RaDAR News – How an OCF Dipole changed my life

I’d used an OCF dipole in the past but wasn’t very happy with the results. It needed considerable height and there is definitely a lot of radiation coming off the coax feedline. This antenna however fits in well with RaDAR for quick deployments and has multiband capability. So I took the dimensions of a resonant 40m dipole, devided the total length of the half wave dipole into three and fed it a third of the way via a LDG 4:1 balun. Good SWR on 40m even without a tuner. Good SWR on one or two other bands too. The antenna however needs a tuner for most of the amateur radio HF bands.

I used my newly aquired second hand FT-817ND and LDG z817 ATU to do the antenna tests using WSPR as a signal source and then I went onto the Internet on the WSPR website to see how the listener stations worldwide could hear my 5W WSPR signal. It’s a pretty nice way to test the effectiveness of any antenna. All the results are stored in a database and you get a graphical representation of where you’re being heard.

All went well but I noticed during WSPR transmissions that my SWR would go sky high at times. WSPR is quite strenuous on a QRP rig running full power (5W) for continuous two minute sessions. I have witnessed the heat generated on finals while doing WSPR when I built the Hans Summers QCX 40m CW transceiver kit that can do WSPR too. The heat generated on high SWR is intense as I once witnessed on a 49er QRPp 300 mW transceiver kit I once built for CW (7.023 MHz only).

The 817 was pushing 5W with an intermittent SWR. I felt the heat sink, it was HOT! The cause of the SWR was a nut on the antenna socket of the z817 auto ATU that had come loose due to regular connecting and disconnecting of the antenna coax. This is a common problem. I tightened it also using a “locktight” liquid so it wouldn’t come loose again as suggested by my friend Jonathan ZS1ARB. It was too late though, the damage had been done and the 817’s output power gradually went to zero. My last QSO was with Jannie ZS3CM on 40m CW. I was in the bush using my link dipole strung up permanently in the blue gum trees. From the report Jannie gave me I wasn’t getting out very well. So after almost 45 years of hamming I experienced my first finals failure!

I accepted the fate of the 817. I did some research on the 817’s finals module and it seems to be a relatively easy process if the whole module is replaced. The whole situation made me think a little differently as I will try to sketch in this article. The 817 can no longer be used for transmitting but it is an excellent rig for receiving signals on the HF, FM Broadcast band (RX Only), Airband (RX Only), VHF and UHF bands. It’s not entirely useless in its present state. Fully legal in the hands of an unlicensed operator and my thoughts went to my grandson Eduan (13) who shows a lot of interest in space having recently bought a telescope to look at the planets and galaxies. I thought maybe he could use the rig to do some short wave listening and to look out for satellite transmissions. I still have my Arrow dual band yagi I use for the sats.

I’ve always promoted the use of QRP but I’m really starting to have my doubts. The problem is QRM. Even where I mostly stay out of town, there is QRM, 59+ QRM! I walk further away from the residential area into the bush where the noise a much less. That helps me to hear better but the majority of hams work from home also in pretty noisy environments, They battle to hear weak signals. I’ve proved that during good conditions 5 Watts is sufficient for CW and even SSB. Conditions lately are mostly not good so QRP is becoming more of a challenge. For RaDAR there needs to be effective communications.

Recently we have been playing around with the digital modes JS8Call a derivative of FT8 but even there I have found QRP power too low to be effective. These are weak signal modes. Allow me just talk about FT8. There is no way I can even be heard on FT8 using QRP. It’s totally useless as the world fires away at higher power trying to make high counts of FT8 QSO’s within a tiny space of 2 kHz per band. It’s a fruitless battle using QRP. Whatever happened to PSK31? (Not to mention the numerous other digital modes available on the excellent software FL-Digi). FT8 is maybe keeping the bands alive but it’s killing everything else ….

Allow me talk about the RaDAR Challenges which are practised world wide. A few years ago we had around SEVENTY participants. Now we have four if we’re lucky. Usually it’s Sid ZS5AYC and his XYL Adele ZS5APT and Kobus ZS6BOS. I try to join in using QRP with a touch of satellite comms which in my mind is the future. It’s there for us to use and is clinically predictable unlike short wave plagued by bad propagation and QRM caused by noisy uncontrolled household appliances. The challenges will continue but we need more participation. Maybe many are in the same boat as myself. I have doubts whether I want to replace my rig with something like a FT-891 which can do 100W. Is it really worth the expense?

I had an eye opener. I set up the 817, WxtoIMG software on a laptop, Arrow yagi on a tripod and showed Eduan how to monitor the NOAA-19 weather satellite on 137.100 MHz. He thoroughly enjoyed it. He tracked the satellite by hand checking the S Meter for maximum signal strength. His school friend from Std 6 (Grade 8) was visiting, they both enjoyed the experience.

On another occasion, Eduan did everything by himself even doing slight doppler adjustments on the FT-817ND’s frequency settings – he was in control! He adjusted the antenna’s azimuth, elevation even twisting for best polarisation. All these fine adjustments made a difference to the overall quality of the weather satellite image transmitted by NOAA-19. He was in total control, not his granddad living in his own dream world and him watching. I realised, this is what young people want, the freedom to be in control. He loved it!!!

My friend Christi ZS4CGR was doing a SOTA activation via the AO-92 and AO-91 cubesats and I wanted to support him. I forgot though but was fortunately reminded by Sid ZS5AYC before the last pass. I set up my TH-D7A handheld, connected to the yagi, headphones on ….. in my own little world ….. and Eduan showed little interest. He couldn’t hear anything anyway, I was listening to the downlink running full duplex on AO-91. I had a successful QSO with Christi. He managed nine QSO’s within a ten minute pass. I was glad to be able to be part of his activation. AO-91 hears QRM as it flies north over central Africa but this is an exception to the norm..

I want to take this opportunity to wish all a prosperous New Year. I think my five year license is renewable in 2020 which I hopefully will be able to do without difficulty. As for replacing a rig for HF, I still need to be convinced that it is a priority amongst other priorities? I can still do FM RaDAR SatComms which can provide effective communications other than 59 “My grid is” ….

In the meantime I no longer have to go away from the family to live in my own little world for an hour or three every now and then and I will now share my experiences with others in a shared world. It’s a happy place!!!

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