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PTT causing problems

Scott Hersha

Well Known Member
Before I call someone at GRT, maybe someone here can help, in fact I?m pretty sure of it. On my RV4 with two GRT screens and a Garmin GTR200B com radio, I often get spurious warnings, like ?EGT too High, or Fuel Pressure too High?. These are visual warnings on my EFIS with no oral warning given, and no exceedences noted on my engine indication system. Funny thing is, this only happens when I key my mic to transmit on VHF COM. My PTT switch is on my Ray Allen stick grip. One wire to the PTT on the stick goes to the -200B, and the other one goes to the ground buss, located on the firewall, where all my grounds are located, except for a couple out in the wingtips for lights. Also, the CHT and EGT time graphs show a dive to zero when I key the mic. Fuel pressure indication sometimes goes crazy too when I key the mic. There is no noise in my headset associated with this. Sounds like some kind of grounding issue to me, but what should I look for? I?m thinking initially of grounding my PTT to an airframe bolt near the point of origin.

Thanks
 
This likely is not the PTT, but rather too much RF in the cockpit.
1. Carefully check your coax from com to antenna. Pay particular attention to the coax shield connections at both ends.
2. Check the antenna ground connections. Make sure there?s no corrosion.
3. If not already done, use shielded cable for the RS232 line from the EIS to EFIS.
4. Wrap aluminum foil around all the wires carrying signals into the EIS.
 
Thanks Bob. I?ll check those items in the order you listed them. I used the GRT supplied harness. None of it is shielded, so I?ll start with the EIS to EFIS wire.
 
This likely is not the PTT, but rather too much RF in the cockpit.

Wouldn't FR always be an issue and not just when he keys the PTT ? RF causes noise. This is presenting like a grounding problem.

I would suspect a potential difference between where various things are grounded or a loose ground. You say everything is grounded to the Buss, but are there also local grounds? Maybe the trays have grounds to the air frame? You could be creating a ground loop every time you hit the PTT.

I think grounding the PTT to the air frame local to the switch VS the buss is a good starting point.
 
Wouldn't FR always be an issue and not just when he keys the PTT ? RF causes noise. This is presenting like a grounding problem.

I would suspect a potential difference between where various things are grounded or a loose ground. You say everything is grounded to the Buss, but are there also local grounds? Maybe the trays have grounds to the air frame? You could be creating a ground loop every time you hit the PTT.

I think grounding the PTT to the air frame local to the switch VS the buss is a good starting point.

When I said RF I meant the actual transmission from the transmitter. Here?s a not real easy test: make up a long (like 50? or more) coax with a connector that mates to your radio on one end. Attach the other end to a 50 ohm dummy load (for short transmissions 3 150 ohm, 1 W resistors in parallel will work (not wire wound!). Connect to radio, place dummy load as far away as possible (outside closed metal hangar door preferable). Repeat test (briefly push PTT, look for egt drop out, false warnings, etc). If they went away then you know the source of your problem. BTW an open braid to antenna ground plane connection will cause all sorts of havoc, like this. I would not ground the PTT at multiple locations. This is the very definition of a ground loop, although I think unlikely to cause problems here.
 
Had something similar...

...on my 1980 Mooney 231; Keying up either KX-155's to transmit would cause all of the instrument gauges to indicate offscale. This was traced to a ****-poor ground contact on the gauge cluster - Mooney used a single point contact "finger" that just oxidized overtime. Fresh ground lead with proper termination resolved the issue.

Look carefully at the EIS grounding - are they using fast-on terminations or PIDG ring terminals?

B
 
...on my 1980 Mooney 231; Keying up either KX-155's to transmit would cause all of the instrument gauges to indicate offscale. This was traced to a ****-poor ground contact on the gauge cluster - Mooney used a single point contact "finger" that just oxidized overtime. Fresh ground lead with proper termination resolved the issue.

Look carefully at the EIS grounding - are they using fast-on terminations or PIDG ring terminals?

B

Yes, a definite possibility. You?ve heard of MOS (metal oxide semiconductors). What happens is an oxide layer between contacts acts like a diode, and, in the presence of RF from the transmitter, generate all kinds of harmonics that in turn cause trouble.
 
Similar problem with E.I. FL-2C

This post just came right in time.

I have an EI FL-2CA installed on my new (old) build Vans RV-9A and during recent tests, I was able to notice something different on the unit. I power up the plane, the fuel quantity comes up normally and stays that way. If I key the PTT (Push To Talk) to transmit on the radio, the fuel quantity slowly goes down until reach zero. Once I release the PTT, the quantity indication start to slowly goes back to were it was.
Have you guys ever seen something like this? My antenna cables runs far from the fuel probe wires.
I have recorded a video in case you want to have a better understanding of the reported behavior:

https://youtu.be/czW2fE2RYms

I will look for potential ground issues as reported for some other problems here.
 
Guess I’ll have to check all my grounds tomorrow. I checked the COM antenna today and the ground plane and braid was grounded solidly. I’ll need to remove my boot cowl to access my ‘forest of tabs’ ground block, but I can check the security of all grounds right there. I don’t suspect a corrosion problem, because I did a panel upgrade just two months ago where I replaced all wiring in the plane, including all new RG400 coax. The wingtip mounted LED position lights, wing LED landing lights, and tail mounted LED position/strobe lights are all locally grounded, but the lights were all off today when I tested my PTT - in my hangar with the engine not running. Pressing the PTT switch resulted in my fuel pressure indication starting to indicate pressure, oil pressure indicating a value, EGT and CHT jumping around. I’m thinking I may need to check the security of my engine to airframe ground(s). I have two fat wires going from engine bolts to the firewall, but not directly attached to the brass bolt that is part of the forest of tabs. The firewall is common to those two fat wires. The fat wires are attached to engine mount bolts that hold the engine mount to the firewall. The inside end of one of those bolts is where the battery negative terminal is connected. Battery is on the cockpit side of the firewall in an enclosure. I’m thinking as I’m typing. Maybe I shouldn’t allow any distance on the firewall between these big grounds, and maybe not use engine mount bolts as a ground path? What do you think? I didn’t have a problem before my panel upgrade, but I didn’t have any electronic gauges, except for the original GRT EIS, and it worked fine. Now I have two new GRT EFIS screens, which is where the problem is showing up.

Opinions about my grounds please.....
 
Another possibility to check: do you have any wires connected to the EFIS on one end and unconnected on the other end? Maybe for something you might possibly want to connect in the future? Such wires could be acting as antenna, picking up RF interference when PTT is pressed.

Erich
 
After researching my Aero-Electric book, it looks like Bob says that engine mount bolts are great for holding the engine on the airframe, but not so good as a ground path. Impedance through bolted connections adds up. I?ll be making new 2-0 ground cables or straps to connect my engine case and battery directly to a brass bolt at the ground buss right on the firewall - like I?ve done before in the airplanes that I built. I didn?t build this RV4, but when I saw two fat wires going from engine case to engine mount to airframe bolts, I thought that was good, having two ground pathways. Maybe not. Guess I?ll find out.
 
same problem

I had the same problem on my -7A during flight testing back in 2010. I tried most of the solutions offered in this thread, and nothing fixed the issue. When I pushed the PTT, it caused an altitude jump, which meant I had to disconnect the AP every time I wanted to transmit.

See this thread for what eventually fixed my problem. I simple RF filter on the d-sub connector going into the AHRS was the fix.

http://www.vansairforce.com/community/showthread.php?t=63836
 
Dave,
That looks interesting and if it works, what a simple solution. I don?t have any audio noise, just the kind of ?noise? that causes some of my engine indications to go batty when I key my mike. I?m going to re-engineer my engine/battery/ground bus system first. If this doesn?t work, I?ll try these D-sub capacitive filters. I assume I would install this on the 25 pin d-sub going to the GRT EIS. The only connection from that box to the EFIS is a single RS232 serial feed.
 
grounding problems

if possible, keep grounds as short as possible (directly to the airframe) long leads any where that are carrying RF will "transmit". just my .02:D
 
I quick test to see if it is RF noise or a ground issue: Turn off the radio and press the PTT. If the issue persists when there is no radio transmission then it is not RF noise.
 
Food for thought. Not all grounds work the same. For better RF noise immunity, braided cable grounds work better due to something called skin effect. They present lower impedance to RF signals that do grounds with fewer conductors.
 
OK. I did what Keith suggested above. I left the radio master off and tried the PTT switch and the issue went away. Then I turned the radio master on but switched off the COM radio (new GTR 200B) and the issue still not not happen. It only seems to happen while transmitting on that GTR 200. I then connected the BNC antenna lead from the GTR200 to my handheld com radio and it didn’t happen then either, although the handheld is only transmitting at 5 watts maximum.
So if my issue is RF noise, why don’t I have any noise in my headset. It only makes some engine indications to go whacky. And how do I fix that?
My antenna is a RAMI-534 as shown below:

https://www.aircraftspruce.com/catalog/avpages/av534.php?clickkey=9801

I ran new RG400 cable from the GTR200 (BNC) to the antenna mounted on the belly and connected as shown on the install diagram (non-BNC). I checked the cable shield grounding at the antenna end and at the BNC/radio end. All is good there.
Some of the engine sense wires are running bundled with the power wire and ground wire running to the radio as well as the shielded headset jack wires. Running out of ideas....
 
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Thanks Bob. Unfortunately after unbundling and then rerouting the power and ground wires, the problem still exists. My PTT wires were running right next to my main bus feed wire, so I rerouted that, which also didn?t help. I?ll need to reconnect my PTT on my stick to a ground. I had it connected directly to the ground bus forest of tabs on the firewall before. Do I still need to do that or can I ground it locally?
I almost ready to throw in the towel, because none of these suggestions have worked. The only one I didn?t try yet was those d-sub capacitive filters. Guess that?s next, but what d-sub should I filter? It seems to me I should filter the 25 pin d-sub on the EIS, but I?ve been wrong about everything else so far, so I don?t have a lot of confidence anything will work. I have d-subs on my HX EFIS screen, my GRT Mini, and my GTR 200B radio. I hope I don?t need to put filters on all of them. Any ideas?
 
My preference is to run all grounds to your forest of tabs.
Since your handheld, using the same coax and same antenna, failed to replicate the symptoms, the only thing left is the com and its installation. You seem to have covered the wiring. All the mounting screws clean and tight? Go thru all the set up menus, see if anything sticks out (no idea what). Last step, try to borrow the same, known good, com and try it in your airplane. Maybe there?s a strange issue with yours. Have you contacted the Garmin exp guy, on this web site? He?s a good source for advice.
 
Scott,
I had a weird one involving the PTT.
The PTT switch and autopilot (Trio) servo disconnect switch are on the stick and every time I transmitted the autopilot servos would disconnect. Eventually traced it to some weird interference between the two wires running through the stick. Solved it by running the servo disconnect wires through a remote relay activated by the disconnect switch on the stick.

You could try temporarily bypassing the stick switch by unbundling and isolating the PTT wire and touching it directly to ground on the airframe well away from other wires and see what happens??

Fin 9A.
 
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Yep - at this point the GTR200 looks like the problem. See if you can swap it out to verify or eliminate.

I?ve only flown one plane that had a GTR200 (as comm #2). I was a not impressed - when transmitting on the GTN-650 the GTR200 (monitoring a secondary frequency) suffered from crosstalk.

Carl
 
Thanks guys. I only have one button on my stick - the PTT switch, which I WILL run back to my ground bus as suggested, and as I did before this troubleshooting scenario. I checked the continuity on this switch and it’s OK. There are a couple GTR200’s at my airport, so I’ll borrow one of them to check - thanks for that one. It’s a good idea and one I hadn’t considered because my radio is new, but Garmin is not infallible.
My panel is very simple with an EFIS, a com radio, and a remote transponder. The GRT Mini was added because of its low cost, and gave me a backup in case I was out on the road somewhere and had a problem, I could get home. This is a VFR airplane. I don’t even have an autopilot.
I will re-engineer my battery and engine case grounds, because I’m running out of possibilities. I doubt that will help, but it’s worth a try. I’ll be calling GRT on Monday for help, although I think I’ve already tried everything. Those d-sub filters are a patch for something that isn’t right.
 
I don't have a Garmin GTR200B, so I don't know if this will help, but maybe some ideas.
My push to talk grounds the mike jack of the headset plug, with all the grounds in the audio system daisy chained back to the intercom ground (PS Engineering PM-3000). The PM-3000 then has a wire that goes to the radio PTT circuit (GNS480). There are two wire from the PTT switch on the stick back to the mike jack.
 
Thanks John. This will have me doing some research into how I did this before, when I had 2 coms, an audio panel, and separate intercom. I don?t have these extra things now. My radio has an internal intercom, and I don?t need an audio panel, but your post reminds me that I did this PTT wiring different before. Maybe that?s the difference. I?ll check that out. Thanks.
 

That type of antenna is known for bouncing RFI back into the plane. The lack of a BNC connector can cause issues like you are seeing. If you have tried everything else a new antenna that has a BNC connector may stop the RFI.

Replacing that antenna in my RV-6 fixed the fuel gauge that went wacky when I keyed the mic. I now have a Delta Pop antenna, nice antenna at an attractive price.

http://www.deltapopaviation.com/VHF_Com_Antennas.html

DSC01755_1.jpg
 
Sam,
Ya, I?ve been suspect of that antenna since I bought the plane. I installed a new connector kit for it when I did my panel upgrade last winter, and it work fine before, but I didn?t have any avionics that operated on tiny amounts of power before the upgrade. I?ve used DP antennas before and have been satisfied with them. If that?s all it takes to fix this, I?m lucky. Thanks for the tip.
 
There are ferrite toroid snap on beads. You can snap on the wires to kill RF in the wire. If that is the issue is your engine indication look at those wires before the EIS and the serial cable to the GRT. You can add it to the power and ground lines as it may be coming in that way.

Ground, a common good ground is golden.

Move or shield wires.

If you have cheap RG58 coaxial consider upgrading to RG400....
 
George,
All of my coax in the plane is RG400 That I installed last winter during my upgrade. I have some of those ferrite bead collars, and I?ll experiment with those today. I have my boot cowl off, so the instrument panel to firewall is wide open and easy to check. I?m suspicious of that -534 com antenna that has an open center electrode connection, so I?m going to experiment with some aluminum foil today to try to effect a temporary ?shield? in that area - before ordering a better BNC connected antenna, as Sam suggested. I?ll figure this out eventually. Everything works, but it?s annoying that some indications get weird momentarily every time I key the mic switch.

Thanks
 
George,
All of my coax in the plane is RG400 That I installed last winter during my upgrade. I have some of those ferrite bead collars, and I?ll experiment with those today. I have my boot cowl off, so the instrument panel to firewall is wide open and easy to check. I?m suspicious of that -534 com antenna that has an open center electrode connection, so I?m going to experiment with some aluminum foil today to try to effect a temporary ?shield? in that area - before ordering a better BNC connected antenna, as Sam suggested. I?ll figure this out eventually. Everything works, but it?s annoying that some indications get weird momentarily every time I key the mic switch.

Thanks

Scott,

I offer that you are chasing 10th order items. For example:
- Antenna connection. If connected, RF energy will always prefer the path of least resistance. It will not ?leak?, just as a bent whip antenna will not ?bounce? energy into the plane. Keep in mind several decades of Cessnas came out of the factory with RG-58 coax running to a ring terminal on the threaded end of a simple whip antenna. The one thing you have not done that is always my first check is put a real antenna analyzer on the radio side of the coax to the antenna. If the antenna and coax as a system does not resonate at your operating frequency then you will suffer problems like this, as well as poor performance. This is the antenna analyzer I?ve used for the last 20 years: https://www.dxengineering.com/searc...r&sortby=BestKeywordMatch&sortorder=Ascending
- Please do not start scrapping paint off of your fuselage to get ?a better ground?. Again, this is RF, not DC power. The antenna analyzer will tell you if the ground is good or not. Star washers on the antenna mounting screws is more than adequate, even if primed on the inside.
- Do not overlook stuff like a bad breaker (as in high resistance contacts) providing power to your radio.
- Do swap out the radio (as in put a replacement in your plane and take yours and install it in the other plane).
- Install a temporary PTT switch and see if the problem is still present. One step better is to install this switch on the radio side of the audio panel to eliminate that audio panel as the culprit.

Let us know how this data run plays out.
Carl
 
Thanks Carl,
I?m going to see if I can borrow another GTR200 radio today and rule out the radio as the culprit. If that?s it, it?s still on warranty and it would be the second time it is replaced on warranty. Garmin isn?t perfect. Trying a different PTT switch is an easy check. I don?t have an audio panel so the PTT goes directly to the radio. I?ll have to see if any of my friends has an antenna analyzer, or take it to an avionics shop. Don?t really want to spend $320 on an analyzer I would use once. New radio, new RG400 cable, new antenna if I end up getting one, mounted on the belly of a metal plane - seems like it ought to work, unless it?s something unrelated to the antenna. I can also change out the 7.5 amp ATC fuse protecting the radio +12V feed. Never heard of a fuse getting a high resistance, but again, very easy to check. I might end up trying on of those d-sub capacitance filters if I run out of other ideas, although I don?t know where I would put it (EIS, EFIS?s, radio). And that only covers up a problem.
 
George,
I?m going to experiment with some aluminum foil today to try to effect a temporary ?shield? in that area
I don't think foil will help troubleshoot even as an temp experiment. Typically shielding is grounded at one end. Don't get me wrong big fan of sheildung writes just don't think foil will be effective. Hey worth a shot. Try and ground one end (usually the source). If it works I'll be impressed. :)

It's possible pulsed signals in the power side are upsetting the micro processor? (Wild guessing)
 
Well, it seems like I have the RF issue cured - maybe. It’s testing good in the hangar. I’ll be more confident when I fly tomorrow if the problem doesn’t return. I tried a different PTT switch - no help, new 7.5a fuse - no help, I put a new BNC connector on the radio end of the antenna cable - no help, tried different grounding locations for the PTT switch - no help, I re-routed power wires away from signal wires where that existed in a couple places - no help, I put a ferrite clip on the serial wire running from the EIS to the EFIS- no help, then I put a ferrite clip on the RG400 COM antenna cable, and like the parting of the Red Sea, it was gone! I moved the ferrite clip to different locations along the cable, and it didn’t seem to make a difference, it still worked. I removed the ferrite, and the condition returned and certain indications went wild. Put it back on, and it’s gone.

So this ferrite (whatever that is) is correcting something that I’ve never dealt with before, and it’s correcting something that is wrong with my electrical system as installed. The original avionics on this airplane, that I didn’t build, worked fine with this same antenna, but it was a bare bones steam panel, except for the early generation GRT EIS system, and that worked fine. Then I installed digital EFIS based avionics and things went wild if I dared to transmit on my only (new) radio. There is a lot of very low power signal data moving around through my new, very organized (at least it was) wiring bundles, and if there is any RF looming around looking for a low energy host it can invade - like a COVID-19 hairball - it’s going to grab it. This is the sort of nightmare I’ve been having lately.
My take at this point is, my antenna, with it’s unprotected center core connection is allowing this RF electronic pathogen to cause a pandemic in my airplane. It seems like a new more modern, BNC connected com antenna is my vaccine cure.
So what do you experts say? As a senior citizen with a rapidly shrinking retirement nest egg, I don’t want to waste money on an antenna of that does no good - although a DP antenna ($125) is a pretty cheap fix in airplane terms, if it is a fix....... and again, the proof will be a flight test tomorrow, not a no noise check in my hangar with the engine not running.

Thanks for all the help. It has been a mostly fun learning experience. And I might not be done yet, but hope springs eternal.
 
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Scott, congrats on killing this snake.

And thanks for reporting on the fix-----may save others headaches in the future.
 
Very good, Scott, hope your test flight confirms your diagnosis. A new antenna will be an easy fix plus you get a sleek new addition to your RV. :)

Yes, those simple antennae flew on many Cessnas, etc but they didn't have the high-falootin' sensitive digital avionics in our modern planes. The Delta Pop antenna added .842 kts to my RV-6. :)
 
Is it possible the antenna was bumped (hard) during the winter? I'd take it apart looking at both the coax center conductor to antenna radiator path (for open circuits, short circuits) and the same for the coax shield to airframe path. Sounds like you're getting a lot of reflected power back up the coax. Or swap in another antenna and see if that fixes it.
 
Bob,
I installed a new hardware mount kit for this antenna (from Spruce) this last January during my upgrade. All parts of the installation except the antenna itself were replaced. I don?t think its damaged. I have checked the pathway to ground from both ends, and it?s intact. I?ll try to borrow an antenna analyzer to test the cable and antenna, but I think I?ll just need a new BNC connected antenna. I think this antenna just reflects a little RF up the antenna shield because of it?s less than robust shielding connector design and it affects sensitive avionics. I?ll find out if the ferrite clip works on my test flight tomorrow. If it does, it points to an inadequate antenna design for this type installation (I think).
 
Just be aware, your cure may have killed the patient. i.e. filtered the RF right out of the radio output.
This points to a bad antenna or antenna connector termination, like was suggested earlier. The RF is reflecting back because the load (antenna) is not matched. A VSWR measurement taken right at the radio output should have showed this.
 
I agree. And a new antenna will fix that. If I can find a VSWR meter and someone that knows how to use it, I?ll find out. The ferrite filter is temporary and mostly just used to help find the problem.
 
I flew 3 times today and all three flights went well, relative to my previous problem. No spurious signals or warnings while transmitting. Almost all readings stay stable. I say almost because the CHT and EGT history lines show a slight change while transmitting, so some RF is still getting through. This should end when I install my new antenna, which I ordered today. Before the ferrite collar, the CHT and EGT displays would all dive to zero when I transmitted, and then bounce right back to normal when I quit transmitting. Now they increase very slightly, maybe 30* while transmitting and don?t cause a warning to appear. All other engine indications are normal, stable, and don?t change. I found a guy with a VSWR meter at my airport, and I will be checking antenna transmitter performance when I get my new antenna. I consider this problem to be over.
If anyone wants a RAMI AV-534 COM antenna I will sell mine to you for...... one beer. It can even be a light beer and I don?t like light beer.
 
IF possible, borrow the SWR meter early (before the new antenna installation) so you can get before-after readings. Just for our information....
 
Good idea Bob. That?s my plan. I would really like to see the difference. I?m also going to try the aluminum foil thing to see if that makes a difference to before installing the new antenna, just because I?m interested in the result. On this antenna there is a ?float? as Garmin calls it between the shielded portion of a CAN bus and the connector. This isn?t a CAN bus, but it carries a whole lot more energy and I think that 2? of exposure might affect radiated energy during a transmitted signal. I?m going to protect the RG400 center conductor attachment to the end of the antenna element from the aluminum with tape, and then make sure the foil covers the ?float? and is grounded near the RG400 shield ground. Just an idea, but it?s worth experimenting with. A fully shielded, BNC grounded installation does the same thing.
I?ll check the SWR before and after. I expect the SWR to be less than 3.0:1 on the new antenna. I?m interested in seeing a result after my Frankenstein mod on the old antenna, and then again after removing the foil and the ferrite collar before removing the old antenna so I have a comparison.
 
Just out of curiosity, is the GRT EMS related to the Dynon EMS? Someone mentioned to me last week there was part commonality.

Our RV9A with SV-1000 and SL40 was doing the exact same thing. The Dynon EMS was at fault and a replacement unit fixed the issue.

Pat.
 
I doubt there are many common parts with the GRT EIS unit itself, other than engine sensors. I?m pretty sure my issue had to do with RF interference from the VHF transmitter cable and antenna. New antenna is on its way. Installation and testing next week.
 
Well - final post on this one. I installed my new Delta Pop COM antenna and a new 90* BNC connector yesterday. Since this antenna has a larger footprint than the one I removed, and it?s located on the belly skin, I made a 6? X 6? .063 doubler plate also. My previously reported RF interference problems are gone. I was hoping to check antenna performance before and after the installation, but was unable to borrow the old CB radio SWR meter a local pilot has, or find anyone that knows how to use it. Don at Delta Pop has tested his antenna across the frequency band and reports an SWR of 2.2 across the band. Apparently that?s pretty good, because it worked for me.
My original antenna, a RAMI AV-534, had too much feedback, or RF reflection, or whatever, even though it was installed correctly. It worked fine until I install a modern panel with sensitive digital avionics signals. The RF caused fluctuations in data transmissions (I think). Anyway - it works great now. This is 4th Delta Pop antenna I?ve owned (3 coms, and 1 UAT blade), and I?ve had very good performance from them every time.
 
This thread is timely for me. Doing a rehab on an old RV-6 panel, installing a GTR-200 and an EIS...
Was initially planning to keep the legacy comm antenna and coax. After reading this, I've decided a new Delta Pop antenna and fresh RG-400 will be a smart move.
Thanks
 
Why RAMI sells these junk antennas still is something I don't get. Having a ring terminal connection on the end of a feedline exposing the center conductor is like connecting a garden hose with a big hole at the end to a sprinkler.

Don's antennas are fantastic and typically are 1.3 VSWR as I've measured them with my VNA. The drawback to this is you will pick up a lot more radio chatter on unicom freqs.
 
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