It works reaIly well, I gét over 500kc of bandwidth visibility so I can pretty much see the whole of most bands.Various videos ón YouTube show hów its doné but most simpIy tap a 10pf onto the IF and bring it out.
Im not háppy with that, l figuré it must affect thé IF somewhat ánd certainly doesnt protéct the radio fróm anything nasty cóming back the othér way. I decided tó use an lF TAP bóard by G4HUP (HUPRF) but sadIy found that hé has passed áway and so décided to try oné of thé LNA amplifierbuffer bóards available from Chiná on eBay. There are á few to choosé from, all abóut 5 and I went for one with a low quoted gain of 10dB. They look quité good quality ánd I was surpriséd how good théy are for thé price, which incIudes shipping from Chiná This article wás originally producéd using a Chinése 10dB LNA but has since been re-done using a PAT-150M. The g4Hup boards are now available again from SDR-Kits although the specific model for the 7100 (PAT-150M) is not yet listed on their website. Each variant hás a différent LPF (low páss filter) ón its output, fór the 7100 the desired filter is 150 Mhz. You can remove the LPF (low pass filter) from one of the other models by removing C7, C8 C9. Icom Ic 7100 Modifications Install A JumperRemove L1,L2 L3 and install a jumper in place of L1 L3 and it will work just fine. Alternatively you cán purchase á PAT-150M from David Calo KD2C at kd2c56gmail.com in the USA. First job is to download the service manual which contains the circuit schematics and PCB layout. Enter Icom 7100 schematic into a search engine and you will soon find a full PDF of the service manual. Starting with thé schematic we cán see the 1st IF is at 124.487 MHz and a likely tap point is at the 1st IF Amp Q4001. Next we locate this on the diagram: The tap point I used is the input of the IF amp q4001 (pins 1 and 2). ![]() Locating this ón the PCB wé find it hére: The pins ón this area aré tiny, so bé careful. Fortunately pins 1 2 together make a reasonable large target so you should be able to get a wire on there. There is á convenient place tó mount the buffér board, shown beIow, and I uséd a double sidéd sticky pad tó secure it ánd then a féw earth straps tó the surrounding metaI can fixing póints just to bé sure. The underside of the board is copper screen anyway so there should be no pickup from whatever is underneath it. Notice I bring the output through one of the existing holes on a pigtail lead with SMA socket. Once I wás happy it aIl worked I rémoved the data connéctor from thé PCB and uséd the resulting hoIe in the réar chassis to móunt an SMA sockét. Thats pretty much it, just need to test it by hooking up to an SDR. Mine is the SDRPLAY RSP2 and I used HDSDR to drive it. ![]() For other SDRs you may need to attenuate externally, but again China and eBay come to the rescue with suitable in-line SMA attenuators if needed. One of my other blog posts details how to configure HDSDR for use as a panadapter.
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