[ARC5] AM broadcast reception on BC-453

[john rose]

Congratulations! You stumbled on one of the best features of a narrow bandwidth IF. Take it from a retired BCB DXer, fidelity be …ahhh… darned. When you get into tight situations, being able to cut one of the sidebands off can reduce interference from adjacent channel powerhouses. It really gets important when DXing ‘splits’, trying to pull stations out of the ethereal ‘soup’ that transmit in a region of the world where the BCB has 9 kc channel spacing. If your BFO is spot on frequency, turn it on. Tune around a bit and see if you can put the station frequency spot on to the BFO. It’s called exalted carrier tuning and sometimes will pull the signal up enough to ID. Works on short wave stations too. Another possibility, and I retreat to my moated fortress before writing this, convert the AM detector to a product detector, works more better. As for fidelity on a strong signal, the sound using just about any of the old timer hollow state jobs will sound pretty good largely because the skirts of the bandpass widen out and you can hear those treble tones. Just remember to tune one sideband or the other. 


As I recall, the best IF alignment started by doing the job ‘by the book’ just like some looie was standing around trying to make a reputation. Then before buttoning the set up, leave the first and third in narrow and set the second on wide. Made things a little more pleasant. Ah, such sweet memories.






From: Leslie Smith
Sent: ‎Thursday‎, ‎March‎ ‎19‎, ‎2015 ‎3‎:‎31‎ ‎PM
To: arc5





  G'day fellow list-readers,
  I built a converter to listen to the AM broadcast band on a BC-453.
  I have a question about sound quality and IF response.

  But first - some extra info.
  About 2 years ago I built a converter to 'move' the 80m band to the
  ARA nav band.
  (In this case I used an older ARA, not a BC-453.  And yes, I do
  understand the '453 is almost the same as the ARA set.)
  The point here is that when I listened to SSB (converted from 80m) the
  voice sounded as expected.

  Now, listening to AM BC broadcasts this is what I hear:
  When the '453 is tuned to what I judge to be the 'middle' of the
  signal (here it's 480kHz) the sound is muffled.
  To get natural sounding voice quality I must tune the '453 a little
  'high'.
  When I tune the '453 'low' the muffled quality is less, but not so
  clear was tuning 'high'.

  Important info.  The slug in the second I.F. transformer is 'stuck'. 
  By that I mean I can't pull it out.  The first and third slugs are
  "out".
  I haven't tried to align the I.F. transformers.  (How stable are these
  sets over 70 years?)

  I'm interested to know how many here listen to the BC band using one
  of the 'nav' sets?
  What quality of sound is heard?

  Other comment.  I'm using a circuit that is somewhat like a JFET
  version of the Pullen - except I don't attempt to 'mess' with G(m) -
  it's just a long-tailed pair.
  The signal goes to the LH JFET gate, is source-coupled to the RH JFET
  gate and thence to the drain (and untuned transformer).  From the
  transformer the signal goes to the '453.
  The L.O. switches the RH FET gate.

  With this arrangement I have excess gain.  Don't even think about
  using this arrangement as a converter to feed a 'command' radio.
  From memory, I think I'm using a one-turn link with the output
  transformer, so I'm attenuating the signal a good deal before the
  '453.

  73 de Les Smith
  vk2bcu at operamail.com

-- 
http://www.fastmail.com - The professional email service

______________________________________________________________
ARC5 mailing list
Home: http://mailman.qth.net/mailman/listinfo/arc5
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ARC5 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html