VK2RH ham radio

Category: Antennas

  • Lightweight portable VHF antennas

    One of my favourite sites is Martin DK7ZB’s collection of pages detailing the construction of practical antennas for VHF and UHF.

    I first visited the site following a link to designs for lightweight portable yagis that would be suitable for SOTA VHF activations. Under the link ‘2m/70cm-Yagis ultralight’, Martin describes a number of yagis for 2m and 70cm that use thin metre long aluminium welding rods mounted on PVC booms.

    “These Yagis are constructed with cheap lightweight materials for electric installations and you can mount and dismantle them without any tools. The boom is made of PVC-tubes with 16mm, 20mm or 25mm diameter, the element holders are the clamps for these tubes.” DK7ZB

    What makes the designs particularly attractive is that they can be quickly assembled from a compact (admittedly metre long for 2m) pack you can carry on your ascent, even designs using a 2 metre long boom.

    The components of a DK7ZB lightweight 6 element yagi suitable for SOTA or any portable operation

    The welding rods – used for TIG welding – are available in Australia in 2.8mm and 3.2mm diameters from welding supplies shops. I’m still on the lookout for 4mm diameter rods. PVC conduit and the mounting clamps are readily available in VK from hardware stores.

    I’ve managed to cut a suitable slot in the end of a 3.2mm aluminium welding rod using a Dremel with a thin cutting wheel. One suggested way of attaching the feedline to the driven element is to crimp the lines into thin slots like this.

    Also of interest to the portable operator are the J Pole designs based on Wireman 450Ω window feedline. There are dimensions for bands from 2m down to 40m. The J pole is essentially a half wavelength dipole where the high feed impedance is transformed by a quarter-wave length matching section (the tail of the J) tapped at a suitable distance to yield a 50Ω match. Follow the ‘Wireman-J-Pole’ link in the left navigation. These pages remind you that the J-pole can be configured in any way so a 40m J pole in a Zepp arrangement starts to look quite practical if you have just under 10m of 450Ω feedline available. I want to start with the 6m design and see if I can make it robust enough with heat shrink etc for portable work.

    Kits for the DK7ZB yagi designs are also available from nuxcom.de, Attila Kocis DL1NUX’s website. Both sites are in German and English.

  • QRP at Bamarang

    Last weekend I had a great time playing radio. Along with half a dozen other families and all our kids we went to spend the Easter weekend at the “mud brick mansion” at Bamarang on the Shoalhaven River, a few km west of Nowra on the south coast of New South Wales. Courtesy of the pod on my car I was able to take quite a few radio bits and pieces along.

    We enjoyed perfect autumn weather while it rained back home in Sydney!

    I even managed to build the neat little EFHW (End Fed Half Wave) Tuner designed by Stu, KI6J on a shady verandah. The kit had arrived a few days earlier and I made sure I had everything I needed to build it away from my attic/shack/workshop. In fact the weekend became a sort of trial for field day and a great way to identify the essentials. If there’s a lot of gear on hand an awful amount of time can be wasted deciding which bits to use and how.

    I was inspired by reports about the EFHW tuner and the appeal of not having to worry about ground radials. What clinched it for me was a photo I saw on one of the (far too many) qrp email groups I try to follow showing a ham on a mountain side beneath his arching squid pole with the little tuner matching the hi-Z of the half-wave antenna to the 50 ohms expectations of the tiny transceiver which was probably an ATS3b.

    So that was my mission for the weekend.

    The tuner kit went together in a very short time. Before accepting my order Stu, KI6J sent me a powerpoint of the assembly instructions so I was sure I could handle the construction. The fiddliest bit was the tiny binocular ferrite core transformer for the bridge. Fortunately he provided enough wire in the kit for me to botch it the first time round and do it perfectly the second!

    After a couple of leisurely hours mostly taken up with drilling holes in a tiny plastic box it was working on the test lash-up. The polyvaricon is delightfully sharp. You tune by dimming the LED – and then switch out the bridge to transmit.

    The KI6J EFHW Tuner kit almost complete with the 5k ohms test load in place. The builder provides the enclosure and connectors. (Photo sourced from instructions)

    I had a 10m (almost 33 feet) squid pole (aka Jackite or crappie pole) with a tiny pulley from a boating store attached to the top with cable ties. I used the guy ropes from my Buddipole setup to hold the pole up straight. It stayed up all weekend.

    The half wavelength formula in feet is 477/freq in MHz, or just on 68 feet (20.7m) for the code end of 40m. The far end of this was held up – via a plastic button insulator – by a fishing line launched up into a tree using a half-filled plastic drink bottle. All too easy! The near end of the antenna simply terminates in a banana plug that connects to the little tuner. I also connected a short 5-6 foot counterpoise, which was essential.

    I had a great time playing with the tuner and my new SDR-Cube pumping out a whole watt of RF, as well as the trusty little FT-817.

    Now I have a clear idea of what’s required for an effective little kit of gear to take up a hill for relatively speedy SOTA style deployment. And maybe I’ll fill the water bottle for those trips.

    If you’re interested in getting hold of one of these nifty little EFHW Tuner kits you should contact Stu KI6J at ki6mwn@yahoo.com. US$27 included shipping across the Pacific Ocean! Fast and very fair!

    My blissed-out second operator in the field at Bamarang, near Nowra NSW. He helped me retain my QRP calm.

    During a trip into the township to replenish supplies I found a fishing tackle shop with an Easter sale on, and bought a couple of handy Plano tackle boxes and some inexpensive 10m lengths of nylon coated stainless steel ‘leader line’ wire which I’m sure can be used for a handy weatherproof dipole. As long I don’t have to solder the stuff.

  • Arctic DXpedition

    Over the weekend sunspot 1112 erupted and produced a strong solar flare. Now according to space weather sites there’s a 25-35% chance of high latitude auroras on 19-20 October.

    And right now a group of four Norwegian friends are enjoying their annual DXpedition to Kongsfjord – well and truly in the high latitudes – at 70°43′N 29°21′E at the top of Norway.

    Kongsfjord, Norway – a nice place to set up your 500 metre long Beverage antenna

    Four of the main participants are Arnstein Bue, from Trondheim, Bjarne Mjelde (host), from Berlevåg, Odd-Jørgen Sagdahl, from Trondheim and Tore Johnny Bråtveit, from Trondheim. As you’ll see if you visit their pages these men are serious medium wave and short wave DXers, with impressive equipment racks and listening achievements to match.

    Arnstein Bue’s blog DX Paradise gives a sense of some of the QSL trophies. DXpedition host, Bjarne Mjelde’s blog Arctic DX has an entry logging their first day last Friday anticipating the weather awaiting them:

    “+2 Celsius, 15-20 m/s (35-45 mph) northerly winds, rain and sleet showers…”

    As I write this it’s early afternoon there and according to their website it’s warmed up to +4 Celsius!

    They also appear to operate remotely from this spot. Their antennas include a new 500 metre long Beverage aimed at the North Island of New Zealand which is clearly working very well. Two shorter Beverages (225m & 330m) and a Quad Delta Flag Array complete this dream DXing antenna farm.

    And if you visit the website you’ll see ample evidence that they clearly know how to enjoy themselves at the dining table as well. Local King crabs are accompanied by the finest New Zealand wines. Their dining notes are as tempting as their DX!

    Main course was pork sirloin marinated in garlic and chili, served with tagliatelle, basil, leeks and cherry tomatoes. With the pork we tried Kim Crawford’s Pinot Noir. Maybe a bit light for the quite tasty meat, but absolutely a super wine!

    For dessert we had local blueberries with grappa – another Kongsfjord signature dish! And now we are off to listen to more recordings and prepare for another – hopefully eventful night. The solar indexes are going down and the K-index for Tromsø is now 0, and we hope that it will remain like this!

    The main website is also the repository of a number of documents on DXing issues by Dallas Lankford. There are also data sheets for a large number of receivers (including AOR, Racal, Rohde & Schwarz, R L Drake Company, Siemens, Harris, TenTec, Icom etc) and information about antennas. Bjarne Mjelde has distilled his experience into a definitive article about the best antenna wire. The conclusion? A thumbs up for galvanised steel and aluminium. A number of his reviews are also aggregated on the site, including reviews of the IC-703 and the Perseus SDR.

    Their sites demonstrate how much a part SDR plays in modern DXing and monitoring. There are some huge SDR recordings and mp3 files available as well. Retrospective analysis of these files enables them to find rare stations as well as – presumably – traditional live listening.

    It’s been a delight checking in on their site each day to catch up with the activities of such a convivial group of friends. Truly inspiring to this reader on the other side of the globe.

  • Homebrew ladder line spacers

    It never ceases to amaze me what wisdom is simmering away amongst those email discussion groups I read.

    Out of the blue today – prompted by mention of a commercial solution on the Elecraft list – came a sequence of brilliant ideas about making effective and easy on the budget ladder line spacers.

    The commercial spacers from K&S Ham Radio Parts look great, but the fact they’re made of nylon prompted concerns about their survival against UV. At 25 cents a piece I think they look fine!

    In response there was a pointer to a YouTube video showing how to turn a box of ballpoints into very neat and secure spacers using black cable ties.

    And then a pointer to another commercial solution from True Ladder Line, and a hint about how to replicate the effect at home using ‘drip sprinkler tubing’ which is the right size and and has just the right amount of rigidity for the job. And there’s Dave ZL1BJQ with his approach based on those plastic chopping boards you can buy at any $2 shop, cut into spacer pieces, notched then pushed on to wires and held in place with hot glue.

    Spacer

    And then there’s this approach by VK2YE using plastic coat hangers, cut to length (5cms) and drilled to fit wire, and then glued to stay in place. In fact this is just one of 138 videos on his YouTube channel.

  • Fabric antenna

    Via Southgate News and MAKE magazine news of a collapsible fabric yagi antenna developed by Diana Eng KC2UHB who has combined two craft skills in a stylish way, electronics and sewing. It’s a design for a Yagi for portable amateur radio satellite operation.

    Diana Eng KC2UHB demonstrates her collapsible fabric yagi antenna

    Her MAKE magazine article is well-written, comprehensive and brilliantly illustrated.

    Diana Eng has also written an earlier article aimed at newcomers to amateur satellites for MAKE that covers:

    • Finding out when to listen
    • Finding the frequency
    • Aiming a whip antenna
    • Following the pass with the antenna
    • Tuning the radio for the Doppler effect

    Check the size of the antenna in that earlier piece and you’ll understand why she aimed at something more portable!

  • The KGD antenna

    Via Julian G4ILO I came across a WSPRnet report from DM1RG on his success with a newly built KGD Antenna from the German site QRP Project. I had actually ordered their other antenna project (a Multiband Fuchs antenna that enables a single 41m wire to operate on all 8 HF bands) a few days ago and earlier tonight revisiting their site I was readng more about the KGD antenna – a very small vertical dipole – how’s 130cm for a 30m antenna that enabled a link from D to VK on 5 watts?

    The centre part of the 40m version of the KGD antenna

    The Kurz Geratener Dipol antenna is no longer available as a kit but the instructions are still online – auf deutsch. I should also have a go at translating the manual. It seems to be quite an effective design. On the 40m version (pictured here from the QRP project site) – all 150cm of it – the bandwidth between SWR 2:1 points is 45kHz.

    Reading about the antenna again on the same evening is clearly some kind of good omen? I can almost imagine one mounted bike mobile!

    See the KGD antenna page for more detailed construction information.