ISTR that in the early 1970s, that to buy an Xtal filter could cost you
half of a week's take-home pay, but now, with the component
supplers selling Xtals for a few pence, the ladder filter is well
within the sights of any and everybody.

No excuse now not to build your HF SSB / CW rig for ooo £100!

On Tue, 11 Feb 2014, gareth wrote:

ISTR that in the early 1970s, that to buy an Xtal filter could cost you
half of a week's take-home pay, but now, with the component
supplers selling Xtals for a few pence, the ladder filter is well
within the sights of any and everybody.

No excuse now not to build your HF SSB / CW rig for ooo ?100!

People were building crystal filters for SSB in the fifties, just look at
the books from the period. But, they were lattice filters, requiring the
crystals to be spaced a certain amount apart to match the required
bandwidth, though I recall the actual spacing wasn't a direct translation
of the needed bandwidth. And if you wanted better shape, you had to
cascade them, requiring more crystals of the same frequencies.

So in the fifties, that meant WWII surplus crystals. There were plenty of
them in the vicinity of 455KHz (various bits of equipment multiplied them
up), and since they were FT243 holders, if you couldn't find exact
matches, you could open them up and grind them a bit.

With the move to HF IFs for receivers and transceivers, that made it
harder. Fewer crystals in the HF range, and most of them were not FT243
holders. One the McCoy filter came along, that started changing things,
people buying and avoiding the whole issue. Then other companies
followed, like KVG. They were expensive, but I'm not sure if they were
overly expesnive. I remember one transceiver by Hayward in QST in the
nineties where he used two KVG filters, "because I had them around",
rather than adding circuitry to switch one filter between the receiver and
the transmitter. But I suspct the ARRL got free supplies of those KVG
filters, they were in a lot of projects.

I remember about forty years ago trying to track down some sort of cheap
9MHz filter, made worse since things coming into Canada tended to be hit
with a high tarriff. I remember contacting Heathkit, since their
transceivers used crystal filters, only to discover that a replacement
filter was really expensive. I noticed that later, Japanese transceivers
with more than one filter, yet if you wanted to buy one in single
quantity, the price was so high that you'd be well on the way to buying
that transceiver for the price of the filter by itself.

Some people were lucky, they ended up with surplus SSB filters. IN the
seventies there was a place in Arizona with pages of filters of various
types, and some were for SSB. I ended up with some odd frequeny filters
at some ham fest that I suspect were for SSB since the frequency is so
odd, but I've never seen specs, and they didn't come with any bfo crystal,
so they just sit there.

Ceramic filters often stayed relatively inexpensive, but of course were
downa t 455KHz. Even today, may rigs use filters at those frequencies.
Though finding them in single quantities can be difficult; the easy to
find ones are for AM.

I thought SSB CB sets might provide a useful outlet for SSB filters. But
for 20 years I never saw an SSB CB set at a garage sale, or at least if I
did, it was expensive. I actually got one last year for five dollars,
complete with a switch hanging out the back, suggesting a modification.
But, the crystal filter is nothing special, it's more like an AM bandwidth
filter. Indeed, for AM the same filter is used. That might work for VHF
use where things aren't so crowded, but at HF, it's not useful at all.

Ladder filters were actually around since the early seventies in ham
magazines. I have a 1974 book that collects bits from "Technical Topics"
and it has some bits about them, I think attributed to someone in France.
QST actually mentioned them at some point in the late seventies, but it
took some time before they took off. Circa 1974, they were using CB
crystals, often quite plentiful, and which were around 9MHz.

It just got easier as time went on, more frequencies becoming commodity
crystals, which is a good thing since having crystals ground to frequency
was never cheap, but it seems to have gotten really expensive in recent
times. But even forty years ago, there was starting to be a wider range
of commodity crystals, as digital circuits took off, when before that, you
could get a 100Khz or 1Mhz crystal for your crystal calibrator, or a
3.58MHz color subcarrier crystal (the equivalent in Europe was something
like 4.43MHz?). Actually I did see some early articles on ladder filters
that used color subcarrier crystals.

The advantage of the ladder filter is that it needs crystals on the same
frequency, rather than spaced. The BFO crystal could be the same
frequency, just pad it down a bit with a capacitor, which is really
important.

So you just needed one frequency. And as commodity crystals became
cheaper, one could spend a bit more and buy multiple crystals on the same
frequency, and just find the ones that were closest in frequency. The
only time you had that chance in the past is if you ended up with surplus
crystals in bulk.

Michael

"Brian Reay" wrote in message
...
Michael's comments re the use of 4.43 XTALS are worth noting Jon.
I think they are about £1 each and £10 worth will provide enough for some
experimentation, if nothing else.
Filters are often grossly misunderstood and there is nothing like some
real
'bench time' to turn theory into real understanding.
Seriously, you may find the tinkering/ experimenting bug bites. Even if
you don't go on to build things like radios, it will help you understand
operating and repairing them.

A positive contribution to the discussion.

Well done, keep it up!

"gareth" wrote in message
...
"Brian Reay" wrote in message
...
Michael's comments re the use of 4.43 XTALS are worth noting Jon.
I think they are about £1 each and £10 worth will provide enough for some
experimentation, if nothing else.
Filters are often grossly misunderstood and there is nothing like some
real
'bench time' to turn theory into real understanding.
Seriously, you may find the tinkering/ experimenting bug bites. Even if
you don't go on to build things like radios, it will help you understand
operating and repairing them.

A positive contribution to the discussion.

Well done, keep it up!


Unfortunately in subsequent posts he reverted to type.