Radio testing ideas

If I can go to 11 volts on the battery, there should be no problem. I will check the volt meter while transmitting. I had a two hour engine off soaring flight on thursday and the battery and radio worked well. Engine started fine after landing, so the battery held.

I forgot to mention that a couple years ago I talked to a Narco factory technician about ideas for maintenance. He told me to check the radio display contacts. He said the display contacts get corroded and this limits output power. I cleaned the contacts with a pencil eraser as he had suggested and that seemed to help.
I did that again last week and it seemed to be corroded again. Maybe this needs to be done annually.

Anyway, I was impressed by the free assistance I got from Narco. I thought it was a good radio. The radio has gotten wet a few times from leaks in the canopy seal. I take it out each flight now to protect it from moist salty air.

The Narco tech said the radio is not designed for water.... but that would be nice in this climate.

This radio testing is kind of interesting. Any books available about aircraft radio service? What does it take to get into avionics service?

Originally Posted by BBerson

...I had a two hour engine off soaring flight on thursday and the battery and radio worked well....

OT, but nice! Ridge day, or just good thermals?

Just thermals. Or perhaps thermals with a bit of "convergence zone". I say a bit of CZ because the lift was over a large area near the end. I circled the airport several times in lift most of time, but had to come down to pee. Convergence zone is an area where wind comes around the mountains from both north and south and collides and the air is forced up.

Originally Posted by BBerson

...but had to come down to pee.

I hate it when that happens.

Originally Posted by BBerson

Convergence zone is an area where wind comes around the mountains from both north and south and collides and the air is forced up.

Fun, isn't it? As you know, we have a rather nice one at Elsinore.

Originally Posted by BBerson

Huh, never thought of that. Can anyone confirm that electromagnet noise has no effect on transmission?

I installed 5K resistor plug caps when I converted to auto type unshielded spark plugs. The 5K resistor should eliminate spark noise.

Maybe I should put some foam on the microphone. I have two headsets, one David Clark and the other is a cheap Flightcom headset. Doesn't seem to matter which headset is used, however.

I measured the cockpit noise, at full throttle it is 90db.
But isn't 90db about average
BB

It sure will affect transmission. I have unshielded mags on the Jodel, with shielded plugs and leads, and the radio picks up ignition noise from the unshielded distributor caps and messes the transmission up. I get complaints about it.

Dan

Originally Posted by BBerson

This radio testing is kind of interesting. Any books available about aircraft radio service?

None that I'm aware of

What does it take to get into avionics service?

1) A lot of expensive, specialized test equipment.
Avionics Test Solutions - Aeroflex

2) The knowledge to use it.

3) Factory authorization as a repair station for their radios.

4) FAA approval as a repair station.

5) An FCC General Radiotelephone license to allow you to work on radio transmitters.
FCC: Wireless Telecommunications Bureau: Types of Licenses: General Radiotelephone

Without the last two you are unlikely to get the factory authorization and without the factory authorization you won't have access to the information needed to diagnose problems or the special replacement parts needed to fix them.

Originally Posted by djschwartz

None that I'm aware of



1) A lot of expensive, specialized test equipment.
Avionics Test Solutions - Aeroflex

2) The knowledge to use it.

3) Factory authorization as a repair station for their radios.

4) FAA approval as a repair station.

5) An FCC General Radiotelephone license to allow you to work on radio transmitters.
FCC: Wireless Telecommunications Bureau: Types of Licenses: General Radiotelephone

Without the last two you are unlikely to get the factory authorization and without the factory authorization you won't have access to the information needed to diagnose problems or the special replacement parts needed to fix them.

Getting the General Radiotelephone License (GROL) looks pretty easy with a $50 lesson book and test fee.
The repair station would not be easy. I have A&P-IA, would that be sufficient? Or is a repair station required to get factory assistance and repair manuals?

My brother signed up for the Cleveland Institute of Electronics home study course about 1970. I was 15, and went through about the first half. The course was quite good, I thought. They have an option now for $200 here:http://www.ciebookstore.com/bookstor.../addtocart.asp

If you're really serious about this I suggest you contact your local FSDO for accurate and up to date information on what this really requires. Then I would contact a couple of the major avionics manufacturers to see if they'll even talk to you about becoming an authorized repair station. I would also suggest that if there is already a reputable avionics shop anywhere close to your location you're very unlikely to ever generate enough business to make back the investment in equipment and supplies you'll need to be a serious operation. Modern radios need far less service than the old ones did and some are factory repair only. And there are far fewer general aviation aircraft being built and flown today and even fewer being upgraded so there is much less business to go around than in the past.

Originally Posted by djschwartz

Modern radios need far less service than the old ones did and some are factory repair only. And there are far fewer general aviation aircraft being built and flown today and even fewer being upgraded so there is much less business to go around than in the past.

That is what I was thinking. My only interest would be in basic troubleshooting. I already know that earning a reasonable income is impossible. I may try to find a book about simple testing and maintenance.
Thanks for your ideas.
BB

dj,

I found my mic jack is installed without any insulated washers. I found the Sigtronics installation here http://www.sigtronics.com/pdf/air_pdf/spa-400.pdf and it calls for two insulated washers per mic jack, just as you advised.

The repair station did not use the insulated washers. Probably because it was easier to just install directly in the aluminum panel.
The Grob G109 is all fiberglass. So maybe it will not make any difference.

Also, I was finally able to read the intercom operating instructions and noted that the co-pilot mic doesn't work when the intercom is off.

Still wondering what a switch on the side of the intercom does that says: "keep alive". Nothing seems to matter if on "keep alive" or "off". So I leave it on keep alive for good luck.

thanks dj

Originally Posted by BBerson

The repair station did not use the insulated washers. Probably because it was easier to just install directly in the aluminum panel.
The Grob G109 is all fiberglass. So maybe it will not make any difference.

It depends on what else might be grounded to that aluminum panel. If the ignition is grounded to that panel along with the mic jacks then you almost certainly will have a ground loop that couples ignition noise into the mic circuit. The panel will need to be connected back to the negative of the battery somehow and all currents coming to that panel will flow through that same ground wire together to get back to the battery. And I'll bet that ground wire isn't very big since it doesn't carry the full battery charge or engine start currents. That's a classic setup for a ground loop. The insulated washers should help and that will be a lot simpler than trying to reroute grounds with heavier wire.

One advantage of a non-conductive structure is that it forces one to think about the ground return side of electrical circuits. In an aircraft with a metal structure people tend to assume they can just attach a ground to the airframe where ever it is convenient. That may work OK for simple DC power to lights, gyros, an other insensitive accessories; but, it can wreak havoc with radios.

Dave

I do not really understand what a ground loop is exactly. But I will install ground wires to the mic jack and see what happens. Right now, the mic jack is grounded in the aluminum panel by the mic jack itself.

Is a ground loop caused by two ground paths?


If I understand correctly, I should eliminate the existing mic ground in the panel by installing insulated washers. Then I will solder ground wires to the mic jack solder lugs and connect these ground wires to the intercom ground. So the electrons will return on the ground wires only and not the instrument panel. Is that right?

Originally Posted by BBerson

I do not really understand what a ground loop is exactly. But I will install ground wires to the mic jack and see what happens. Right now, the mic jack is grounded in the aluminum panel by the mic jack itself.

Did you take a look at the wiring tips on the EAA Chapter 902 website that I referenced earlier in this thread? I think that will help. If not, let me know and I'll try to add more to it.

Originally Posted by BBerson

Is a ground loop caused by two ground paths?

Actually, it is caused by having a circuit grounded at more than one point which results in two circuits sharing a portion of the ground path.

Originally Posted by BBerson

If I understand correctly, I should eliminate the existing mic ground in the panel by installing insulated washers. Then I will solder ground wires to the mic jack solder lugs and connect these ground wires to the intercom ground. So the electrons will return on the ground wires only and not the instrument panel. Is that right?

Yes, that is correct. And what that means is that ground currents from other circuits, such as the ignition, strobe, or alternator will not be carried on the same ground wire as the microphone.