[HBR] Current day HBR

[Walt Hutchens]

Tim said:
> The problem is, hams want their ham radio to also be a general
> coverage receiver, and when they buy a receiver part of the spec is
> the frequency coverage, but the spec doesn't show (very well) the
> tradeoffs in making a general coverage receiver. This has led to
> poor HF radio performance the vast majority of hams for the past
> couple of decades, because it looks like general coverage receiver
> ability is a feature, when really it means compromises in receiver
> performance unless it ends up looking like a R-390 :-)

This is unarguable, I think.  However the way it applies to an
HBR-type design isn't quite a grim as this modern (and more general)
picture suggests.

It's likely that anyone building an HBR would follow the specs and use
the methods to optimize it for ham band service. That would likely
mean a bandwidth that's a compromise between SSB and AM reception,
stability as good as possible so as to allow satisfactory SSB
performance, and a tuning rate that makes SSB use practical.

Adding general coverage by means of an alternate set of coils that
connects additional tuning capacitance (the 3-gang AM/FM cap
previously described) won't yield a top grade general coverage
receiver. For one thing, general coverage receivers with mechanical
tuning need major attention to the tuning rate. A GC functioning
version of an HBR will be very tough to use on GC SSB signals, even if
it's fine on the ham bands.

The thermal stability won't be great, either, particularly on the
highest band. Nor is this just a matter of super-careful temperature
compensation: With a wide tuning range, good compensation is generally
impossible over a whole band unless you do separate L and C
compensation and trim each at the appropriate end of the band.

However adding GC functions in this manner also doesn't require
compromising the hbr performance in any substantial way. A brass and
silver ham band only tuning cap with porcelain insulation is a bit
better than an aluminum and phenolic FM unit, but the difference will
be slight, probably not even noticeable, and many of us are using the
aluminum caps anyhow.

It seems to me that this approach to a both-function HBR can still
yield a first rate ham band receiver (for this level of complexity and
expense) and add to it a general coverage function that is better than
any of the common consumer grade SW receivers of the vacuum tube era.
It won't be an R-390, but it won't cost like one or weigh 100 pounds
(or whatever it is) either.

In other words, when adding this function to an HBR you don't have to
go back and completely redesign the conversion scheme and LO signal
generation (as in a modern radio), thus compromising the ham band
functions. I may have missed something but I can't see any real loss
and the extra work is just two or three more coil sets and
calibration.

Walt
KJ4KV