Suffolk Red hosted a field weekend from their field day site at the Suffolk Aviation Heritage site near Ipswich. The weather was set fine, with temperatures close to 30C and with the option to camp out for the weekend.
George M1GEO, Chris G8OCV and I set up the operating tent and populated it with the following equipment.
HF – Icom 7610 and 1.3K Linear from expert
VHF – Icom 7100 and 300w VHF amplifier from Linear amp UK
RACAL push up mast
Power – Honda 2KW generator
The object was to try something new, so I opted for 9e LFA on the Racal push up mast and tried to work as many EU stations as I could on both phone and FT8. VHF seemed quite lively, and with good take off into Europe I was soon working into France, Germany, Denmark and Belgium.
LMR 400 coax was used to keep the losses down, and the masthead amp compensated for any RX losses.
Masthead amplifier for 144 MHz was originally published in the RSGB magazine RADCOM plus issue 1 designed by Ian White GM3SEK. The details are published on his website, detailed as the DG8 low cost, high-performance preamp for 144 MHz.
Over the course of the weekend I completed 50 QSO in 25 squares, the map is shown below. If you are new, or even not so new to FT8 you may find this operating guide helpful.
A while ago I completed the QRP labs WSPR transmitter, you can read about that project in this article. I wondered how easy it would be to set this up in the garden, solar and battery powered.
The QRP labs unit transmits around 200mW, and the idea was to have this running 24×7 transmitting around 80% of the time and band hopping. I have the multi-band option, with BP filters for 3.5, 5, 7, 14 and 21 MHz.
Searching eBay I found a low costs solar charge controller and solar panel. I also needed a voltage regulator to drop the 12v to 5v for the QRP labs unit.
The items I selected are not “high quality” it was more proof of concept. The charge controller is in fact so high quality even China didn’t put their name on it.
Using the club call M0SNB June saw another chance to operate 70 MHz outdoors in the RSGB contest, with perfect weather at 24c. The contest site at the Secret Nuclear Bunker was used, at some 110m ASL it has good take off in most directions.
Using the homebrew 6e 70 Mhz beam, and the solid-state amplifier to deliver 160w worked a treat, with our best DX EI2FG @ 568 KM.
At the SNBCG operating site we have the opportunity to out up some large antenna, and for some time we had wanted to try 472 KHz using George M1GEO WSPR transmitter.
The plan was using the onsite 50m cellphone mast* to pull up some wire, and with some work hopefully, enough wire to have a 1/4 wave on 472 kHz. We calculated it would require around 150m of wire, and we had a pully on the mast at 42m, so we could pull up the first 50m as a vertical, and then have the next 100m sloping down from the last forming an “L” shape as best as we could into the next field.
The transmitter would be grounded to the mast earthing point, and we would run the 10w transmitter at the base of the mast overnight.
*for the avoidance of doubt we have permission to use the mast from the site owner.
The antenna slops down from 42m towards the ground.With a little bit of tinkering, we had a resonant antenna on 472 KHz
We left the transmitter running overnight from JO01DQ with the call GB0SNB, and was delighted to see a number of reports all around Europe.
Here you can see the tower and yellow wire making its was up from the base, and then into an adjacent field.
With field days just on the horizon, I decided to make a couple of Balun (common mode choke) for field day use. I often use a vertical for 7 or 3.5 MHz, and a 1:1 choke is needed to stop the feeder becoming part of the antenna system. Sure you can purchase them online, but your never sure of the quality or the power handling and they are easy to make.
You will need a suitable box, ferrite toroid (FT240-31) is good for the lower HF bands and some coax. The type of coax you use will depend on the power handling, RG58/RG316 would be fine for 400w but if you want some margin for error then RG142 is a better choice.
The RG142 is quite expensive, but its capable of much higher power handling and it has a PTFE centre insulator. The coax typically costs around £5 per meter, and 1 meter should be sufficient for a single core balun.
FT240-31 Toroids cost around £9 each, so a typical project would cost around £20 for a single toroid or £30 for a double toroid QRO version.
If you purchase one already made they cost around £40 to £60 depending on the power handling.
Once assembled you should have something like this. The “QRP” version is good for 400w, the QRO version is good for 1KW.
The subject of choke may need some further explanation, so you may want to watch this video by Callum M0MCX. I would also suggest reading this excellent article by Steve G3TXQ
Steve explains in his article how you can measure the choke impedance, and he provides some measured data showing the effectiveness of various combinations of ferrite and number of turns. This gave me the idea, how hard would it be to measure the choke impedance at various frequencies?
Turns out it’s not as simple as you think, the first try with a VNA produced some interesting but mostly meaningless figures. It turns out you cant just sweep the choke with the VNA as it presents very high impedances outside the range where the analyser can be expected to be accurate. The VNA can be used, but the results will require some further maths before meaningful data can be obtained. At our recent radio pub meeting, I asked Dr David Mills (G7UVW) if he could assist, and he completed the measurements and the maths! Thanks, Dave.
VNA plot QRP single 240-31 Torroid
VNA plot QRO 2x 240-31 Torroid.
And now for the measured data, you are looking at the frequency on the left, and choke impedance in ohms on the right. We would typically say anything over 3,000 is very good.
As you can see both the chokes work very well over most of the HF spectrum. The target for me was to have something with very high choking impedance below 14 MHz.
Thanks to Dave G7UVW for his assistance, and I leave you with a picture from our radio pub meeting.
At last, the warmer weather has arrived, today gave me the first opportunity to operate outdoors without a coat.
It was a pleasant sunny afternoon so I decided to operate outdoors and make the most of the nice weather. Using the Icom 7100 and 65Ah leisure battery and a white stick for 145 MHz and slim jim for 70 MHz allowed me to work a number of local stations.
The 70 MHz Slim Jim is mounted on the fibreglass pole on the right.
The metal mast on the right had been given to me by Richard G4DDP and it was its first chance to try it out in the field. Its very heavy duty, and I think would have originally been designed to take a speaker at a gig, now upscaled to amateur radio.
On 145 MHz I worked M0FAQ Martin in Braintree, M0WJL Gordon in Corringham.
On 70 MHz I worked 2E0HPA/M Andy in Tadlow, G4YBI Paul Rainham, M0XTA Selim, G0ENN Southend.
Here you can see the Icom 7100 setup and operating on 70 MHz