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241.6MHz clock crystal source

Hello all!

I've got a wireless karaoke microphone system that a friend asked me to repair. The transmitter is a VERY basic RF design using what appears to be some high frequency overtone crystals for its carrier generation. Unfortunately, it has a dead crystal. The crystal has no identifying markings other than MJ and T=241.6MHz on the side. It's a typical two-legged through hole type metal can package. But I have no other information on any other paramters. Does anyone know where I can source a crystal of this frequency that would most likely work for this basic analog RF transmission circuit?

I have another one of the units and was able to swap out the crystal into this transmitter and everything fired up fine, just a slight tuning to tweek it into the circuit.

I just need to find this one little odd beast and if anyone knows where I could get one, I'd be greatly indebted.

I know, I know... it's a very cheap and silly almost toy of a unit, but it was providing some entertainment and fun for my friend's family and I'd hate to toss it out just because of a simple part like this.

Thanks so much!

Dan

Reply to
Dan Charette
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"Dan Charette"

** The actual frequency of the crystal is not as marked on the side - the number that has been marked is the frequency of the transmitter it is intended to use with.

IME with numerus VHF FM radio mics, the actual crystal frequency is some whole like 5, 9 or 12 times under the marked number.

This is the result of the mic using one or two stages frequency multiplying after the crystal oscillator.

Replacement crystals are usually only available from the company supplying the mics ( or very similar mics) in your country.

..... Phil

Reply to
Phil Allison

Phil,

Thanks so much for your insight. I have a 2nd working transmitter and I'll probe around on it a little and try to discern what it's doing. The transmitter itself is some inexpensive Asian product and I don't know that I'm gonna easily be able to contact them and get the crystal I need. I was hoping to come up with something out of the junk bin here that would work close enough to make it happen. There are some tuning coils in the circuit and I was able to retune the circuit for the working crystal from the other transmitter into this dead one. So, maybe if I can measure the base frequency close enough and see if it correlates with the whole number multiple as you said 5, 7, 9, etc, that would arrive at 241.6MHz. Maybe I could find something close that would work.

Thanks again for the help.

Take care!

Dan

Reply to
Dan Charette

Interesting frequency, in the band defined by the ERO as the 'Harmonised military band' and close to the 242.95 - 243.055 part 'only available for distress and safety purposes': see

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Did you hear the one about the rogue set-top box in Portsmouth area (UK, or was it Plymouth?) that, reportedly, set off a SARSAT at one of the distress frequencies (may have been 121.5 MHz) resulting in a Search & Rescue helicopter being scrambled (£?k) to look for the casualties? See:

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etc.

... and that was accidental. Perhaps the OP isn't located in an area where such frequencies are used in this way.

Chris

Reply to
christofire

Well, I didn't really ask my friend just how this mic is being used...

Maybe it's a mil spec karaoke wireless mic. :D

Thanks for the heads up on the frequency allocation tables. I be sure to mention it to the owner of this unit and maybe he'll be able to receive some interesting transmissions from time to time with the receiver.

Reply to
Dan Charette

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