[HBR] HBR-?? progress at NT4C

[waltah at earthlink.net]

Wow, *nice* work!   And I thought I was the only one on the list 
with time for homebrewing this summer.   

Band imaging gives you a whole lot of receiver for not too much 
complexity and is much to be recommended if you don't want to do 
bandswitching.  

Band imaging can either be done with the local oscillator halfway 
between the bands and the IF equal to half the difference or put the 
IF in between and have the VFO around half the difference.   One of 
those frequencies will be ballpark 1600 kcs, the other 5550kcs.   
I've done both a band imaging receiver and an 8-watt transceiver on 
the second scheme.  

With either of these schemes you can tune the front end with a 
single sweep of a pretty large capacitor -- 80 tunes near maximum 
capacitance and 40 is close to minimum.   

Another combination that was popular in the early days of SSB 
was a 9 Mcs IF and a LO tuning 5 to 5.5 Mcs, band imaging 80 
and 20 meters.   There were a lot of 9 Mcs filters made at one 
time, Miller made IFTs ...  

Going the other way -- VFO tunes 8.75 to 9.25, IF is 5.25 Mcs -- 
has the advantage that if you do the IF for USB then the conversion 
scheme automatically puts you on LSB for 3.5-4 Mcs.   I believe 
the NCX-3 and some other sets used that one.   I don't care for the 
job of building VFOs at 9 Mcs, though.   

These schemes need a bandswitched front end; you can't cover 3.5 
to 14.35 Mcs with any practical variable capacitor and if you did the 
LC ratios would be terrible.   

I probably have a socket for that calibrator crystal; tell me the 
spacing and pin diameter/type and I'll check stock.  

The cover over the dial is something I hadn't thought of as a way to 
handle the command set type of dial.   Maybe you'll have a light in 
there?   

I don't consider using silicon diodes as violating the rules of 
vacuum tube home brew; everybody knows that you can replace 
them with 6AL5's.  Time, space, and filament power, that's all.  
Now building a decent local oscillator with a vacuum tube, *that* 
tests your manhood.  

Walt
KJ4KV