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gizmointheskywithdiamonds

Wide range receiver

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Hello people,

Rcuniverse has a thread about converting "our" normal receivers to receive 900mhz to 2.4ghz:

QUOTE

As I had stated in an earlier post, I have been building a universal video receiver.

It is based on the control board sold by http://www.radio-kits.co.uk/

Using 2 law-mate receivers and an antenna divider rated at 2.5 GHz I am able to tune in all of the 900, 1.2 and 2.4 GHz bands from one unit.

END QUOTE

Anyone know how this can be done and/or have a schematic?

Buying three different receivers from Mobi Comm is out of my budget ...

Thanks in advance,

Gizmo

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Inside the Comtech sardine can is a 5055 PLL IC that controls the Rx's operating freq. The IC is manipulated by an external microcontroller to change the oscillator divider rate.

Video Rx's, like the BWAV unit, do indeed have a microcontroller in them that reads the DIP switches and "talks" to the Comtech module. This is what happens when you change the RF channel. Ham Radio ATV'ers have gone beyond this and substituted their own custom microcontrollers to do extraordinary things (including being able to dial any freq they want).

The big issue is that the Rx's other RF components are chosen for the operating band. So, forcing a 2.4Ghz Rx to work at 900Mhz is expected to dramatically affect performance. Has the fellow that did the hack reported range statistics with the modified Rx when dialed to the alternate RF bands? It would be interesting to hear what the range was for 900 versus 2400 MHz.

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forcing a 2.4Ghz Rx to work at 900Mhz is expected to dramatically affect performance.

You are bringing up a very good point, Thomas.

The thread I was refering to was aimed at making a much more accurate and sensitive receiver than the one supplied by the vendors that sell that specific brand name.

Somebody also made a comment like: "These receivers were tuned simply by getting a video picture on the screen and hearing a hiss on the audio channel" :o

The receivers I was looking at were:

http://cgi.ebay.com/High-quality-915-MHz-A...tem140067115283

http://cgi.ebay.com/High-quality-1-2-GHz-A...tem140067137976

http://cgi.ebay.com/Highly-sensitive-2-4GH...tem140098320047

Any ideas as to how to blend the signal, if possibile at all?

Thanks,

Gizmo

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The thread I was refering to was aimed at making a much more accurate and sensitive receiver than the one supplied by the vendors that sell that specific brand name.

That sort of effort would be difficult. The important performance areas involve areas outside the PLL circuit. With Rx designs, the front end noise, RF gain, selectivity, and so forth, are where the rubber meets the road. Tweaking the PLL won't improve many of those RF issues.

Somebody also made a comment like: "These receivers were tuned simply by getting a video picture on the screen and hearing a hiss on the audio channel"

Sadly, I have to agrees with that. Generally speaking, I doubt the mfg subjects the assembled unit to a detailed performance test. I could be wrong, but I think they just use a classic "light bulb" test.

Many of us have discovered that once a good Rx model is identified, then consider it a keeper. Until then, beware of poop in a pretty box. As far as the links you posted, I have seen others ask about them too. I have no idea if they are gold or if they are poop. Someone needs to buy them and report on their experience. My only comment is that their -80dBm sensitivity is a bit low. It's also hard to say if their audio sub carriers will be compatible with the various video Tx's that are in use.

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