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  • May 8, 2010 at 3:03 am #810
    Anonymous
    Guest

    Hi

    I need to calibrate my fm transmitter, I was wondering if you could share a few words of wisdom

    1) Initially we were using a small digital radio for this, checking if we can get close to 75khz+/- deviation, we adjusted the TX modulation control with some tightly compressed music using a cd player, but unfortunately this was too crude as the stepping of the radio was 50khz (I don’t know if this would work anyway)

    2) So I discovered one of my old stereos (toshiba 3538) has test points on the board, one is labeled MPX-VCO and there is also a GND one too, can I use MPX Tool with this if I build a buffer amplifier?

    I also found a couple of devices for doing this kind of thing, one is from deva broadcast (band scanner pro) and one from pira.cz (fm broadcast analyzer with software)

    Any ideas would be helpful

    Thanks Russell

    May 8, 2010 at 5:52 pm #14501
    knigget
    Member

    Hi there,

    I too have adapted my tuner for this purpose so shall attempt an answer…

    Firstly, get a service manual for your tuner – you will then be able to see what ICs do what
    or
    Take the lid off, write down the IC part numbers and start googling them.

    Ideally, probe the test point labelled MPX-VCO using a scope with sufficient bandwidth and FFT display – that will show you what’s what.

    As for a buffer amp, it may not be required. Currently I have the tuner running straight into E-MU 0202 with no buffer amp – I’m just using the gain controls on the E-MU (roughly @ 10oclock).

    Hope that helps

    😀

    P.S – If you do get this working, remember to submit some recordings of stations in your area!

    May 8, 2010 at 10:42 pm #14502
    Anonymous
    Guest

    Hi thanks for the response!

    Well I don’t have a scope atm and couldn’t find a service manual for it, but I have a 192khz onboard realtek 888 (I think) on a junk computer that I tested out, I looked at the mpxtool instructions on the site, so I connected it up with a 3.5mm TS jack with the cable going to the mpx-vco connection and GND

    I can see what appears to be a pilot tone at 19khz, its quite tall. I didn’t have alot of time to calibrate it properly so I’ll do that later.

    For note the tuner is a Toshiba ST-3538, I’ll upload some pics later 🙂

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