18 May

I never appreciated the benefit of a panadapter until I had one with my IC-7300 and missed not having one with my IC-7100 so decided it was time to add one. Various videos on YouTube show how  it's done but most simply tap a 10pf onto the IF and bring it out. I'm not happy with that, I figure it must affect the IF somewhat and certainly doesn't protect the radio from anything nasty coming back the other way.

I decided to use an IF TAP board by G4HUP (HUPRF) but sadly found that he has passed away and so decided to try one of the LNA amplifier/buffer boards available from China on eBay. There are a few to choose from, all about £5 and I went for one with a low quoted gain of 10dB. They look quite good quality and I was surprised how good they are for the price, which includes shipping from China!

This article was originally produced using a Chinese 10dB LNA but has since been re-done using a PAT-150M. The PAT-150M gives a much better result.

The g4Hup boards are now available again from SDR-Kits https://sdr-kits.net/index.php?route=web/pages&page_id=64_64 although the specific model for the 7100 (PAT-150M) is not yet listed on their website. Each variant has a different LPF (low pass filter) on its output, for 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. Remove L1,L2 & L3 and install a jumper in place of L1 & L3 and it will work just fine. Alternatively you can purchase a PAT-150M from David Calo KD2C at kd2c56@gmail.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 the schematic we can 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). Some of the YouTube videos show it being taken earlier after the 1st IF mixer but that would only yield HF and miss the VHF which I particularly want.

Locating this on the PCB we find it here:

The pins on this area are tiny, so be careful. Fortunately pins 1 & 2 together make a reasonable large target so you should be able to get a wire on there.

There is a convenient place to mount the buffer board, shown below, and I used a double sided sticky pad to secure it and then a few earth straps to the surrounding metal can fixing points just to be 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. These are also easily available from eBay/China for a few £/$. Once I was happy it all worked I removed the data connector from the PCB and used the resulting hole in the rear chassis to mount an SMA socket.  The red wire shows where I located the 8v supply.

That's 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. The input signal is a bit strong but the RSP2 can attenuate that. 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. It works really well, I get over 500kc of bandwidth visibility so I can pretty much see the whole of most bands. Within a day of fitting I spotted an opening on 6m I would otherwise have missed and worked half a dozen stations into eastern Europe. This has totally transformed my 7100. I have since made the fixture more permanent.

I de-soldered the Data1 connector from the main PCB (just 3 pins) and used the resulting hole in the case to mount an SMA socket. I figure I can easily put it back if need be, but I'm so pleased with the result it's going to stay that way.

Thanks to all those who posted YouTube videos for inspiring me to do this. 

Now the indemnity waiver! Only do this if you are 100% confident in your abilities. I am not liable if you choose to do this and things go wrong!

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