Rich said:
Well, maybe it was that those guys could afford Collins gear, so a
$100.00 mechanical filter was a drop in the bucket. ;-)
But the manufacturer's cost has never been the retail price.
Over thirty years ago, looking for a crystal filter, I contacted
the local Heathkit outlet to check the price of one for one of
their SSB rigs. You could buy the parts for replacement purposes.
The price I was quoted was a significant percentage of the cost of
the rig itself, which is something fairly constant. So the manufacturers
were getting a good price on filters, be they crystal or mechanical,
because otherwise the rigs would be far costlier.
But I seem to recall seeing them in the Allied catalog for way
less than that, albeit for the era, the price might have been
equivalent to $100.00 at today's prices.
I suspect you saw the Japanese made mechanical filters, that were
in the catalogs and showed up in some of the early made in Japan
ham equipment, and from the ads I saw (later) seemed relatively
cheap.
Hams also saw Collins mechanical filters because they appeared on
the surplus market, either by themselves or inside surplus eqipment.
And I've _always_ wondered what's inside those 2Q4 plug-in
phase shifters!
Not much. Something like four capacitors and four resistors.
But then, they weren't wideband, they were intended for voice-bandwidth.
And users could get by with a limited suppression of the unwanted sideband.
It was the relatively early days of SSB for amateur radio, and once they
got rid of the carrier, getting rid of the opposite sideband was icing
on the cake. So they could live with not that great opposite sideband
rejection.
And as I said in a previous post, those phasing networks were mostly
seen in transmitters, where the signal they saw could be limited
by a audio filtering (if the voice itself wasn't actually limited
to 300-3000Hz or so), so the phasing network didn't have to deal with
a wide range of signals.
Amateur SSB was dominated by the phasing method in the early days, because
it was doable. Circa 1947, there wasn't much else, and it was relatively
cheap to get a few matched resistors and capacitors. Unless one started
with LC filters at a very low frequency, and then worried about image
rejection as it was heterodyned up to the desired frequency. But the late
forties or early fifties brought the mechanical filter, so that started
changing things. And then the mid to late fifties, hams caught on that they
could use surplus crystals in the 455KHz range to make crystal lattice
filters. There were a lot of crystals lying around from WWII in that range,
because they'd been multiplied up to a desired frequency, and since they
were in FT-243 holders that could be unscrewed, if the frequency wasn't
quite right, one could always grind the quartz a bit.
I think those proceeded the introduction of commercial crystal filters,
but my memory of the details may be wrong.
Then a few years later, they were able to make useful crystal filters
in the HF range, both by hand and commercially, which bumped things up
a notch.
ONce there were filters, commercial or home made, that put the phasing
networks aside.
It was only in more recent years, I guess it's about twenty now, that
phasing was looked at again seriously. SOlid state helped, since
fancier audio phase shift networks didn't come at the cost of more
bulky tubes.
ANd I suspect even more interest has been driven by digital processing.
SOme have used it for the audio phase shift networks, but it just seemed
as commercial interest rose in that area, it was like a pointer saying
"look at all you can do with phase shift networks".
Michael
