Sunday, May 15, 2022

Built the QRPGuys AFP-FSK Digital Transceiver III kit

A QRP Labs QDX digital transceiver kit is on order but in the mean time I was looking for information on the technique Hans uses to modulate the Si5351 from a computer generating FSK modes, such as WSPR. The manual mentions that the way it works is to measure the frequency of the audio coming in from the computer and then directly set the Si5351 frequency. This means there's no mixing and no opposite sideband. Very clever!

It turns out that this idea is not new and dates back many years, even implemented on a Z80.

While QRP Labs keeps much of their source code secret, another vendor - QRP Guys - have a transceiver that uses the same system and they supply the source code.

I have just finished building and debugging their Digital FSK Transceiver. It's not as neat as the QDX as it uses analog audio in and out. Transmission is by VOX so it's not a huge problem.


The kit went together well but I couldn't get it working even though the display showed the right things. It didn't auto-detect the low pass filter band (there's a resister divider to signal the band by voltage).

I downloaded the source code and wrote to QRP Guys to tell them they linked to the wrong source. I was wrong of course and failed to read the file called README First which explained that the same source file is used for a few different projects.

Ken LoCasale replied with LOL after I realised my error. Nice quick response from the QRP Guys.

Unable to get the kit working, I built the code and flashed an Atmel ATmega328p chip in an Arduino Uno. When I swapped that chip into the VFO board the receiver sprang to life.


As you can hear, SSB reception is good but the 1kHz tuning step is a little large for SSB reception. I haven't calibrated my oscillator so that might help.

Driven with audio from WSJT-X I saw 38V peak to peak into a 50 ohm dummy load running on 13V.

After calibration I had an FT8 contact without any problems.


20m is very active today. For such a simple receiver (Si5351 + NE602), it does a great job:


It's great that QRP Guys have shared their code.

Interestingly the code that made version 3 of this project possible was shared by Kazu Terasaki AG6NS. There's a discussion here. His GitHub page has several projects and there's a branch with the official QRPGuys version.

I'm very much looking forward to the QDX which has a single USB interface to the computer and an apparently very good SDR receiver. This is a good kit and fun to tinker with.

Wednesday, May 11, 2022

Wifi router, Gl-inet GL-AX1800 makes measurable improvement to speed

My internet here at Drummond isn't great. It's NBN Fixed wireless. While the download speed is OK I experience packet loss and have trouble with video calls some times.

Recently I've noticed that the Apple TV would sometimes have very low download speed such that streaming video dropped back to a very low bitrate version. I have been using Google Wifi mesh devices but was frustrated by the very limited control available through the Google Home app.

I decided to buy some Wifi routers that run OpenWrt, I chose the GL•iNet AX1800s. AKA Flint.


If the client is capable, these routers can provide gigabit speed over wifi. Of course, my internet connection is way below this. Having replaced the Telstra Wifi router with one of these I find that the broadband speed, as measured with the Ookla app is about 10Mbps faster than previously.


Note the terrible 12% loss though (not in my network). Interestingly ping loss is zero but I see loss during speed tests so I guess it's larger packets that are dropped.

Here we have two buildings and they are linked with ethernet so a second router is used in the shed to extend the network by setting it to "Access Point" mode.


The meaning of this setting was not obvious to me and googling how to do this on OpenWRT led me down a complex and incorrect path before I reset the router and looked more deeply.

Access Point mode means that the router shares the network available on its WAN port via ethernet and Wifi without doing its own DHCP or NAT.

Wednesday, May 04, 2022

Insulated shack with antenna pass-through

Here at my low-noise country lair the storage shed I use for my ham radio shack was going to get very cold now that winter is coming.

I've had a carpenter insulate and line the space and a challenge was figuring out how to connect radios to antennas. 

Ross, EX0AA, suggested SO-239 bulkhead adapters:


I asked the carpenter to create a lined port to the outside and I've mounted a plate on the inside wall like this:


On the outside I've mounted a hinged plate to keep rain out of the cavity.


Underneath coax can connect.


The gaps around the port were filled with expanding foam filler.

With some, rather off level, shelves; the shack is now working well.


The concrete floor needs a bit of carpet.

Last night I joined the Macedon Ranges Amateur Radio club 80m net. It was 10C outside but, with the help of a small heater, it was a toasty 22C inside the shack.