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tazin river
 Post subject: radio problems
PostPosted: Thu Jul 05, 2012 1:49 pm 
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Location: Way up north
Ran into some radio problems yesterday when returning from a lake north of Yellowknife. Could not talk to the tower...radio transmits but the voice does not get carried over....and it receives perfectly...

How do I start troubleshooting? PTT?

Thanks


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avyonx
 Post subject: Re: radio problems
PostPosted: Thu Jul 05, 2012 2:47 pm 
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Do you have an audio panel? If so the PTT switch can be verified by a solid XMT light or the Mic selector flashes. Really depends on model. If you are single Comm using a Intercom system then there should also be a light to indicate VOX (usually red) and XMT (Usuallly Green)

Now that you have checked the PTT is operational........... Make sure you are transmitting on the correct comm. I know thats dumb but audio panels let you transimt on 1 while receiving on everything. Easy finger trouble selection that everyone has encountered.

Then try re-racking the radio. If that is a no then its time to inspect the wiring of the Mic Hi line to your radio. Does your intercom work? This will eliminate the Mic Jack is bad but could possibly mean the mic hi and lo's are not making it to the raio iteself.

Did you say you had sidetone?

If that all checks out, then remove radio, accidentally drop it so that the technicians at the bench shop you choose can justify charging you $1000 to fix a radio when thats exactly what the unit is probably worth.

Just so you know......its really hard for us guys to help without giving us more information about your avionics package. Like Radio type, how many radios and audio panel information

That gives you something to try anyways.


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donnybrook
 Post subject: Re: radio problems
PostPosted: Thu Jul 05, 2012 2:56 pm 
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check your headset/helmet before you do anything to the aircraft....


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tazin river
 Post subject: Re: radio problems
PostPosted: Thu Jul 05, 2012 3:32 pm 
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Location: Way up north
Thanks guys

I appreciate how difficult it is to diagnose something with little info.

Flying back to Yellowknife yesterday, I could see the radio (Narco) was transmitting as it would display the transmit signal and the folks in the tower could read the static signals from my radio when I was pressing the the PTT...Press a couple click if you're NORDO he would say and was able to communicate with him (sort of).

The intercom works as I was able to chat with the passenger.

This morning, I reached underneath the dash, disconnected the antenna from the radio, reconnected it and surprise was able to talk to the folks in the tower for a radio check. Almost sounds like a bad conenction somewhere.

I should also add that I had to use my back-up portable PTT in order to transmit as the one in place with the aircraft was not working. I had done the same yesterday in flight but did not have any success then...

So somehow, it seems to either be a bad antenna connection and/or something to do with the old PTT switch/wires...

Is there some type of cleaning spray that can be applied to the antenna connectors to help cleaning it up?

Having said all this, I really don't know much about avionics!

Cheers

Bruno


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avyonx
 Post subject: Re: radio problems
PostPosted: Thu Jul 05, 2012 3:58 pm 
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It sounds like you simply need to replace the coax connector at the back of the radio. Over time they lose tension between the pin and socket on coax connectors. Narco = Old so I would assume this is an older installation and maybe Original Equipment.

You could try spraying Electro Contact Cleaner made by LPS. Not sure if it will do anything. Here is the link to the product http://www.lpslabs.com/product_pg/cleaners_pg/ECC.html

The PTT works like this. The Radio requires a signal of when it is to transmit. The signal it gets is a ground (or LO) from the crew member transmitting. This can be done by either grounding the tip of the mic plug of your headset or through a momentary push switch that switches ground.

Since you said an alternate PTT worked but the one installed did not then one of two things has happened. One is there is no ground to reference when the button is pushed or the wire has broken (become open) to the PTT input of the radio. I guess 3 things, the push button could be buggered. Which is also very common and you could spray that sucker too with the cleaner you just bought.

Let us know how you make out.


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cgzro
 Post subject: Re: radio problems
PostPosted: Thu Jul 05, 2012 4:32 pm 
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In general with electronics its the mechanical stuff that goes first.
Likely problems are the jacks which rust a bit or lose tension or any wire that flexes can break inside the cladding.

Cleaning all connectors and trying a new headset is a good start. Next Id look at the ptt and its wires for flexing problems.

Oh a low battery can cause problems in xmit too.,


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Colonel Sanders
 Post subject: Re: radio problems
PostPosted: Fri Jul 06, 2012 12:01 am 
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Quote:
disconnected the antenna from the radio, reconnected it and surprise was able to talk to the folks in the tower for a radio check


A little electrical contact cleaner from Canadian Tire is your friend, on the connectors at both ends of the coax. If that doesn't permanently solve the problem, replace both connectors on the coax. Cheap and fast, your choice crimp or solder.

Next, remove the antenna and check for corrosion on the ground plane surface. This can really screw up an antenna.

I suspect you just had a bad antenna cable connection.


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azimuthaviation
 Post subject: Re: radio problems
PostPosted: Fri Jul 06, 2012 8:10 pm 
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Your coax and antennas are probably fine, problems there won't give the faults you describe. You're transmitting rd with no modulation but your Mic works. You're receiving modulated rf in your earpiece. The antenna and coax are common to both so look elsewhere. I would guess the audio hi line going to the radio. If its broken, you will transmit only unmodulated rf. Narco utilized a sort of blade type connector on their avionics, a pin making poor contact between the audio hi line n radio would give you an intermittent fault like you describe.


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Colonel Sanders
 Post subject: Re: radio problems
PostPosted: Fri Jul 06, 2012 11:32 pm 
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AA: I have seen problems where the comm could RX ok - but scratchy - but the TX was horrible. Was a cabling/antenna problem. I guess you can sort of RX with a really crappy antenna but you can't TX worths beans with a really crappy antenna. SWR and all that.


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azimuthaviation
 Post subject: Re: radio problems
PostPosted: Sat Jul 07, 2012 2:59 am 
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Yeah that's true, but remember, amplification of the rx signals only happens in the radio. So if corrosion is preventing a ten watt signal from transmitting properly it won't allow an rx signal of a couple picowatts through. The way I'm seeing it is there's a strong rf signal getting out but no audio, so if I was being paid to troubleshoot I'd look at the audio hi line. But considering the op's existing setup and where he flies, whatever the fault is I'd recommend repairing it by installing a GNS430W.


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Colonel Sanders
 Post subject: Re: radio problems
PostPosted: Sat Jul 07, 2012 3:54 am 
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Quote:
I'd recommend repairing it by installing a GNS430W


:lol:


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single_swine_herder
 Post subject: Re: radio problems
PostPosted: Sat Jul 07, 2012 4:26 am 
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If tower was receiving a carrier with no modulation, the issue is not the antenna, its in the audio input path, dirty or poor mechanical connection at the radio tray, or perhaps an intermittent on the printed circuit board ... cracked trace, cold solder joint, etc.

I'd suspect that when you reached around to disconnect the ant coax, you jostled something in the audio input. It will most likely fail again before too long.

Intermittent electronics problems don't fix themselves for very long.


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CID
 Post subject: Re: radio problems
PostPosted: Mon Jul 09, 2012 1:47 pm 
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Your antenna forms part of the tuned circuit of the receiver and transmitter. Bad connections have MUCH less effect on receivers than on transmitters, especially some of the older Narco radios. Picowatts???

Anyway, if you're close to the airport there is a good chance that you can receive but not transmit effectively on a radio. I've witnessed this myself on a system that had a broken coax connector. the cable end was cracked and not connecting the outer conductor to the antenna. Received almost perfectly but detuned the hell out of the transmitter.

Some of the early sold state Narcos like the Mark 16 and Comm 11 were notorious for having their transmitters go completely sideways when the antenna wasn't perfect. Some people replaced their tube Mark 12 with them and found they wouldn't work very well at all until they also replaced the steal rod antenna with one that was much more tightly tuned.

The Mark 16 in particular actually will not modulate with a bad antenna. If you have one of those, I would HIGHLY recommend you replace it and put it on eBay as a boat anchor. The Comm 11 is better but still a little sensitive to bad antennas.


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Beefitarian
 Post subject:
PostPosted: Mon Jul 09, 2012 6:22 pm 
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Two questions.

How much installed is a new Nav/com? And how much is a typical used one in value?

Obviously I'm looking for very rough estimates and I'm not going to whine later if I go to buy one.

I'm guessing a decent new radio is going to be around three thousand dollars and the old one in the plane is worth between $30 and maybe a grand.


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avyonx
 Post subject: Re: radio problems
PostPosted: Mon Jul 09, 2012 7:28 pm 
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Used Garmin 430W's will run you about $6500. Thats just the unit, not installed and you may be able to negotiate the required antenna/rack/installation kit. That usually runs you another $200 or so.

You can get a new SL30 NAV/COMM for about $3000 (not too many used ones around) and a straight SL40 Comm is around $2000 or less.

It depends on what you have installed but is usually best sold at a marina for anchoring purposes.......

KX155 are worth more than people think. Especially if they are straight 14V with Glideslope.


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Beefitarian
 Post subject:
PostPosted: Mon Jul 09, 2012 8:31 pm 
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Ok, I should have read this. I think my PM response is packed with ignorance. Oops. Thank you for responding avyonx. :D


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Colonel Sanders
 Post subject: Re: radio problems
PostPosted: Mon Jul 09, 2012 11:40 pm 
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Quote:
Bad connections have MUCH less effect on receivers than on transmitters


Exactly!

http://en.wikipedia.org/wiki/Standing_wave_ratio

Quote:
A problem with transmission lines is that impedance mismatches in the cable tend to reflect the radio waves back toward the source end of the cable, preventing all the power from reaching the destination end


A broken/disconnected coax center is going to reflect incredibly ...


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CID
 Post subject: Re: radio problems
PostPosted: Tue Jul 10, 2012 1:41 pm 
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A broken shield will reflect badly too. So will a poor groundplane or a cheap antenna. SWR is a property of RF transmissions lines and certainly is important to consider but the Maximum Power Transfer theorem should be considered too.

http://en.wikipedia.org/wiki/Maximum_po ... er_theorem

In transmissions lines we deal with the "characteristic" impedance of the transmission lines and antennas. You won't measure 50 ohms on the coax or antenna of 50 ohm transmission lines using an ohmmeter. The characteristic impedance of a coax cable is a property of the ration of the diameters of the inner conductor and the outer conductor. The characteristic impedance of antennas is primarily based on the physical characteristics but there are ways to tweak the impedance to better match the transmitter impedance. Tuning, of course is another consideration. You can have a perfectly matched characteristic impedance in your transmission line and antenna but if it's not the right wavelength, it won't respond well to the frequencies you're trying to work with.

Antennas work best when they are physically the full wavelength of the signal but they can work effectively when they are 1/2 or 1/4 of the wavelength. On aircraft, 1/4 wavelength antennas are the norm in order to achieve a good balance between performance and size.

So the "size" of the antenna an easily be calculated by dividing the wavelength by 4. Wavelength is the speed of light (3E8) divided by the frequency. HF systems require massive antennas because of the low frequency but they cheat a little by using antenna couplers that make relatively short antennas work with the transceivers.


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tazin river
 Post subject: Re: radio problems
PostPosted: Sun Jul 15, 2012 2:24 pm 
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Thank you all.

I cleaned up all coax connections with the LPS spray as recommended and also where the headset jack's plug in to the intercom. I have not had any other issues since I first mentioned this problem here and I flew 1/2 dozen time at least.

My AME is back from vacation and will look at the plane in a couple days and see what he can do. I certainly do not want to get this problem to happen again so I might start by getting new coax cables and connections.

Cheers

BC


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FlyGy
 Post subject: Re: radio problems
PostPosted: Sun Jul 15, 2012 4:37 pm 
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I know nothing, so don't flame me too hard.

Could this also be a poor power connection to the radio(corroded power supply)? From what I understand, a radio requires more power to transmit than it does to receive. If there is a poor connection it may not be drawing sufficient power to be able to transmit, yet reception will still work fine.


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CID
 Post subject: Re: radio problems
PostPosted: Sun Jul 15, 2012 10:09 pm 
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Flyguy, yes. Totally possible. Poor connection add resistance to the circuit. The more current that is drawn, the more voltage drop there will be in the bad connection and less voltage at the radio power connections. Could work in receive only to fail on transmit.


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