[AMRadio] retro 75

johndtate at post.com johndtate at post.com
Sat Apr 10 23:53:25 EDT 2010

Hi Brett and the group.  You guys are having way too much fun with 
these kits!! Just had a QSO with a few people and among them was Jack, 
W9GT and although he was very hard to copy here in Louisiana, I was 
amazed that I did catch a few words here and there despite an S9 noise 
level.  Had it been December or January with no noise, the 2.5 watts 
would have easily made the trip here.  Anyway, I just put in my order 
to Dave and Brett maybe you could make a document with the mods you 
applied for everyones benefit.  I'm looking forward to building this 
kit and putting it on the air.

John KX5JT

-----Original Message-----
From: Brett Gazdzinski <Brett.Gazdzinski at verizon.net>
To: k1swl at earthlink.net
Cc: amradio at mailman.qth.net
Sent: Sat, Apr 10, 2010 10:21 pm
Subject: Re: [AMRadio] retro 75

As a big home brewer, I tend to pick things apart...
Besides the lack of agc, the receiver really works well for such a low 

I received my modulator chip today, thanks, and installed it.
I got about 30% modulation with the led flashing, using an old electret
condenser microphone.

I changed some values around, and tried a small pot to set the 
levels, but am still working on it.
With the feedback loop open, its possible to get over 100% modulation, 
good sign!

The microphone sounds semi nasty, but very punchy, which is what you 
with low power.

Thanks for the fun kit!


----- Original Message -----
From: <k1swl at earthlink.net>
To: <Brett.Gazdzinski at verizon.net>
Cc: <amradio at mailman.qth.net>
Sent: Saturday, April 10, 2010 8:07 AM
Subject: RE: [AMRadio] retro 75

> Brett-
> Glad you found a solution. So far, I haven't heard from anyone else
> experiencing this issue.
> I set the audio volume on the Retro-75 up for 'room-filling' levels. 
> ALC control engages only at high signal levels and keeps the LM386 
> final from clipping.  With the 3" speaker I'm using, I can fill the 
> house with audio before this happens. It's admittedly not much of an 
> function per se.
> It wouldn't be too difficult to improve on the receive AGC action, 
but it
> would take more complexity. In particular, an additional audio amp 
> would provide the levels needed for a lower AGC threshold. The AF gain
> control would also need to be relocated outside the control loop.
> Otherwise, the gain control does nothing once the threshold has been
> reached. I solved this on the old WM-75 with a 100-ohm pot/rheostat 
> at the audio output.
> 73- Dave Benson, K1SWL

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