Tag: yagi

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.

RSGB 21/28 MHz contest

The RSGB contest provided an ideal opportunity to focus activity on the higher HF bands. Previous John M0UKD and I had built beams for  28 MHz 3e beam and  21 MHz 4e beam using the design on DK7ZB website.  28 MHz is a compact design using a 3m boom, and 21 MHz is somewhat bigger at 5m boom.

The Racal PU12 mast was used for the 28 MHz antenna and Clark 10 for the 21 MHz antenna. Power was provided by the Honda 2KW silent generator and the radio was provided by George M1GEO the Icom 7700 delivering 200w RF.

John M0UKD helping to assemble to 21 MHz (Left) and 28 MHz beams.

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The operating was alfresco as the October weather was  sunny and warm. The shack table was positioned close to the mast ready for armstrong rotation.

The Clark mast was modelling some new blue legs, recently fabricated by Brian 2E0FHU. They worked perfectly and once assembled they provided a sturdy base.21317020033_44fe6db48c_z

A quick check with the MFJ analyser confirmed the antenna was spot on resonance, and so the CQ calling could commence.

Despite a valiant effort on both 21 and 28 MHz conditions did not support the number of QSO we had hopped, in fact you could say it was a challenge to work anyone at times. QSO could be hard to tease out, and we decided the best method was to work anyone we could  hear. Some big DX did arrive, as we managed to work ZS6AI, ZS5DCF, CX8DS, VP8NO and PS8BR to name a few. The bands did seem to be open, at one stage we listened to a CW beacon in South America that was very loud (apparently 10w).

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M1GEO George driving the Icom 7700.

 

 

 

 

 

21 MHz beam (Left) on Clark 10m mast — 28 MHz beam on Racal PU12 mast.

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Despite the lack of activity or poor band conditions we enjoyed our time operating outdoors in the sunshine.

Both homebrew beams worked well, and this may well be the last time we operate outdoors in 2015.

Further pictures from the day are available online.

Thanks to everyone we worked 73 Dave M0TAZ

21 MHz 4e Beam Part #3

You can read Part 1 and Part 2 of the project

Part 3

Members of the Havering ARC took part in the LEFARS radio event over the bank holiday weekend 23/24/25 May provided the ideal opportunity to test the beam. George M1GEO and Chris G8OCV provided the 12m SCAM mast and so the fun began. The club operated from a farm site in Harlow, giving us enough space to test even the most ambitious projects. As described in parts #1 and #2 the antenna has a 5 meter boom, and although it isn’t too heavy it still provides a challenge lifting this onto the mast.

On the tower

 

Once again a quick VSWR check using the MFJ antenna analyser suggested it was ready to go, and so the next phase was to pump up the mast. The Scam provides 12m (45ft) of elevation, and provides a suitably robust (heavy) construction that makes it a firm favourite for our HF field days.

Its up

The station was a Kenwood TS990 and Explorer 1200 Amplifier. Here is a picture of George M1GEO working a pile up.

George M1GEO

Over the course of the next 3 days we were able to test the antenna, band conditions seems reasonable on the day and improved early evening on most days. We found the directivity to be good, and pointing towards Japan in the early evening provided a pile up of JA’s calling us.

Some highlights VU3DMP Chetz from India

Some really nice calls from Japan as well including JJ1LWA Hal near Tokyo using 200w and 3E beam

We also found conditions very good into the USA late evening and working West coast with signals 59+ was quite a surprise. It was also nice to see the GB2LRS station generating some interest on the HF band, with one USA station suggesting the phonetics should be GB2 Loud Radio Station !

The USA and JA pile ups were quite a surprise, listen to one here and see what you can pull out.

The the weekend finally coming to an end on Monday we had worked 600 stations in 58 countries, the highlights being A9 Bahrain, C6 Bahamas, BY China, VU India, HI Dominican Republic, EP Iran, P2 Papua New Guinea, KL Alaska, XE Mexico, and YB Indonesia. The top two countries in the log were 376 Q into USA and 71 into Japan.

I think given the quantity and quality of stations worked this weekend I can now declare the 4E mono band for 21 MHz a success. Thanks to everyone who worked us and made the weekend possible.

Homebrew 21 MHz Beam Part #2

Read Part 1 of the homebrew project

Now the exciting phase, nearing the end and a moment to complete the final stages.

Construction of the matching phase, and mounting the driven element.  The antenna feed point is 28Ω, and the method of feeding the antenna is described on DK7ZM site. Once constructed from 2 lengths of 75Ω and formed into a choke this could be mounted.

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The driven element was separated with a solid plastic tube, this extended 250 mm into each side of the element. The bolts and wing nuts would provide the ideal termination point for the coax.

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The next phase was getting the aerial into the air, and checking the VSWR. The design suggested it was quite broadband, and as you can see it was 52Ω @ 21.030 MHz. A little lower than planned, but it was 1:3 at 21.250 MHz and so well within design.

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The band seemed quite lively, and we could hear a special event Indian station working a huge pile up of EU and NA. Despite calling a few times we wasnt able to make that, but a little further down the band we did hear VK and a Taiwanese (well he was from Leeds) working a few.

After finding a frequency and calling CQ we was able to work WA7M Gavin in Arizona USA.

More tests to follow soon …

73 Dave M0TAZ

Homebrew Project 21MHz 4E Yagi Antenna

Months ago I ordered some aluminium in preparation for another antenna project.  Wtih the assistance of John M0UKD the plan was to build a 21 MHz 4E Yagi. The aluminium was ordered from aluminium warehouse, and cost around £100 including delivery.

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The on-line shop provides and delivers lengths of up to 5 meters, and they have a vast selection of grades and lengths available.

The design was by DK7ZB and was chosen because of the short boom length and high gain. The boom is 5 meters, and made from 40mm box split into 2 x 2.5m.  The reflector is 7.2 meters long and director 2 is 6.4 meters long (to give you some scale) You will find all the measurements, VSWR and gain data on Martin’s very extensive website.

The antenna construction involves sections of the elements telescoping into each other, and Martin points out this is a critical part of the design. The aluminium was ordered with this in mind, and while some sections required no adjustment others didnt quite go to plan. We needed to “grind” some of the sections just a little, to ensure they would fit and telescope correctly. This part of the construction required 1 complete grinding disc and around 2 Hrs. work !

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Once each section that required attention was ground down, the elements were mounted on the boom. I used various places to source all the parts but some on-line resources have been linked.

As with any home construction project you always get some unexpected challenges, the first was how to get the elements to lay flat on the plastic formers. The former needs to be mounted to the boom by a nut, and this isnt easy to recess, meaning we had to cut a small hole to locate the nut into the element, allowing the element to lay flat.

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With this type of beam it presents 28Ω (by design) and so requires a coax matching section. This is yet to be constructed, but the final build phase will include this and mounting the driven element.

You can see the progress so far, and further updates and pictures will be posted once tested.

73 Dave M0TAZ
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© 2015 Dave, M0TAZ