TK-880 in Crop dusting aircraft audio help needed

camsdad · Post by **camsdad** » Fri Dec 29, 2006 4:45 am

Does anyone have any good experience with quality helmet TX audio utilizing a aircraft helmet with noise canceling mic for a UHF LTR 12.5kc sys?
Utilizing a home grown mic bias interface the TX audio quality is very poor when the aircraft is in the air.
When on the ground or not running at all the TX quality is quite good.
any help would be appriciated.
Thanks!

Camsdad

n5tbu · Post by **n5tbu** » Fri Dec 29, 2006 4:03 pm

What value blocking cap are you using on the mic high?
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camsdad · Post by **camsdad** » Tue Jan 02, 2007 12:19 am

For some reason Im thinking 47mfd.
As soon as I find my notes or crack open a radio, I wll let you know.
It's been chaotoic with the holidays.

jwb8734 · Post by **jwb8734** » Tue Jan 02, 2007 7:50 am

How are you having the mic run? Are you coing through the mic port on the front or are you using the accessory port in the back?

Also is your aircraft radio connected to the same headset and can be changed by a switch?

n5tbu · Post by **n5tbu** » Tue Jan 02, 2007 9:33 am

I am assuming that you are getting engine/wind noise? I have done a few dusters and ended up using a .0047mfd,works great but the pilot will have to "kiss" the mic.No more back ground noise.
I have never seen a duster with an aircraft radio in it!
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jwb8734 · Post by **jwb8734** » Tue Jan 02, 2007 11:41 am

n5tbu wrote:I have never seen a duster with an aircraft radio in it!

I guess maybe I'm to much of a city slicker. I thought all aircraft had to have aircraft radios to talk to there local controllers for any clearence into airspace.

I know that some of the Traffic Planes in the Boston area use the accessory port on the back of there radios.

camsdad · Post by **camsdad** » Tue Jan 02, 2007 1:59 pm

Back again,

jwb8734,
The helmets are connected to the rear accessory port of the radios with some quick disconnect avaiation audio jacks. NO switching.

n5tbu,
Yes it is getting engine/wind noise, and they do kiss the mic.
It is extreemly bad IMO while the aircraft is in the air. ON the ground everything is fine.

n5tbu · Post by **n5tbu** » Tue Jan 02, 2007 4:25 pm

Try that .0047 and you will be pleased!
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camsdad · Post by **camsdad** » Thu Jan 11, 2007 8:29 pm

Well I finally got a look at the home grown Mic Bias circuit.
Yep! I was right I am using a 47uf electrolyic cap.

n5tbu · Post by **n5tbu** » Thu Jan 11, 2007 8:45 pm

Yep,passing too much audio!
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camsdad · Post by **camsdad** » Fri Jan 12, 2007 12:46 am

So where can I find these .0047mfd electrolyic cap's?
Or are you using Aluminium electrolytic cap's?
And at what voltage rating?
Sure not Radio Shack

n5tbu · Post by **n5tbu** » Fri Jan 12, 2007 8:09 am

At your local Radio Shack 2 to a bubble pack,Not at the shop to give you the part number.
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