Transmission1

Hello everybody !
Do you know how modulation at JFK President ( mainboard PA338AB ) can be increased?
I made the microphone change from the dynamic variant to the elecret. It is ok, but I would like to increase the modulation a bit.

Vr12

Thought you might have tried this first before going to the trouble of changing the element.

@ ch25 : I'm not VR12 on motherboard .I looked better on the motherboard and I think it's VR5 ... What do you think?

Nope, it is PWR pot. Any AM mod/AMC labelled?
Chris

Only SQ , DEV , RF.M and S.M .
I think it must be RF.M ...?

On 338 board there is no am mod adjustment. Just found a schematic.
You can try to remove Q31 to disable limiter, but you need to adjust micgain to avoid overmodulation. Try that, if it will be too strong we try to modify AMC level other way.
Chris

OK, I'm trying. Thanks!

DEV is for FM modulation [DEVIATION] Dont adjust it too high though or you may over deviate.

ch25 wrote: ↑10 Jan 2020, 20:23 On 338 board there is no am mod adjustment. Just found a schematic.

Weird, or what ? Something to note for the future, and yet another reason not to buy a JFK

@cb4ever104 : No problem, I like to experiment Radio is great !

Hello





@+
Claude

What is have to do with topic we discuss here Claude?

The limitation with Q31 I see is for AM ... For FM I am interested in canceling the limitation.
I did not find any other references on the internet related to this ....
I think in the last instance I try to increase the power from the adjustable VR5 motherboard.
Does the power increase to the left?
Do you need any further changes?

Do not cancel FM limiter, you will become unreadable.