PW-5 Antenna Replacement

[John DeRosa]

My club owns a PW-5 whose transceiver's receive is fine but the transmit is terrible (no one can hear the pilot).

We tried lots of things to try to track down the issue.  Ultimate, we used a meter to check the VSWR and got a reading of 3.4 which is TERRIBLE.  FYI a lower reading is better with 1.0 being perfect.  As a comparison we plugged a rubber duckie antenna onto the radio and got a VSWR of 1.3.

I did replace the BNC connector (compression/solder type) which I am confident is good.  So, I believe that the antenna (or coax) is bad.  

My question is, assuming that the antenna/coax is truly bad (and imbedded into the vertical stabilizer) ... what to do?  We currently have a TE probe installed just behind the pilot's head so I was thinking of installing a quarter wave RAMI type antenna (and ground plane) nearby.  

Your thoughts will be appreciated.

John (OHM)

https://aviation.derosaweb.net/presentations/#transceivertrouble

[Tom Watson]

John, Do you have room for a vertically polarized half wave dipole? Easy to build and you don’t need a ground plane. Best, Tom W4APQ

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On Sep 26, 2025, at 7:04 PM, John DeRosa <jhde...@gmail.com> wrote:

My club owns a PW-5 whose transceiver's receive is fine but the transmit is terrible (no one can hear the pilot).

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[Dave Nadler]

John, you didn't say - you did have the radio checked?

[John DeRosa]

Dave,

Yes I did verify the radio.  What I always start with in troubleshooting radio problems is determining if the transceiver is the issue.  

I checked the following;

> My club's fleet has standardized on the Becker AR4201 so I swap with a known working radio.  The problem was still there.

> The microphone worked in transmit but was only heard within a few feet.

> The coax's BNC connector was dicey so I replaced it.  

> PTT worked.

So the antenna seems like the fault.  Maybe the coax has been nibbled on.

I should have asked originally > Is there a way to get to the antenna in the tail of a PW-5?  And replace it?  With what?

- John 

https://aviation.derosaweb.net/presentations/#transceivertrouble

[John DeRosa]

Thermaler,

That is a possibility.  I assume that you are speaking of a center fed antenna like this > https://www.cumulus-soaring.com/store/aae-vhf-5l.  Being 42" long It would need to be horizontal somewhere in the boom and I am unsure if I can gain access.  It is mentioned that "Note that they are designed to be oriented vertically (standing up) - not horizontally (laying down)."  Hmmm.

Certainly it would be better than drilling a hole into the fiberglass turtle deck to mount an external antenna like the RAMI.  We have those in some of our aluminum gliders and they are very robust.

Thanks, John

https://aviation.derosaweb.net/presentations/#transceivertrouble

[Tom Watson]

John, Another thought is construct a 1/4wave Coaxial. You could probably get the radiator somewhat vertical in the back corner of the cockpit. The choke portion could just trail on the side or floor. I’m 2 hours from our PW5, so please excuse my clumsy suggests. Best, Tom at TSS

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On Sep 27, 2025, at 3:18 PM, John DeRosa <jhde...@gmail.com> wrote:

Thermaler,

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[Craig Funston]

John,

I had a similar experience with the antenna in the rudder of my Nimbus 4. Measured SWR was horrible at first, even after replacing the coax from the rudder to the cockpit. I finally found success after chasing the connections as far as possible towards the antenna. A borescope was helpful in evaluating options. 

I suspect the PW-5 is similar in that the antenna is bonded to the fiberglass structure. There’s really very little that can go wrong with the antenna. It’s the connections that go bad over time. Hopefully you’ll be able to find the smoking gun and not have to resort to surgery. 

On Sep 27, 2025, at 12:18 PM, John DeRosa <jhde...@gmail.com> wrote:

Thermaler,

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[Peter Hudson]

I have a similar issue with my AC-4C...VSWR of about 2.9 and very poor bandwidth and that's tuned at 135 Mhz...it's much worse at 123 MHz.  I'm still thinking about a sort of laparoscopic surgery to remove the old one and make one with copper foil (per the Jim Weir RST instructions).  But access is SO limited even if I plan to cut access holes and repair (not on OML but in hinge cove and end closure rib). 

I have also considered moving that same dipole foil antenna design up towards the cockpit just aft of the spars...that requires a lot of "V" shape and it also curves around the fuselage sides to fit.  Analyzing that weird shape with  MMANA seemed to show it would work though. 

Meanwhile, I'm living with what I've got...at least the tow plane can hear me (and people on the ground when I'm in the pattern too.)

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[Dan Daly]

Did you exclude the microphone as a cause? Perhaps swap your radio into a known good installation to do that before antenna surgery.

[chris behm]

Dan Daly, he said he swapped in a known good radio to the plane and it worked fine, so I would assume from that statement that it is not the microphone.

I suppose it COULD BE the connection to the microphone on the radio in question though....

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[John DeRosa]

Chris, Dan,

We confirmed that the microphone is working.  We tested with a rubber duckie antenna and received TX audio at a distance.  We tested with the "bad" antenna and were able to receive marginal audio while close to the aircraft.  

Thanks, John (OHM)

https://aviation.derosaweb.net/presentations/#transceivertrouble

[Moshe Braner]

Examine the coaxial cable, all parts that are examinable.  E.g., with similar symptoms regarding a glider at our field, we found that the connection of the cable to the BNC connector on the radio was damaged.  That was a lot easier to fix  (attach new connector) than dealing with the connections hidden inside the tail.  Presumably you've already done that in this case, though.

If moisture has worked its way into the cable, it can deteriorate, even though no damage is visible.  It's possible that replacing most of the cable - leaving the inaccessible portion in the rear of the tail in place - may restore operation to an acceptable level.