[HBR] RE: HBR 2006 and a question

[N2EY at aol.com]

In a message dated 4/9/06 11:41:12 AM Eastern Daylight Time, dkelly42 at cox.net 
writes:


> I believe the idea is completely within the concept of the "Old Timers"
> who built the HBR receivers. What always interested me was how they used
> the technology at hand to build their receivers. I don't think they were
> just purists building tube receivers. They were merely trying to build
> good receivers.. period. Who knows what designs these fellas would have
> developed if some of the current components and designs had been
> available to them back then.

Well, yes and no.

Even in their time, the HBRs were a bit of a technological anomaly. They used 
plug in coils long after bandswitching was pretty much standard. They used 
LC-derived selectivity far from the antenna, even after HF crystal filters were 
available. They didn't have narrow selectivity for CW either. They didn't use 
the newest or hottest tubes, nor the latest circuits and techniques. 

The point of the HBR designs wasn't to build the best possible rx, but rather 
to build a good solid home-brew amateur rx using all-new parts available from 
the common ham manufacturers of the time. A decent performing receiver that a 
reasonably knowledgeable ham could build, align, and maintain without a shack 
full of tools and test equipment. No surplus or hard-to-get parts (hard to 
get back then, anyway). And the total cost was competitive. 

That said, there's no reason not to use an HBR front end and SDR tail end. 
But such a receiver would hardly be "home brew" in the classic sense of the 
HBRs. 

__

If one is going to go the hybrid analog front end/SDR tail end, though, some 
interesting possibilities arise.

For example, how high can the SDR function? Let's say for argument's sake 
that it can do up to 10 MHz. With a 5 MHz VFO and the SDR set for 9 MHz, we can 
cover 80 and 20. If the SDR IF is reset to 2 MHz, the same VFO range will tune 
40 meters. SDR IF at 7 MHz will get you 160. 

You get the idea. Multiple IFs wouldn't be that practical in an all-analog 
RX, so we usually change the VFO range or do some other heterodyne tricks. But 
if the SDR IF setting is a matter of software.....

> 
> There is a picture of a fella who used a rotating bowl for a dial
> mechanism for his receiver. That is one of the most interesting designs
> in your archives. Shows how clever those guys were mechanically as well
> as electrically.

Thanks! 

I built that receiver back about 1974. Only the xtals and the 88 mh toroids 
were bought -  all the rest was scavenged from various sources, mostly TV sets 
and AM BC receivers. (Note the chassis isn't a commercial one). 


> 
> I have a question. Most of the HBR designs show a capacitor across the
> primary of the audio output transformer. Would someone explain the
> concept and use of this capacitor? I assume it is to either flatten the
> response of the audio output or peak it. 
> 

It's to roll off the high audio frequencies. No point in having a ham rx with 
audio response above a few kHz.

73 de Jim, N2EY