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[Solved] Which crystal and where to buy to get Channel 36 and 37 on a Midland 13-893?

I should have mentioned earlier, but crystals do pull better up than down, so if in the extreme case with the trim cap shorted you cant get it down to 8.549, you will need to add a little series inductance.

edit: i now see in the schematic they have an inductor at the base of the transistor already, so you shouldn't have any issues.
 
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brandon7861 said:
I should have mentioned earlier, but crystals do pull better up than down, so if in the extreme case with the trim cap shorted you cant get it down to 8.549, you will need to add a little series inductance.

edit: i now see in the schematic they have an inductor at the base of the transistor already, so you shouldn't have any issues.
Click to expand...
I was worried for a bit if I could adjust it some so it can get closer to where it needs to be. :) Good to know it should work.
 
doffo said:
I was worried for a bit if I could adjust it some so it can get closer to where it needs to be. :) Good to know it should work.
Click to expand...
There should be enough range to blow right past your target frequency, and if I am wrong, I'll wire you the $9.99 :)
 
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doffo said:
Hello fellow CBers!

Making sure if I got this right. The Midland 13-893 is essentially a Cobra 138 23 Channel SSB radio. That being said, according to this page, one would need a 8.549 MHz crystal to obtain Channel 35, 36, 37, and 38. 138,139, Midland 13-893, 13-895 Crystal Mixing According to that link, all 3 are added up to give you the final frequency. I just first added 11.0035 + 7.8025 to get 18.806. Then I did 27.355 - 18.806 to give me 8.549. Just making sure I did that right to figure out which crystal to try and get.

That being said... Where to buy a crystal that could work? :) I didn't yield much luck in results or a good place to buy some.
Thanks for reading and any help. Enjoy the day and some radio time!
Click to expand...
Try Kens Electronics

CB & Amateur Ham Radio crystal frequency list at Ken's Electronics, (Wholesale & Retail Electronic Parts) Kalamazoo, Michigan

CB & amateur ham radio crystals are available from Ken's Electronics, (Wholesale & Retail Electronic Parts) Kalamazoo, Michigan at reasonable prices
kenselectronics.com
 
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The ebay link I shared only had one of those 8.550 crystals and kens does not have one listed. Doffo got the only one they had.

Edit: I did see some FT-243's at 8.550, but I dont think there is room to put them in there.
 
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brandon7861 said:
There should be enough range to blow right past your target frequency, and if I am wrong, I'll wire you the $9.99 :)
Click to expand...
The crystal came in. I did put it in my base Cobra 139 for the time being as I know it works vs The Midland is having some weird issue on SSB (Currently recapping), but I could only get it as close as I could on frequency with the voice lock all the way to the right, and adjusting the potentiometer from the inside. I am unsure if I could do something to try and help bring it in better, or if the only way is another crystal.

Otherwise, its almost right in the middle of the frequency, but slightly off. No worries. for now I am just listening on the 139.
 
doffo said:
The crystal came in. I did put it in my base Cobra 139 for the time being as I know it works vs The Midland is having some weird issue on SSB (Currently recapping), but I could only get it as close as I could on frequency with the voice lock all the way to the right, and adjusting the potentiometer from the inside. I am unsure if I could do something to try and help bring it in better, or if the only way is another crystal.

Otherwise, its almost right in the middle of the frequency, but slightly off. No worries. for now I am just listening on the 139.
Click to expand...
There are a couple things you could try. The first is changing the cap that is in parallel to the trimmer. Schematic says 40pF. You could try 82pF, or even 150pF. The other option is to add more inductance (to that crystal only). I know not all crystals are made equal lol, but I sure figured it would slide in there. My offer stands.
 
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I appreciate it, but wont be necessary. When you say to put inductance with just the 1 crystal, like putting a resistor between it and ground? If so, how many ohms of a resistor we takling?
 
doffo said:
I appreciate it, but wont be necessary. When you say to put inductance with just the 1 crystal, like putting a resistor between it and ground? If so, how many ohms of a resistor we takling?
Click to expand...
The inductances I have seen in various schematics usually range from a couple hundred ohms to around 3kohm reactance at the crystal frequency. So i would assume you could add up to 40 or 50uH in series with the crystal. How much more pull range that will give you, I honestly don't know. Yes, in series with the crystal.

I think, if adding inductance was necessary, I would probably stick that crystal in its own oscillator board and pipe the signal into the crystal socket with a little piece of shielded cable. That would give you room to play with inductors. If you get tired of messing with it, I'd be more than happy to try getting that crystal on 8.549 on a separate board.
 
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brandon7861 said:
The inductances I have seen in various schematics usually range from a couple hundred ohms to around 3kohm reactance at the crystal frequency. So i would assume you could add up to 40 or 50uH in series with the crystal. How much more pull range that will give you, I honestly don't know. Yes, in series with the crystal.

I think, if adding inductance was necessary, I would probably stick that crystal in its own oscillator board and pipe the signal into the crystal socket with a little piece of shielded cable. That would give you room to play with inductors. If you get tired of messing with it, I'd be more than happy to try getting that crystal on 8.549 on a separate board.
Click to expand...
That is a good idea to put it on a little board by itself, then this way its easier to work with. For sure I may try changing out the 40PF to those two values you mentioned. I am looking through old CB boards for some lol. Fun stuff, but for the most part, if I can bring it just a bit closer to the middle, that would be completely fine. I am OCD, but never cared for the clarifier knob having to be in the middle.
 
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