[Premium-Rx] Re: Premium-Rx Digest, Vol 25, Issue 20 Microtel 550

[Kmec at aol.com]

Hi All!
The MicroTel 550 was a bug hunter used by the State Dept. It is quite old  
and relies on harmonic mixing. The LPA is not really "active" in the sense that  
it has no preamp, only a YIG filter and a single ended diode detector (HP 
diode  mount?) used as a harmonic mixer, mixing harmonics from  the 1-2 GHz from  
the cavity LO in the mixer with the filtered desired frequency.  A really  
poor scheme that was scrubbed once broadband microwave parts became available.  
The LPA is a Dorne and Margolin 1-12.4 (as I remember) and comes off the  
little green box, becoming the most useful part of the whole  radio.  The small 
waveguide mixers with attached horn were made by  DeMornay-Bonardi, a name long 
vanished from the microwave world, having been  bought up by Systron Donner 
long ago. These are also OK, but use point contact  type cartridge diodes, not 
very sensitive, but better than nothing. This  way predates the PR-700 and was 
replaced by the 903 then the 904/904A Microwave  boxes.  I used to fix these 
for the State Dept. way back when, and if I  still have the manual, it would 
cost a fortune to duplicate.   I owned many sets of these radios, complete with 
all accessories at  one time in the late 80's when they were dumped by the 
State Dept. (MicroTel  would not service them any longer, no parts available), 
they came in grey field  boxes, one had the radio, one the locking frequency 
counter, accessories were in  the lids. They also painted with this latex based 
green sticky paint that was a  real pain, came off on everything and dirt stuck 
to it like glue.  I sold a  bunch at the Dayton hamfest years ago.  Good 
doorstops, I think you will be  disappointed with the performance. The little 
beaded cord that acts as the dial  cord drive line strips and the pointer doesn't 
move, a real problem to fix as  all MicroTel equipment is very poorly designed 
from a mechanical point of view,  real hard to take apart and put back 
together.  WJ microwave stuff was  much better in the same time frame with the same 
vintage parts.
Cheers!
Jeff Kruth
WA3ZKR
KMEC
**************One site keeps you connected to all your email: AOL Mail, 
Gmail, and Yahoo Mail. Try it now. 
(http://www.aol.com/?optin=new-dp&icid=aolcom40vanity&ncid=emlcntaolcom00000025)