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[TenTec] 1254 Receiver

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Subject: [TenTec] 1254 Receiver
From: pbigelow@us.ibm.com (Paul Bigelow)
Date: Wed, 1 Apr 1998 13:29:37 -0500

I have built the 1254 receiver and it is a nice little unit.  A real joy to
build, use
and tune around.  I haven't had this much fun in ages!

1. Great sensitivity (compared against the NRD-525)
  and the sensitivity is relatively consistent across the 100kc-30000kc
  receiving range.
2. Good selectivity (for a 4kc filter)
3. Reasonably stable
4. Excellent quality boards
5. Easy to service (except for removing parts from the
  plated through holes)
6. Convenient to use
7. Informative, relatively easy to follow instructions

Suggested change:
Mount an RCA jack with a nylon washer on the outside to the back panel to
  reduce stress on the board.

Quirks noted and possible remedies:
1.)  Lots of birdies and display induced signals on the lower half of the AM
broadcast band.
   Remedy:  Have attempted to shield out the multiplexing emissions by spray
painting a
  graphite EMI/RF shield to the inside of the front cover.  It helped a little
2.)  Reduced sensitivity on the lower half of the AM broadcast band.
  Remedy: Put a jumper across R72, eliminating that input filter.
3.)  FM intermod from strong FM stations.  Just add 90  (2* 1st IF) to the
received frequency
  to detetmine offending frequency.
  Remedy: Have tried with some success (but none totally satisfactory):
  a) Snap-on RF choke on power cable
  b) Soldered on a shield on trace side of the board around the 1st Mixer
  c) Incorporated FM trap (from Radio Shack) in the antenna lead
4.)  The rotary Encoder loosens up with use causing the frequencies to jump
  around (sometimes) when tuning from one step to another.
  Possible Remedy (have not tried yet): Sandwiching a large, black, felt washer
  the tuning knob and the tuning knob recess to reduce play.
5. ) Hum from the power supply.
  Possible Remedy  (have not tried yet): Install a 15V IC regulator in the
power supply.
6.)  Deafening thump upon turning on the 1254 when using headphones.  REALLY
 Remedy: None yet although I suspect a large capactior may resolve this one.
7.)  A little bit of "thumping" due to slow synthesizer lock.  Not too bad,
really, considering
  the price.


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