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Author Topic: Changing frequency of a fixed frequency wireless microphone  (Read 282 times)

Daniel Levi

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Changing frequency of a fixed frequency wireless microphone
« on: March 25, 2021, 01:11:02 pm »

Posted this on the vintage radio forums but thought i'd cross post it here as I might get other answers,

Bit of backround, Having an interest in older professional wireless microphone systems I have recently acquired a Samson Concert TD system from the late 80's, now there was not any real information on this system online and as such I had to make a best guess that it used a legal frequency given that it was from a UK seller.
Unfortunalty after receiving it and it luckily being supplied with a manual I have found that ot unfortunately uses 186.6Mhz which is neither in the licence free VHF, Shared user licence (there is a gap between 176.6 and 191.9 mhz) of fixed licence sections so must have been designed for somewhere else (186.6Mhz being legal in the US I understand).

Now both the transmitter and reciever appear to have 186Mhz crystals (marked 4R186 W.S.S) so could I simply replace those crystals with, for example, 174Mhz ones so that it transmits within the licence free VHF allocation. I also believe that the transmitter power may also need reducing (quotes 50mW max but that is only allowed for body worn transmitters in the UK), but as there are no schematics or any other real info on the older Samson systems thus may not be possible,

I also realise that there might be many more things that would have to be done to make it properly legal and naturally I do not want to operate something that is illegal, though for the short periods of time it would be used legal in spirit (i.e. simply transmitting on a legal wireless microphone frequency and not worrying about the extra TX power) would be mostly acceptable.

Note that I am just playing around with said systems and not using it professionally so reliability or sound quality is not really important, plus I understand if it may be the case of simply cutting my losses with this system if it can't be easily made legal. Though as these were top level units at the time it would be nice to make it legal.

Any thoughts/ideas much appreciated even if it is a case of nothing being possible.
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Henry Cohen

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Re: Changing frequency of a fixed frequency wireless microphone
« Reply #1 on: March 25, 2021, 05:40:26 pm »

Posted this on the vintage radio forums but thought i'd cross post it here as I might get other answers,

Bit of backround, Having an interest in older professional wireless microphone systems I have recently acquired a Samson Concert TD system from the late 80's, now there was not any real information on this system online and as such I had to make a best guess that it used a legal frequency given that it was from a UK seller.
Unfortunalty after receiving it and it luckily being supplied with a manual I have found that ot unfortunately uses 186.6Mhz which is neither in the licence free VHF, Shared user licence (there is a gap between 176.6 and 191.9 mhz) of fixed licence sections so must have been designed for somewhere else (186.6Mhz being legal in the US I understand).

Now both the transmitter and reciever appear to have 186Mhz crystals (marked 4R186 W.S.S) so could I simply replace those crystals with, for example, 174Mhz ones so that it transmits within the licence free VHF allocation. I also believe that the transmitter power may also need reducing (quotes 50mW max but that is only allowed for body worn transmitters in the UK), but as there are no schematics or any other real info on the older Samson systems thus may not be possible,

I also realise that there might be many more things that would have to be done to make it properly legal and naturally I do not want to operate something that is illegal, though for the short periods of time it would be used legal in spirit (i.e. simply transmitting on a legal wireless microphone frequency and not worrying about the extra TX power) would be mostly acceptable.

Note that I am just playing around with said systems and not using it professionally so reliability or sound quality is not really important, plus I understand if it may be the case of simply cutting my losses with this system if it can't be easily made legal. Though as these were top level units at the time it would be nice to make it legal.

If both the receiver and transmitter specs indicate a functional frequency range encompassing the frequency you want, then yes, changing the crystals, and a bit of retuning oscillator capacitors and inductors, will permit the unit to operate on the new frequency. Your biggest hurdle, aside from access to a proper communications service monitor, will be acquiring the crystals: I believe there's only one or two manufactures of radio crystals left between Europe and Asia (there's one in the US), and everything now is build (grown?) to order, with a couple of months lead time and at significant cost. You might be better off scouring the internet for a used crystal based radio set using the same crystal form factor in the frequency range you need.

And FWIW, I would hardly call Samson "top level units at the time"; in the 80's Micron, Sennheiser, Sony, Vega, and to a lesser extent Swintek, were the best technology going , used by Broadway, West End, broadcasters throughout the world, and major touring SR companies/bands. By the late 80's, Shure was making their presence known in the RF space.
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Henry Cohen

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Daniel Levi

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Re: Changing frequency of a fixed frequency wireless microphone
« Reply #2 on: March 25, 2021, 07:02:08 pm »

If both the receiver and transmitter specs indicate a functional frequency range encompassing the frequency you want, then yes, changing the crystals, and a bit of retuning oscillator capacitors and inductors, will permit the unit to operate on the new frequency. Your biggest hurdle, aside from access to a proper communications service monitor, will be acquiring the crystals: I believe there's only one or two manufactures of radio crystals left between Europe and Asia (there's one in the US), and everything now is build (grown?) to order, with a couple of months lead time and at significant cost. You might be better off scouring the internet for a used crystal based radio set using the same crystal form factor in the frequency range you need.

And FWIW, I would hardly call Samson "top level units at the time"; in the 80's Micron, Sennheiser, Sony, Vega, and to a lesser extent Swintek, were the best technology going , used by Broadway, West End, broadcasters throughout the world, and major touring SR companies/bands. By the late 80's, Shure was making their presence known in the RF space.

Yes I understand that getting the crystals is going to be an issue, though this is a long term project and doesn't need to be done straight away as I don't need to use it.
For doing some simple frequency checks I have some other UK Licence Exempt VHF systems which aren't fixed frequency that I can (A Trantec S3500 and AKG WMS60) and some other fixed frequency receivers (2 x Trantec S2000 and a Beyerdynamic (Trantec) S350.
Interestingly where my gran lived there is one of the few crystal manufacturers IQD station road Crewkerne.

As for the quality level, well Duran Duran, Depeche Mode, Meatloaf, Pet Shop Boys, Phil Collins and many others used Samson wireless kit back in the day, seemingly both the VHF and UHF units, though naturally the are not in the higher end market anymore in the same vein as Nady. Notably these were made in Japan (and France?) and newer models were still being sold by Maxon. It certinaly feels like good quality given the Mic body is solid brass and it does have the SM58 head.

Here is Phil Collins using what I would guess is the same or similar system as I acquired, https://www.youtube.com/watch?v=36XZ9L0XUd0

And this is what I brought https://www.ebay.co.uk/itm/Samson-CR-2X-Concert-TD-Series-6-Channel-Receiver-With-CH-2-SM58-Wireless-Mic/373297707249 the seller must have been using it illegally for a while, something I would not entertain.
Luckily my other recent vintage wireless purchase that was purchased blind, A 1980's TOA WM230, transmits on 175.0Mhz so it perfectly legal despite it's age, and you can't sniff at it's supposed 30hr battery life! Do need to get the proper reciever though.
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Re: Changing frequency of a fixed frequency wireless microphone
« Reply #2 on: March 25, 2021, 07:02:08 pm »


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