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najones

Trying to control the tuner in a 900MHz receiver

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I am trying to wrap my head around tuning the receiver in my 900Mhz video receiver. The tuner is a BSS 479 LAID FM - http://www.comtech-tw.com.tw/pdf/bsm479laidfm.pdf

The receiver uses these inputs (found on the last page of the PDF):

Pin 1 - Ground

Pin 6 - AGC out (not used, but useful) [ranges from .1 ~ 4.8]

Pin 7 - 5V

Pin 8 - BB Out

Pin 9 - SDA (I2C)

Pin 10 - Tuner [~9v]

Pin 11 - SCL (I2C)

According to page 2 of the data sheet section "Tuning Voltage Curve", 900MHz should be about 1.8-2V, however this receiver (I have 2 of similar design) is always locked on about 8.9-9V. It is obvious that this receiver isn't being tuned with voltage, so it must be controlled with the I2C bus. I can't make any headway with the specifications on page 4...

Ultimately, I would like to be able to take control of this receiver as it is not just for 900MHz, but 900-2.4GHz. I don't really need to do this, but I am trying to learn electronics and this seems like a fun and tricky project to try out.

If it helps, I have an arduino that I could use to attemp to snoop out the I2C bus, although I haven't done any I2C yet.

Does anyone have any points for controlling a tuner with the I2C bus?

Thanks,

Nathan

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Maybe this will help with the I2C control: http://f5ad.free.fr/Docs_Composants/SP5055.pdf

I'm not sure if you'll gain any advantage, other than to create a continuously tunable 900Mhz Rx. Given that the Tx's frequency choices are fixed, this probably won't do you any good. If your goal is to improve the Rx's overall performance then the I2C control won't help much at all.

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Thanks for the link, I will read through and see what I can make of it. I was hoping you would reply, but I didn't want to directly trouble you.

I would eventually like to understand how to have and fully control 1-4 receivers in 1 box for a diversity system. If this works, I would also like to throw a cheap easycap in it for an all in one unit. Having the ability to tune it precisily tune it would just be cool.. :)

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