[Milsurplus] Re: mechanical modulator ... definitely not a
wobulator
G. Lofstead
jerrylofstead at bellsouth.net
Sun Sep 14 13:46:58 EDT 2008
Mike ET ALL,
re: USE OF fm ON am SIGNAL .
It was a main stay for the submarine fleet during WW II.
AM Radio station WIOD in Miami FL, had such a scheme. at 570KC, the carrier was FMed for RTTY contact to subs at sea. It worked great and the enemy never detected it!
I have been in the "Secret Room" at the station many times. The RTTY eqpt is / was there the last time was there.
So FM on an AM signal does work and works well...
Jerry
W3CDE
-------------- Original message from Mike Morrow <kk5f at earthlink.net>: --------------
> >The 2/42 Radio News defense edition says the localizer has 90 & 150 hz fm
> >a mechanical modulator
> It's very, very safe to say that NO wobulator was ever used in any localizer transmitter design. That would create frequency modulation, not amplitude modulation. ILS localizer receivers, regardless of frequency, have always been
> AM.
> As an aside, wobulators might not even produce significant FM if the localizer was NOT operating above the VHF band. The USN tried before WWII (and dropped before end of WWII) the "Air Track" ILS (ZA, ZA-1, ZAX, AN/ARN-9) that used an MF (not VHF) localizer receiver (hence those R-23 and R-24/ARC-5 receivers with the somewhat rare MX-19/ARC-5 ILS adapter). If the localizer that Marty mentioned was MF (say, 350 kHz), it would *not* be easy to mechanically FM-modulate it with a "wobulator" device. For the USAAF's SCS-51 ILS with a VHF localizer, then perhaps, with difficulty. But there is no point to FM
> modulation in a AM system.
>
> The AN/APN-1 altimeter transmitter is a 440 MHz oscillator that is frequency
> modulated by a wobulator. It's a very different application from that of a
> localizer transmitter.
>
> As far as "mechanical" modulation goes, another candidate would be the system
> used by the SCR-178/179 modulator BC-188. It uses a vibrating element to
> generate a MCW tone, which is applied to the input of a couple of 27 tubes to
> modulate the 865 PA tube. In that sense, mechanical means are only used to
> generate the tone frequency, not to do the actual modulation.
>
> The term "wobulator" still has *current* use today for large steam turbine
> control systems. A speed wobulator takes effect during turbine start-up to
> accelerate the RPMs through regions of rotor resonance (critical speeds).
>
> Mike / KK5F
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
-------------- next part --------------
Skipped content of type multipart/related
More information about the Milsurplus
mailing list