Terrible Transmission above Idle

Radios, intercoms, headsets and GPS systems
jimbrain
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Re: Terrible Transmission above Idle

Post by jimbrain » Sat Apr 09, 2011 22:23

Griphos,
Definitely get the intercom out of the circuit before you try anything else. Generally ignition noise is heard while receiving. Also check very carefully before you put a P-lead filter on a Slick mag. I believe there is a feed through capacitor in the mag and adding another is not good. Paul A. probably knows. When you press the PTT key with only the radio in the circuit you cut off the receive path. With an intercom who knows what is going on. You may be getting some kind of feedback. A bad sidetone circuit could be the culprit. If you are not hearing this on receive only, you probably don't have antenna orientation problems. These are educated guesses because as an earlier poster said"its black magic.

Jim

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Re: Terrible Transmission above Idle

Post by pablo » Sat Apr 09, 2011 22:38

Phil:
If you have an ANR (active noise reduction) headset that might be your problem. I talked to Lightspeed about it and they do not recommend any of their ANR headsets (including the Zulu) with hand held radios. I suggest you connect your cheapest, oldest headset directly to the radio, use not the radio PTT, but an external PTT, and use your rubber antenna.
I have tried Bose and several Lightspeed ANR headsets with the same undesirable result. Good Luck!
Pablo

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Griphos
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Re: Terrible Transmission above Idle

Post by Griphos » Sat Apr 09, 2011 23:23

This is all very helpful. I now have several things to try to ferret out the actual problem and I'm anxious to give these tests a try. I am using an ANR headset. It's the Marv Golden branded headset that Lightspeed made but doesn't make anymore (QFR). Hope I don't have to give them up. Very comfortable and I love the ANR.

I've been thinking about what everyone has said, and I'm wondering if what is happening is that the intercom sounds fine because it is voice activated, and, of course, only the headset mike is on when talking on the intercom. I'm wondering if there might be some way that even though I'm using an external PTT, that the radio mike is also hot when I push the PTT and I'm just picking up the cabin noise through the radio's internal mike. That way I'm transmitting all the cabin noise through the radio mike along with my voice through the headset mike. That's why it's fine when I'm at idle. Very little cabin noise then! :-)

Doesn't that sound like it might just be the problem?
Phil
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Griphos
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Re: Terrible Transmission above Idle

Post by Griphos » Sun Apr 10, 2011 17:15

Yep, that's the problem. I tried several headsets, ANR and regular. Plugged the headsets directly into the headset adapter and into the intercom and used the external antenna and the rubber stubby and in all cases, the mike on the radio itself was hot whenever I pushed the PTT button no matter if it was the radio PTT or the external PTT. The one exception was with the rubber antenna. With it, I just got feedback when pushing PTT. So my problem is that I'm picking up all the noise in the cockpit, and the radio mike is pretty sensitive. It picks up the cockpit noise better than it picks up any of the headset mikes.

Here's the headset adapter schematic:
Adapter.JPG
Adapter.JPG (24.21 KiB) Viewed 3306 times
I have an external PTT plugged in as this suggests.

Here's a schematic from my Flightcom intercom manual:
intercom.JPG
intercom.JPG (42.53 KiB) Viewed 3306 times
I could buy another external PTT from them, I guess. The PTT Gold, which plugs in inline, but I'm not sure this will make a difference. Any opinions on that?

I can't figure out why the A-24 won't mute the internal mike when I push the external PTT. I mean why even provide a headset adapter with a PTT plug if when using it, the radio mike stays hot? That's absurd!!

Any ideas about how to fix this now we know what the problem is? Do I need to buy a new radio? I'll call Icom tomorrow and talk to them. If I get a Sporty's, can I hook it up this way and it will work without broadcasting the cockpit noise through the internal mike? Those of you who have an A-24 setup like this, I'm guessing this doesn't happen in yours? Do you have yours hooked up as I do? Is my unit just buggered?
Phil
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Griphos
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Re: Terrible Transmission above Idle

Post by Griphos » Mon Apr 11, 2011 11:48

Icom was not helpful. Their response was basically that it shouldn't do that. I should send it in for them to look at (at $84/hour + parts + shipping both ways).

Hmmmm......

Anyone have an A14? If so, do you like it? I don't need the nav of the A24. If the A14 seems to be as good a comm radio as the A24, and doesn't have this problem with headsets and external PTT (I believe my adapter and PTT will work with the A14 as well), then I may just go that way.
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rkittine
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Re: Terrible Transmission above Idle

Post by rkittine » Mon Apr 11, 2011 12:10

Lots of good advise and recommendations. I have an A-24 hooked up to a Softcomm Intercom along with a set of David Clarks. When I first installed it I had ignition noise on both receive and transmit when I was above idle. If you are only getting the noise on transmit, then your iginition is probably emitting RF that is mixing with the output of your radio. Having the antenna in the plane adds to that.

A dipiole is a Balanced Antenna, one side is the radiation (usually 1/4 wavelength) and the other side connected to the shield, another 1/4 wave length. Balanced radiators do NOT need a ground plane, so do not ground one side of the antenna, though the shield of the coax (outter braid) should go to ground and if you are running it on internal batteries, that is probably not happening so the whole length of coax is acting as an antenna allowing for the pick up of spirious emmissions. You should try grounding the radio with a strap from the antenna connector to the frame.

Use of a 1/4 wave antenna, over a ground plane, will insure that you have the braid side gounded if what you use for a ground plane is attached to the frame in some way. I have my 1/4 antenna on the wing fairing on the right hand side and have metal tape inside the wing creating more ground plane. You should have at least 21"s in each of at least two dimensions if you want a true RF ground. (This is not a DC ground, which is much different).

When taxing past our office, the ICOM A-110 in the office picked up the emmissions from my engine. Replacing of the wiring with Shielded Cables, installation of the Filter Capacitors and a Braided Ground strap from the antenna / radio to the frame eliminated all the noise on both receive and transmit.

One last thing to consider, if you are running the radio of power in the plane, that is provided by a generator or an alternator or even a battery hooked to one, you can pick up noise that way also. The handhelds do not have the same Noise Cancelling circuitry as does the panel mounted radios. One way to eliminate that is to fee the radio with an ICOM CP-20L battery eliminator, which is a filtered 11 volt (the radio does not run on 13.6 volts, and will shut off if Directly Fed with anything above 11 volts. The CP-20 will provide filtered 11 volts to the radio from any source of up to 35 volts.

Cheers - Robert
WA2YDV
Robert P. Kittine, Jr.WA2YDV
West Nyack Aviation, L.L.C.
New York, New York 631-374-9652
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Re: Terrible Transmission above Idle

Post by EDGEFLY » Thu Aug 23, 2012 10:56

Griphos,

I am currently experiencing similar problems as you described in your thread which ran in April of 2011. There is different hardware involved and no intercom but the problem sounds identical. could you let me know what solution you came to with this ? I am going to have to back to ground zero and do everything otherwise. I suspect that there is less "Black magic" than characteristic problem here, at least I hope so.

Dale

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Griphos
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Re: Terrible Transmission above Idle

Post by Griphos » Thu Aug 23, 2012 11:11

Hello,

Well, I bought the A14. That did seem to make a difference. I'm pretty sure the A24 was simply picking up a great deal of cockpit noise. I also bought a leather cover for the foam wrap on the mic to further reduce cockpit noise. It was a little hole in it for voice transmission. It's made for open cockpit flyers. I forget who makes it. I'll look that up for you if you like.

I also found that the intercom batteries really need to be fresh, or transmission suffers quickly, but since you don't have an intercom, you don't have to worry about that.

I've asked quite a few people how they hear me now, and everyone says I'm clear without much noise, so I guess my particular problem is solved.

Good luck on yours.

Phil
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rkittine
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Re: Terrible Transmission above Idle

Post by rkittine » Thu Aug 23, 2012 16:20

Hi Phil,

A half wave dipole is an "unbalance" antenna and depending on the installation will provide an impedance of between 45 and 75 ohms, rather than the 5o ohms that the radio likes to see. The farther off the Standing Wave Ratio (SWR) is, the more of the RF (Radio Frequency) will come back down the shield of the coax and cause its own issues.

A Dipole is a Ground Independant antenna and therefore is not aided by a ground. If you ground one side, you will get a 1/4 wave vertical, which might cause more problems.

As others have said, you should check to see if you have:
Capacitor Filters on your Mags
Shielded Spark Plug Leads
Both of the above will cause you problems if you do not have them and will help reduce the problem if you do.

The next thing I would try, assuming that you have enough coax, is to wrap about 6 turns with a diameter of aboutr 6" and tape it. This should be right at the feed location to the antenna and becomes an RF Choke to keep the reflected RF from coming back down the coax.

Moving the antenna sometimes helps too, but as someone else said, this can be a problem that takes a lot of patience chasing.

Best Regards, Bob WA2YDV
Robert P. Kittine, Jr.WA2YDV
West Nyack Aviation, L.L.C.
New York, New York 631-374-9652
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Re: Terrible Transmission above Idle

Post by rkittine » Thu Aug 23, 2012 16:24

Also, Early ICOM handhelds go to transmit with a pull to ground on the audio lead and do not have a separate PTT line. Newer ICOMs have a real separate PTT line, which means that the radios are hooked up to intercoms differently or you will find that in come cases, just plugging in causes the radio to go into Transmitt.

The old A20 have the Pull to Ground, while the most recent A24 has the separate PTT line.
Robert P. Kittine, Jr.WA2YDV
West Nyack Aviation, L.L.C.
New York, New York 631-374-9652
rkittine@aol.com

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Re: Terrible Transmission above Idle

Post by EDGEFLY » Fri Aug 24, 2012 07:45

Rob,

I agree with your comments about fractional wavelength antennas and the need to maintain a good SWR on the element following the transmitter. However, any SWR in the 1:1 to 1:1.6 is probably adequate. I doubt that many small aircraft antennas are even measured, let alone design corrected for a proper ratio. An excellent example of this is my Chief which has an under belly antenna but is cabled with RG 6, a 75 ohm characteristic impedance. I will be replacing it shortly with RG 58 to get everything back to 50 ohms. Right now, I am trying to use a Sporty's A 300 to get some kind of communication capability set up. It has very definite ignition static problems despite having shielded ignition harness but no filter capacity on the new slick mags which I can see. What doe this kind of package look like? Could you give me a product reference ? My A300 with its' rubber ducky is adequate for short distance work, but I really want to get the antenna system going for the future so that I have a clean communications format if I need it. I.

Also, have a David Clark 10-40 headset with an integral PTT switch. At this point, it does not seem to be compatible with the A 300 although the proper cabling is available to connect the two. Do you happen to know if there is a Pull- to-Ground versus separate PTT problem there ?

Dale

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Re: Terrible Transmission above Idle

Post by rkittine » Fri Aug 24, 2012 08:54

Hi Dale,

Very true. I have just seen many installations where there was so much Decoupling due to the proximaty of other metal to the antenna, that the SWR was sometimes over 2.5:1. Worth checking if you have an SWR Bridge. I use an ICOM A-24 in my Champ and run a ground strap from the radio chassie to metal (Not really a ground, but helps at RF) and that helped keep unwanted stray RF out of my radio. I have even seen the mike cord pick up RF and put it into the audio. I turn off my iPhone in the plane for just that reason, because when it pulses to let the towers know where it is, I get a buzz on my transmission.

Ciao and Good Luck - Robert
Robert P. Kittine, Jr.WA2YDV
West Nyack Aviation, L.L.C.
New York, New York 631-374-9652
rkittine@aol.com

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Re: Terrible Transmission above Idle

Post by EDGEFLY » Tue Oct 23, 2012 09:28

Bob,

This post is relative to yours of 8/23/2012 on this thread re: radio noise problems experienced by Phil. In it you made some recommendations to limit comm noise caused by ignition etc. which included shielded leads and capacitor filters on the Mags. During its recent annual and my verbal review of it with the A&P, I asked about the Mag filters for my A/C which has a set of Eiseman Slicks. His response was that, although he had removed a pair of capacitors from an old set of boxcar Eisemans to solve a timing problem on a Cessna once, he was not aware of a product applicable for my Slicks. I have also looked online (commercial) for such a thing and have not found it. Do you know of such a Product or alternatively a component sizing and schematic connection for reactive components which would not have negative side effects ? I already have shielded leads and the proper plugs but still have some ignition noise which I would like to eliminate. I can probably "Shade-tree" this but would rather use a proven fix and spend my time flying.

Dale

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Re: Terrible Transmission above Idle

Post by EDGEFLY » Tue Oct 23, 2012 09:28

Bob,

This post is relative to yours of 8/23/2012 on this thread re: radio noise problems experienced by Phil. In it you made some recommendations to limit comm noise caused by ignition etc. which included shielded leads and capacitor filters on the Mags. During its recent annual and my verbal review of it with the A&P, I asked about the Mag filters for my A/C which has a set of Eiseman Slicks. His response was that, although he had removed a pair of capacitors from an old set of boxcar Eisemans to solve a timing problem on a Cessna once, he was not aware of a product applicable for my Slicks. I have also looked online (commercial) for such a thing and have not found it. Do you know of such a Product or alternatively a component sizing and schematic connection for reactive components which would not have negative side effects ? I already have shielded leads and the proper plugs but still have some ignition noise which I would like to eliminate. I can probably "Shade-tree" this but would rather use a proven fix and spend my time flying.

Dale

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Re: Terrible Transmission above Idle

Post by EDGEFLY » Tue Oct 23, 2012 09:28

Bob,

This post is relative to yours of 8/23/2012 on this thread re: radio noise problems experienced by Phil. In it you made some recommendations to limit comm noise caused by ignition etc. which included shielded leads and capacitor filters on the Mags. During its recent annual and my verbal review of it with the A&P, I asked about the Mag filters for my A/C which has a set of Eiseman Slicks. His response was that, although he had removed a pair of capacitors from an old set of boxcar Eisemans to solve a timing problem on a Cessna once, he was not aware of a product applicable for my Slicks. I have also looked online (commercial) for such a thing and have not found it. Do you know of such a Product or alternatively a component sizing and schematic connection for reactive components which would not have negative side effects ? I already have shielded leads and the proper plugs but still have some ignition noise which I would like to eliminate. I can probably "Shade-tree" this but would rather use a proven fix and spend my time flying.

Dale

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