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drawde

27MHz frequencies

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I picked up a job lot of crystals to use with my old 27MHz Acoms Techniplus radio gear. I tested them and they all worked as expected. They were in need of new labels, so I printed some up. When I took the old labels off, the frequencies printed on the metal casing were as expected for all of the transmitter crystals, but for three of the receiver crystals the frequencies printed on the metal casing were different to the frequency marked on the labels, and the printed frequencies were not ones I was familiar with. See table below:

Channel

Colour

Expected Frequency

Marked Frequency

1

Brown

26.995

26.540

2

Red

27.045

26.590

5

Green

27.195

26.740

The job lot also included some crystals without labels, with frequencies printed on the casings that I'm not familiar with. They are:

  • Tx 26.690 and Rx 26.690
  • Rx 26.800
  • Rx 27.175

Does anyone know what's going on here?

 

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Ok I figured it out. I noticed that the difference is always 0.445MHz, and when I googled that I found an article that said that receiver frequencies are always 0.445MHz lower than the transmitter frequency (it didn’t say why though), and that different manufacturers label them in different ways. 
 

That solved everything except the 27.175MHz crystal which I’m happy to leave as a mystery

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2 hours ago, drawde said:

Ok I figured it out. I noticed that the difference is always 0.445MHz, and when I googled that I found an article that said that receiver frequencies are always 0.445MHz lower than the transmitter frequency (it didn’t say why though), and that different manufacturers label them in different ways. 
 

That solved everything except the 27.175MHz crystal which I’m happy to leave as a mystery

You got to the bottom of the frequency offset on the RX crystals. They aren't always marked that way.

27.175 would be a yellow/green "split" crystal as alluded to above.

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On 9/1/2022 at 8:05 PM, drawde said:

That solved everything except the 27.175MHz crystal which I’m happy to leave as a mystery

Sold a full set of splits a while back, and just found the pic I took for ebay.

(Actually bought these, when I got back into RC ,and went to run at a club with my Futaba Attack R. Some looked confused, when I asked about the 'peg board'.....🙄🤣)

 

20200214_111155

 

20200214_111148

 

As above, yellow/green split.

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