On Sep 2, 4:12�pm, Gary@ removenospamandputkf9cm.com wrote:
I am looking for some Heterodyne conversion crystals for a receiver I am
making.
The frequencies a 5 MHz, 7 MHz, 10.5 MHz, 13.5 MHz, �17.5 MHz and 21.5
MHz.
The variable mixing frequency will be from 3 to 3.5 MHz. I would prefer all
the same type holder.

Once source of crystals is eBay. Another is AF4K (google his call), he
has quite a stock in various holders.

But be prepared to pay more than a few dollars per crystal!

Actually, when you adjust for inflation, crystals cost about as much
now as they did 30-40 years ago. Three dollars back in 1965 is the
equivalent of about twenty dollars today.

You can also do things like use harmonics and overtones of the
crystals to get the higher frequencies.

--

But before you start building, I suggest you reconsider that mixing
scheme.

As I understand it, the receiver will consist of a tunable section
that covers 3 to 3.5 MHz, and a converter section which converts the
various ham bands to that tuning range.

So for 160, you would take the 2 to 1.5 MHz range, subtract it from 5
MHz, and get 3 to 3.5 MHz

For 80, you would take the 4 to 3.5 MHz range, subtract it from 7
MHz, and get 3 to 3.5 MHz

For 40, you would take the 7.5 to 7 MHz range, subtract it from 10.5
MHz, and get 3 to 3.5 MHz

For 30, you would take the 10.5 to 10.0 MHz range, subtract it from
13.5 MHz, and get 3 to 3.5 MHz

For 20, you would take the 14.5 to 14 MHz range, subtract it from 17.5
MHz, and get 3 to 3.5 MHz

For 17, you would take the 18.5 to 18 MHz range, subtract it from 21.5
MHz, and get 3 to 3.5 MHz

I guess you don't plan on 15, 12 or 10 meters.

The main problem I see with this design is on 80 meters. On that band,
the tunable frequency is too close to the band being covered, and
you'll likely have troubles with feedthrough. For example, when you
are trying to listen to a signal on, say, 3.6 MHz, the tunable section
will be on 3.4 MHz, and the front-end selectivity probably won't be
able to stop strong signals from leaking through.

I suggest you look at other heterodyne schemes, because 80 meter
operation will be compromised using the scheme you describe.

Here's one to consider, from G2DAF:

Tunable range is 5 to 5.5 MHz

For 160, you would take the 2 to 1.5 MHz range, subtract it from 7
MHz, and get 5 to 5.5 MHz

For 80, you would take the 4 to 3.5 MHz range, subtract it from 9
MHz, and get 5 to 5.5 MHz

For 40, you would take the 7.5 to 7 MHz range, subtract it from 12.5
MHz, and get 5 to 5.5 MHz

For 30, you would take the 10.5 to 10.0 MHz range, subtract it from
15.5 MHz, and get 5 to 5.5 MHz

For 20, you would take the 14 to 14.5 MHz range, subtract 9 MHz from
it, and get 5 to 5.5 MHz (Note that the 9 MHz xtal works on two bands)

For 17, you would take the 18 to 18.5 MHz range, subtract 13 MHz from
it, and get 5 to 5.5 MHz

For 15, you would take the 21 to 21.5 MHz range, subtract 16 MHz from
it, and get 5 to 5.5 MHz

For 12, you would take the 24.5 to 25 MHz range, subtract 19.5 MHz
from it, and get 5 to 5.5 MHz

So you cover 8 ranges below 25 MHz with 7 xtals

Ten meters is left as an exercise for the reader.

For the higher frequencies, harmonics of the can be used. For example,
an 8 MHz xtal could be used for 15 meters by doubling.

Here's another one:

Tunable range is 3.5 to 4.1 MHz

For 160, you would take the 2 to 1.4 MHz range, subtract it from 5.5
MHz, and get 3.5 to 4.1 MHz

For 80, the conversion section is bypassed and you use the basic
tuning range

For 40, you would take the 7.5 to 6.9 MHz range, subtract it from 11
MHz, and get 3.5 to 4.1 MHz (Note that the second harmonic of the 5.5
MHz xtal used for 160 is 11 MHz)

For 30, you would take the 10.6 to 10.0 MHz range, subtract it from
14.1 MHz, and get 3.5 to 4.1 MHz

For 20, you would take the 14 to 14.6 MHz range, subtract 10.5 MHz
from it, and get 3.5 to 4.1 MHz

For 17, you would take the 17.6 to 18.2 MHz range, subtract 14.1 MHz
from it, and get 3.5 to 4.1 MHz (Note that the same xtal that gives
you 30 meters also works on 17 meters)

For 15, you would take the 21 to 21.6 MHz range, subtract 17.5 MHz
from it, and get 3.5 to 4.1 MHz

For 12, you would take the 24.5 to 25.1 MHz range, subtract 21 MHz
from it, and get 3.5 to 4.1 MHz (Note that the second harmonic of the
10.5 MHz xtal used for 20 is 21 MHz)

So you cover cover 8 ranges below 25.1 MHz with 6 xtals. If you use
harmonics of certain xtals, those 8 ranges can be covered with just 4
xtals.

Ten meters is left as an exercise for the reader.

There are lots of other schemes.

73 de Jim, N2EY