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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 5th Jul 2017, 2:42 pm   #1
Biggles
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Default Mini FM transmitter as a signal booster.

This has probably been done many times before but it occurred to me the other day while having problems receiving my (low power) local FM radio station around the house to connect a tuner on an external aerial tuned to the required station to a low power FM transmitter input to rebroadcast the signal at reasonable strength on a different FM frequency around the house. A sort of repeater if you like. The only problem I can foresee is that the tuner may be desensitized by having an in-band transmitter so close. A bit of experimenting is called for.
Apologies if this is a well tried and tested system already. Sometimes it takes me a while to twig!
Alan.
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Old 5th Jul 2017, 3:15 pm   #2
Jonster
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Default Re: Mini FM transmitter as a signal booster.

The power from a microtransmitter should not upset a good quality FM tuner unless the aerials are very close together. Just make sure there is a good separation between them and that the frequencies are opposite ends of the band, and all will be well.
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Old 5th Jul 2017, 6:15 pm   #3
merlinmaxwell
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Default Re: Mini FM transmitter as a signal booster.

My "car" (it's in the kitchen) DAB adaptor has VHF output, it works very well and is self contained.
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Old 5th Jul 2017, 7:29 pm   #4
G6Tanuki
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Default Re: Mini FM transmitter as a signal booster.

Can you stick an external directional antenna up somewhere that gets a good signal from your desired station?

In the past some of us used a couple of directional antennas [5-element Yagis] coupled together with a "masthead" type preamplifier in between to shunt Band-II and Band-III broadcast-FM/405-line-TV signals around local obstacles in mid-Wales.

The important thing was that neither of the antennas should be able to see each-other, or the whole thing woukld do the VHF equivalent of the audio-feedback you get when someone turns the volume up too far on a public address system.
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Old 5th Jul 2017, 9:39 pm   #5
Biggles
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Default Re: Mini FM transmitter as a signal booster.

I once rigged up an internal rebroadcast antenna coupled to an external one via an amplifier to improve a poor signal inside a depot where vehicles had to receive data on VHF high band and no one was more surprised than me when it worked. The aerials were well spaced and isolated so no problems with instability occurred. It's probably still there, doing it's obsolete job if no one has discovered where to switch it off yet!
Alan.
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Old 5th Jul 2017, 10:33 pm   #6
paulsherwin
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Default Re: Mini FM transmitter as a signal booster.

You will probably find that there is an internet stream which gives a better and more reliable source than a weak off-air FM signal. You can use any old smartphone or tablet to create analogue audio to feed to a microtransmitter.
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Old 10th Jul 2017, 4:42 pm   #7
Mach One
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Default Re: Mini FM transmitter as a signal booster.

Before the little low-power FM modulators were legalised about ten years ago or so I found that if I modulated an FM oscillator with the output of the FM radio receiver - with the requisite 50us HF boost - it also broadcast the stereo pilot signal and the stereo difference signal from the FM transmission.

At the time I wanted to hear Jazz FM in London on 102.2MHz which was a very marginal signal at home and it provided a good level of stereo signal into any radio within the home and garden quite nicely.
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Old 10th Jul 2017, 5:21 pm   #8
robinshack
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Default Re: Mini FM transmitter as a signal booster.

Put a Monolithic microwave integrated circuit (MMIC) on the o/p of the booster if not strong enough in your own home?
Rob
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Old 17th Jul 2017, 10:42 am   #9
Arqiva BOC
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Default Re: Mini FM transmitter as a signal booster.

Quote:
Originally Posted by G6Tanuki View Post
In the past some of us used a couple of directional antennas [5-element Yagis] coupled together with a "masthead" type preamplifier in between to shunt Band-II and Band-III broadcast-FM/405-line-TV signals around local obstacles in mid-Wales.

The important thing was that neither of the antennas should be able to see each-other, or the whole thing woukld do the VHF equivalent of the audio-feedback you get when someone turns the volume up too far on a public address system.

A technique still in use in Wales for DTV, known as an 'Active Deflector'
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Old 17th Jul 2017, 6:55 pm   #10
Dai Corner
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Default Re: Mini FM transmitter as a signal booster.

Bethesda is an official active deflector. The writer of this page gives a good description of the technique, wonders why it was done and concludes it may have been just 'because they could'.

There are doubtless unofficial installations too though probably fewer than there used to be as DTV is more robust than analogue and in particular doesn't suffer from ghosting.
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