[HBR] Yet ANOTHER HBR Project -- Preface

[hbr@mailman.qth.net]

Jim said:

> Ya think yer hooked now, wait'll ya build an rx with that cap. But I'm
> gettin' ahead o' meself....

I can quit *anytime*.

Re the W5OMX receiver:

> I think the RF amp and 2 high Q tuned circuits ahead of the mixer
> covers up a lot of problems. 

... by raising the mixer signal levels to hide the lower-level birdies ... I 
didn't think of that.  

> The biggest booboo was the simple premixer and its single tuned
> circuit output. All kinds of crud hitting the mixer with that setup. 
 
Yeah, I agree.   All you can say for it was it was a premixed set that 
pretty much any ham could have duplicated.

Re the SS-1R:

> I don't see how the AF would use such a limited-coverage ham rx. 

Right, of course.   I'm assuming there was a variant that was general 
coverage.   In fact until it was discussed here, I didn't know the SS-
1R was ham-band-only.   I thought the context in which I first heard 
of Squires-Saunders was some sort of high grade professional quality 
receivers for intercept work.   I can't swear this wasn't a mistake, but 
that's my memory.

> I like a bit of overrun at the bandedges, which you won't get of you
> try for true 0-500 operation. 

True, and I agree with you.   However there are tradeoffs in 
everything, and I'd rather have the linearity and direct calibration than 
the overrun.   And with the 240 degree cap, the overrun is there -- it's 
just not calibrated, except on the knob.

> Building that box with just a hacksaw, flat file, vise, drills and
> hand tapping is a story for another time. 

A man after my own heart.   

> Unit oscillator, shaft vertical, dial drum horizontal, tube vertical
> next to the drum. 

Much to be said for that, but I'm going to use the calibration as-is so 
that sets the basic layout as per LM.   The tubes (two unless I use a 
dual triode -- don't know of a low power battery operated one) will 
need to go above the tuned circuit if at all possible, behind it if not.   
The unit oscillator is definitely the way to go -- you simply can't get 
the kind of stability that parts of this quality deserve with coils and 
caps here, there, and everywhere.   

As for example, in the 1MHBR.   ;)  

Looks like the box holding the tuning cap and oscillator will mount on 
the right end of the dial mechanism.   I have the 3-screws-in-front 
type of cap.   It makes a rather wide subassembly -- almost 8" -- 
which is awkward, but it can overhang the chassis a bit.   The cap 
has an 0.265" shaft so I have to find a drill for the coupling.   Could 
save 3/4" by moving the drum to the right side but that puts it way far 
away from the knob/dial.

The IF/audio chassis will go to the left, placing the dial near the 
middle of the receiver.  That puts the oscillator box on the right side 
of the set, as far as possible from the major heat sources: With any 
ventilation at all in that area (say from below the chassis) it should 
stay very cool.   

I have in the past, pressurized chassies with a tiny blower into the 
backside; this might be the time for that.   The 1" and 1-1/2" 
computer fans that are so common now are essentially silent and I'll 
need a low voltage DC supply anyhow, for the oscillator filaments.   
It's amazing how little air flow is required to greatly reduce heating.

I'm guessing that the bandswitch goes at about the center of the front 
end assembly, power switch to the right of that.   No dial light as 
such -- probably will light the hole for the drum and possibly the 
vernier; I like receivers you can operate in the dark.   

LM theme -- I'll use the various knobs and also the switches if I can 
get them out without excessive destruction -- mine are staked.   

> You need multiple segments to cover 10 anyway

I'll skip the rest of 10, for now -- part of the goal is to prove the 1.75 
Mcs Hahnel concept as a way to get most of the bands with 
minimum complication.   Long term, another oscillator of 
conventional type using overtone crystals to pick up those bands 
would solve the problem.

Alternatively, a Hahnel oscillator with a 500 kcs crystal might allow 
for a general coverage receiver.   The VFO (or IF) might have to be 
changed to accomodate.   The price would be more difficulty 
eliminating the unwanted multiples and (with something like 60 
bands) a considerable bandswitching problem.    I'll build the ham 
band-only version first!

> Or say the heck with pure linearity and just do the drum. 

Linearity and resolution are main goals -- if I were going to do that I 
might as well use a simpler dial and tuning capacitor.    

There used to be a saying:  "If you want to measure the frequency, 
get a Collins, if you want to hear it, get a National."  A receiver of this 
type ought to be able to beat them both.  

Walt
KJ4KV