Tag: antenna

RSGB IOTA contest

Members of the SNB contest group came together to play some radio in the RSGB IOTA contest. Some stations make the trek to far flung Islands in exotic parts of the world, we opted for the contest site close to Kelvedon Hatch in Essex.

The SNB contest site has the added bonus of a 50m onsite mast, making an ideal platform to hang dipoles. George M1GEO and myself decided to operate our respective calls from the two radio setup, using 3.5, 14, 21 and 28 MHz. George also added his 50/70 MHz beam on the mast, and this provided some interesting contacts using MS and JT65.

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Two pump up masts provided the following setup.

Scam 12m – Tri-band Beam A-3S covering 14, 21 and

28 MHz and 50/70 MHz beam.

Clark 10m – 15m 4e homebrew beam

Bunker mast – 3.5 MHz dipole at 30m

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At various times we added some RF power from either the solid state expert 1.3KFA or the hal1200_atlantic amplifier. We had some interaction between the close sited antennas, and at times this dictated the operating modes / times.

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Fred G3SVK joined us as our CW operator, Fred can often be found in the lower pasts of the bands chasing big DX.

 

 

 

 

 

 

 

 

 

It was a casual operation, allowing time for sleep, meals and frequent cups of tea. The weather was fantastic, so camping out onsite was very enjoyable.

 

 

M0TAZ added around 49 DXCC and 350 QSO over the weekend. The highlight for me was AL7KC Alaska on 14 MHz  and VP8LP Falklands on 21 MHz.

14 MHz 2e Homebrew Quad

Homebrew 2e Quad for 14 MHz

The project was to build and test a 2e Quad antenna for 14 MHz, I wanted it to be lightweight and portable. The antenna had to be packed away in the car after a contest, so some parts of the antenna had to conform. The boom could be no longer than 3.5m, and the spreaders must be retracted for storage.

Cost should be under £100 for all the parts delivered.

The design uses fiberglass fishing poles, each pole is 4m fully extended. The project uses 8 poles. The poles will be fixed to the centre clamp using exhaust brackets, as they come complete with “U” support bracket. The size of the exhaust clamps will depend on the size of the roach poles.

The aerial will be 8m long, and 5m wide (see diagram) and the feed point will be at the bottom of the driven element. You may require some matching at the feedpoint, although mine was close to 50 Ohms.

You can find many online quad calculators, one that worked well for me is located here.

Here you will see the basic quad element, the basic construction is the same for both the driven and reflector. Here you will see the basic layout.

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Photograph of parts required. (Click to expand pictures)

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Having fun with the Quad and linear amplifier. QRO HF portable

Comparing the Wellbrook Loop to a Doublet Antenna

This evening I decided to complete a test using two different HF setups in an effort to compare the receiver performance of my antennas.

Radio 1, Kenwood TS 990, doublet antenna 10m per leg @ 9m

Billy offers support.

Billy offers support.

Radio 2, Elad SDR, Wellbrook RX loop @ 3m

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I decide the best way to test on receive would be to leave both radios receiving on 7076 KHz for 90 minutes, using WSJT-X. Both receivers had been set to 3 KHz bandwidth, and over the course of the next 90 minutes they each collected over 600 measurement reports.

The test started at 1830 Hrs and continued to 2000 Hrs. The doublet collected 633 measurement reports, and the wellbrook 740. This was the first indication that the Elad coupled with the Wellbrook was out performing the Kenwood / doublet setup. The next stage was to look in detail at the reports, WSJT has an option to write all received data into a text file, this includes time, s/n and decoded text. I used this to select at random some calls that represented a selection of EU (and DX if possible) and compare the relative signals received at the very same time on both radio 1 and 2.

The following table shows a selection of data points

wellbrook v doublet

After reviewing the data it was clear the Wellbrook loop improved the quantity of stations decoded, and in many cases also improved the s/n received.

This is by no means a definitive test, but it does indicate the Wellbrook loop (as many others have reported) work well in somewhat noisy urban environments.  The wellbrook loop can be reviewed online at the Wellbrook communications website, the version I used for the tests was ALA1530  its 1m and designed for medium and shortwave 50 KHz to 30 MHz. Steve Nichols G0KYA completed a review in January 2012 Radcom You can see the Eznec plot as photo 3 in the review.

The other factor to consider is the loop antenna has some directivity, I didn’t rotate the antenna at any point during my tests. In many cases rotation will improve / reduce signals as the antenna has directional properties.

The Welbrook performed well on 7 MHz, I suspect it would be even better on 1.9 and 3.5 MHz… to be continued….

Dave M0TAZ

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