I have some new projects in the pipeline.
LOOP TUNER
A longer term idea is to fit a stepper motor to the loop tuning capacitor to remotely step up/down and eventually auto tune the AL-705 loop.
This is the state of the development with stepper and Arduino. Button drive it up/down and pot adjusts speed. Code is here.
Some progress has been made, my son has kindly designed a mount for the loop tuning capacitor in its box and the stepper motor. This he has 3D printed. We have a few problems with it. One is that the capacitor on the Alpha Antenna AL-705 tuner is NOT in the centre, but about 1mm offset to one side, meaning the stepper does not line up with the capacitor shaft! Thank you Alpha... will have to re-design and re-print...
Another issue is to find a flexible coupler from the stepper shaft to the capacitor shaft, the capacitor seems to have a strange diameter, may be American "Imperial" not metric? It measures just <8mm, but is loose on the 6-8 coupler I bought on eBay... my son has an engineerng company and he says he can drill out a 5-6 coupling to fit.
The other issue is whether the stepper has enough torque to drive the capacitor which is quite stiff. This can be check only when I can get the coupler problem solved.
I have tested it. Here are some photos
There is an expected problem, the stepper driver is a switching signal of 1A, this generate a S9+ interference on reception. So the stepper driver must be switched on only to tune the loop, not all the time. This is implemented in the latest ANT_TUNER Arduino sketch, here
There is wiring to do and a control box to build. And a software problem to solve - to inhibit the driver while not moving, so to stop the switching RF interference, hopefully.
I have mounted all the electronics and wired it up, bit of a rats nest, but... And I have built a controller box, pot for speed control and a `left and `right buttons for tuning.
IT WORKS superbly, fast is just right to scan across the bands, and slow is just right to nudge across a band, while watching the NanoVNA resonance frequency and SWR.
I feel clever.
WSPR
Second I want to TX on WSPR on an ongoing way, i.e permanently on. I have built a QCX+ CW transceiver which has, it claims WSPR programming, but Ihave been unable to get it to work. I think the problem is that the class-E PA is not running in class-E due to some inductances being wrong - I get only about 2W output on 40m*. This in turn generates quite a lot of heat in the PCB substrate which is used as the PA heatsink. This heat in turn is heating the Si5351 xtal and causing it to drift over the 100+sec TX period. I can see this drift quite easily on my base station RX (ELAD FDM-DUO). It is also not decoding with WSJT software as a consequence. Anyway I don't like the QCX+ software UI for Beacon use...
So I will build the QRP-Labs U3S WSPR TX which has a GPS calibrated frequency control or an oven controlled xtal oscillator circuit to stabilise the frequency. This kit was ordered back in Dec 2020, but QRP-Labs have had long delays in getting a new GPS module built and tested and so my order was completed only at the beginning of June...
* since found my power meter is reading about 6dB LOW! So this is probably 4-5W in reality...
QRP-LABS U3S built.
Quite a tricky kit as very tiny boards and lots of link options for different operating uses. I have the GPS board, but cannot fit it as QRP-LABS do not seem to supply the nylon standoffs for this and I have had to order some from eBay. Also had to order new push buttons as one is faulty. I have bought a small 12V to 5V regulator board for the power supply. I think it is wrong that QRP provide a 1/4" jack plug for 5V input as this size is traditionally used for 12V and could cause an accident. Could have used a USB B socket? To start with I have not built the OCX temperature controlled synthesiser module and will try with the standard Si5351 module. Here's the result on 30m when feeding 200 mW to my loop antenna:
I struggled with the menu system. But it is ingenious and when I had it sussed out it was easily done. Initially when I programmed in the frequency of 10,140,100 the U3S output was 10,140, 316 which is outside of the WSPR band (Only +/-100Hz wide). But after I left the system running for 24 hours and self GPS calibrating after each transmission, the frequency had been reduced to 10,140,206 which is closer to the band centre, probably as close as it goes... We shall see if it moves further. Very impressed with self calibrate feature.
By the way I calibrated mu ELAD FDM-DUO at 10MHz by reprogramming a small Ublox GPS module to output 10MHz in place of the usual 1pps. See down this blog...
The output spectrum has tons of harmonic side lobes (phase noise?) not a single neat carrier. This is typical of the Si5351 and I have seen it in many other projects I have built. Locally decoded this brings 3-5 decode lines, the main central frequency and 3-4 other side lobes, only 10-20dB down. Not much to be done about this, unless there is a better way to program the Si5351 to remove these side lobes...
Here's the output power into 50R load, as seen on my home made power meter (described further down this blog as part of BARSICLE project)
I have tried it driving a small loop (Wonder loop) and the result are disapppointing, pity I was planning to use this a a permanent installation for propagation monitoring. But connecting it to my new AL-705 loop brings results.
By the way there is a new version, an update, of the excellent MAC and iPhone app "WSPR Watch" which you can use to see your spots and display some stats and trends.
Update to U3S. Have installed all 3 BS170 MOSFETs, power output unchanged, as need to use higher Vcc to get more. May try 12V line to PA..
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