Chinese Model ST-15B 1.5/15 Watt FM Transmitter
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Thread: Chinese Model ST-15B 1.5/15 Watt FM Transmitter

  1. #1

    Chinese Model ST-15B 1.5/15 Watt FM Transmitter

    Greetings ! Perhaps I may be on the wrong turf here for my topic and equipment but here goes, please forgive me if I made an error posting this thread here but I am a 'newb'.. I recently purchased 2 Chinese Model ST-15B FM BCB Transmitters for use out of the USA. Upon initial testing using a Bird Model 43 Wattmeter with correct slug into a dummy load. In low power mode I read about 1 watt, tops. In high power mode I am able to get no more than around 3 watts of power. I am using the correct power supply capable of the 5 amps of current required. These particular transmitters are the Model ST-15Bv2, which claims to be capable of 1.5 watts in low power mode and 15 watts in high power mode. I was wondering if anyone else on this forum has worked with any of these cheap FM transmitters and if so, have any of you experienced this same issue ? Any information about this unit and this problem would be most appreciated ! If anyone may posses a schematic diagram of this transmitter, that would be priceless ! I should mention here that I am an Extra Class Amateur Radio Operator and have been an electronics technician for 37 years. If any of you may be able to contribute any helpful information regarding this issue I sure would appreciate it ! I doubt I am the only one having this or similar issues. Also, in closing, I'd like to point out that the craftsmanship of the unit and the quality of the circuit board are quite good !
    Thank you all in advance for any assistance you may be able to provide !

  2. #2
    I don't have any experience with these devices, but a couple things come to mind:

    Some Asian standards are matched to 75 Ohm or higher impedance loads. I assume you're testing this thing into a known good 50 ohm load (dummy load), it may not like 50 ohms. Confirm the correct operating impedance.

    Sometimes these cheap devices will get RF back into itself on the IF or modulator side. Make sure the test load is at least five or more feet away from the transmitter.

    Finally, seems to me that a 5 amp DC power supply is too small, especially trying to run this thing at 15 watts output.

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