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  1. #21
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    Re: Radio receiver from old analogue tuner - some questions, I am preparing for the p

    The inductance of IFT2 has to make it resonate at 10.7MHz with the 120pF capacitor across it so it should be: 1.844uH

    IFT1 also need to resonate at 10.7MHz. The schematic suggests it is a salvaged IF transformer form an old receiver but 'RED' isn't much help to identify an exact type. As most transformers have a color coded core, it probably refers to the one they used in the prototype but there is no standard for coding. The original manufacturer would have used any color they wanted or their customer specified as long as it distinguished it from other coils in the same radio.

    It may help you to buy one of these: do a search on Ebay for "LCR-T4 m328", they are very inexpensive and surprisingly accurate. If you connect a coil across the socket it will tell you its inductance.

    Brian.
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    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



    •   Alt19th October 2017, 16:42

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  2. #22
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    Re: Radio receiver from old analogue tuner - some questions, I am preparing for the p

    Quote Originally Posted by betwixt View Post
    IFT1 also need to resonate at 10.7MHz.
    Does it have to be adjustable?

    I've tried to find any manufacturer that's still producing RF transformers and found that:
    http://www.coilcraft.com/prod_wideband.cfm
    I havent searched all of them, but they have documentation here for each part:
    http://www.coilcraft.com/pwb.cfm
    so maybe one of them would be suitable?



    Quote Originally Posted by betwixt View Post
    It may help you to buy one of these: do a search on Ebay for "LCR-T4 m328", they are very inexpensive and surprisingly accurate. If you connect a coil across the socket it will tell you its inductance.
    That's great! I've ordered one right away. Suprisingly, the Ebay one is 2$ cheaper than the Aliexpress ones (they both offer free shipping).

    Can you recommend anything else helpful that I can buy? I am planning to make few more receivers in december, so more tools would be definetely useful



    •   Alt20th October 2017, 15:15

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  3. #23
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    Re: Radio receiver from old analogue tuner - some questions, I am preparing for the p

    so maybe one of them would be suitable?
    All the Coilcraft ones are broadband transformers, that is almost the opposite of what you need. The ideal inductor would have a high Q factor at 10.7MHz rather than a very flat response across a wide frequency range. The first inductor is to match the output of one IC to the other but it also works as a filter to reject anything except 10.7MHz, the second one is to provide a phase shift for the FM discriminator at 10.7MHz so they both have to be fairly accurate in value and preferably adjustable for peak performance.

    Can you recommend anything else helpful that I can buy?
    Obviously the most useful tester for radio work is a signal generator so you can produce a known good signal to adjust to. Next I would say an RF voltmeter but you can adapt a normal DMM quite easily to work at higher frequencies. Here I have a signal generators covering 0.1Hz to 3.2GHz and a spectrum analyzer for taking high frequency measurements as well as a reasonably good oscilloscope (Tek MSO 3032) that can measure up to about 300MHz.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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