. He called his invention the Audion. De Forest himself and many others greatly underestimated the importance of this invention. De Forest thought it might be useful for a few military applications. In fact, it became the fundamental device at the heart of radio, telephone, television, radar, sonar, computers, and countless devices of the electronic age until the transistor was invented in 1947. It took 25 more years, into the late 1960s, for the transistor to largely supplant the vacuum tube. Even today, some applications are best handled by vacuum tubes.
An important detail is that De Forest’s tubes were not made using a “hard” vacuum, but included a small amount of gas. Little attention was paid to impurities inside the glass envelope. Irving Langmuir surmised that many of the problems with triode tubes of the time, such as non-linearity, instability, and limited frequency response resulted from impurities in the envelope. His development of tubes with a hard vacuum inside and scrubbed of all impurities solved the problems. Fleming diodes could only handle low voltages. Langmuir’s could handle hundreds of thousands of volts. Langmuir’s triodes were linear, with higher gain, much higher frequency response, and could handle high voltage. The true vacuum tube was born. This work occurred around 1913 and triggered the rapid adoption of vacuum tubes in long-distance telephone amplifiers. The first transcontinental phone call happened in 1915.
Early radio (the electrical era of radio) had many fathers, including Maxwell, Hertz, Tesla, Marconi, De Forest, and others. Modern radio (the electronic era) had just one father, Edwin Armstrong. Every type of radio receiver in use today was invented by Armstrong. In 2018, one can say that every radio device you’ve ever used, from AM, FM, shortwave radios, to cellphones, garage door openers, or wireless thermometers, was either a superheterodyne or superregenerative design. Armstrong was a brilliant scientist and inventor.
While growing up, Armstrong had experimented with the flawed and gassy De Forest audion tubes and desired to gain a full scientific understanding of how they worked, which was unknown. By 1912 there was a basic scientific understanding of vacuum tubes, and it was around this time that Armstrong made his breakthrough invention of “regeneration”.
Audion tubes and early vacuum tubes were primitive and had low performance compared to later vacuum tubes. They had low gain (they amplified, but not by much) and had high interelectrode capacitance, which greatly limited performance. Armstrong discovered that using positive feedback resulted in stunning increases in gain. Instead of an amplifier stage producing a gain of 8 or 10, Armstrong obtained gains of 10,000 and more in a single stage, while using the mediocre tubes of the time. In 1913, Armstrong prepared demonstrations of his invention, scientific papers, and he applied for a patent. The patent issued in October of 1914.
In 1914, Armstrong was an undergraduate at Columbia University, studying electrical engineering. There, he presented the first scientific paper that fully characterized De Forest’s audion tube, complete with oscillographs showing the “characteristic curves”. It amazing that it took six years for someone to do that work. It’s also amazing that the manner in which Armstrong presented the data is the same way we illustrate device data for transistors today.
De Forest discounted Armstrong’s invention and filed a series of competing patents that essentially copied Armstrong’s claims, stating that he discovered regeneration first. Obviously, De Forest realized the importance of the invention. Competing claims were also filed by Alexander Meissner of Germany and Langmuir at General Electric. This was the beginning of many court battles that continued into the 1930s, with lawsuits, and countersuits, and two cases before the US Supreme Court. It seems that whenever there’s an important invention, this happens. In one of the early court cases, Armstrong and De Forest argued face to face. Armstrong easily demonstrated to the court that De Forest hadn’t the faintest idea how his audion tubes worked or how regeneration worked. Yet, the courts finally found in favor of De Forest, which today, is just stunning. The entire engineering community was shocked and appalled, but that’s how it ended up.
Another example of this kind of injustice was Marconi winning the patent battles and the title “Inventor of Radio”. He even won the 1909 Nobel Prize. Fortunately, this miscarriage of justice had a just but too-late outcome. It took 40 years for the courts to finally overturn the previous decisions in favor of Marconi and award inventorship to Nikola Tesla. After all, Tesla was using radio for remote control purposes when Marconi was but a child. However, it was too late and Tesla died penniless.
There are many more examples of such injustices. The takeaway is that the showman always wins. The person who wins is not the smarter person, but the person who is the better promoter, the better politician, the better financier, and the better people-person.
Armstrong’s invention of the regenerative radio was the right invention at the right time. One vacuum tube and a few parts, some of which could be made by hand, resulted in a high-performance radio. Anyone who was interested could afford to make one. What do I mean by high-performance? High-performance means a radio that can capture signals all the way down to the noise floor, the limit of what is possible. (There are modern digital techniques that can get quite a way below the noise floor using computers, but none of that was even dreamt of in 1914.)
What is the noise floor? As you make a radio receiver more and more sensitive, you run into an electrical noise limit that cannot be avoided. Natural and man-made electrical noise sets this limit. In the AM radio band, which is what we’re discussing, this noise floor is quite high. There are 15,000 lightning strokes on Earth every second, and each contributes to the noise. Cars, power lines, and electrical equipment radiate noise. Thermal noise in the antenna adds more. You can’t get around physics. The regenerative radio readily reaches this noise limit. You can’t do any better in terms of sensitivity no matter what kind of radio you design.
But, there are no regenerative radios made today, except by hobbyists for fun. This is because the regen has some major drawbacks. It takes skill to tune a regen. To tune in a signal, you have to operate two controls at once. Once it’s tuned, it’s unstable. Changes in temperature, drafts, wind moving the antenna wire, even your hands near the radio cause the tuning to drift. A regen needs constant readjustment. It was great for pioneer enthusiasts, but it’s not a good consumer product that can be set once and left to play for hours.
In addition to sensitivity, a radio must be selective. It must have a narrow enough bandwidth that you only receive the desired signal and not several others at the same time. If you’ve used a crystal radio in an urban environment with lots of radio stations, you know the problem. No matter what you do, you hear more than one station at the same time. If there is only one strong signal it’s okay. The regenerative radio achieves both high gain and high selectivity using almost no parts. This is great, but it has the instability problems mentioned above and other problems of a technical nature that I won’t get into here.
In 1916, Alexanderson patented the TRF radio (Tuned Radio Frequency). Without regeneration, tubes didn’t provide enough gain for a tuned circuit to be sufficiently selective to receive just one station. His idea was to cascade several stages of tuning and amplification — each feeding the next. This actually works well enough if you cascade five to seven such stages. The problem with the TRF is each stage must be independently tuned to the same frequency or you get almost no signal out the end of the chain. Tuning is extremely challenging and requires great patience. Tuning for a certain signal is a process of successive approximation. TRF radios were equipped with precision dials, so that the settings could be written down and found again later. The TRF works. It’s stable. Once tuned, it stays put. But it’s very user-unfriendly.
Many attempts were made to gang-tune the stages of a TRF. In other words, to drive all the tuning capacitors from a common shaft and a single knob. But it couldn’t be done. The mechanics and precise matching of the capacitors was impossible.
Part 3 – The Radiola 20
Which brings us to the Radiola 20. I haven’t explained the superheterodyne radio, also invented by Armstrong, because it’s not necessary for this story. All consumer AM and FM radios made since 1935 are superhets. The superhet solved all of the above problems, but required a lot of parts, a lot of power, and cost a fortune. In 1924, RCA wanted to come up with a radio that was consumer friendly and didn’t cost a fortune. Armstrong was on the RCA staff when the Radiola 20 was designed, so he surely had a hand in it. RCA came up with an efficient hybrid design that used only three stages of TRF plus a small amount of regeneration. Precision manufacturing of the tuning capacitors and mechanics enabled RCA to achieve usable gang-tuning of three stages of TRF using a single dial. This provided enough selectivity, but not enough gain, so the third TRF stage includes some regeneration. This trick was possible because they had the inventor of regeneration, Armstrong, along with his patents, on staff. Melding these two technologies was clever and effective.
The result is a radio using only four low-power X-99 tubes, that just sips battery power, that tunes frequency with a single dial. The second dial, called “Amplification” is the regeneration control. Since the tuning is TRF-style, the radio is stable. Tune it once and it plays all day. A fifth vacuum tube is an audio power amplifier that delivers nearly one watt of room-filling audio to the optional speaker. If you’re listening in headphones, you can unplug the fifth tube and save power. The Radiola 20 sold for $115 at introduction in 1925, dropping to $102.50. RCA sold 135,121 of these radios. That’s about $225 million in sales in 2018 dollars.
The Radiola 20 was a radio for the masses. It was affordable and anyone could learn to use it.
If you own one of these pieces of electronic history and are interested in the information we gathered, there’s a link in the comments below. The link enables you to download an 80 MB zip file containing everything we could find on the Radiola 20 and many other radios from that time period.
In the previous post I showed the loop antenna I’m using at present. Full wave loops will resonate on all harmonics so a 40 meter loop can also be used on 20, 15, and 10 meters, however, you can’t get a perfect match on all bands. What’s more, if the antenna length and feed impedance are adjusted for a perfect 1:1 match on one band, the other bands will suffer. I prefer to go with a “happy medium” approach, where all bands provide an acceptable match. With this antenna that means an SWR of around 2:1. That happy medium occurs, for this antenna, at about 115 ohms.
Below I’ll describe the matching device I built for this antenna and the resulting measurements. The objective for the feed is to match unbalanced 50 ohm coax to a balanced 115 ohm load. The feed shall also choke off or isolate common mode currents so the signal travels inside the coax and not on the shield.
A transmission line transformer configured to transform from one impedance to another is always an unun. It cannot provide isolation. If we also want isolation we must use two separate transmission line transformers in series. In this design, isolation is provided by a transmission line transformer configured as a 50 ohm 1:1 balun followed by a transformer that steps up the impedance. Loss in a well designed transmission line transformer is less than one percent so the combined loss of two in series is still negligible.
We begin with the impedance transforming unun using a T140-61 core and some 16 AWG magnet wire. Type 61 material is more expensive but I chose it for this transformer because it has very low losses from 3 to 30 MHz. This toroid works like an autotransformer so there is some magnetization of the core and low loss is, thus, important.
Ferrite is a very hard material so I like to cover toroids with one layer of Scotch 33+ to provide some padding for the wire. This ferrite is non-conductive and the edges are smoothed so the tape probably isn’t necessary but it makes me feel better.
Next, I cut small strips of the fiberglass tape shown above to make the transmission line as shown below. The tape has a silicone adhesive, is rated to over 500 degrees F, and most importantly it doesn’t stretch. Taping the wires like this makes it much easier to wind the toroid core while keeping the conductors side-by-side.
Below is the finished toroid with eight trifilar turns. These will be wired in series and used like an autotransformer with a 1.5 to 1 turns ratio, giving a 2.25 to 1 impedance transformation. In other words, this configuration is a 2.25 to 1 unun, transforming 50 ohms to 112.5 ohms.
Next we use an FT240-43 toroid and a two conductor transmission line made from 14 AWG magnet wire to make the isolator or 1:1 balun. The objective here is to come up with the highest common mode impedance using the least amount of wire. I chose type 43 material which is cheaper, has much higher permeability, and higher loss, for the following reasons:
We want to minimize inter-turn capacitance in order to keep the self-resonant frequency of the balun as high as possible. That means we want as few turns as possible. Type 61 material has a permeability of 125. Permeability of type 43 is 850, allowing fewer turns to reach a certain inductance.
Type 43 material has higher loss but in this application it doesn’t matter — it’s actually a benefit. Core magnetization in this type of 1:1 balun is theoretically zero. If there’s no core magnetization then there’s no loss. The only core magnetization that might occur results from the small common mode currents that we’re trying to get rid of. If those disappear as heat in the core, so much the better. Core heating in this kind of balun only becomes significant at power levels well beyond 1500 watts so it can be ignored.
Type 43 material costs much less than 61, which is nice, but didn’t drive the choice.
Below is the finished isolator with six turns, connected to the 2.25:1 unun, ready to be installed in an outdoor rated housing. Note the crossover. The crossover has no effect on the performance of the transformer and provides for the input and output wires to come out on opposite sides, which is handy in this case.
Below are the two transmission line transformers installed in a Bud NEMA4 waterproof polycarbonate box. All hardware is 18-8 stainless.
Shown below is the first test setup. A 115 ohm 1% resistor is fixed across the balanced output terminals and the analyzer was swept, taking 500 samples from 3 to 30 MHz. SWR measured nearly flat with 1.01 at 3 MHz, rising to 1.09 at 30 MHz. The photo shows the analyzer at 14.1 MHz reading 51 ohms, exactly what one would expect with 115 ohms on the output terminals.
Below is a 500 sample sweep from 3 to 30 MHz of the final installation. I originally made the antenna using 143 feet of wire, which in my experience is a little long so I can trim it. Because this installation has one leg of the triangle parallel to and 10 feet off the slope of the hill behind my house. The antenna resonated about 3 percent low. My calculation said to shorten it by 5 feet, which brought the antenna to exactly where I want it.
The antenna can be used on all four bands without a tuner.
Look for me at night around 7070 kHz on PSK31, Contestia, Olivia, Thor, PSK63F, and Hellschreiber modes. 73 de KW2P.
This QTH is problematic for antennas. The lot is very narrow, just 25 feet. The house is tall, long, and narrow, just 18 feet wide. It’s kind of like living on a sailboat. The attic is impractical to access. There is an attic trap door but it’s too small for an adult to fit through. There is no back yard, just a steep drop behind the house and the front door opens to the sidewalk. Ground radials are not an option. However, there is a tall tree, part way down the hill just behind the house.
My favorite band is 40 meters so that was the main target. I considered several antennas including an end-fed wire, an off-center fed wire, a vertical dipole, a C-pole, and a loop. Modeling the various antennas with NEC2, the C-pole for 40 meters looked promising. It’s shorter than a dipole and needs no radials but it’s a single-band antenna.
I decided to go with my favorite antenna, the full wavelength loop. The question was if 143 feet of wire could be made to fit. Loops work well, are easy to tune, have high radiation efficiency, and work on all harmonics. Using my laser measure I found that there was just enough space for a triangle running from the upstairs window, to the far branch of the tree (40 feet), then down to an insulator, and back up to the feedpoint at the window.
Using my line launcher and a one ounce lead sinker, I shot non-conductive nylon monofilament line through the tree. As expected, it overshot and landed across the power lines behind the house. I slowly pulled the line back off the power lines and lowered the sinker to the ground. There I attached paracord and hauled it up, over the tree, and to the house. With the paracord I hauled into place the 18 AWG copperweld wire for the antenna. Shown below is the configuration.
This loop performs very well. Loops almost always do. Below are some plots showing the nearly omnidirectional pattern. Polarization is about 80 percent vertical and 20 percent horizontal.
After a long hiatus, I’m back on the air. QTH: Clarksburg, West Virginia, Harrison County, locator EM99tg. Primary mode is digital. Antenna is a 40 meter vertically oriented triangular loop, which gives good performance on 40, 20, 15, and 10 meters.
I’m also working with my daughter, KC7BNH, in Coeur d’Alene, Idaho, to help get her back on the air as well.
In a perfect world we’d have full-size 160m Beverage antennas fanning out like the spokes of a wheel from a centrally located shack, and the feedpoints would all be located near the shack. Most of us don’t have the necessary 80 acres of land so the feedpoints to our Beverages often end up far away and must be fed through long runs of coaxial cable.
For example, let’s say I want to install a unidirectional Beverage aimed northeast and the shack is located in the northeast corner of the property. The Beverage wire must extend 800 feet towards the southwest of the shack, the termination resistor must be located at the shack end and the feed is all the way at the southwest end. I have to run the 800 foot Beverage wire plus 800 feet of coax to bring the signal to the shack. You can’t do anything to change the geometry of this problem but I’ll show here how the coax can serve both as the feedline and the Beverage wire.
Sometimes we build reversible Beverage antennas that require long runs of coax plus distant relay boxes to perform the required switching. The coax is often buried, making it susceptible to physical damage, especially on farmland, and subject to contamination from constant exposure to moisture. Buried coax can be punctured by nearby lightning strikes. Locating the damage and making repairs can mean replacing the entire run of coax.
THE CLASSICAL BEVERAGE ANTENNA
EMBODIMENT ONE: The basic idea.
The basic design concept is shown in the following diagram. The additional embodiments below use the same technique described here. The coaxial cable is suspended above the ground and the outer skin of the coax shield serves as the “wire” of a classical Beverage antenna. The tiny currents induced in the antenna wire (the outer shield of the coax) are referenced to earth ground and are presented to the 450 ohm primary of matching transformer T-1, exactly as in the classical Beverage shown above. T-1’s secondary connects to the shield and center conductor of the coaxial cable feedline, which happens to be the same coax that forms the active element of the antenna. The RF signal injected by T-1 propagates inside the coax to the opposite end (the terminating resistor end) of the antenna. Note that T-1 is an isolation transformer with two independent windings.
At the terminating resistor end of the antenna, we are faced with the problem of extracting the signal we want, which is propagating inside the coax, while preventing the RF currents traveling on the outer surface of the coax shield from flowing beyond this point. This is a common problem in antennas that is solved by means of a balun (L1). However the problem in this case is bigger than we usually face with ham antennas. In the case of a Beverage antenna we are likely working at 1.8 MHz, which means the inductances required are large. We are also working with an impedance that is 10 times higher than what we normally work with so the required inductances are that much higher still. (Remember that the balun is concerned with blocking the outside surface currents at the 500 ohm impedance of the Beverage. The 75 or 50 ohm internal impedance of the coax is irrelevant as far as the balun is concerned.)
The rule of thumb for baluns is to present an inductive reactance that is 10 times the impedance we’re working with. For 50 ohm coax you aim at 500 ohms. In this case, the impedance of the Beverage wire is 500 ohms so we’d like to see the balun present 5000 ohms of reactance. At 1.8 MHz, this is a relatively huge amount of inductance–about 450 uH. However, working in our favor is the fact that losses at the terminating resistor end of a Beverage have somewhat less effect on signal output than losses at the feed end of the wire so we can fudge down on the 5000 ohm requirement and call it 2500 ohms. But even so, we are still looking at 225 uH. Suitable baluns are discussed at the end of the article.
EMBODIMENT TWO: Feed it anywhere.
It’s probably obvious to some readers that since the coaxial cable (in terms of the signal traveling on the inside) is untuned, its length does not matter. The coax does not have to continue for the full length of the Beverage antenna as shown above and the feedline can be brought off at any point. The advantages of this are clear. Instead of worrying about where the endpoints of the antenna are with respect to the shack, all the antenna has to do is pass nearby the shack and the feed is brought off at the nearest point. Several Beverages covering different directions can be installed and as long as they pass near the shack at some point the feedlines can all be very short.
EMBODIMENT THREE: Reversible KW2P Beverage
This variation may also be obvious to some readers. Note that I have never built and tested this variation but I have no doubt that it would work fine. I’m hoping to find and acquire a piece of land large enough to try this out.
Reversible Beverages invariably have relay boxes at the far ends of the antenna to switch between feedline and terminating resistor in order to reverse the antenna pattern. The concepts shown above in embodiment two demonstrate bringing the feedline off at any point along the antenna’s length. The same method can be employed to bring the terminating resistor to certain points along the antenna or all the way to the opposite end. Directional switching can take place in a single box located at either end of the antenna or at certain points along the antenna’s length. Switching directions is simply a matter of swapping the feedline for the resistor at L1 and L2.
Now comes a question: Note that in the first two embodiments, the length of the coaxial cable(s) did not matter. In this third embodiment, I assume that the lengths of coax are halfwave multiples (electrical length), taking into account the velocity factor of the coax (inside). The reason for the 1/2 wavelength multiples is to ensure that the resistance of the termination resistor is reflected accurately at the other end of the coax as a pure resistance. However, if the impedances of the Beverage wire / matching transformers / coaxial cables are all matched closely enough that SWR inside the coax is low, the lengths should not matter and it should not be necessary to hold to 1/2 wavelength multiples. This remains to be tested empirically.
One thing to consider when building Beverages is ease of construction and low cost of components like transformers and baluns because these components are frequently destroyed by lightning. A Beverage is a very long wire so lightning strikes hundreds of feet away can still induce plenty of current to vaporize baluns and transformers, puncture insulation, etc. Spark gaps at strategic locations are inexpensive, low-tech, and well worth the effort. Each support should be equipped with a ground rod and spark gap. Nothing will save you from a direct or very close hit but spark gaps will protect against most of the nearby hits. It is also a good idea to frequently inspect the antenna and spark gaps. A spark gap that was vaporized by yesterday’s storm won’t protect you today.
Matching transformers cannot be made lightning resistant but fortunately they are cheap and easy to make. If you’re going to make one, make several at a time. You’ll probably need them.
There are several ways to build a suitable balun for this antenna. The type of balun needed in these designs is actually an unun (unbalanced-unbalanced), also called a “current balun”, or a Collins balun. What the balun is doing is it simply uses inductance to choke off or block the antenna currents traveling on the outside of the coax, keeping them “up on the antenna wire” and not traveling down the feedline into the shack.
Construction parameters to consider are:
1) Keep inter-turn capacitance as low as possible to keep the self-resonant frequency of the balun as high as possible so the antenna can be used on 80m and even 40m if desired. If operation on bands other than 160m is not planned then self-resonant frequency is not that important as long as f0 is well above 2.0 MHz.
2) Baluns can be and should be designed with lightning surges in mind. A direct hit near the balun will likely destroy it no matter how it’s constructed but most lightning surges will come from induced current from nearby strikes that a properly made balun can withstand. The more surge resistant you make the balun, the less often you will have to replace it. Making the balun more lightning resistant mainly consists of making the balun physically large and distributing the surge voltage across the whole balun so that it doesn’t arc over between turns. The best way to achieve this is with a long solenoid-shaped coil that keeps the first and last turns as far away from each other as possible and distributes the voltage evenly. This also minimizes inter-turn capacitance mentioned above.
Some Numbers for Solenoid Baluns
Here are some numbers for suitable baluns
Coax Len Ft
Coax Len Ft
Coax Len Ft
Coax Len Ft
** A single layer of RG-6 on a 4.5 inch form is impractical. One way to cut down on coil length and reduce the amount of coax in the balun is to wind a 2-layer coil. A conventional 2-layer winding that runs to one end, then reverses back over the first layer gives a neat-looking result but is a bad idea. It brings the first turn very close to the last turn and defeats the main reason for winding a solenoid instead of a toroidal or Collins balun: high arc-over resistance. However you can quasi-scramble wind it to keep most of the benefits and reduce the length of the coil. Wind two or three turns on the coil form, then cross back and wind two or three turns in a second layer over the first three turns. Then put three more turns on the form, cross back and put a second layer on those, and so on. It’s not as neat looking but it creates a 2-layer coil that keeps almost all the benefit of a single-layer coil.
Coax losses at 2.0 MHz are shown below. Values are for 150 feet and SWR of 1.5:1. Except for RG-174 miniature coax, losses at 2 MHz are so low they can be ignored.
A Collins balun is very easy to make and consumes about half the amount of coax as a solenoid. However, unlike a single-layer solenoid it offers little resistance to arc-over from lightning.
To make a Collins balun, simply wind the coax lightly on a round form, all in one spot, then slide the coax off the form and tape or wire-tie it into a ring. Unless the coax is very limp and pliable, an extra pair of hands from a helper is useful for this step. A slightly tapered form can be handy for sliding the coax off. Small plastic wastebaskets or barrels often have a good shape.
30 turns of RG-6, 12 inches in diameter, yields about 450uH and consumes 94 feet of coax (in contrast to 170 feet for the same inductance on a solenoid)
Toroidal baluns can also be used with these antennas. These antennas are receive-only so there are no issues of saturation or power handling. The target inductance is 450 uH so we want to use the highest permeability ferrite that will handle the frequencies of interest. Good old Type 43 is probably the best choice. It has a permeability around 850+ and handles 160, 80, and 40 meter frequencies. An FT-240-43 core yields 450 uH with 20 turns. The problem is the window of this core is 1.4 inches in diameter so it will only accommodate 12 turns of RG-6 (0.332″ dia.). Stacking two cores reduces the required number of turns to 15, but that’s still too many. Since the balun is really just an inductor, and inductors in series add together, we can get even closer to the goal with two 225 uH baluns in series. This gets the number of turns required down to 13 on each core which is still more than the 12 turns that will fit, but close enough.
Building the balun with RG-59 (0.242″ dia.) coax solves the window area problem because 19 turns fits easily through a 1.4 inch window. And only one core is needed instead of two, which may be a concern because FT-240-43 cores cost about 10 dollars apiece.
The best solution in my opinion is to use RG-174. It only takes about a couple of feet of RG-174 for 20 turns. The added loss of a couple feet of RG-174 can be ignored.
While a toroidal balun will work fine it provides almost no lightning protection and be prepared to replace ones damaged by lightning.
I hope these Beverage designs can be of use to other hams, make your installations easier to build, easier to maintain, cheaper, and more reliable.