[GreenKeys] FRF FSK conv. (was - Two eBay Novelties)
Duncan Brown
duncanancy at earthlink.net
Sun Feb 9 18:29:36 EST 2014
Nick,
I know LO radiation can still be a problem. The FCC still has a spec
for LO radiation from all radio receivers sold in the US to minimize
interference. The Enigma cover-story might be the real reason - I
hadn't heard that story, but it makes sense, at least at night (in the
daytime, a sub could probably see a ship before they could pick up any
LO radiation). It just seemed to me that the 455KC IF input or the
20-50KC IF radiation from the FRF would be minimal and not propagate
very far. But if it was for a cover story, then actual facts would
have little to do with anything.
I once had a BC-645 IFF transceiver (the one with the thermite
grenades). It had a RF gain stage on the RX input, but it had no B+
voltage on the tube! That was apparently the only way it could pass the
wartime LO leakage spec. The IFF transceiver would not have needed much
sensitivity for plane-to-plane communications.
have fun,
Duncan
K2OEQ
On 09-Feb-14 17:41, Nick England wrote:
> Oh, now you've opened up the recurrent can of worms! we'll see what
> the responses are.
> There was a pretty stringent spec for rcvr radiation and designs were
> modified with an extra RF stage to cut down on LO radiation. The
> reason given at the time was DFing by subs. There is a theory floating
> around that this was actually some sort of cover story for the success
> that Enigma decrypts had steering convoys away from wolf packs. "Our
> receivers are so quiet that they can't find us" rather than "I wonder
> how we are avoiding the U-Boats". Who knows....
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com/>
>
>
> On Sun, Feb 9, 2014 at 5:26 PM, Duncan Brown <duncanancy at earthlink.net
> <mailto:duncanancy at earthlink.net>> wrote:
>
> I don't think there would have been much leakage through the steel
> hull of a ship. The actual radio receivers were probably
> radiating a lot more of their LO energy back out their antennas.
>
> Duncan
>
> On 09-Feb-14 16:41, COURYHOUSE at aol.com <mailto:COURYHOUSE at aol.com>
> wrote:
>> they mean radio signal leagage that would allow bad guys to
>> find and torpedo you
>> In a message dated 2/9/2014 2:22:26 P.M. Mountain Standard Time,
>> duncanancy at earthlink.net <mailto:duncanancy at earthlink.net> writes:
>>
>> The FRF looks like an early version of the CV-31B/FRA-7 used
>> in the AN/GRC-26 (c1950) and discussed here recently.
>>
>> I wonder about the "Warning - Radiation exceeds safe limit
>> -Do not use aboard ship" label. Were they worried about
>> RFI? to or from the FRF??
>>
>> The specification for the FRF is available at
>> http://jptronics.org/radios/Military/JANAP161/an.fcfg/an.fga-type.frf.pdf
>> . It mentions tone _oscillators_ at 170 cps apart. It
>> almost implies a multiplexed system of 170cps shift signals
>> on one carrier or sideband (which was done in WWII), but I
>> think the FRF (and certainly the CV-31) is a single channel
>> output (one TTY signal). It was probably designed for 850 cps
>> shift, though might work down to 425 cps shift. Military
>> converters often had a keyed tone (OOK) output if the
>> demodulated TTY signal needed to be sent any distance from
>> the RX site to where the actual TTYs were located.
>>
>> The AWA Museum has a CV-31B/FRA-7, so we will not be bidding
>> on this, but it does belong in a museum!
>>
>> have fun,
>>
>> Duncan
>> K2OEQ
>>
>> On 08-Feb-14 21:04, David Burns wrote:
>>> WWII Navy Western Electric Model FRF Receiver Frequency
>>> Shift Ham For Teletype
>>> <http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=221370706399&fromMakeTrack=true>
>>> This is an odd duck...Navy dual-channel I.F. demodulator
>>> with 170 shift, but preset at eight odd military
>>> frequencies, designed to interface with 1940 RBB/RBC
>>> battleship receivers. There is stuff on the web if you
>>> search with the "CW-####" FRF numbers. "Not for shipboard
>>> use", but the shipboard equivalent equipment seems to have
>>> been canceled. Which would explain why this unit was never
>>> used. I sent mail to the seller suggesting they list the
>>> associated teletype machine /they still have crated up!/
>>> (That could be very interesting!)
>>>
>>> Telegraph / Teletype Machine WUTEL Western Union Quotation
>>> Service
>>> <http://www.ebay.com/itm/231153851639?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT>
>>> This ticker is missing the motor (and other parts?)
>>>
>>> -Dave in Boston
>>>
>>>
>>>
>>>
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