[AMRadio] When talking about AM power


b.gaz at comcast.net b.gaz at comcast.net
Sat Oct 10 23:26:58 EDT 2015


There is no front end to overload, its a high Q tuned circuit. 
The antenna input is shorted to ground and I turn the rf gain down. 
It matches the mod monitor (they track). 

As far as the sdr goes, its an sdr-iq at the moment, which I like because it works with many programs. 
The home brew receiver works better (less noise) but the display is great, it shows my signal and other signals, how wide they are, how strong they are, if they are off frequency or not, where people are, and a good amount of info about the modulation. 
Sync detection with the ability to listen to one sideband or the other is QRM is on one side. 
A 16 bit unit is a VERY good receiver (the sdr-iq is a 14 bit unit), low noise, high fidelity, any filter width you want and the fantastic display. 

As a transmitter, the sdr stuff is great also, but limited to 25 watts carrier like most modern 100 watt (pep) radios. 

I like it all, home brew tube stuff, sdr stuff, if it does AM its ok with me. 
I got tired of the vintage ham stuff many years ago and sold it all off. 
It was all crap, with loads of built in weak points, trouble spots and poor performance. 



----- Original Message -----

From: "Geoff" <ars.w5omr at gmail.com> 
To: amradio at mailman.qth.net 
Sent: Saturday, October 10, 2015 5:49:09 AM 
Subject: Re: [AMRadio] When talking about AM power 



On 10/09/2015 08:01 PM, b.gaz at comcast.net wrote: 
> I have and use a scope off the receiver IF, 

The problem with that is, the IF gets saturated and the AGC of the 
receiver doesn't respond accurately. 

Let's say you're running a transmitter like John/WA5BXO built up, that 
has enough audio power in the modulator to properly modulate his carrier 
with his peak'ed asymmetrical voice. If you try to monitor that signal 
in the IF of a receiver, you'll never see the positive peaks of the 
signal, until you turn off the AGC and reduce the RF Gain to the point 
where the signal is not overloading the front end of the receiver. 

Best thing to do for a monitor scope is to take some small coax and feed 
it into the scope's BNC or banana-jack input, and run the other end 
outside near the antenna. 5 or 6 turns and a couple of inches diameter 
(nothing is exact) of some stiff copper wire connected to the coax and 
supported somewhere will give a much truer reading of what your 
transmitter is producing. Monitor transmitted signals, not those that 
are passed through multiple stages in a receiver. 

> and an sdr spectrum display. 

Now, that's something I'd like to get into, as well. The spectrum 
display on an SDR device. 

SDR intrigues me. I've played with a couple of on-line SDR receivers 
and seeing the actual bandwidth of some stations is amazing. Having a 
receiver with no other noise and only monitoring the transmitted audio 
would tell a lot about some other components of the transmitted signal. 



73 = Best Regards, 
-Geoff/W5OMR 
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