[AMRadio] When talking about AM power


Larry Szendrei ne1s at securespeed.us
Sat Oct 10 19:44:05 EDT 2015


On 10/10/15 10:09 AM, Todd, KA1KAQ wrote:
>
> As to the SoftRock approach you mentioned Larry, I recall a writeup on 
> 'fone a several years ago done by Gary/W2INR about the SoftRock kit 
> made for the R-390A receiver and probably others. Basically it gave 
> you the benefits of the display while still using your old tube 
> receiver. The best of both worlds. I still need to track down one of 
> those kits. Interesting that you used something similar or maybe the 
> same kit on your SX28. That must provide quite a display - panadaptor 
> deluxe!
>
> ~ Todd,  KA1KAQ/4
(Hi Todd!)

AFAIK, there is no Softrock specifically made for the R-390* receivers. 
But what is now called the "Softrock Lite II Combined Receiver Kit" can 
be built for several frequencies, for example, a segment of 40M (whose 
range of frequencies around the "center frequency" is limited by the 
sample rate of your soundcard), or, 455KHz as I mentioned. I have the 
latter (and recently was given one of the former, as well) and it was 
hooked up to my SX-28 until recently, when I tried it it with my 
R390/URR. I found the signal off the IF output on the back panel of the 
receiver was way too strong and overloading the Softrock - no wonder 
with 5 or 6 stages of IF. I forget the exact number of stages, but it's 
one or the other. Even with the RF gain control backed off results were 
lousy. I had a homebrew 50 ohm attenuator someone had given me many 
years ago - I don't even know the dB of attenuation (but my curiosity is 
up so I'm going to measure it) - so I stuck it between the R390 and 
Softrock - it was perfect! Probably reinventing the wheel here, and 
there may well be a better or simpler way to do it. You'd want to run 
the R390 bandwidth wide open at 16 KHz, and let the SDR do the filtering 
as much as possible. Now who needs a CV-157 or CV-591? ;-)

Never had an overload issue with the SX-28, but there I'm getting the 
signal prior to any IF amplification.

See 
http://fivedash.com/index.php?main_page=product_info&cPath=1&products_id=5 
for more info on the Softrock (again, no connection with fivedash.com, 
etc., etc.)

73,
-Larry/NE1S





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