[HBR] Another Project -- 1MHBT -- Part 1

[Hopperdhh at aol.com]

Walt,
 
Would you happen to have a schematic of this receiver available?  I  have 
most of the parts to do something similar.  Could send you SASE plus  cost of 
copying.  Am looking forward to seeing the pictures.
 
Dan K9WEK
 
 
 
In a message dated 3/7/05 1:43:38 P.M. US Eastern Standard Time,  
waltah at earthlink.net writes:

Over the  last month I've returned to the 'One month HBR' project to 
clean up loose  ends.   This was a project along the lines of the Ted 
Crosby  HBR's, using four 85 kcs command IFTs for the 2nd IF, two 
1415 kcs IFTs  retuned to 1665 kcs for the first, with a single IF 
tube at each  frequency, and rewound command set plug in coils 
through the front  panel.  

The thing works surprisingly well.  The dynamic  range is not terrific 
but it's in line with the better receivers of the  60's, stability is 
perfectly adequate -- it's tough to do better than  'adequate' with 
plug in coils.  It sounds great.  The calibrator  is kind of a mess -- I 
stupidly put a 100kcs calibrator in the same dual  tube as the 
85kcs BFO, so there are beat notes everywhere if both are on  at 
the same time. But that's not an operational problem:  For rough  
calibration I turn off the BFO and just peak on the calibrator; for  
precision I set to the 100 kcs mark on the dial and trim to zero  
beat.  

One problem I'm going to work on is blocking by very  strong 
signals maybe 10 kcs away.  This is a frequent problem with  
double conversion receivers where the selectivity is at the 2nd IF  
because the 1st IF isn't sharp enough to greatly attenuate these  
signals and the RF, 1st mixer, and 1st IF boost them to the point  
where the 2nd mixer bias is upset, reducing its sensitivity.    
However I can reduce the gain of the first three stages 
(compensating  in the 85 kcs IF) and possibly change the 2nd 
mixer circuit slightly to  minimize the effect.  

Most double conversion designs of this type  use no gain at the 1st 
IF (1st mixer directly feeds the 2nd mixer) but I  wanted to keep 
stability issues to the minimum by distributing the gain  across all 
frequencies.   Definitely a trade-off, probably one I  got wrong.   

The plug in coil scheme works fine.  I've  had coil sets in and out 
maybe a few hundred times and there's no sign of  significant wear --
all they've done is smooth up considerably.  I do  have them well 
lubed.

The pictures of this radio were lost in the  termination of one of our 
web sites; I'll get new ones up with the next  post on this subject.
 
Transmitter part snipped



Walt Hutchens
KJ4KV