[HBR] questions about HBR-11

[waltah at earthlink.net]

Joe LeKostaj wrote:
> 4) Pictures of the underside of the HBR-11 show that L4A and L4B (the 
> 1610 kc IF transformers) do not have shield cans. Is that really how 
> they're supposed to be?
> 
> 5) Has anyone experienced direct IF pickup of the AM broadcast 
> stations that are now found between 1600-1700 kc? (I suppose one's 
> proximity to such a station would be the main culprit.)

The first bit of research I'd do is take a modern digitally tuned radio 
(so you can get precise frequencies) and inventory stations in the 
area you're in.   Then when you build, jigger the 1610 IF (if 
necessary) to be in the biggest hole you can find nearby.   

Note that you don't want to get on a multiple of the 2nd IF, either 
because that may give you pickup of the BFO.  For the 100 kcs IF 
that means avoid 1600 and 1700; for 85 kcs it would be 1615 and 
1700 if my mental math is right.   I used 1660 Kcs in my (sort of) 
HBR 13 project.
 
Commercial IFTs have a pretty wide tuning range so this won't be a 
big problem.  The 85 Kcs units are tougher -- they have just a 
couple kcs of tuning range and if you use a crystal for the 2nd 
oscillator you'll wind up having to make the final adjustment of the 
1st IF so it will match the crystal/85 Kcs IFT combination.  

You're really better off with using just the 85 Kcs units from a 
single receiver.   Mine were junkbox units from who knows what 
receivers and I wound up having to go in and tweak the fixed caps 
in there to get them all to where they'd tune the same freq.  

Returning to the local BC station issue, it's not just direct pick up 
you have to be concerned about.   A good ham antenna is not that 
bad a BC antenna and it's perfectly possible for a local station to 
blast right through the front end of your receiver and enter the 1st IF 
by that route.   You can use a trap or low pass filter to control this, 
but it's best to start by putting the IF as far from such signals as 
you can.

Walt
KJ4KV