[HBR] HB 67 Receiver Introduction

[hbr@mailman.qth.net]

In a message dated 4/9/02 11:11:00 AM Eastern Daylight Time, 
gswynar@durham.net writes:

> Hi Jim...
>  
>  Yes, that's quite a neat circuit and well worth looking into...
>  
>  The designer's philosophy was to make the front end completely "bullet
>  proof" in the matter of selectivity---and that's ALL selectivity, i.e. both
>  immunity from the Novice keying his rig directly across the street from
>  you, as well as from junk on parts of the band slipping past the front ends
>  of less robust rigs.
>  
>  He really did a job of it, too, with that "quad" set-up of L/C networks!
>  The grounded grid RF amplifier was put in place strictly to compensate for
>  circuit losses therein.

Yup. The basic idea is as described by W1DX in "What's Wrong With Our Present
Receivers?" 15 years earlier. The design puts as much selectivity as near the 
antenna as possible.

Note also that the tunable oscillator is in its own heavy metal box, and the 
preselector is not ganged to it. 
While this can be a bit inconvenient, it makes mechanical and electrical 
design much simpler and eliminates
compromises. 
>  
>  If one were to forgo the mechanical filter, conventional IF transformers
>  would be an absolute must in the IF chain...have you ever shorted out the
>  IF filter in an SB-301 to see what its effect might be on selectivity?
>  (Heath used a similar scheme). It'd be BROADER than any barn door you could
>  find!

During development of the Southgate Type 6 series, I did just that. The whole 
band comes in at once!

The IF filter must be as close to the antenna as possible to give really good 
dynamic range, though. 
>  
>  That heterodyne nulling circuit would be a worthwhile addition to the HB-67
>  as well--simple, but effective, according to the author.
>  
It's derived from the 75A-4 circuit. 

>  I don't know that the average Ham would really need all that elaborate a
>  front end, but as you say, the piece is full of good ideas & thought
>  starters!

It all depends what kind of performance is the goal. W1KLK wanted a receiver 
that was all but impossible to
overload and had really good selectivity against both nearby and far off QRM. 
He also wanted a really good dial,
solid construction and no trick circuits. His design obviously delivers on 
all counts. One wonders how it would compare to a current model 
top-of-the-line ham transceiver.

73 de Jim, N2EY