Hi Charles,, Keith here in at work on the late shift...
You have the IF figured correctly. International Crystal in OK can make
the new crystals, but hold onto your wallet, they aren't cheap.
Figure $30 - $45 per channel.
For an exercise, let's say that you want to crystal the HT for 29.050
MHz. The TX frequency crystal would be cut for 29.050 MHz and the RX
crystal would cut either for 455 KHz above or below the TX frequency.
Here is the issue, the image rejection on these radios is not great.
So, for the example, let's put the RX crystal on the low side:
29.050 MHz - 0.455 MHz = 28.595 MHz. The RX image frequency is 455 KHz
lower than the RX crystal, or 28.140 MHz. A signal on that frequency
will interfere with your 29.050 MHz RX.
For the high side:
29.050 MHz + 0.455 MHz = 29.505 Mhz. The RX image frequency in this
case will be 455 KHz higher, or 29.960 MHz.
There are CW and digital signals on 28.140 MHz, there aren't signals on
29.960 MHz typically. Based on this, high-side injection would be best.
The best way to ensure that the crystals will work would be to send a
working pair of crystals on the CB channel with the order and ask
International to match the characteristics. This is a normal procedure
with older land-mobile gear, they should have no problems providing you
with the right rocks...
Like I said, it WILL be expensive, but it is something that is do-able.
73, Keith, WB2VUO/work
BTW: I have done this, but in the 70's when I did my conversions, the
crystals were only about $6.00 each...K
On 12/03/2015 20:27, Charles Spitler wrote:
Hi all,____________________
I picked up a few Realistic TRC-213 2W HTs for the CB band. I was
thinking of converting one for beacon use or 10m AM. The problem is,
how do I calculate the IF frequency for it's 455 kHz IF amplifier? It
currently uses a 27.125 / 26.67 TX/RX crystal pairing.
Or am I just wasting my time and should part it out?
Thanks,
Charles
KCØJCA
