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.

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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.

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IOTA 2017

IOTA 2017 once again provides a great opportunity to work some big DX. This year we decided to run two separate stations, and just work as many as we could while having some fun on the bands. The weather forecast on Saturday afternoon was not good, and so we concentrated on getting the operating tent and antenna setup first thing before the rain.

George M1GEO operated his Icom 7700 and Expert 1.3K FA while I operated my  Icom 7600 and Expert 1.3K FA. Both stations were capable of operating at full legal power. We setup the following antenna for the weekend.

3e beam 10/15/20m bands

1/4 wave vertical 40m

Dipole for 80m

Here you can see John M0IDA (operating) and Peter G0IAP.

Band conditions have been somewhat variable, but by the evening’s things have usually improved. The tri band beam performed well, providing some good DX on all bands, and it was nice to see some openings on 10m.

We shut the stations down overnight, as this was more of a fun event with an opportunity to work some stations. In the morning the weather improved, the mostly sunny conditions dried out the tents and made the pack down quite pleasurable. We also had a nice visit from Geoff G0DDX and Linda G0TPX who both assisted with the pack down.

In total George worked 500, and I worked 400, with some nice DX.

Most notable being CV7S Uruguay, YB5BOY Indonesia, PW7I Brazil, PJ4DX Bonaire, YW450ARV Venezuela, 8P2K Barbados and KH7XS Hawaii.

You can view the KML file for my QSO here.

Thanks to everyone we worked, the preferred method of QSL is via LoTW but via the RSGB bureau is also available if required.

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Suffolk RED Sunday Radio and BBQ Social

Sunday 23rd July was a Suffolk RED outdoor event, a chance to play some radio and put on the special event call GB0RED. The team at Suffolk RED had a nice gas BBQ and kindly provided a selection of healthy and not so healthy snacks (Chocolate cake was lovely BTW)

The Camb-Hams were in attendance with Flossie the CRG shack complete with 20m mast. The team came equipped with a selection of antenna to cover the HF bands on both phone and CW.

The field was large enough to support a number of station, Peter G0DZB was active on 10 MHz CW.

Steve M1ACB was active on satellites, giving a demonstration and working Rob M0VFC on a narrow boat!

We also had time for a chat, it was nice to meet a selection of amateurs from around Suffolk, Norfolk and Essex. I had a chance to operate GB0RED from Flossie.

I also had a chance to fly the drone, and captures some panoramic views in between the odd rain shower.

A special thanks to Sarah 2E0ISJ for pulling the event together and looking after everyone on the day.

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70 MHz Trophy Cup

The RSGB 70 MHz Trophy Cup ran from 11 till 5 on Sunday,  Team SNBCG assembled at the Kelvedon Hatch Secret Nuclear Bunker. The contest promotes activity on 70 MHz, but it just one of many contests run by the RSGB to promote activity on the amateur bands.

The beam was homemade, 6 elements on 70 MHz using a 4m boom.

Setting up

Checking the antenna

We used John M0UKD newly acquired Icom 7300 and George M1GEO Expert 1.3K-FA amplifier to provide 160w PEP. The contest exchange was a little more involved than some and included signal, serial, locator and first two letters of your postcode.

A 12m push-up mast provided the support for a homebrew 6e beam. The beam had recently been reworked with some new insulators and the boom has been split into 2 parts to facilitate easy transportation in the car.

We operated alfresco using a 2Kw Honda generator to provide the power for both the amplifier and radio.

The screen on the Icom 7300 looked very nice, and the waterfall was helpful in finding band activity.

The band had a fair level of activity, with a number of the regular contest stations evident on the bands. We managed to work 74 stations in 7 countries. England, Scotland, Wales, Northern Ireland, Gurnsey and the Netherlands.

Audio clip from working Alex GM4NFC (518KM)

Audio clip from working David GI4SNA (524 KM)

You can view the claimed scores online

A map of the QSO can be seen below.

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MFJ Versa Tuner III MFJ-962C review

The MFJ-962C is a high power 1.5kW manual ATU capable of matching balanced or unbalanced antennas typically from 1.8 to 30 MHz. It uses a T matching network, and the ARRL has provided an interesting article on “Getting the most out of your T match without snap crackle and pop

 

The ATU has a rating of 1.5kW, but this power rating must be taken as a guide, for example, try matching a 1/2 wave on 80m using 800w. The power rating will depend on the suitability of the antenna, and working on the principle that a poor antenna matched is still a poor antenna.

 

 

 

 

You have the possibility of 2 antenna positions, and a coax direct option allowing you to connect 3 antennae to your transceiver.The inductor in common with most ATU is switchable from A to L allowing you to select progressively larger {or smaller} inductance.

The capacitors are large enough to cope with the high voltages often found in a QRO ATU, and should with care provide many years of service. The internal quality of my ATU looks good, although I have found the level of finish does vary quite a lot of MFJ products. If you purchasing a similar product I would suggest you give it the shake test and listen for rattles.

The ATU is quite large, 27cm wide, 38cm long and 12cm deep.

The capacitors used are 12cm long by 6cm wide.

 

 

 

 

The case is made from aluminium and uses 12 screws to provide a rigid construction. I have used the ATU with a selection of doublet antenna, using my own 1:1 balun on many of the HF bands, power has often been at the UK maximum 400w without an issue.

 

The ATU has a cross needle VSWR and power meter, wth low and high power settings. The power meter can be adjusted with the pots inside the ATU, although I have found mine to be accurate. You also have an average or peak hold setting on the meter, this is helpful for SSB when trying to read the PEP.

 

 

 

12v can be used on the rear to provide a light in the metering, but otherwise, the unit can run without power.

The ATU was recommended to me from John M0UKD and purchased second hand, and its performed very well over the years.

These are no longer produced new but do come up for sale on Ebay or your local amateur radio store.

Here is a look at the high power 1:1 balun I use with this ATU.

You can download the manual for the ATU online.

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© 2015 Dave, M0TAZ