Thomas Does Radio or Something

Rockwell International produced the 251-9735-010 6 GHz amplifier many years ago. It was a popular amateur radio choice surplus around the turn of the millennium and might still be a decent choice if found at a good price. The one I have looks to be new old stock passed through amateur hands along the way with a paper label handwritten "+37 dBm 5W | 5.76 GHz AD" alongside the factory test tag with matching serial number. That inspection (not really warranty) sticker wasn't about to last very long… New-old-stock, as-found Rockwell 251-9735-010 6 GHz Amplifier

190 Q x 2 pt x 69 sections = 26220 total to DZC Single-op QRP unassisted (Q) with limited antennas operating portable at the lakeside of Governor Nelson State Park (US/KFF 1452) without any camping. Operating with KX3 + PX3 onto my MacBook Air for logging with 3 and 4.5 Ah Bioenno LFP packs. Antennas were 71' EFRW sloper plus 15m 1/4l elevated radials on Saturday, 20/15/10m 1/4l elevated radial verticals then 28' EFRW on Sunday. It was a long slog in the cold, but this is a new personal best for me in Sweeps Phone in raw score. I was considering dropping off Sunday night with sunset, but seeing that I was close to my score from last year motivated me to keep operating. A thermos of hot water was waiting for me to close out the contest to pack up with KY as my final section. First section and first duplicated section were both STX. Best part was getting first-call into two different PAC section stations on 10m on Sunday. Worst was skipping new band/day entries on big contesters...

Since I have access to a 7.5 GHz spectrum analyzer, I decided to take and share some more data showing the output spurious performance of the AD936x transceiver. My DUT is an AD9363 set to AD9361 mode for additional frequency output on the LOs in a HamGeek PLUTO Plus. To have login access to set the wider frequency mode, I'm using the 0.38 firmware supplied by the vendor that actually uses the default credentials, unlike the stock/QSPI firmware shipped on the device. This exercise is partly to compare with the one published example that gets thrown around from a 2 GHz span on a Sigilent spectrum analyzer showing plenty of spurious responses from a ~140 MHz fundamental. I've seen it referenced multiple times, but the version I have at hand is from K0SM's talk  (slide 32, page 16) for the Rochester ARA. It's shown with a probably 144 MHz fundamental on a 0-2 GHz span with no markers. That gets the point across that filtering after the PLUTO's balun is key with the thi...

In eventual hope for getting on 2.3 GHz, I picked up a pair of very low cost surplus panel antennas originally intended for SISO 2.4 GHz ISM operation. These were likely for WISP or other internet range extension use. I'm going to presume that they're broadband enough to extend down into the narrowband amateur segment, but maybe I'll get the chance to test that before applying much power. Blank, smudged radome of a TP-24-20-18 antenna

One of the follow-up questions on optocoupler bias generation  was if optical LEDs would be a decent candidate for generating a higher voltage output without needing to handle the 8+ volt output from the isolated gate driver photocouplers. The short answer is no, probably not even in comparison to stacking multiple 0.5 V output optocouplers. Energized green SMD LED driving another unit of the same part number 

Over at SignalStuff, there's a new directory of Radio Models  intended to help with handheld transceiver identification and antenna compatibility. Since I've got a small stable of HTs and a desire for another blog post, here are my entries for the database.

Another round of funny enough morning clouds to throw on the blog. Sky over Fitchburg, Wisconsin on the morning of 2025-09-11. Shot with Samsung Galaxy S25+, unprocessed JPEG.  

In an effort to be prepared for figuring out how to work an integrated microwave SDR, I picked up three amplifier modules for 900, 1300, and 2400 MHz. They're all from the same eBay seller and presumably the same factory with matching enclosures, labeling, and design techniques. Lineup of the three amplifier modules (labeled 2.4G 10W, 1250, and 915) with the heatsink planned for future use.

After reading the W1GHZ GaAsFET LNA Bias entry, I wanted to see what the performance of these exposed-base optocouplers are. The concept comes from the IEEE Microwave Journal Application Notes: Photovoltaic Bias for Depletion-Mode Devices in Low-Noise Amplifier Applications (DOI 10.1109/MMM.2022.3226635). It's not open access, so I figured some publicly available characterization data would be cool to share. I have access to a dual-channel precision SMU (source-measure unit, Wikipedia ) and that's exactly what we need to characterize the photovoltaic behavior of optocouplers! Keysight B2902B SMU front panel during a 20 mA input, open circuit output measurement