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Can you guys settle an argument for me?

Josh380

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I have recently come to discover that the Solarcon-99 (A-99 replacement) is a DC grounded antenna. My radio guy (whose shop will go unmentioned, but is well known) seems to disagree with me and states "The A-99 is not a ground plane antenna". But if you google how to determine whether your antenna is a DC Grounded antenna (continuity on a multimeter shows a short at the antenna's coaxial connection), vs an antenna that is not DC Grounded (no short at antenna coax connection), and then use this test on the Solarcon-99, the answer is quite clearly that the antenna is, in fact, a DC grounded antenna.

Now, is it me that's confused here, or him? My understanding was that electrical grounding was different from RF grounding. He had suggested installing a coaxial air core balun near the base of the Solarcon-99. I may have made the diameter of the air core balun too small, but the SWR reading on my NanoVNA went from a 1:1.13 (1 to 1.13 to avoid confusion) to an unusable 3.0+. I am not sure yet if it was because of the small diameter of the air core balun I made, or of the design of the antenna and the air core balun concept causing a mismatch. Some argument has suggested quite vaguely that something must be "wonky with my setup, because the air core balun should work" (gee, that's helpful), while other argument has suggested that installing a coaxial air core balun with the Solarcon-99 will cause the SWR to skyrocket, BECAUSE it is a DC Grounded antenna.

What's got this argument started was all over RF coming back down the shielding to my radio (RCI 2970N2 which has an integrated amplifier so there should be no amp mismatch). This is sending RF into unwanted portions of my radio, such as the aftermarket IF Tap that was installed. This is then bleeding onto my SDR, which as some of you may know, is not a good thing. The IF Tap is specifically designed to shutdown on TX, and it is doing just that. It's obvious by the red indicator TX light on the board, and the noise floor completely dropping out (on my sdr program), when transmitting.

Not knowing that my antenna was a DC Grounded antenna, I installed a gas discharge lightning arrestor at the antenna input, then grounded that to my 8' copper ground rod via a solid copper wire. Since the discovery, I purchased a PolyPhaser IS-50UX-C0, which from what I've read, is better suited for a DC Grounded antenna, and is installed at the ground rod, rather than near the base of the antenna. The radio chassis is also grounded to that same ground rod.

I'm hoping that installing the correct lightning arrestor (the Polyphaser) will provide better static bleed off for lightning protection, as well as eliminating the issue of RF coming back down the coax. I could be completely wrong too. I'm not sure if there are different methods for eliminating RFI on a DC Grounded antenna vs a non DC Grounded antenna.

Before anyone says anything, I always double check my coax connectors for proper installation, and that there are no shorts in the line before I put it into service. I've already eliminated that possibility. Not to mention my NanoVNA will quite distinctly show a short in the line if one is present. There is none.
 
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Josh380

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It should also be noted that the currently installed gas discharge lightning arrestor is capable of handling only 50 watts..much less than the output of my RCI2970N2. Oops.
 

prcguy

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The A99 is not a "ground plane" antenna, its an end fed half wave with matching transformer in the base. A ground plane antenna would have ground radials or some other type of artificial ground surface beneath it for the vertical element to work against.

The fact that an antenna shows a short across the coax has nothing to do with it being a ground plane and most ground plane antennas do not show a short across the coax. the A99 shows a short due to the design of its internal tapped matching transformer.

Lightning arrestors don't care if your antenna has a short across the coax and there are no specific arrestors for that kind of antenna.
 

Josh380

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I meant simply that gas discharge arrestors allow static to buildup to a certain point until it reaches max, then gas discharges, then after awhile, things are reset and good to go. From what I've read, there are a limited amount of discharges a gas discharge arrestor has before it just plain won't work anymore.

The fact that it is only capable of handling 50 watts of input power is a little more concerning to me. This is not a post about lightning suppression. The PolyPhaser arrestor (not gas discharge) works off the concept that a strike will follow the coax shielding, if a strike occurs. This is why it's installed at the ground rod. We all know that static buildup is a precursor to a strike. According to Solarcon, since the Solarcon-99 IS a DC Grounded antenna (again, there IS CONTINUITY at the antenna coax connection), a lightning arrestor is not required, because any static that builds up on the antenna is shunted to ground via the COAX shielding. I'm not taking any chances with a $600 radio. I know the safest thing to do is disconnect, but if I'm away, and can't disconnect, it would be nice to have some insurance. Since the PolyPhaser arrestor claims to "protect equipment from MULTIPLE STRIKES" (uh..ok), that's good enough insurance for me.

What I am trying to figure out is how to eliminate RF from coming back down the line. My thinking was because this antenna is a DC Grounded antenna, the "air core balun" concept might not work with this particular antenna...the SWR results from said air core balun certainly showed that the antenna didn't like it. Like I said though, I don't know if I made it too small, and that's why my SWR skyrocketed, or of just an air core balun in itself, whether correct in diameter or not, is the reason.
 
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prcguy

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A commercial repeater or TV/FM broadcast site that is designed and built from the ground up can often survive a direct lightning strike and survive many times. A home installation will not and even with a Polyphaser in line your radio and most of your home electronics will be destroyed. That's just how it works.

Its better to know and understand this and take meaningful precautions before a lightning storm like disconnect everything, and even then there is no guarantee. Not that long ago a friend here in So Cal (Orange County in fact) where lightning storms are fairly rare, got a direct hit and one of his radios completely disconnected from power/antenna sitting up on a shelf got destroyed. If lightning hits your antenna and the feedline is going into the house, even a mic cable connected to a radio can pick up enough energy to destroy the radio.

For a gas discharge arrestor to handle more power than 50 watts it will need to fire at a fairly high voltage and that is usually more than it takes to protect a receiver. For example full legal limit for amateur is 1500 watts and that would be about 274 volts RMS or about 387 peak volts. Since radios and antennas are not exactly 50 ohms and a higher impedance will result in higher voltage, a lightning arrestor has to pass more than 387 volts to withstand 1500 watts of RF. So if you use a high power rated lightning arrestor will your radio handle 400 or 500 volts coming down the coax before the arrestor does its job? I don't think so.


I meant simply that gas discharge arrestors allow static to buildup to a certain point until it reaches max, then gas discharges, then after awhile, things are reset and good to go. From what I've read, there are a limited amount of discharges a gas discharge arrestor has before it just plain won't work anymore.

The fact that it is only capable of handling 50 watts of input power is a little more concerning to me. This is not a post about lightning suppression. The PolyPhaser arrestor (not gas discharge) works off the concept that a strike will follow the coax shielding, if a strike occurs. This is why it's installed at the ground rod. We all know that static buildup is a precursor to a strike. According to Solarcon, since the Solarcon-99 IS a DC Grounded antenna (again, there IS CONTINUITY at the antenna coax connection), a lightning arrestor is not required, because any static that builds up on the antenna is shunted to ground via the COAX shielding. I'm not taking any chances with a $600 radio. I know the safest thing to do is disconnect, but if I'm away, and can't disconnect, it would be nice to have some insurance. Since the PolyPhaser arrestor claims to "protect equipment from MULTIPLE STRIKES" (uh..ok), that's good enough insurance for me.

What I am trying to figure out is how to eliminate RF from coming back down the line. My thinking was because this antenna is a DC Grounded antenna, the "air core balun" concept might not work with this particular antenna...the SWR results from said air core balun certainly showed that the antenna didn't like it. Like I said though, I don't know if I made it too small, and that's why my SWR skyrocketed, or of just an air core balun in itself, whether correct in diameter or not, is the reason.
 

Josh380

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A commercial repeater or TV/FM broadcast site that is designed and built from the ground up can often survive a direct lightning strike and survive many times. A home installation will not and even with a Polyphaser in line your radio and most of your home electronics will be destroyed. That's just how it works.

Its better to know and understand this and take meaningful precautions before a lightning storm like disconnect everything, and even then there is no guarantee. Not that long ago a friend here in So Cal (Orange County in fact) where lightning storms are fairly rare, got a direct hit and one of his radios completely disconnected from power/antenna sitting up on a shelf got destroyed. If lightning hits your antenna and the feedline is going into the house, even a mic cable connected to a radio can pick up enough energy to destroy the radio.

For a gas discharge arrestor to handle more power than 50 watts it will need to fire at a fairly high voltage and that is usually more than it takes to protect a receiver. For example full legal limit for amateur is 1500 watts and that would be about 274 volts RMS or about 387 peak volts. Since radios and antennas are not exactly 50 ohms and a higher impedance will result in higher voltage, a lightning arrestor has to pass more than 387 volts to withstand 1500 watts of RF. So if you use a high power rated lightning arrestor will your radio handle 400 or 500 volts coming down the coax before the arrestor does its job? I don't think so.

Again. This is not about lightning suppression. 50w INPUT MAX from the RADIO to the arrestor. Does anyone not see this as a problem?

Please read my post again carefully. I'm trying to figure out WHY RF is coming back down my coax to the radio. The amplifier mismatch is eliminated because the amplifier goes with the radio.it is one.

My pl259's are good. Antenna match is good. Coax is good. What is my problem? Grounding, right? My grounding issue involves the arrestor because it is grounded with the DC grounded antenna. (DC continuity IS PRESENT at the antennas coax connector aka so239 input to antenna)
 
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prcguy

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Sorry, I just read your first post again. An A99 antenna has little to no common mode rejection and can light up the mast and coax with RF, that's what they all do. An air core balun or some coax would up is a very poor RF choke at best and most of them do nothing. You have to have the exact amount of turns at the right spacing to target 27MHz and you really need some test equipment to get it right. An then you will have a poor RF choke. Use a ferrite loaded choke instead that actually absorbs RF instead of bouncing it around.

What may have happened is your air choke has added possibly a resonant length of coax and changed the tuning slightly on the antenna like adding a tuned radial. I have seen this before and I've also seen an A99 with a great match on a 5ft mast change for the worst on a 10ft mast and so on, whatever is attached to them can skew the match.

Grounding doesn't automatically fix anything and in many cases it brings in noise problems. Grounding an antenna is just another path RF can take but RF doesn't automatically go to ground, it divides among all conductors based on the impedance they present to the source of RF, in this case the antenna. Adding a ground wire to an antenna presents another RF path and you get whatever good or bad that path causes. Grounding your coax in a new point mid way will possibly change the SWR on an A99 since the coax is sort of a tuned part of that type antenna. If your lucky and your mast is a low impedance conductor at 27MHz then changing coax length or adding ground wires will have less effect than if the mast is a high impedance at 27MHz and the ground wire or new ground point for your lightning arrestor is a lower impedance path, which can now change the SWR. If you use a different type of antenna that doesn't have the RF problems the A99 has you wont have these problems.

On the 50 watt rating for the lightning arrestor, that would be a low power or receive only arrestor and those are fairly common. Its what you really want if you have a low power transmitter or just a receiver because the gas tube will fire and shunt voltage on the coax at a lower level than a higher power rated arrestor. The trade off is what I mentioned in the last post, at some point you don't really have much protection if the arrestor will allow a kW or more to pass through it.

How much power are you running? If its a fairly stock CB then a 50 watt rating is plenty.


Again. This is not about lightning suppression. 50w INPUT MAX from the RADIO to the arrestor. Does anyone not see this as a problem?

Please read my post again carefully. I'm trying to figure out WHY RF is coming back down my coax to the radio. The amplifier mismatch is eliminated because the amplifier goes with the radio.it is one.

My pl259's are good. Antenna match is good. Coax is good. What is my problem? Grounding, right? My grounding issue involves the arrestor because it is grounded with the DC grounded antenna. (DC continuity IS PRESENT at the antennas coax connector aka so239 input to antenna)
 

Josh380

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Sorry, I just read your first post again. An A99 antenna has little to no common mode rejection and can light up the mast and coax with RF, that's what they all do. An air core balun or some coax would up is a very poor RF choke at best and most of them do nothing. You have to have the exact amount of turns at the right spacing to target 27MHz and you really need some test equipment to get it right. An then you will have a poor RF choke. Use a ferrite loaded choke instead that actually absorbs RF instead of bouncing it around.

What may have happened is your air choke has added possibly a resonant length of coax and changed the tuning slightly on the antenna like adding a tuned radial. I have seen this before and I've also seen an A99 with a great match on a 5ft mast change for the worst on a 10ft mast and so on, whatever is attached to them can skew the match.

Grounding doesn't automatically fix anything and in many cases it brings in noise problems. Grounding an antenna is just another path RF can take but RF doesn't automatically go to ground, it divides among all conductors based on the impedance they present to the source of RF, in this case the antenna. Adding a ground wire to an antenna presents another RF path and you get whatever good or bad that path causes. Grounding your coax in a new point mid way will possibly change the SWR on an A99 since the coax is sort of a tuned part of that type antenna. If your lucky and your mast is a low impedance conductor at 27MHz then changing coax length or adding ground wires will have less effect than if the mast is a high impedance at 27MHz and the ground wire or new ground point for your lightning arrestor is a lower impedance path, which can now change the SWR. If you use a different type of antenna that doesn't have the RF problems the A99 has you wont have these problems.

On the 50 watt rating for the lightning arrestor, that would be a low power or receive only arrestor and those are fairly common. Its what you really want if you have a low power transmitter or just a receiver because the gas tube will fire and shunt voltage on the coax at a lower level than a higher power rated arrestor. The trade off is what I mentioned in the last post, at some point you don't really have much protection if the arrestor will allow a kW or more to pass through it.

How much power are you running? If its a fairly stock CB then a 50 watt rating is plenty.

My RCI 2970N2 does about 210w on SSB, which is where I mostly operate. I was specifically curious if because that arrestor is rated at only 50 watts, if it's possible that it's causing the additional power to feed back to the radio.

The antenna is currently on a 10ft galvanized aluminum top fence post.
 
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prcguy

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If the arrestor is working properly then it may be firing and shorting out the coax when you transmit. And it may be shorting only on voice peaks since you are using SSB. That would make your SWR meter go crazy and cause your signal to sound chopped up to others. As far as "feeding back to the radio" only in the sense that high SWR is reflected power.

My RCI 2970N2 does about 210w on SSB, which is where I mostly operate. I was specifically curious if because that arrestor is rated at only 50 watts, if it's possible that it's causing the additional power to feed back to the radio.
 

Josh380

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If the arrestor is working properly then it may be firing and shorting out the coax when you transmit. And it may be shorting only on voice peaks since you are using SSB. That would make your SWR meter go crazy and cause your signal to sound chopped up to others. As far as "feeding back to the radio" only in the sense that high SWR is reflected power.
Well my signal doesn't sound choppy to others, so not sure that's happening.
 

Josh380

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I would remove the lightning arrestor and coiled up coax choke and see if it works like before you added those items.
I removed the coil as soon as I saw the over 3 SWR. Unfortunately the arrestor has been a part of the setup since my homebrew 102" dipole was up. Changes are in the plans. Just waiting for my friend to get over covid. He doesn't want anyone else on the roof. Plus I'm still waiting for a few things to arrive.
 
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hitechRadio

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How long is your run of coax to the antenna, and what type of coax?

Do you have the ground plane radials on the A99?
 

Josh380

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How long is your run of coax to the antenna, and what type of coax?

Do you have the ground plane radials on the A99?
Couldn't tell you how long the coax is. I just made it long enough to reach from the antenna to the radio. Maybe 50 ft or so. It's quite a long run no matter how I slice it. I'm using LMR240 and no ground plane radials for the A-99.
 

hitechRadio

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Couldn't tell you how long the coax is. I just made it long enough to reach from the antenna to the radio. Maybe 50 ft or so. It's quite a long run no matter how I slice it. I'm using LMR240 and no ground plane radials for the A-99.
It has been years since I had a CB over 20 anyway. But I had an A99 and had some RF getting back, the redials did help. Also it helped notable on local communications, bring the lob down a bit. In addition I did not interfere as much with the TV's in the house, when I added radials.

The only time I didn't have radials on the A99 was when it was mounted above a 3 element beam, the beam was likely acting as the ground plane.

You could make your own radials (3 or more) with some wire cut to 1/4 wave length.

I have heard the A99 is a piece of junk without the radials, and from my experience, I would have to agree.
Your coax and aluminum pipe is acting as your counterpoise.

Side note: Make sure that Aluminum pipe is grounded. And don't tape the coax to the pipe without radials, have it coming from the antenna at a 45.

I personally like DC grounded, helps keep the static crackles down (lower noise floor). But being that it DC grounded has nothing to do with the RF coming down the coax or the polyphaser.
 

Josh380

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It has been years since I had a CB over 20 anyway. But I had an A99 and had some RF getting back, the redials did help. Also it helped notable on local communications, bring the lob down a bit. In addition I did not interfere as much with the TV's in the house, when I added radials.

The only time I didn't have radials on the A99 was when it was mounted above a 3 element beam, the beam was likely acting as the ground plane.

You could make your own radials (3 or more) with some wire cut to 1/4 wave length.

I have heard the A99 is a piece of junk without the radials, and from my experience, I would have to agree.
Your coax and aluminum pipe is acting as your counterpoise.

Side note: Make sure that Aluminum pipe is grounded. And don't tape the coax to the pipe without radials, have it coming from the antenna at a 45.

I personally like DC grounded, helps keep the static crackles down (lower noise floor). But being that it DC grounded has nothing to do with the RF coming down the coax or the polyphaser.
Unfortunately I can't add ground radials to the antenna without drawing too much attention from the city. They only allow strictly vertical antennas.

I'm currently set up good enough to keep the RFI down at a level that doesn't get into my SDR, and I've got a great match. I currently have an mfj 915 line isolator at the radio, followed by a short length of coax wound around a type 31 ferrite core, and finally a low pass filter before the coax heads to the antenna. I'm also using LMR 240 with SMA connectors for the line to my SDR, covered end to end with ferrite snap on chokes. I've also purchased a "nulled out" length of coax to install at the antenna.

So I'm just going to reroute the coax, get rid of the gas discharge arrestor and put the PolyPhaser inline.

I will however take your advice about the coax and ground the mast.
 

merlin

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The confusion is DC ground has nothing to do with ground plane.
The DC ground is result of the tuned circuit at the base of the antenna.
You can have a ground plane that is not DC grounded. A magnet mount has no DC ground to the body/frame but the antenna plug can show a DC short.
Some base loaded antennas (IE: K-40 firestick) have no DC ground.
 
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