My First Panadapter

I like older radios. I think part of it is nostalgia from when I had my first ticket (late ’80s/early ’90s, KB5KHR). But they’re also easy to work on. And radio hasn’t changed much in 30+ years. So I decided to bring a rig into the 21st century.

I’ve wanted to add a panadapter every one of my rigs for a while.¬† After my success at minor repairs and adjustments the other day, I decided to try to add one to my HF rig, an Icom IC-751A. I already had the SDR and some RG-316 cable with SMA connectors on it, so I went to work.

The IC-751A on its side with the RF board cover removed.

I took off the covers and found the IF tap point that I’d read about online (thanks to Gary Rondeau). I cut off one end of the RG-316 cable I had, leaving about 24 inches of RG-316 with a male SMA on the other end, perfect for my SDR. I stripped the end and prepped it to be soldered to the IF tap connector (I didn’t have a 2-pin connector, so I just decided to brute force it).

The stripped RG-316, ready to be soldered to the IF tap.

The IC-751A service manual came in handy here to show me which pin was ground and which was the IF signal. Once I had the cable soldered to the connector, I put the RF shield back on and decided to test it before I put the whole rig back together.

The RF board cover replaced and the IF cable routed out an existing gap.

So I hooked up the SDR, brought up HDSDR, and used the settings that Gary had mentioned on his blog. Turning on the rig didn’t let out any magic smoke, and then…

It works!

My 30-year-old rig now had a 21st century panadapter!

I played with it for a day or two like this: IF straight into the SDR. I noticed that I could listen to conversations on the radio itself that I could barely hear, if I could hear at all, on the SDR. I know that some people put buffer amps and IF amps on their panadapters, and I had planned ahead for this: I had bought a $10 10dB amp board on eBay months ago. I also bought AM broadcast (2.6MHz high pass) and FM broadcast (87MHz low pass) filters to clean up any potential RFI. I didn’t have all the connectors needed, so I left the FM broadcast filter on (I get a lot of FM station noise here) and added the amp. I mounted the whole thing to the side of the rig with a bit of double-sided tape and called it good.

The SDR, FM broadcast filter, and 10dB amp mounted to the left side of the rig.

It’s still a bit quiet; I think I need more amplification. But it’s a big help when glancing at a band and deciding where to go.

For now, I’m not controlling the rig with HDSDR since I think I found a bug when doing so, but I can see the current IF passband while tuning the rig; that works for me. I read the frequency and mode from the radio, and that sets HDSDR correctly. I can tune around on the radio, and HDSDR follows.

It seems that people have added panadapters to all sorts of rigs of all ages and makes. So if you want to add one, a simple Google search might turn up a page telling you exactly what to do. And for $25-50, you can add this incredibly useful tool to your radio. I plan on doing this to my other radios, too. It’s an amazing upgrade for any rig.