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LPE200 out-of-band RX

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mitaux8030

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Hi all,
I've a requirement to get a 900 MHz LPE200 to receive in the uplink band eg 896-901 MHz, to check for & locate some input interference from foreign ITU region devices. Now while I could lug the spec-an or service monitor around in the vehicle with me, it'd be so much easier if a sacraficial LPE could be made to RX in the uplink band.
I was thinking SC4 files, a la Orion out-of-band, and if necessary some mods to the VCO.

Does anyone have any experience with this?
 
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mitaux8030

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Well, I had the chance to play about with this today.
SC4 files will only go so far, about 8 MHz either side of the standard band edges. Not enough for my purposes (trying to RX the 900 MHz uplink band 896-902 MHz).

But after studying the schematics, I think there may be a way; with a 800 MHz LPE200.
With TX talk-around, the radio causes the VCO to shift by 45 or 39 MHz, for 800 & 900 MHz variants respectively. The TX offset mixer is then applied to get to the TX talk-around band.
I was thinking, with a 800 MHZ LPE, the standard local oscillator generated freqs are 940-960 MHz, or there abouts. When talk-around is activated, this then adds 45 MHz, so the LO becomes 985-1005 MHz. This is acheived by pulling a line low during TA, and only during TX.

Well, I was thinking that an 800 MHz LPE modified so that the TA line was hard wired low, the RX LO of 985-1005 MHz equates to 896 to 915 MHz. Perfect! It would of course mess up TX permanently, but thats fine with me, I'm going to dedicate this device to uplink interference hunting (mainly errant ISM stuff)

All that would remain to do is modify or replace the ceramic front end filters, and voila! A LPE operating in the 900 MHz uplink band for RX only.
 
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