[ARC5] RAT/RAV radios question

[Kenneth G. Gordon]

On 22 Jun 2020 at 17:52, Michael Hanz wrote:

> Well, the owner would have had to have some patience to use it without modification, but maybe 
> the band wasn't as crowded back then.  The receiver has a selectivity of about 14kHz, and the 
> 12SK7s are probably starting to pant a little at that frequency, requiring 20uV to produce the 
> 10mW audio power output described in the manual at https://aafradio.org/flightdeck/RAT.htm
> 
> On 6/22/2020 4:43 PM, Tim wrote:
>     OK Mike (and Mike) - thanks for recalibrating me!  HiHi.  The TX in use must have been 
>     something more mundane at the time.  Guys were Hammering command transmitters to 10 
>     meters back then so that was likely what I remembered seeing.. But I DO kind of remember 
>     that the RX actually had a dial that covered 27 mc - I knew enough about them to realize it 
>     was not the typical lower HF coverage set that I was seeing in the surplus shops at the 
>     time...

Although I am not knowledgeable about the RAT/RAV receivers, some of you may remember 
my adventure with a BC-454 which someone had begun to convert to cover 10 meters back 
in 1950 or so, but never finished, and my travails with it. I described that in detail here, asking 
for advice when I ran into problems.

When the entire project was finished, I was most surprised to measure an MDS (Minimum 
Discernible Signal) of 1 microvolt on CW (BFO on) at 29 MHz using the original 12SK7s. It 
showed about 3 microvolts for AM.

Switching the RF amp and 1st IF to 12SG7s did reduce the noise, but didn't really appear to 
improve MDS at all. S+N/N ratio obviously improved, but I didn't measure that yet.

The receiver tunes just short of 28 MHz to just above 30 MHz and works very well.

Ken W7EKB