Month: August 2017

LEFARS and SNBCG Field Weekend.

The August bank holiday provided a great time to play some radio, and join forces with another club for the weekend. Many of team SNBCG are also members LEFARS, and with an active portable group, this was set to be a busy weekend.

I arrived on Friday evening with Peter G0IPA and Dave G7UVW to setup the initial masts, we put up the 144 MHz beam  (9e + mast head LNA).

The 18 MHz 3e beam was recently constructed and required some further testing, although initial results were very promising.

The 7 MHz vertical was constructed from push up poles and 8 radials.

A BBQ was planned for Saturday evening, with Ron G6LTT, Karen and Sharon doing a great job in feeding the masses. Dave M0MBD also provided a very nice Chili con carne with rice. We also had burgers and sausages and some salad, a really nice and very welcome meal. The weather was excellent, with temperatures getting to 27c in the day, and not falling below 18 in the evenings and ideal for camping. The turn out from both clubs was excellent with members travelling from far and wide to partake.

A WSPR transmitter was setup for the weekend using the QRP Labs with a 200mW output into some wire. This provided an indication of the band conditions and was active throughout the weekend.

John M0IDA dropped in on Sunday with his arrow satellite antenna and provided a demonstration on working through satellites.

Altogether a very successful weekend with members operating on 3.5, 7, 10,14, 18, 21, 24,50 and 145 MHz over the weekend, making close on 1,000 QSO in 80 countries.

Further pictures from the weekend are available here.

18 MHz beam project (Part 2)

If you haven’t arrived here from Part 1, you may want to check this out first.

Part 2 final assembly and testing. 

The collection of poles had been previously cut to size, this weekend was about the final assembly and mounting the driven element to facilitate testing.

The beam is 3 elements and requires a 5m boom. The element mounts for the driven and reflector had been previously purchased online and milled out to fit onto a 38mm boom.

John M0UKD had the idea of mounting the driven element on something a little more substantial than the element supports I had used for the director and reflector, this should help avoid element sag. Dave G7UVW mentioned he has some Paxolin board that was 8mm thick, this would make an ideal support for the driven element.

The driven element was mounted on the boom, with the Paxolin providing insulation and support. The addition of 4 exhaust clamps to lock the elements in place, providing a very neat and droop free solution. The other elements were mounted on the boom, and the coax matching system was constructed. The antenna is 28 Ohm, and so needs to be matched to 50 Ohm using 2 lengths of 75 Ohm coax. Matching is further described in the DK7ZB article.

The next stage was to measure out all the elements and fit the jubilee clips, one slight mistake in that I had ordered 25mm clips to fit 30mm pipe. This was rectified by looking in the spares box, and soon the beam was ready for bracing and mounting. The boom is split into 2 x 2.5m to allow easy storage and transportation in the car.The boom is the braced and joined by a further 1m section of 38mm box linking the two sections of the boom together.

This method has been previously used with the 4e 21 MHz beam previously constructed.

Elements measured, boom joined it was now time to add elevation and measure the SWR. The antenna was mounted on a 10m pump up Clark mast, and with some trepidation the SWR measured. It’s always encouraging to see the antenna is resonant on 18.120 MHz.

Team SNBCG had successfully converted a pile of aluminium into a beam for 18 MHz.

Over the course of the weekend, I worked 100 Stations on SSB, mostly in Europe and Fred G3SVK worked 50 in CW. Fred was able to work some DX including USA and JA.

The beam construction really was a team effort and was made possible by Chris G8OCV, George M1GEO, Peter G0IAP, John M0UKD and Dave G7UVW.

18 MHz 3e Beam Project (Part 1)

In 2015 I finished a 4e beam for 21 MHz, the performance was very good allowing me to work some great DX including a pile up of JA.stations You can read more about that project here.

A handy guide showing the aluminium sizes required (in both metric and imperial) and the total order lengths required is available as a guide. You will need to verify these sizes for yourself, information provided as a guide.

This year’s beam project was 18 MHz, a non-contest band and one that often provides very good propagation into the USA and South America. The design was once again from DK7ZB website detailed here, Its a 28 Ohm version on a 5m boom with 5.7 dBd of gain so 400w in should give around 1.5kW ERP.

I selected this design for a number of reasons, the website contains great detail and the antenna fits onto a standard 5m boom making construction a little easier. It also means you can just have one boom joiner section, allowing easy transportation in the car.

The aluminium was ordered from Aluminium Warehouse, they have a good range of sizes and include lengths up to 5m. Delivery or collection is both possible, and they will cut to size if required. The aluminium required needs to concertina starting with 30mm, then 25mm, 20mm and finally 16mm.

Some careful planning is required to ensure the inside diameter is sufficient to allow this construction. This can be especially tricky as some of the sizes need to be in imperial and others in metric depending on what sizes are available. The initial stage involved checking the internal diameter, do each of the sections fit inside each other, thankfully they did although some sections were quite a loose fit. Chris G8OCV cut all of the sections using his chop saw, making the process much quicker and easier than the hack saw method used on my 21 MHz version. The band saw was then used to cut some slots in the elements, and with the use of a jubilee clip, this should clamp the elements into each other.

Looking at this picture you could be mistaken for thinking the antenna isn’t that large. The boom is 38mm box, and the reflector is around 8.5m long.

Thanks to Chris G8OCV, George M1GEO, Peter G0IAP and John M0UKD for their assistance with the project. Without their time, effort, encouragement and technical input this project would not have been successful.

The next phase will involve bolting the sections together, completing the matching section, and hopefully its first on air tests.

Part 2 final construction and on air testing is available here.

© 2015 Dave, M0TAZ