On Mon, 14 Oct 2013, Richard Knoppow wrote:


"Hank" wrote in message
...
In article
,
Richard Knoppow wrote:

James Millen was one of the founders of National but
eventually was pushed out of the company. He started his
own
company, also in Malden Mass, and probably made many parts
for National as well as his own stuff. Millen made very
high
quality components.

Millen Mfg., at least at the time I worked there, was in
direct
competition with National Co. on several products, and
neither
company supplied the other.

The National HRO was a revolutionary receiver in its
day
and stayed one of the favorites for both ham and
commercial
use for some thirty years. The mechanical design is
attributed mostly to James Millen and the electronic
design
mostly to Herbert Hoover Jr., son of the president of the
US.

While the HRO was a legendary product, I'd hardly call it
"revolutionary." It was a follow-on to the AGS line, with
objectives
to maintain AGS performance at lower cost-to-manufacture,
and to
normalize the coil-set interface so that the tuning coils
could be
built all-in-one-box and interchangeable. An examination
of the
schematic will show it to be essentially a copy of
higher-end home
entertainment circuits of the era, with a crystal filter
and bfo
added. Much of the actual performance came from use of
better coils
(house-built) in the RF and IF stages, a house-built
tuning capacitor,
and the house-built tuning dial was superior to almost
anything else
around. In short, a relatively straightforward
tried-and-proven
electrical design, but extremely well-executed in
component quality
and mechanical structure, pretty much hallmarks of Jim
Millen's team.

Worth noting that the NC-100, National's follow-on
product, had
similar performance, with the advantage of having
internally-mounted
and switchable tuning coils.

Hank

While the HRO had similar circuits to home receivers of
the time I rather think there was not that much variation
available. The HRO did use pentode mixers in place of
hexode or pentagrid mixers resulting in low noise. The
NC-100 was certainly a clever design but had only one RF so
its image rejection is not as good as the HRO.

And that the HRO had two RF stages seems to be a significant factor.

Even in the seventies, when Ray Moore wrote a number of articles about
receiver design in Ham Radio magazine, he pointed out that one reason the
HRO stood out was the 2 rf stages, which mean much better image rejection
than the average receiver. The HRO-60 (or was it the 50?) added double
conversion on the higher bands, but the earlier models were still
contenders in that period for good image rejection on the higher bands.
And of course, the design was good, so the extra stage actually helped
rather than hindered.

A superhet is a superhet, it's small details like this that made some
better than others.

A couple of years ago, I found at a garage sale for 2.00 a Grundig/Eton
pocket shortwave receiver. It's a pretty crummy receiver, but without
adding cost to it, they included a frequency counter. So a receiver
probably as bad and as simple as my Hallicrafters S-120A from 1971
instantly gets a giant improvement in tuning because of that frequency
counter. And once they did away with the analog dial, they could break
the tuning segments up into smaller ranges, helping the tuning process.

What initially complicates the receiver tremendously (or would if the
frequency counter wasn't a single IC that also included a clock function
and cost very little and took up little space), actually simplifies it.

Today, you can stick with a 455KHz IF and then fuss over image rejection,
or you can move to a higher IF and simplify the front end. Or go with
double conversion, getting the easier image rejection, yet selectivity
down where you can do things like use LC circuits.

A single conversion receiver with 455KHz and one RF stage (if that) can't
be much different from a circa 1930s receiver, communication or consumer,
but you can now make simple receivers with other methods that actually
mean better performance.

It amazes me that over the past 7 years or so I've found shortwave
receivers at rummage and garage sales, all nice and cheap, that are so
much better than that 1971 Hallicrafters. Or even buy a new digitally
tuned portable receiver for about the price I paid in 1971 for that
Hallicrafters, and get nearly infinitely better capability.

Michael VE2BVW