Diff between xtal with 3 leads vs. 2 leads?
 

Hi,

Working on converting an old CB to a 10 meter beacon. Obtained some
xtals in the correct range I need, but they have 3 leads instead of 2.
Are these resonators? Can I use them as direct replacement for xtals in
the CB radio? Where does the 3rd lead go?

BTW, if anyone has a schematic for a barebones 10M tx, 1W +/-, please
send a copy if you can with parts list.
Tnx!

Diff between xtal with 3 leads vs. 2 leads?
 

Working on converting an old CB to a 10 meter beacon. Obtained some
xtals in the correct range I need, but they have 3 leads instead of 2.
Are these resonators? Can I use them as direct replacement for xtals in
the CB radio? Where does the 3rd lead go?

Do a search for 21.4 MHz filters. They have three leads and are used as
bandpass filters in UHF CB radios and may also turn up in 27MHz radios.
The middle lead probably goes to ground.
Alan

Diff between xtal with 3 leads vs. 2 leads?
 

C wrote:
Hi,

Working on converting an old CB to a 10 meter beacon. Obtained some
xtals in the correct range I need, but they have 3 leads instead of 2.
Are these resonators? Can I use them as direct replacement for xtals in
the CB radio? Where does the 3rd lead go?

BTW, if anyone has a schematic for a barebones 10M tx, 1W +/-, please
send a copy if you can with parts list.
Tnx!

Andy writes:

Use an ohmeter to see if one of the leads is connected to the case
of the device. If it is, it certainly is a ground lead....
I have seen regular xtals with the third lead used as a case ground,
as well as xtal filters, which normally have a ground lead...

Andy W4OAH

Diff between xtal with 3 leads vs. 2 leads?
 

Allison,

You might be misunderstanding. I'm modifying a Midland 13-380 to
transmit in the 10 meter band for use as a CW beacon. The xtal is
9.4MHz to replace the transmit xtal per instructions he
http://www.4sqrp.com/resource/10m_beacon/10m_beacon.htm

Should put the freq up in the 10M beacon portion of the band if I can
hook up the 3 leads correctly and if it is indeed a proper application
for the part.

Thanks!

- C

wrote:
On 3 Jun 2006 10:46:21 -0700, "C" wrote:

Hi,

Working on converting an old CB to a 10 meter beacon. Obtained some
xtals in the correct range I need, but they have 3 leads instead of 2.
Are these resonators? Can I use them as direct replacement for xtals in
the CB radio? Where does the 3rd lead go?

BTW, if anyone has a schematic for a barebones 10M tx, 1W +/-, please
send a copy if you can with parts list.
Tnx!

If you can be more specific on the CB I can give a better answer.
I will assume US AM/SSB radios.

The likley case is a 10.695 crystal filter.

The second likely case is ground lead on common crystal.

IF foreign (outside usa) FM radio then a 10.7mhz crystal filer is
packaged that way. Those filters are available in 4.5nhz, 10.7, 10.8
21.4 and 45mhz commonly and there are others.

Allison

Diff between xtal with 3 leads vs. 2 leads?
 

Thanks Allison.

The Midland is of the second variety you described and will require
retuing the sections once the TX xtal is replaced. Will take further
questions off-line.

73,

C

wrote:
On 4 Jun 2006 21:51:57 -0700, "C" wrote:

Allison,

You might be misunderstanding. I'm modifying a Midland 13-380 to
transmit in the 10 meter band for use as a CW beacon. The xtal is
9.4MHz to replace the transmit xtal per instructions he
http://www.4sqrp.com/resource/10m_beacon/10m_beacon.htm

Seems I do understand but you still didn't answer the question.

OK, that is a CB radio (USA 11M AM flavor). Likely that is a crystal
of the three legged variety wher one leg is a case ground or anchor.

However I have a RS40ch radio in my parts bin where the 10.695mhz
three legged thing is a crystal filter!

Should put the freq up in the 10M beacon portion of the band if I can
hook up the 3 leads correctly and if it is indeed a proper application
for the part.

The question was is it a crystal or a crystal filter? As both come
packaged that way. At 9.4mhz it's likely a crystal. If so the
middle (case ground) is optional.

I don't happen to have the 13-380 schematic but I can make a general
set of comments:

ANY CB radio with a 10.240 mhz crystal and an IC near it has a PLL for
frequency control and conversion 10M is not as simple as just changing
the 10.240 rock. The reasonis the 10.240 is not direcly the TX or RX
"rock" but the reference for the PLL.

CB radios come on three basic flavors. Cheap and old, used a crystal
per channel and were often limited to 3 to 12 channels. OLD 23
channel that used usually combination of 37.x, 10.1xx and 10.5xx
(or 23 and 14mhz) crystals to get RX and TX by mixing the result.
Newer (very late 23ch and ALL 40ch) used PLL system with 10.240 as
reference and PLL chip like 858, 5807, 14506 and maybe a dozen other
part numbers. Those are the most challenging.

Old and cheap crystal per channel just reqires a rock of the correct
type and frequency and some retuning.

Old 23ch required picking a pair of rocks or atlest one to get
the mixed pair to be 10M and then retuning the whole synth and
TX chain. Often changing the rocks from 37.6 and 10.595 (27.005 CB
ch 4) to a 37.6 and 9.56 (for 28.040) means the 10.5mhz osc needs to
be retuned and the tx bandpass filter retuned from 27mhz to 28 before
the unit will transmit at all. If the 37.x osc crystal is changed
that will also have the same effect as then that osc needs retuning
and the band pass filter as well.

The newer PLL based radios are a whole different story and there are
three different topologies for getting the TX frequency. Some are
easier than others. Some will not go without a fight. In any case
schematic for the radio and some understanding of how the PLL
for that radio works is needed to get a result that works. FYI: the
PLL based designs have a TX lockout circuit if the PLL is out of lock
or misprogrammed.

We can discuss off line at kb1gmx at arrl dot net.

Allison