Antenna went bad in glider

[2G]

A friend of mine was having radio problems; sometimes he came thru loud and clear, but other times it sounded like he was 100 miles away behind a mountain. Then it went completely bad - it could not even receive the airport ASOS w/o turning off the squelch. I happened to have a VSWR meter and the SWR measured 4.8 (a factory glider antenna should measure less than 1.5, 1.0 being ideal). The BNC connector on the coax looking brand new. He had a gear-up landing earlier this season, so I suspected damage to the coax. Inspection of the coax under the seat pan showed no damage, and the routing of the cabling was well up the side of the fuselage. He decided to use a handheld for the remainder of the season. The glider is an EB29.

Any thoughts on what might be wrong?

Tom

[Dan Marotta]

Try hooking the glider's antenna to the hand held radio and listen to
AWOS.  That should tell you if it's the antenna or not.

Dan
5J

[Dave Nadler]

On 7/22/2021 8:55 PM, Dan Marotta wrote:
> Try hooking the glider's antenna to the hand held radio and listen to
> AWOS.  That should tell you if it's the antenna or not.

Good point!

[Dave Nadler]

On 7/22/2021 8:28 PM, 2G wrote:
> A friend of mine was having radio problems; sometimes he came thru loud and clear, but other times it sounded like he was 100 miles away behind a mountain. Then it went completely bad - it could not even receive the airport ASOS w/o turning off the squelch. I happened to have a VSWR meter and the SWR measured 4.8 (a factory glider antenna should measure less than 1.5, 1.0 being ideal). The BNC connector on the coax looking brand new. He had a gear-up landing earlier this season, so I suspected damage to the coax. Inspection of the coax under the seat pan showed no damage, and the routing of the cabling was well up the side of the fuselage. He decided to use a handheld for the remainder of the season. The glider is an EB29.
>
> Any thoughts on what might be wrong?

As you no doubt know, main source of problems is in coax termination.
Suggest, of course using correct $$ crimping tools+dies, replace BNC.

Alternatively, your friend could fly his spare EB29.

See ya, Dave

[Dave Nadler]

But I forgot to mention: manipulating the cable/BNC can cause an
intermittent to connect. So you won't really prove its a radio problem
if the handheld seems to work OK.

What kind of radio is this?

[Roy B.]

[Roy B.]

Try a radio check with both canopy open and canopy closed.
That will tell you if the problem is the antenna connection at the rear of the radio.
Canopy open stretches' the cable.
ROY

[Moshe Braner]

On 7/22/2021 8:28 PM, 2G wrote:

Using the handheld radio (except for testing) would be a pain. How
about, if the problem is indeed in the antenna, building a temporary
alternative antenna and plugging it into the radio that is in the panel?
If the glider is mostly carbon (presumably), that won't work very
well, but neither will the handheld. Try and put the temporary antenna
close to the plexiglass and as far from the carbon as possible. If the
antenna will be horizontal rather than vertical inside the glider,
that's not ideal, but will still work.

Note: a "rubber ducky" antenna (borrowed from the handheld) is NOT a
good alternative antenna if you dangle it on the end of a length of coax
- it's missing its "ground plane" (the body of the handheld). Need a
dipole antenna, or something better than that.

For our clubhouse radio I've built a vertical "resonant feedline dipole"
and it worked great. Simple and omnidirectional. It is a dipole made
of a quarter-wavelength of just the center conductor of the coax on top,
and another quarter-wavelength made of the intact coax on the bottom,
and right under that the coax is coiled to create an RF choke to isolate
the bottom half of the dipole from the rest of the coax that runs to the
radio. Theoretically that coil is supposed to be dimensioned so it
behaves like a resonant LC circuit, not simply a choke, but my
semi-arbitrary coil dimensions seemed to give low SWR on a wide band.
(A recipe for 146 MHz said 9 turns on 3/4" pipe, I used 11 turns on 1"
pipe, that was with RG58 type coax.)

[2G]

Yes, we tried connecting the coax to a handheld and the result was equally as bad. The fuselage is carbon fiber, so an antenna that doesn't poke thru the glare shield is worthless, and there isn't much space above it. We thought about replacing the BNC connector, but couldn't find anything locally. He decided to fly with the handheld for the rest of the season. I was hoping someone else here had a similar failure as to get insight into its cause. I think something done to repair the gear-up landing damaged the coax, but we are not in a position to look further than under the seat pan.

Tom

[Eric Greenwell]

Is there access to the antenna, so it could be tested directly for SWR? Does anyone have
TDR to perhaps locate the fault?

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[Charles Longley]

Disconnect the coax on both ends and check it with an ohm meter.

Charlie

[andy l]

Years ago we checked someone's glider. The SWR was 6. Eventually the fault was found: a joint just behind the undercarriage, consisting of two BNC plugs and a joiner adaptor, which was open circuit (i.e. SWR still 6 when disconnected). Redid both plugs, then OK.

Is the antenna in the fin, and could there be cable damage near it? Or is it inside the rudder, like for instance the Nimbus 4, in which case check that connector.

[andy l]

Answered my own question:

https://binder-flugmotorenbau.de/eb29.html?&L=1

radio antenna in rudder

I'd look there

n.b. I think this rudder installation can be a bit directional, at a guess shadowed by the fin so poorer to straight in front of the glider, which might explain the variations before the fault

[John Godfrey]

If the gear up landing caused the coax to deform (flatten), could be the problem. One test would be the SWR with another radio connected.

[kinsell]

Wonder if they have a barrel connector at the rudder to allow the rudder
to be removed for service? If so, that hardware could be a source of
trouble.

Dave

[Stuart Venters]

On 7/22/21 10:55 PM, Eric Greenwell wrote:

>>
> Is there access to the antenna, so it could be tested directly for SWR?
> Does anyone have TDR to perhaps locate the fault?
>

a NanoVNA is pretty cheap and might be able to localize the fault from
the end of the coax.

Search for nanovna on amazon


Setup for TDR mode
https://groups.io/g/nanovna-users/topic/72891049

[Dave Nadler]

On 7/23/2021 6:09 PM, Stuart Venters wrote:
> a NanoVNA is pretty cheap and might be able to localize the fault from
> the end of the coax.
>
> Search for nanovna on amazon
>
> Setup for TDR mode
> https://groups.io/g/nanovna-users/topic/72891049

https://www.amazon.com/Upgraded-Analyzer-Measuring-Parameters-Standing/dp/B08277YZT9

Very cool!

Coincidentally, an OSTIV presentation today discussed using TDR for
embedded strain gauge kinda-continuous load measurements inside glider
structures (but their sensor system really isn't yet good enough, some
further work required).

[John DeRosa OHM Ω http://aviation.derosaweb.net]

Try following the advice found in my presentation, "Transceiver Troubleshooting".

http://aviation.derosaweb.net/presentations/#transceiver

Best of Luck,
John (OHM)

[2G]

We located the problem: it is a bad connection in the vertical fin. He hasn't taken the fin off yet (he will leave that to the annual at the end of the season).

I have ordered an interesting troubleshooting device, a nanoVNA (VNA stands for vector network analyzer). Ham radio operators use them for troubleshooting antenna problems, along with other components. It only costs $60 (https://www.amazon.com/gp/product/B07Z5VY7B6/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1). Here is a short video on how to use a nanoVNA:
https://www.youtube.com/watch?v=xa6dqx9udcg
This assumes you know something about Smith charts, which most of you don't, so here are background videos on it and related topics:
Understanding VSWR and return loss:
https://www.youtube.com/watch?v=BijMGKbT0Wk
Understanding S parameters:
https://www.youtube.com/watch?v=-Pi0UbErHTY
Understanding Smith charts:
https://www.youtube.com/watch?v=rUDMo7hwihs

Tom

[John Godfrey]

Isn't a separate antenna in the fin unusual? I thought the standard nearly universal practice was to create an end fed dipole by simply folding back the shield to the correct length, thus avoiding a (corrodable) connection?

[2G]

Here are a couple more videos that go thru more detail on operating the nanoVNA that are worth watching:
https://www.youtube.com/watch?v=QJYeFpiqY8c
https://www.youtube.com/watch?v=tLMAStiaAxU
and one on how to measure cable length with a nanoVNA:
https://www.youtube.com/watch?v=9thbTC8-JtA

To find distances to a fault you will need to find the type of cable used so you can look up the velocity factor. For example, RG58 has a VF of 0.535. The cable type is printed on the outside of the coax.

Tom

[2G]

I do not know how the antenna is physically constructed in the EB29 or if a connector is used, but we found that moving the rudder to the right cleared the problem, while moving it the other direction recreated it. The rudder will have to be removed to find the source of the fault. The good news is that no holes will need to be cut in the fuselage.

Tom

[John Godfrey]

Warning thread drift.
Tom,
What is your take on the usefulness of this device for Flarm antenna testing?

[2G]

A Flarm antenna is an antenna just like any other, so it should be ideally suited for checking it. Full disclosure: I have never used a VNA in my professional career, so I am also on the learning curve here. However, I am very impressed with what I have seen so far. I should get mine in in a couple of days and will give it a good test as we are grounded here at Ely for the rest of the week (after I fix a flat tire on my ASH31Mi!).

Tom

[Craig Funston]

Having spent the last maintenance season replacing the coax to the antenna in the rudder of my Nimbus 4, I can definitely sympathize. The reason for a rudder mounted antenna is that some gliders require a full carbon fin and fuselage. The only RF transparent real estate available is the rudder. Detailing of the coax going into the rudder is definitely finicky and prone to wear. I ended up making a number of modifications to improve the routing and durability.

The original lasted 20 years, but finally started exhibiting limited transmission range. I've tried with limited success to diagnose with a SWR meter, but more by process of elimination, I've concluded there's a bad connection at the antenna (which is inside the rudder). Might be time for surgery next winter.

https://www.amazon.com/Gam3Gear-SURECOM-125-525-Digital-Handheld/dp/B075H8FDDR/ref=sr_1_1?dchild=1&keywords=Gam3Gear+SURECOM+SW-33+Mark+II+100+W+125-525+Mhz+Mini+Digital+VHF+UHF+Two-Way+Radio+Handheld+Power+%26+SWR+Meter&qid=1627351975&sr=8-1

I'll be interested to hear what you find. If you want to contact me off channel, I've got photos of routing, etc. Good luck with the EB.

Best regards,
Craig JN

[Stuart Venters]

Tom,

Glad you found it. Wiggling beats test equipment if it works.

The chipsets for the NanoVNA are evolving quickly. The V1 you found a
link to works up to 300Mhz with the fundamental and then with reduced
capabilities up to 1500 with harmonics. This is fine for HF and VHF.

You might want a V2 instead. It works up to 1500 with a fundamental, so
is better for Flarm and transponder stuff.

https://www.amazon.com/NanoVNA-Analyzer-Measuring-Parameters-Standing/dp/B08FY4Q8JY/ref=sr_1_2_sspa?dchild=1&keywords=nanovna&qid=1627353884&s=industrial&sr=1-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFZTVhWVFBERlVYTkUmZW5jcnlwdGVkSWQ9QTA0NTIwMzUxVDRWTTVPN1NXMFhaJmVuY3J5cHRlZEFkSWQ9QTA0MDIwODAyUU5UWlhOMzVXR1Y2JndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==


Both are amazing considering what a real VNA costs.


-Stu

[Tim Newport-Peace]

On 26/07/2021 22:51, John Godfrey wrote:
> Isn't a separate antenna in the fin unusual? I thought the standard nearly universal practice was to create an end fed dipole by simply folding back the shield to the correct length, thus avoiding a (corrodable) connection?

As described, that sounds like remarkably bad practice. It would allow
moisture to capillary between the screen and feeder, which will then
give you poor SWR. You need a moisture-proof connection where the co-ax
splits into the two poles.

[kevin anderson]

When the antenna went bad on my Silent club, I had to replace it. As I recall, the coaxial was mounted straight inside the fuselage, and there was enough tail on the antenna to reach over and connect. It was a flat aluminum dipole type. Yours may be entirely different. You may have enough tail to just change the connector, but if not below is what I used and how I replaced it.

I was able to replace it with the Becker
https://www.cumulus-soaring.com/store/categories/antennas/becker-1a005

I taped the antenna on a small diameter wooden dowel so it would stay straight, and took a couple of other long bigger dowels mounted to a syringe with epoxy. Securing the rudder so the trailing edge was the most dependent part I placed the antenna inside the rudder it and tacked it in several places along the inside of the trailing edge. Worked great and had a great result.

Hope this helps

92

[John Godfrey]

Should have added that the ones I have seen (just a few) are also potted in resin inside the channel that the leading edge of the rudder fits into. Not perfectly dry, but better than open to the air (which would definitely have the problem described)

[John DeRosa OHM Ω http://aviation.derosaweb.net]

On Monday, July 26, 2021 at 9:15:42 PM UTC-5, Craig Funston wrote:
> Having spent the last maintenance season replacing the coax to the antenna in the rudder of my Nimbus 4, I can definitely sympathize. The reason for a rudder mounted antenna is that some gliders require a full carbon fin and fuselage. The only RF transparent real estate available is the rudder. Detailing of the coax going into the rudder is definitely finicky and prone to wear. I ended up making a number of modifications to improve the routing and durability.
>
> The original lasted 20 years, but finally started exhibiting limited transmission range. I've tried with limited success to diagnose with a SWR meter, but more by process of elimination, I've concluded there's a bad connection at the antenna (which is inside the rudder). Might be time for surgery next winter.
>
> https://www.amazon.com/Gam3Gear-SURECOM-125-525-Digital-Handheld/dp/B075H8FDDR/ref=sr_1_1?dchild=1&keywords=Gam3Gear+SURECOM+SW-33+Mark+II+100+W+125-525+Mhz+Mini+Digital+VHF+UHF+Two-Way+Radio+Handheld+Power+%26+SWR+Meter&qid=1627351975&sr=8-1
>
> I'll be interested to hear what you find. If you want to contact me off channel, I've got photos of routing, etc. Good luck with the EB.
>
> Best regards,
> Craig JN

Craig,

For VSWR testing I prefer this model (link below) as it also shows frequency as well as power and SWR. It also has more robust N-type connectors than SMAs. I have a kit with adapters to BNC, SMA, etc, with extension cabling. Don't forget a dummy load for bench testing!

Its just slightly more expensive than the device you mention. But yours is certainly smaller and more portable.

https://www.amazon.com/Mcbazel-Surecom-Digital-125-525Mhz-Antenna/dp/B01D86IKIQ/ref=sr_1_8

[Mark Mocho]

Kevin- After mounting the antenna in the rudder, did you check the mass balance of the control surface, or was the antenna installed in the vertical fin? Note that "Rudder" implies the movable part that makes the yaw string act like a windshield wiper, while the "Vertical Fin" is the non movable part that is supposed to inhibit the windshield wiper action.

[Stuart Venters]

On 7/27/21 7:50 AM, kevin anderson wrote:

>
> I was able to replace it with the Becker
> https://www.cumulus-soaring.com/store/categories/antennas/becker-1a005
>

Paragraph 3 from this antenna's instructions sound like this somebody
has been here before?

"When assembling the antenna in the rudder of the tail unit the transit
holes for the cable should not be too small so that the cable is not
chafed from rudder deflections over time."

[andy l]

I'm going to reply to more than one post, but not mess about trying to do multi quotes.

It sounds like my suggestion of check the connector has become the most likely. And there must be a connector.

As I said earlier, the Binder website says the antenna is in the rudder. So it's like the Nimbus 4. I've helped a former N4 owner remove and refit the rudder more than once. One person holds the rudder close by in mid air while the other does up the aerial connectors, then the hinges are lined up, taking care not to kink or pinch or sever the lead, and to leave it in a nice alignment that avoids doing so in future. It sounds like yours might be under some tension at one full deflectíon, so check the routing and check the cable for loosening inside the plug. Types of BNC plugs may have the centre wire connected by push fit only, or crimped or soldered. So pulling the first type out a couple of mm can leave only the screen connected in that plug, while the others may slightly retract the pin so it doesn't reach the other connector, then back in later and it's apparently OK again.

Incidentally, I think I remember the N4 cable is balanced twin feed in the rudder, perhaps partly supported with extra layer of heatshrink sleeving across the gap. I've wondered if the cable could be subject o fatigue failure after repeated bending, and perhaps this is the problem Craig F had/has, or perhaps it is inside after his repair an song at.

Back to a previous post, on older gliders, and possibly some still now, the antenna is usually halfwave dipole (at 130 MHz halfwave is 1.15 metres) aluminium tubing about 20-25 mm diameter, divided in the middle, with coax feeding into the tube at the lower end and connected inside to the two halves, usually fixed just front of the fin spar, and possibly with the bottom end just through the base rib inside the fin.

There might be some with just plain wire dipole, which ideally would have balanced twin feed leaving the centre at right angles. More recently there are foil types, laminated on to the inner skin. Anyone interested in more might view the Dolba & Dolba website, which also has antennas for Flarm, tramponders and so on, and supplies all the major glider manufacturers.

As another previous post says, any retro installation inside the rudder will need the mass balance checked. A heavier antenna will need to be nearer the hinge line than the trailing edge, but then there may be more directional masking by the carbon fin. If I'm ever in this situation I might consider or consult on removing paint to bare structure, foil antenna on the outside, paint over it. Or maybe this is a daft idea for reasons I haven't thought of.

[2G]

I received the nanoVNA yesterday and checked it out on a few handheld antennas and a length of coax. It was pretty easy to use after I (re)watched a few short Youtube videos. I connected a 6' coax with BNC female connectors to it using an SMT-BNC female, BNC tee (male-female-male) after calibrating it with the provided adapters. The first thing that I learned was that the coax, RG59/U, has TWO velocity factors, depending upon the manufacturer. After I used the correct VG, I was able to measure the correct cable length PLUS the length of the adapters. The open connection on the tee showed up as a minor peak 1" from the nanoVNA. Obviously, I would have been able to detect the position of any opens or defects in the coax.

I then tried the SWR vs frequency function on a handheld amateur antenna I had recently bought. They advertised that it was tuned for 144 and 430 MHz, and they were right. Unfortunately, the SWR climbed steeply below 144 MHz to 6-7 at 130 MHz from 1.3 at 140 MHz.

I still have a lot to learn about it, but overall, I am very impressed with the functionality and quality of the nanoVNA.

Tom