Changing Shure wireless microphone frequency

180.4 divided by 20.05, is near as dammit 9, so the crystal oscillator stage is probably running through two tripler stages ( these are just 'dirty' amplifiers with appropriate tuned circuits in their collectors or drains, to pick off the third and then ninth harmonics. ) First stage may well be the oscillator itself.

In theory, all you need to do is sub the crystal for one at 1/9th the frequency of the desired output, so for 218.5, you would need a crystal at

24.277 MHz. The oscillator will probably be ok with this comparitively small change of frequency, but the tuned circuits in the multiplier stages will need to be adjusted. The first tripler stage will probably be in range, but the second will be nearly 40 megs off tune, so you may have difficulty getting it there without altering values in the tuned circuit. Also, if there is a following RF PA stage, this may well require retuning also, depending on whether any tuned circuits are just broadband tanks, or harmonic filters.

Finally, crystals can have many different specifications in their cut scheme, and load capacitances, depending on whether they are designed for series or parallel resonance, or overtone use. Crystal cutters understand what is required if you can let them have a copy of the oscillator schematic. At this sort of frequency, it will probably be a series crystal with 30pf loading.

Also be aware that the band that you are proposing moving the mic to, is not in general, a license-free band for this sort of use, so depending on where you are in the world, you would probably be contravening telecoms regulations, and could render yourself liable to prosecution, if you cause interference to other legitimate band users.

Arfa

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And unless you have a communications test set, i would advise against it. If your determined to do it, send it back to shure to have it done at the factory. Of course, its probably not worth it. Better to sell it on Ebay or such and find a used one with frequencies that are better suited to your uses. VHF wireless are on there way out. WHo knows what frequencies will be clear in the future. Basically in the USA, VHF is from around 169 to 215 MHz or so. You need to know what TV channels are in use in your area now.

Bob

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One thing to be accutely aware of is the fact that the "L" series is for use by Broadcast Stations only. The microphone (transmitter) HAS to be licensed under part 74 (Broadcast), and only TV/Radio station are eligible. If you are playing with this in your house, it's probably not a real risk. If it's at a public location, you need to use something that either doesn't require a license, or something that you can (and did) license. It's not as if the FCC is going to hunt you down. They now offer "snitch rewards", which gives motivation to individuals to look for unlicensed users. I know of a couple of underpaid local broadcast engineers that have played the game and won.

COPY FEDERAL COMMUNICATIONS COMMISSION WASHINGTON, D.C. 20554

GRANT OF EQUIPMENT AUTHORIZATION COPY Type Acceptance

Shure Incorporated 5800 W. Touhy Ave Niles, IL 60714-4608 United States Date of Grant: 07/24/1989

Application Dated: 02/13/1989

Attention: Dillard Gilmore , Senior Engineer, Global Compliance

NOT TRANSFERABLE EQUIPMENT AUTHORIZATION is hereby issued to the named GRANTEE, and is VALID ONLY for the equipment identified hereon for use under the Commission's Rules and Regulations listed below.

FCC IDENTIFIER: DD4L2

Name of Grantee: Shure Incorporated

Equipment Class: Licensed Broadcast Station Transmitter Notes:

Grant Notes FCC Rule Parts Frequency Range (MHZ) Output Watts Frequency Tolerance Emission Designator M4 74.861 174.0 - 216.0 0.05 0.005 % 60K0F3E

M4: Operation of this unit is limited to use at stations licensed for use under Part 74 of FCC Rules.

Mail To: None Specified, MET Electrical Testing Co. 916 W Patapsco Avenue Baltimore, MD 21230

8904278315022250

Really? there are thousands of those units still out there in churches, schools and such across the country. Even though they are suppose to file license applications, my guess is there is less than 5% compliance across the USA. The FCC could bust most of the churches in the country if they were stupid enough to do so.

Bob

The microphone (transmitter) HAS to be licensed

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Thank you all for the info and suggestions.

One more question. If I change the receiver's frequency to match the mic instead, would it require any retuning? The receiver's spec list a frequency range of 180MHZ to 250MHZ.

Thanks.

If the receiver tunes across that range, then it just does. No tuning other than setting it to the frequency that your radio mic is outputting on, will be required.

Arfa

It depends on how you read it I suppose. I was assuming that he had a tuneable receiver - some kind of VHF scanner or programmable handheld or something, which is why I said that if it tunes that range, then it just does. How it does this is of no consequence to the user. I have an Icom 706. It tunes from topband to 2 metres with a couple of button pushes - I don't have to go inside to retune coils, or change caps. My TV set tunes from

470MHz to almost 900MHz virtually continuously ( small break between bands IV and V ). My satellite receiver tunes from 920MHz to 2050MHz, so I don't think that 70MHz is an " awfully wideband " receiver.

Of course, if it is a fixed single frequency or channelised and rock-bound receiver that's merely *capable* of operating over that frequency range, then yes, you are probably right, unless it's synthesised, in that you would have to replace the L.O. crystal. I would not necessarily expect to have to retune the front end or change coils and caps though, if it is specced for that frequency range. It may actually have a real barn door antenna circuit. However, I agree that if it was mine, and the front end was tunable, I would probably peak it up for best performance on the specific frequency.

Arfa