Antennas

Now there's something I didn't stop to think about regarding a tower as an antenna - thank you MJ! I'd forgotten that, at radio frequencies, a long conductor (such as a tower) grounded at one end, is not necessarily a short, but that it instead depends where in the wavelength the feedpoint is on the antenna, with them swapping from open to short and back every quarter wavelength. So, using a VNA at the transmitter end will also take the feedline into account and tell me how much of which reactance I need to add. (Of course, if I would have to climb it myself; I'm so glad I don't have a 630 foot tower! :confused:)
 
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On amplifiers, I was speaking with an older and very experienced Ham and he was telling me about his all solid state Elecraft with automatic tuning, SWR, ope, and short protection and more. I looked it up and it truly is a wonderful amp, BUT, at $7K, it's tad bit expensive. I had no idea that they got up that high.
 
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Yeah, they can get expensive. Grady told me he could design a broadband no-tune amplifier based on a broadcast tube. All you'd need to do is switch the band and it would be so broad over the whole band that it wouldn't require tuning. Band-flattening is his thing.
 
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Oh, in the 80s.
 
The tubes or transistors wouldn't be the problem - most of either component made today easily would work at frequencies up to at least the 10m band, likely even to 6m. For tubes, they'd almost certainly be used in a grounded grid configuration. The issue I believe that is difficult to resolve is the matching network needed to match the amplifier's output impedance, which will vary with frequency, to the feedline/antenna impedance. Tapped coils are generally used to switch among the bands and then the plate and load capacitors must be adjusted within each band. It might be possible to make the amplifier flat enough within many of the bands so tuning is not necessary, but the super-wide 80m band presents a more significant problem.

I love the idea of an ultra bandwidth amplifier that needs no adjustment, but I can't conceive of a way to do that. OTOH, what I don't know is vast and worse, this is not my area of expertise. I'd love to talk the Grady to better understand his idea., if that's ever possible.

I watched an hour long video of him being interviewed in 2019 about the HEBA installation in Webster, MA, and he certainly knows what he's doing. I found the station's location on Google Maps and may try to finagle a tour - it's an extremely interesting new antenna design, and the fact they're driving the mutual impedance of two closely spaced elements 90 degrees out of phase with 50 foot antenna and no radials, and it works, is a fascinating concept - I need to know more - I've never heard of anything like this.
 
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In simple terms, Jerry, it's about the ratio of the band vs: the operating frequencies. So, at 20m, the band is 14.000 MHz to 14.250 MHz. Compared to 14 MHz, 250 KHz is very small. It's relatively easy to flatten the bandwidth to pass 250 KHz when you are operating at 14 MHz. Of course, the curve will be a smiley, but it's within usable limits.
 
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MJ, we totally agree, and using your example, (14.35 – 14 = 0.35MHz). 0.35/14 shows that the 20m band is 2.5% of the lowest frequency wide; this small calculation gives us a way to view the width of our band in a quantifiable way - the ratio as you said. Now, take the 80m band (4 – 3.5 = 0.5MHz) and you have 0.5/3.5 = 14.3% wide — that’s a much bigger spread to flatten.

I have a Palstar AT2K ATU which I really like — it’s a top notch, expensive tuner. On most bands, I can set the roller inductor and capacitor settings for a band and they hold for the entire band. But on the 80m band, I have multiple different settings depending on where I am in the band. Without all those settings, I would not be able to keep the SWR below 2:1 across the band. I measured the SWR through the ATU and feedline to the antenna so I could see the SWR of the entire antenna chain, which is exactly what the ATU needs to tune. I took the measurement with my Vector Network Analyzer which displays the SWR, the real and imaginary values, and the actual Smith chart of the measurement, so I’m comfortable with my ATU settings. And in actually using different points in the 80m band, those settings work very well with minimal reflected power — it’s mostly all going out the antenna.

I’m not in any way saying one cannot flatten even the 80m band in an amp, especially by Grady, now that I’ve learned more about his accomplishments and heard him explain the HEBA. Rather, I am saying flattening a band as wide as the 80m is a significant challenge, and I’d love to learn more about how he’d approach it, because I would likely want to build one for myself.
 
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I was wondering if I might improve my G5RV in several ways:

1. The two wires that make up the dipole connect to a center glass epoxy plate that operates as their insulated center anchor and is also where the window line connects to them. I presume that the 450 ohm window line connects directly because that is the approximate impedance of the dipole in the center; is that correct?

2. My concern is that, on a multi-band antenna, the impedance almost assuredly changes with frequency, so that has to be a point of mismatch and reflections depending the band being used and where in the band the frequency being transmitted is located. Am I wrong?

3. Similarly to 2, above, at the other end of the window line (34 ft. away), the 50 ohm coax connects through a PL-239 mounted on another glass epoxy insulator and connects directly to the window line. For sure, the RG-8 coax has a nominal 50 ohm impedance, so that definitely has to be a mismatch. I use the ATU in the shack to match the transceiver to the coax, but I was wondering if I was to make 9:1 balun to place between that PL-239 and the window line, would I reduce reflections and therefore losses?

I've looked around for different G5RV designs and schematics and am surprised to find that all of them I located were all connected this way. I found a less effective smaller G5RV for use in smaller spaces, but it was connected similarly.

Do you think the work to make up a 9:1 balun, drop the antenna, install it, and raise it again is worth it? Or is it likely that this has all been done before and there's a reason this design has been this way for 74 years? I know Ham involvement is for experimenting, but I hate to repeat what's been done before when time is so limited. That's why I consult broadcast experts like you. :D
 
The G5RV is an amazing design that would appear to violate the principles we studied to get our licenses!

The balun is not necessary, even though it would appear to be unbalanced.

Edit: a 1:1 balun will prevent the coax shield from radiating and may be desirable to some. The balun would be placed at the transition of the coax to ladder line.
 
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I agree. Varney definitely gave it a lot of thought, experimentation, or both because it's element lengths are intermediates that, when combined with the 34 foot length of the window line, this antenna radiates well from the elements or the elements and feed line over so many bands, that's why I'm going to build one at twice its dimensions as soon as the weather lightens a bit and the snow melts. By doubling the size, I'll be able to use it on 160m as a balanced radiator without tying the two window line conductors together and connecting the coax shield to ground, which would also end up making the coax and my station part of the antenna system. I do currently have a 12 wind choke of coax at the transition to the window line to keep those voltages out of the coax and station surfaces which does what you were suggesting with the 1:1 balun.

I found another article that better explained how the G5RV antenna works, and as always, you are correct, again (and yes, that's driving me crazy!) But hey, there's got to be a reason that you're one of my elmers, right?

The other thing I'm pursuing at the moment is researching VHF rigs. I'm looking to buy a 2m/70cm rig to use for local communications and accessing the local repeaters. I'm currently doing that using Echolink, but I think a radio would be more fun. Mind you, I have used and will continue to use Echolink to communicate to other states where I could never raise them with a radio in these bands except with high sunspot activity, but for local comm, I'd like an actual radio.

I have to admit, I initially got my ticket for the drone stuff, and went to extra only because I could get access to all the bands. But I'm actually enjoying being able to chat with other Hams like yourself about these technical areas more than I expected. Fortunately, learning is still great fun! Thanks again for your counsel!
 
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My gosh, Jerry, you're such a great engineer that I would be embarrassed to even be considered an elmer to you! (For our readers: the term "elmer" refers to a ham operator who mentors newer hams).

I have to admit, I initially got my ticket for the drone stuff, and went to extra only because I could get access to all the bands. But I'm actually enjoying being able to chat with other Hams like yourself about these technical areas more than I expected. Fortunately, learning is still great fun! Thanks again for your counsel!

Ham radio is incredibly fun with so many different facets to the hobby!

I also use Echolink, btw.
 
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One of the considerations of the G5RV is that it takes into account the nominal impedances of feedline and elements at their respective lengths. The ladder line is a matching section and the length is critical (you know all this already, Jerry). But it does really illustrate the point that if you take the nodes, zero crossing points and standing waves into account you can do some amazing things. Another prominent Boston engineer told me a story of a local FM station:

The station chief went up to the transmitter site for the monthly inspection. As he drove up the hill, he noticed there was a big hole in the sky: the tower wasn't there! Yet, he was hearing the station on his car radio!

When he arrived, he found that the tower had indeed fallen and had neatly cut the transmission line in half. He ran into the shack and looked at the transmitter. It was functioning normally. All operating parameters were within tolerance as if nothing was wrong. The kicker was that no one even knew the tower was down or even when it fell. Nothing in the operational logs indicated anything strange at all.

It turns out that the tower had cut the transmission line at the exact length for a 50 ohm stub at the station's operating frequency. The transmitter was outputting full power into that stub, since for all intents and purposes, it could have been a dummy load. Furthermore, they also had a city grade signal over the city of license so they weren't even out of tolerance!

The engineer rushed back to the station and told the station manager who asked the engineer: "Can we leave it that way until Christmas is over? We're completely sold (all advertising slots were booked) and we can't afford to be off the air right now while they put up a new tower and antenna."

True story.

This reminds me of that antenna design I mentioned that was basically lumped reactances. As long as the rig sees a good load you're good to go.
 
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That is an amazing story about the Boston FM station! I am surprised the transmitter was still able to transmit an adequate field through a stub laying on the ground to reach its listening base. As you stated, it was really more of a dummy load than a radiator, but if it was a city grade signal, it was working. I presume they really did wait until after Christmas to make the repairs?
 
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Thank you for your kind words! Of course, it’s definitely better that you not know of my mistakes, of which the numbers are high enough to write a book. I still appreciate and benefit from your advice.

Since becoming a Ham, I’ve read the antenna section of the ARRL Handbook and the entire four volumes of their Antenna Handbook series as well as several other books on the topic that they sell – building my library. But there’s so much there to take in that it takes time to digest. And while I’ve gone back to a number of the topics multiple times and feel as though I’m developing a better feeling for the vagaries of antenna function, the sheer number of permutations that can exist can be confusing, at least for me. I feel as though I get tripped up mostly with the interactive aspect.

The basic tenets of impedance matching, SWR, Ohms Law, Smithcharts, etc., I know well. They are the same whether we’re talking transmitters or electrical grid power. On the utility side, the frequencies are much lower (though ELF transmitters do exist, especially by the military), and the power levels are much higher, but the theory is identical. Impedance matching for maximum power transfer is a given for all circuits regardless of application. SWR and power factor are just two different ways of looking at the same mismatch, so that part, stubbing, hairpins, gammas, etc., while not used in the power industry because, at 60Hz, their size would be gigantic, they’re still easily understood. For me, the new and sometimes difficult to assimilate aspects are those that are wavelength dependent (such as grounding by wavelength) and those caused by mutual coupling in one form or another, like the effects of other metal (gutters, metal poles, a parked car, etc.) too near an antenna; these aspects make things so much more complicated. So wavelength dependencies everywhere, mutual coupling, and parasitic affects are where I need to learn much more to develop an adequate feeling for these kinds of interactions, and I’m just starting out.

And that’s why your explanations and examples are proving so helpful. Understanding theory makes for a good foundation, but without actual experience, one doesn’t truly understand it, and more so, can’t make realistic and informed decisions on how to fix a problem or exploit an opportunity. I need much more experience and that’s why I need to build more of these antennas, modify them, and learn from the many failures that will likely be part of the process. Hopefully, advice from you and other elmers (yes, you really are) will get me there sooner and with less wasted time on the mistakes (and hopefully, less wasted money on burned out parts).
 
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Of course, if you want to know more about the vagaries of the power industry, perhaps I can be your elmer. :)
 
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@Peter Batah The RF stuff is very useful because I used to be an RFI investigator. I have tons of stories of how I tracked down where the signal from the local radio station was getting into someone's telephone, studio, and in one case, a police precinct's E911 recording system. I made a bundle doing that back in the day :). Taiwan has probably the dirtiest power supply I've seen (with Thai/Lao being a possible exception) and along with that and the computer hash, I'd been keeping my troubleshooting skills sharp, I'll tell you! Fortunately, things like chokes and other components are dirt cheap here. I got 2 good sized chokes for my USB cables and they can handle several turns each. About a buck and a half, USD.

Glad to hear the studio is coming along well and kudos to you for taking your time and doing it right. I'm guilty of rushing things sometime so I can get back to work. I still have cables and tools all over the place and I've done several mixes/masters nevertheless. That means that stuff is staying for awhile, lol.

TaiwanLiveTV: I usually go live (my time) Thursday and Sunday evenings. I also stream events that are happening and not on any particular schedule. Thanks for watching!
 
Kindly define "chokes" I told you that it wouldn't be long before I started picking your brain.
 
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A choke in an inductor that "chokes" off a portion of the RF spectrum. This is good for stopping RF from moving along a cable's shield and into the equipment.

RadioShack Snap-Together Ferrite Choke Core: Electronic Component Ferrites: Amazon.com: Industrial & Scientific

What I have is very much like this. You make a small tight coil of the cable you want to protect and then snap the choke around it so the wires coil though it.

If you look at good USB cables and good power supplies, the bulge in the cable is a choke.
 
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@-mjk- Ahh yes. Now that you mention it I have seen plenty of those over the years. I believe that they place them on VGA connectors as well.
 
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