[Milsurplus] SCR-522 Alternate Uses

[Bruce Gentry]

I have seen plenty SCR-522 transmitters modified for FM years ago. Using 
the receivers  to slope detect FM broadcast stations works surprisingly 
well, but a few friends rewound the final IF transformer and added 
switching circuits to allow am or discriminator FM detection.  Another  
hack  was to modify a BC-603 to the FM broadcast band for use in cars 
and trucks. It was a bit of work, but they were very cheap because they 
didn't cover 10 meters, and 12 volt dynamotors and a couple 717 tubes 
for the front end were easy to get. FM car radios were rare and quite 
expensive at that time, so we had a very low cost alternative.


      Bruce Gentry, KA2IVY


On 7/20/18 11:17 AM, B. Smith wrote:
> The SCR-522 has a rich history of alternate uses and modifications. 
> You can even use  the set on on your local FM repeater. Connect a 
> varicap from crystal socket to ground then inject audio via a external 
> amplifier through an  RF choke to the crystal side of the diode. We 
> used a small value varicap or you can even try a power supply diode.   
> On CR-18/AR crystala 1 to 2 Kcs  swing at the  fundamental freq  can 
> be obtained but you want a smaller value of deviation near  250 cycles 
> due  to the X18 multiplication.
> On the Receiver use slope detect.
>
> The 522 was occasionally pressed into repeater service during the 
> early days of 2 Meter FM as Motorola 80D's etc. could be expensive. 
> Usually the frequency was 146.94 - Most large towns started off with 
> a  .94 repeater and you only needrd one set of crystals when mobile.  
> :-)   There were also  experimental AM repeaters  which were 
> interesting as the carrier stayed on continuously.
>
> Due to the multiplication factor on receive you can use same receive 
> crystal for  7 different receiver frequencies. For instance you can 
> use a crystal and multiply by X12 to cover 108-116 and then use the 
> same crystal in a different multiplier scheme such as X14 for 124-132 
> Mcs or X16 for the 2 meter band. My favorite demo frequency was to 
> channel up for the   ATIS at the nearby airport but you can also 
> cruise the lower VHF frequencies for aircraft comm.
>
> Remember that the receiver can go down  into the edge of the FM Radio 
> band which has a top edge of 108 Mc and you can slope detect those 
> stations.
>
> k4che
>
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