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Load capacitance for custom IF crystal?

T23

Active Member
Apr 17, 2010
645
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I have two crystal synthesized 11 meter rigs that I want to change the working band on. I calculated that a new hc/25u crystal of 8.2525mhz would be needed. What I need to know is that how do I calculate the load capacitance required for the custom crystal? When I called icm for pricing, they wanted this information.

Thanks
 

I'm relying on memory from a ordering a crystal from JAN many years ago to re-rock a Ten-Tec 10 to 2meter transverter but I believe I had to contact Ten Tec for that info. Sounds like your working on an old CB so I'm not sure where you would find it. Maybe in the repair manual for the radio.

Heathkit used to include crystal specs for their crystal controlled rings in the assembly manuals.
 
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It sounds like it should be about 30pf. Saw two articals with yaesu rigs and it qouted a 30pf capacitance for the mixing crystals to move them to 11 meters.
 
Load capacitance is a figure usually provided by the manufacturer. You may have to consult a manual or a user group on the net for that info if the manufacturer is not able to provide it.
 
Is there a way to measure the crystal thats in place? I doubt ill find factory specs that detailed.
 
I could be wrong here but is this not just a matter of looking at the schematic and determining the value of capacitance in parallel with the rock?
 
Thanks 399, looks like I was close. I just got the Pace 1000B in and its got some kind of weird crystal selector to get channels 35 and 38 some how... One thing that gets me is the pace does not have a mic gain... but seems to get great sounding modulation none the less. Haven't tested the Midland yet but that does have a mic gain.

But anyway... I calculated that changing the IF crystal from 7.8025 to 8.2525 will put channel 1 on the dial at 27.415. And of more interest channel 12 on 27.555. The best thing about these rigs is that the clarifier works on both TX and RX out of the box with pots for clairifier range adjustment.

If anyone is interested....

1 = 27.415
2 = 27.425
3 = 27.435
4 = 27.455
5 = 27.465
6 = 27.475
7 = 27.485
8 = 27.505
9 = 27.515
10 = 27.525
11 = 27.535
12 = 27.555
13 = 27.565
14 = 27.575
15 = 27.585
16 = 27.605
17 = 27.615
18 = 27.625
19 = 27.635
20 = 27.655
21 = 27.665
22 = 27.675
23 = 27.705
 
One thing that gets me is the pace does not have a mic gain... but seems to get great sounding modulation none the less. Haven't tested the Midland yet but that does have a mic gain.
The mic gain knob on the radio face attenuates the audio circuit. Without a knob, the gain is wide open all the time.
 
Ah, thats what I thought. Without that variable resister, its just direct to the audio pre-amp.

I'll have to give ICM crystals a call back now that I got the capacitance Info I needed.

Thanks

K.M
 
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