[App_rpt-users] Small audio amp needed

Bryan D. Boyle bdboyle at bdboyle.com
Sat May 18 21:26:51 EDT 2013

Figured I'd throw this out...

I'm interfacing a batwing Systel repeater for 440...basically 2 GP300
HTs stripped out of their cases, mounted on a headsink in a box with
interface circuits (which I'm not using, lifted the necessary signal
resistors so that the signals don't use the onboard controller,
etc)...well, gone through the schematic, and have the proper pickoff for
rx, can get it to recognize (using the PL detect pin going high +5v to
give me a COR), asterisk recognizes carrier (faking it out by using the
PL detect), keys up the xmt side...however, no matter HOW high I set the
audio into the transmitter in radio-tune-menu, it is barely deviating.

Now, I can take an audio generator from my streaming studio, and,
injecting a 1K @+4dBm tone, I can get non-distorted deviation at 3.2K by
hanging on the tx input pin.

So..wondering what the audio level out of the URI is?  I'm thinking it's
lower level then that, maybe -10?.  And based on the low level
deviation...I'm thinking that even the +6dB amp onboard won't do much...

I know that RB had to build an amp to get enough drive to modulate the
220 Micor using direct FM injection when they built my rig; does anyone
have a simple schematic of a 5534 or some such op-amp that can give me a
reasonable amount of gain so I can try and get decent (well, how about
understandable) deviation out of this thing?

Thanks, all.


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