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Missed Radio Calls


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Hi, I am running a oldish XCom and now a Bose A20 headset. I have found that there are times that I am not receiving radio call's and are looking for some input. Need to work out if it is a headset issue or compatibility with the radio.

 

The radio has had a full upgrade, including firmware and output drivers so is supposed to be equivalent to the latest model. The volumes are run on the high end, so should be plenty to trigger the headset.

 

I also notice the headset doesn't respond to the radio volumes, and must be adjusted on the headset. This is also abit annoying as there is no discrimination between the calls (internal / external) but I assume is just the way it is with ANR headsets.

 

Haven't had an issue with my old clunker headset, but quality and comfort is far from what the Bose definitely offers, so are keen to understand what the cause is so it can be repaired.

 

Cheers, Chris

 

 

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Sounds like squelch problems. Radio squelch should be adjusted so background noise is not heard. Normally adjusted when the engine is running. Don't wind on too much squelch or weaker signals will not be heard. Intercom squelch is similar but normally adjusted so your voice can be heard (and your passengers voice) but background noise cannot. Are you twiddling your knobs accordingly?

 

 

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Had the same problem and worried like mad about it being the the Bose A20 headset but they worked perfectly in other aircraft, so first step check them on other aircraft.

 

The radio was changed and the problem went away

 

 

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Sounds like squelch problems. Radio squelch should be adjusted so background noise is not heard. Normally adjusted when the engine is running. Don't wind on too much squelch or weaker signals will not be heard. Intercom squelch is similar but normally adjusted so your voice can be heard (and your passengers voice) but background noise cannot. Are you twiddling your knobs accordingly?

Hi

 

That is a very good point, hadn't checked the receive squelch, had setup the intercom squelch properly, but not looked at the main one on the front panel. I had thought about doing a factory reset on the radio and starting the setup from scratch again, which I probably will do and will make sure the squelch is set on the minimum

 

required.

 

The other thing I have noticed, is the call's I have missed have all been from aircraft on the ground while I am in the air. My antenna is mounted onto of a square fuselage so is slightly in the shadow. One was actually from a aircraft at our strip while I was in a circuit.

 

I have aslo found that these Comant antennas are ground dependant, which I didn't realise. I had assumed they would have a loading coil and be ground independent like UHF. The next step is to buy a SWR meter and measure antenna performance. I have sprayed alot of ACF 50 through my airframe over the last

 

12 months and have had the landing light stop working due to earthing. I now have to run an external earth for it up the strut to the wing. After checking the antenna, I will replace the washers with shake proof ones which will penetrate the aluminium and make sure the antenna has a good ground plane.

 

I want the SWR meter first so I can see if there is any change.

 

I would say it could be a combination of a few little things adding up to a problem.

 

 

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Loading coil does not make for a 'ground independent' antenna. If your plane is metal, I'd expect the antenna to be a quarter wave mounted somewhere externally with the metal body acting as a ground. If the plane is fibre (like my Jab) then the quarter wave radiator will have a quarter wave piece going in the opposite direction, basically making a dipole. In some fibre planes, the quarter wave radiator will 'act' against a ground made of a thin foil Not sure if that would have to be connected via a wire back to the electrical ground. All the antennas should point vertically so the 'doughnut' shape radiation pattern is used to best advantage. Being an old fart, my theory is a bit vauge and possiblly out of touch. Having said that, if any Hams are reading, I hang out on 7Mhz and the callsign is VK5KKS.

 

 

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Loading coil does not make for a 'ground independent' antenna. If your plane is metal, I'd expect the antenna to be a quarter wave mounted somewhere externally with the metal body acting as a ground. If the plane is fibre (like my Jab) then the quarter wave radiator will have a quarter wave piece going in the opposite direction, basically making a dipole. In some fibre planes, the quarter wave radiator will 'act' against a ground made of a thin foil Not sure if that would have to be connected via a wire back to the electrical ground. All the antennas should point vertically so the 'doughnut' shape radiation pattern is used to best advantage. Being an old fart, my theory is a bit vauge and possiblly out of touch. Having said that, if any Hams are reading, I hang out on 7Mhz and the callsign is VK5KKS.

Trying to remember back, the loading coil shortens the physical length while maintaining the correct electrical length?

 

I presume these Comants lie back at 45 degree's for aerodynamics and to look pretty on modern aircraft?

 

 

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According to my memory (and the ARRL handbook, 1977); An antenna that is physically short becomes capacitive so the coil adds inductance to cancel it (the capacitance) out. If you measure the length of wire in some coils it does not make up for the shortness of the antenna. It's a very complex topic and like the generation of lift by a wing, many folks have their own 'expert' opinions as to what's really going on. I would hardly see a quarter wave on the aircraft bands being too short, so any coil would have some other 'impedance matching' purpose. (sloping back at 45° is purely for looks.)

 

 

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I had the same problem with the Bose and the XCom. Get in touch with XCom technical support (in Brisbane). He readjusted my headset and have had no more problems.

Thanks alot, that is the music to my ears. Have called M Coates a couple of times but they were busy / engaged, so will try again this coming week.

 

Cheers,

 

 

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It's probably a good idea at a busy field to have someone with a radio who can check that yours is working. I knew that a particular person monitored the local frequency and I requested a radio check before I went to another busy airport. Very handy to know your equipment is functioning. Nev

 

 

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Bob,

 

I spoke to Kev from XCom and he was very helpful, and I now have a couple of things to play around with.

 

He said a bad SWR can cause damage to the output drivers & also some receive circuitry. I am not suspecting this to be the case though. My SWR meter turned up today so I can

 

check that and power readings over the weekends.

 

The other problem he has come across, more with the lightspeeds is the mike gain being to high and overpowering the system. There is some tricks but the light speed can be adjusted with

 

a bit of no how. The bose however is not adjustable. I have noticed though, that the volumes on the Bose control are always set very low to stop you blowing your ears out. Generally the receive

 

volume is acceptable, but sometimes the inbound calls can be a bit soft. It comes down to my originally feeling, that there is an imbalance in the way it is all setup. I'm going to play around this

 

weekend with a few options, including using the mike of a standard headset while listening in the bose. I assume the bose is amplified, and may be just too strong for the radio, although the

 

intercom volume isn't that much different in level if the headset is turned off. See what happens after some testing.

 

Cheers

 

 

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Hi

 

Issue has been resolved, at least until proven otherwise.

 

SWR meter tests were very bad, and fault was located to be faulty BNC connector on the bottom of the antenna. Connecter wouldn't clip in properly, and so had vibrated loose.

 

Replaced BNC connector and SWR now 1.3. Power readings right on spec as well.

 

Experimented with headsets, BOSE v's passive talking into one and listening in the other, and yes the mic on the BOSE is much more responsive to the passive. Tuned all the volumes

 

to suit the BOSE, and now have nice discrimination between the audio signals again. The system is balanced so can still use the passive if needed in a flight, but would be a bit

 

quiet until radio adjusted. Will have to decide what to do for a second headset long term though.

 

Very happy with results,

 

Cheers All.

 

 

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no mystery re the Lightspeed gain adjustment - there is a very small plug on the forward side of microphone, when this is removed you will see a fitting (pot) with a phillips head slot that is turned (VERY carefully, as it's very lightweight in construction) to change gain settings.

 

BNC antenna connector - they usually either click in place or not - most times if not then it's because the hole for the fitting through the skin is too small which prevents the BNC from seating properly, may or may not have happened in this case. Just saying so that others can look out for that scenario to possibly prevent hours of unnecessary troubleshooting.

 

Chris - glad for you that your 'issues' are fixed:smile:

 

Jake J

 

 

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  • 1 month later...
HiIssue has been resolved, at least until proven otherwise.

SWR meter tests were very bad, and fault was located to be faulty BNC connector on the bottom of the antenna. Connecter wouldn't clip in properly, and so had vibrated loose.

 

Replaced BNC connector and SWR now 1.3. Power readings right on spec as well.

To add to the comment from the VK5 above and some other comments on aerials and groundplanes. VSWR is a good indication that the circuit i.e. the feeder and aerial are tuned to the frequency in use. However it gives no indication of efficiency. Many shortened aerials give a very good VSWR, but so does a 50 ohm dummy load!

In most cases an aluminium aircraft with a well bonded structure will provide an excellent groundplane, as will a fibreglass one if sufficient conducting tape or foil is applied as a ground plane. The short rubber counterpoise some use is more to achieve a match (VSWR) than to provide effective radiation.

 

There is no need to run any wires back from foil groundplanes to anywhere, just ensure that the braid of the coax is well connected to it.

 

From what I've seen there are few standards when it comes to radio connections, in fact non-standard seems to be the standard! Pleased to hear that somebody got a good response from Xcom.

 

 

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All working like a charm. Hear calls from all round the state, as far south as Rainbow beech and out to Emerald.

 

I think the next investment for the tool box will be a dummy load. Never needed one before, but from what I now see

 

will be very handy for diagnostics.

 

 

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In simple terms SWR is really only what the radio looks into as a load. If the SWR is under 1.5:1 then the radio will be happy. Resonance is a different matter. This is the bit that makes the antenna efficient and how much signal it radiates. The rule of thumb is easy for the radiator in free space (not a loaded antenna) is 300 divided by the frequency in megahertz then divide the result by 4 this will give you the proper length ( quarter wave) for resonance at that frequency. Now all antennas need a ground plane to work or reflect off. So if you have a all fibreglass aircraft the best option is to have a copper or aluminium sheet that is either square or round in a diameter of a quarter wave. So you have a standard radio antenna base with a stainless steel whip screwed on it, that base should be connected to as much metal as possible in a glass aircraft a sheet that is attached to that antenna base ground connection will be the best possible outcome. Say we cut the antenna to be a centre frequency of 125 mhz then using the formula above the radiator needs to be around 600 mm long. The plate for the ground or foil should be 600 mm square or round this will give you the most efficient system. Now remember the bandwidth of the antenna will be lucky to be 4 mhz each side of the centre frequency so you need to make sure that you try to get the best compromise for the best bandwidth. If you want the antenna to operate from say 118.800 to 126.7 then I would slightly set the centre frequency to the side of the most used frequency to get the best "SWR"

 

Mother nature determine all of this and of course you know you can not muck around with those sort of rules. This is a somewhat simple explanation there are quite a few other factors involved BUT in general this will work every time. Of course cables and connectors come into it but that is standard stuff anyway and are easily fixed or fault found

 

Mark

 

 

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  • 9 months later...
Hi, I am running a oldish XCom and now a Bose A20 headset. I have found that there are times that I am not receiving radio call's and are looking for some input. Need to work out if it is a headset issue or compatibility with the radio.The radio has had a full upgrade, including firmware and output drivers so is supposed to be equivalent to the latest model. The volumes are run on the high end, so should be plenty to trigger the headset.

 

I also notice the headset doesn't respond to the radio volumes, and must be adjusted on the headset. This is also abit annoying as there is no discrimination between the calls (internal / external) but I assume is just the way it is with ANR headsets.

 

Haven't had an issue with my old clunker headset, but quality and comfort is far from what the Bose definitely offers, so are keen to understand what the cause is so it can be repaired.

 

Cheers, Chris

Hi Chris , Last weekend I had same problem with my XCOM ( older model-2007) it was very embarrassing . Frustrated to the max took it out from my Savannah and it is in Brisbane now being tested by XCOM service guys.

Awaiting some news this week

 

George

 

 

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