Automatic antenna tuners are expensive, manual antenna tuners are slow. So it has been a long time I dreamed of making my own automatic system.
As this year I was following a raspberry pi class and we needed to make our own project I decided to finally try to make this automatic tuner.
Summary: – Forward and reflected power are measured with a Boxa Swr bidirectional coupler combined with an ADC – SWR is calculated in the raspberry pi and displayed on an LCD – When SWR is to high an alarm is sounded in CW – after pushing a button the capacitors and the coil in the tuner are reset to 0. For the capacitors I use 2 servos, for the coil I use a stepper motor. All mechanical connections are made using 3d-printed parts. The reference point for the stepper motor is made using an infrared port. – next is the tuning operation: — the ‘transmitter’ capacitor is sweeped over it’s full range and swr is measured every degree. Then this capacitor is returned to it’s best position — next idem for the ‘antenna’ capacitor — sweeping operation is repeated for maximum 4 times, if the SWR is below 1,5:1 then tuning is stopped. If SWR is above this limit then the coil is moved to the next setting and the sweeping is repeated – built in securities: — all alarms on the LCD and in morse code — alarm when SWR is to high — alarm when tx-power is to high for tuning — coil/stepper can not be switched when there is rf-power
Remarks: – no tuners have been harmed in any way for this operation! – Was the raspberry pi the best choice for this? This could probably have been done using some microcontroller instead but the class I followed wat not arduino or esp 32 🙂
Or at least that’s what I found out a few days ago… I was doing some tests on a bidirectional coupler (more about that project in a future post) and I didn’t pay enough attention so I cranked up the power of my transmitter to 100w. And, of course, after a few seconds I got the smell of burned electronics in my shack.
That’s when I decided to go through my junkboxes and find the resistor I once bought to build myself a decent dummyload.
These are the results:
The resistor is an RFP 250-50 TC so this should handle up to about 250w.
SWR between 160m and 6m is max 1.04:1. I have not tested any higher frequencies because my antenna analyser only goes up to 54 MHz.
The heatsink is salvaged from an old telephone switchboard (made by Bell Telephone in 1980).
What does a ham do when the weather is bad and there is nothing exciting going on on the bands?
For some tests I needed a coax switch and I found my old Daiwa CS-201 in my drawer. I vaguely remembered there was something wrong with it the last time that I used it.
As soon as I connected a coaxial cable I noticed one of the N-type connectors on the switch was loose. So it was time to get out the screwdriver.
This is what I noticed:
Look at the contact at the red arrow! Due to the top right coax connector rotating when connecting a cable the contact was barely touching the post it should touch. Not visible on the picture was that the bottom contact had the same problem but of course this was rotated in the other direction.
And, this is a switch rated for 1 kW!
I could pretty easily fix the problem by unscrewing the little black screws and rotating the coax connectors back to where they were supposed to be. But I guess this will only last until I have connected and disconnected the coaxial cables a few times again.
Finally my OB11-3 and new rotator made it up the tower.
For now no QSOs have been made because of course there’s still a lot of work to do like running new coax cables and the rotator control cable up to the first floor shack and putting the wires for 30-40-80 back up.
Time permitting I’ll try to be on the air in a week or 2 max. I’d like to test in the DMC Rtty contest in 2 weeks from now.
Here are some pictures:
I wish to thank Tom from Optibeam for the advice and help provided in choosing the ideal antenna configuration for my needs!
My new contest secret weapon worked very well… for exactly 1 QSO.
For the moment I have only these (permanent) antennas for contesting: a Fritzel FB33 3-element tribander at 16m and homemade inverted V dipoles for 40 and 80m at 15m.
So for SO2R I have always used an extra Fritzel GPA404 vertical for 10-15-20-40m. But to avoid the hassle of installing this antenna before the contest and taking it down after the contest I recently decided to purchase an Inrad HF Triplexer so I could use the FB33 on 2 bands simultaneously.
Last week I had the specs of the Triplexer tested by Luc ON7KZ and all seemed to match the specs as in the Inrad web page.
I installed the triplexer between my Sixpak and the FB33 the day before the contest but I didn’t have enough time to thoroughly test it. (I did check all connections twice though!)
Once the SCC Rtty championship started I made a S&P QSO on 20m and during the QSO I saw the SWR on 20m going up to alarming levels :-(.
A lot of things have happened since my last post here but I didn’t really feel like writing anything about them lately.
A small summary:
we did the Region 1 SSB fieldday with the club station ON6CK/p (and came in second behind the OQ8A/p team)
the belgian guys conquered Rockall, congrats to the team!
the british guys decided not to go to Rockall. I don’t really understand the reasons, if all those who wanted to climb the Everest would have cancelled their plans because someone was there before them then only a few people would have done it. Moreover the pileups from Rockall will not be less for the second team going there than for the first one. And I still need EU189!
I finally ordered a new transceiver!
I modified my RTTY setup to do FSK instead of AFSK (with the FT990)
I made a portable setup to take on holiday
The last 3 of the list will probably be the subjects of some future posts!
So what makes me write this in the last hours of CQ WW SSB? I’m at the qth of my girlfriend and to tired to set up the portable station. Wedding parties are probably more tiring than 24hrs of contesting 🙂 Moreover we have to leave for an other party in less than an hour.
A few days ago I found a nice piece of software on the internet: BoxCar 2D. This is a way to design a car using a genetic algorithm: a population of cars is created at random and then tested on a track chosen by the user. Then the best cars ‘mate’ to get a next generation. Together with a set mutation rate the cars improve over the generations.
Warning: watching this is addictive, it’s far better than television!
My programming skills are rather limited but I wondered if someone maybe could design antennas using one of the (mini)NEC engines and this genetic system?
Update: it seems that this is not such a new idea, at least for developing antennas. A little googling for ‘genetic algorithm antenna’ gave me some 160000 results 🙂
SuperNec seems to be great software for this but at $6080 it seems I’ll stick to Eznec and MMANA for a while.