Tag Archives: antenna

Spring Hill VK2/ST-036 with diamond quad  

How would you find a new source of unique callsigns for your 10m log?  Operate in a dx contest.

The ARRL 10m contest ran for two days of the weekend of 12/13 December 2015.  I decided I would operate on 10m on one of the contest days.

I arranged to operate from Spring Hill, using the IC703 at 10 watts.  I had a 10m dipole and a quarter wave vertical that could be used for this event.  To give me another antenna option I decided to cut and tune a diamond quad for 10m.

The quad is a full wave loop, closed at the end opposite the feedpoint.  The conventional square quad is fed in the centre of one of the horizontal legs, usually the lower end.  By rotating it 45 degrees you have a diamond quad, a square with one apex closest to the ground.  This format has a great advantage for a backpack station, as it can be made using wire, with the outer corners held in place with guys.  The wire antenna is simply attached to a stock standard squid pole (aka telescopic fibreglass fishing pole).  I used a 7m pole and located the feedpoint about 1.8m above ground.

I used insulators made from chopping board plastic.  One was required for each corner of the loop, the top and bottom being used to attach the loop to the pole and the two lateral corners being points where the guys were attached.  I was unsure whether guying those points would maintain the loop in the right shape but it did seem to be ok.  If the insulators slipped along the wire, the guy would have to be attached to the pole at the top of the loop.

Matching the quad

The feed impedance of a loop is in the region of 100-120 ohms depending in the height above ground.  To feed this antenna with a 50 ohm line a transformer is required.  I decided to use a quarter wave of 75 ohm feedline, using the impedance transforming behaviour of quarter wave feedlines.

The transformer action is given by the formula ZL/Z0 = Z0/Zi

or Zi/Z0 = Z0/ZL

where Zi is the input impedance of the quarter wave feedline, ZL is the load impedance and Z0 is the impedance of the quarter wave transformer/ feedline.

For a quarter wavelength of coaxial cable the length required is the free space quarter wave adjusted for the velocity factor of the cable used.  Most solid dielectric coaxial cable has a velocity factor of .66 and the cable I used was of that type.

The “free space” length of the quarter wave transformer was 300/28.4/4 = 2.64m approx.  This length needs to be adjusted to account for the velocity factor, so our final length is 2.64 x 0.66 = 1.74m.

I had a “video cable” of almost that length so I set up the antenna with the 75 ohm section connected to the feedpoint, then connected a short 50 ohm (RG58) extension to the radio.  The antenna displayed a reasonable SWR of about 1.2 on 29.4 MHz so I had to add some wire to the loop.  the difference in a full wavelength at 29.4MHz and 28.4 MHZ was about 400 mm so I added that length to the loop.  The SWR then was optimum at 28.4 and acceptable (1.5) at 28.0 to 28.8 MHz.

After testing and adjusting the antenna at home, I rolled up the wire and its guy ropes, ready for deployment on the hill.

How did it work?

Quite well.  There was a very strong sporadic E propagation in the first few hours of operation from the hill, giving excellent reports from VK5 and VK4.  This was very encouraging and I made steady progress in my log, handing out contest numbers to those who wanted them and giving others the SOTA summit code.

I later set up my standard linked dipole and was able to compare the quad loop with the dipole.  In some directions the dipole received and transmitted stronger signals than the quad, consistent with the orientation of both antennas.

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I did find that during the afternoon, signals from Japan were more consistent on the quad than on the dipole.

As for my unique callsigns score, I did make enough contacts to add 28 new uniques.  I had hoped for more, but conditions were just not good enough for contacts into the USA and that was a factor.  Still, the antenna experiment was fun and worth doing.

VK1DA

The 20m vertical – what was wrong with it?

I built a 20m vertical antenna for sota use. A squid pole supported the vertical section and the radials were elevated about 1.5m above ground.

When I first used it, results were not good. On receive, it sounded dead or near to it, with very little of the normal band noise I expect to hear on 20m. On transmit, the impedance was way out, an antennna matchbox being required to make it accept power from a radio designed for a 50 ohm load. Clearly something was wrong with the antenna.

It was simple enough. A quarter wavelength of wire attached to the side of a fibreglass squid pole. Three or four radials connected to the outer conductor of the feed line. The connections for the main radiator and the radials were on a plastic box. An SO239 socket was at the base of the box and another at the top for the vertical element.

Possible problems were considered. The connections in the box were simple enough. The length of the vertical element was checked. A quarter wavelength on 14.1 MHz, adjusted for a 95% length due to the wire thickness and the insulation calculated at 300/14.1/4*0.95 = 5053 mm.

I asked on the yahoo group SOTA_Australia whether anyone else had experienced detuning of wire elements laid along a squid pole, or had noticed losses introduced by a squid pole. Some comments were made by list members about their experiences – mainly good. Warren VK3BYD offered me some segments of the fibreglass from a broken squid pole, and I took up his offer. In a few days I received a Jiffy bag containing three segment of fibreglass tubing, probably the top and thinnest element of a squid pole.

At the Canberra Radio Club meeting in October or November I took the fibreglass segments along to do some experiments on the impact of the squid pole material on the losses in an inductor. Dimitris VK1SV brought his antenna analyser and a tuned circuit made from an air cored inductor and a tuning capacitor. Measuring the losses in a tuned circuit comprised of the inductor and a variable capacitor in parallel showed a very low resistance component of less than an ohm. Introducing various materials into the inductor core had various effects. The fibreglass sections from the broken squid pole had almost no effect. A piece of pine wood about 50 x 20mm and 100 mm long had a huge effect, the losses in the wood introducing many ohms of resistance into the circuit.

The focus then turned to the connections inside the antenna base, a box containing a few wires and sockets. I then discovered that at least one of the connections to the radial socket was not well soldered. I reconnected and resoldered all the connections between antenna, incoming feedline and the radials.

Next time I tried the antenna was at Spring Hill, the site of the original operation. This time performance was much better, with several European contacts made on CW and SSB, using the 10w from the IC703.

The frequency of best match was still not 14.1, tests indicated it was resonating lower than 14 MHz. The main element was electrically shortened by folding over about 100mm of the radiator at the top bringing the SWR curve of the antenna to a much more satisfactory level.

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Vertical antenna's base
Vertical antenna’s base

When used at Bowning Hill in a joint activation with Andrew VK1NAM, the antenna performed well, with the ATU not required. We made a number of contacts with European chasers.

Andrew Vk1NAM with radio equipment on Bowning hill 9/3/2014
Andrew Vk1NAM with radio equipment on Bowning hill 9/3/2014
Antennas - vertical on the left, linked dipole on the right
Antennas – vertical on the left, linked dipole on the right

The IC703 and IC706 have a very handy SWR curve feature allowing you to choose a band segment and measure the SWR at each of 3, 5, 7 or 9 spot frequencies, spaced by 10, 50, 100 or 500 khz, depending on the band and the frequency span you need. Using the 50khz increment centred on 14.250, with 9 spot frequencies allows for a quick check of how the antenna behaves across the band. I used that feature when adjusting the resonant frequency of a helical whip and wrote about it in an earlier post.

The outcome is that the antenna is now operating as it should and tests done on Bowning Hill comparing it with the linked dipole indicated that it is equally effective as a dipole at 7m above ground. When the dipole was end-on to the signals from the UK, there was a marked reduction in the signal level received at the EU end of the path.

The vertical is simple to erect and has no wind loading additional to the squid pole itself. For this reason I think it is a good option for SOTA operations.

SOTA activation of Mt Cowangerong VK2/ST-001

On Sunday 6th October I activated VK2/ST-001 which is the site of a weather radar installation owned by the Bureau of Meterology.

The previous activators from Canberra had provided plenty of good information about how to get there and what to expect when I arrived.  See VK1NAM’s blog and VK1DI’s blog for those details.

The Cowangerong Track off the Captains Flat road was littered with stones, rocks, dirt etc, due to recent road treatment by the machine parked on the side of the road a few hundred metres in.  It is about 10 mins drive to the mountain from the Capt Flat road.  I drove right up to the peak and turned back down to be sure of being outside the activation zone.  This took me almost all the way back to the Cowangerong Track.

It was a few minutes walk back up the slope to the summit, where the compound surrounds a few buildings and the weather radar tower.

I first setup in the clearing to the south of the compound but after listening to 7 mhz and having one contact with the background noise at s7 I decided to spend a bit more time and move my whole station further away from the compound, going about 20m into the forest roughly south of the compound.

39 contacts made.  Stations worked: VK1NAM/3 VK3AFW VK3PF VK3GAJG VK3JM VK1RX VK2YW VK5LY VK3CAT VK3FPSR VK2FHRK VK3FB VK3UBY VK3LO VK3DET VK3GHS Vk5WG VK5CZ/p VK3AMB VK3YY/p VK3YE/pm VK1DI VK3MCD VK2GEL/p

And after 0000 UTC, VK3CAT, VK2JI (30m) VK7NWT VK5LA VK5PAS VK3AFW VK3UP VK1DI VK3PF VK1MA/2 VK3FPSR VK3UBY VK3MRG and VK1NAM mobile in vk3.

Duration of operation from first contact to last was about 2 hours 30mins less the 20mins while moving the station away from the noise.  This operation was completely done using a 3S LIPO battery, which was 12.4v at the start of the operation and was 11.4v at the end.  The two SLABs I took were not needed.  The ATU ran off the LIPO too, for the few seconds of power it requires when changing bands and resetting.

The radio, ATU, log book, pack
The radio, ATU, log book, pack
Black squid pole just visible centre
Black squid pole just visible centre
VK1DA operating the gear
VK1DA operating the gear

SOTA activation combined with special event call Vi100ACT, 1 March 2013

The Canberra Region Amateur Radio Club received authorisation to use the callsign Vi100ACT during the month of March 2013, to recognise the Canberra Centenary.  I volunteered to coordinate the roster of members who were keen to use the callsign during the month and rostered myself on for the 40m, 20m and 2m bands on the evening of 1 March when I would be activating Mt Ainslie as a SOTA station.

For this activation I set up the 20m dipole as well as the 40m dipole.  I made about 15 contacts on 40m including VK1/2/3/4/5/7, ZL2 and FK8.  A few contacts were made on 2m FM, then I moved to 20m and self spotted on sotawatch.org to announce that I was calling on 14.061 CW.  I then worked 8 contacts into England, Germany, Austria and France (G, DL, OE and F) with reports varying from 339 (weak) to 559 (fair).  This seemed a fair result for the first use of the 20m dipole, not yet optimised for length or angle.  The power output of the FT817 is 5 watts.

The two dipoles shared a common feedpoint at the top of the squid pole support, and the dipoles were strung out in roughly the same plane, the longer one at the top and the shorter one below it.  No impact on the 40m antenna behaviour was apparent.  The SWR on 20m was not ideal as there was some reflected power indicated on the 817 meter.

Dipole feedpoint at the top of the pole
Dipole feedpoint at the top of the pole
antenna wires
Antenna wires

The Vi100ACT callsign is to be used on various bands by different club members during the month of March 2013.  The official centenary of Canberra’s founding/naming ceremony is on the 12th of March.

 

Holiday constructed 40m dipole

The dipole was made using a square shaped plastic souvenir mini road sign (Kangaroo warning) as the centre insulator, a 10m reel of speaker wire from a consumer electronics shop, RG58 coaxial cable and a connector for the radio. It was held up in the air by a telescopic fibreglass pole (squid pole).

Holes were cut in the insulator to protect the connections from stresses.  I did not have a drill so I used a hobby knife.

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The coaxial cable was prepared by removing the outer insulation, then sliding the braided shield wire down the inner insulation, exposing a gap in the braid and feeding the inner conductor through the gap. This allows the braid to remain braided giving it strength and form that is lost if it is combed out as a multi strand conductor.
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The antenna wires and coax were routed through the holes in the insulator, then soldered together.
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The antenna was lifted into the air, cords were attached to the dipole ends and tied off. The length of the antenna may need to be adjusted by folding it back on itself. This prevents/avoids cutting it and having to add some when too much is cut off. 300/7.1 gives the wavelength in metres, each side of a half wave dipole should be a quarter of that length, less the end correction factor of 3 to 5%.

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In the location this was originally built for, the dipole sides were only separated by 90 degrees due to space restrictions. I did work a few stations in VK and JA using this antenna on 40m and 30m. CW.

QRP Hours contest 2011

This is a short contest for QRP operators.  It runs for one hour on CW mode, then 1 hour on SSB.  A truly easy contest to participate in.  All licence classes can participate as QRP (low power) or their ordinary power.  The contest was sponsored by the CW operators QRP club.

I wasn’t sure I would have an opportunity to operate in this contest but at about 6:30pm on Saturday 2nd April I decided I should put up an 80m antenna and have a go.  At 6:40 I had identified a two section telomast and was measuring out some guy ropes for it.  Having found some stakes, guying ring and found the wire antenna cross-boom with the attached halyards and pulleys, I was able to assemble the mast, attach the cross-boom, lay out the guy ropes and do a trial setup to get the guys set to the right lengths.  Once that was done I hammered in three stakes and attached the guy ropes to two of them.  Walking the mast up to vertical showed I had set one guy at an impossibly long length so it all had to come down.  Next time was ok so I could walk the third guy out to the stake and tie it off.  One 20 ft feedpoint suspender ready for action. Time about 7:15.

I had a 80/40m dipole assembly last used two years ago at a rental property in Canberra.  I attached the centre conductor to one of the halyards and hauled it up to the dizzy 20ft height of the mast.  Then I attached some light cords to the antenna ends and tied it to the fence at one end, and to some ground stakes at the other end of both dipole wires.  This work was completed in the dark as the sun set at about 6pm local time.

The two dipoles are joined at the centre.  This works because the 80m antenna is a very high impedance on 40m, so is virtually “not there at all”. The 40m dipole detunes the 80m one slightly but I went through the adjustment process with this antenna about 20 years ago and have simply rolled it up when I finished using it each time.

Then I got out the FT817 and found a suitable keyer cable, microphone, power supply.  On 80m the dipole presented a 1:1 match on the CW end of the band so that was fine.  On 3690 it was about 1.3 but my Emtron tuner handled that mismatch with a fairly broad dip.  The time now was about 19:45 local and the contest started in 15 minutes, or so I thought.

At 20:00 local time I heard a station calling CQ TEST so I answered, received a number, gave a number, signed off.  Good start to the contest, I thought. Then I called CQ TEST myself.  No replies.  Tuning around showed nil activity.  Called CQ again.  This time I got a reply from an operator who kindly advised me that the contest was not due to start until 2100 local time.  I opened up the computer and checked the contest rules.  Start time 1000 UTC, which was 9pm local, but somehow I had reverted to non DST in my calculations due to daylight saving ending later that night.  1000 UTC was almost an hour away.  So I had time for some dinner!

About 45 minutes later I went back to the radio and started the contest again at the right time.  Signals were strong and most stations were in the vk2, 3 and 4 areas though there were some vk5, vk7 and ZL stations worked too at signal reports of 559 or so.  I made 10 cw contacts in this hour.  A slow contest compared with the DX contests but it was also quite relaxed and unrushed.

At 1100 UTC the SSB section commenced, operating between 3550 and 3590. Signals were very strong from some stations.  Again a few names were exchanged as well as the contest numbers.  15 contacts on SSB, and I got the impression the antenna was working well, as mostly my replies were answered after only one call.  Quite good for a 5 watt signal.

I have sent in my log and I don’t think this is the only QRP event I will operate in.  This was a very enjoyable process and quite rewarding for the minimal effort required to get on the air.  Next time: antenna up another 10 feet.  And the ends should be higher too!  Should be no problem.  I might even do most of the work in the daylight next time.

Mast and 80/40m dipoles
Mast and 80/40m dipoles
Feedpoint of 80/40m dipole
Feedpoint of 80/40m dipole

VK9NA expedition

Late comments about the VK9NA expedition I joined in January 2011.  This was a VHF/UHF/microwave and 2m EME operation.  Due to quite poor conditions for tropo across to the mainland, we eventually did most of the operation on 2m EME.  However we did try to make contacts and ran a lot of CQs on 144 MHz every day.  We did make some contacts but there were nowhere near the number of tropo contacts made last year.  The 144 MHz band was the main band used for this work.

We activated the station every day on 6m as well, from the hotel site.

Due to the high winds experienced on the hill we moved the EME station to the Guide Hall where we had been kindly offered the use of the grounds.

On Norfolk the internet access is provided by Wifi connections at hotels/resorts and a few in the Burnt Pine business area. I found it was necessary to buy several different cards to get access via NIDS, Norfolk telecom and another account for access at the hotel I stayed at. Wifi access from Mt Pitt was good, from the hotel the others stayed at, access to NIDS was not good.

The radio conditions on vhf up were not as good as they had been in 2010. This was partly due to physical weather conditions, including strong winds for the duration of the operation from 8th to 20th January. On the weekend of the summer field day conditions were very poor and the only contacts made with the mainland that weekend were on 6m, and there were not many of them.

The 2m EME operation was very successful.  Over a hundred contacts were made using JT65 via the FT897 and a laptop computer running the WSJT software.  A TE systems amplifier boosted the output power of the FT897 for EME work.  The list of stations worked is at the VK9NA website.

I greatly enjoyed the event.  I learned how to use WSJT on both FSK441 and JT65B, and learned a bit about pointing a very large 2m antenna (19 elements, 12 metres length) at the moon and periodically repointing it. For about half or more of the time, the moon was not visible so we were relying on compass bearings corrected for mag offset/declination and an inclinometer for the elevation.

I also became familiar with the FT897 and found what a great radio it is for this kind of operation. The other radios used were FT817 and a TS2000 which I found to be a very good radio too.

The TS2000 has an option to automatically transmit CW at a 700 hz offset (actually the offset equals your selected cw beat note and sidetone frequency) when you switch from USB to CW. It also has an option to automatically switch from SSB to CW mode if you press the key, whether it’s an automatic key or a hand key. Very neat.

Apart from the radio aspects it was also great to get to know Michael VK3KH, Alan VK3XPD, Kevin VK4UH. We were fortunate in being well organised on the social and meals front by Michael’s wife Roz and her sister Gail, and Alan’s wife Aileen all of whom made this event that much more enjoyable.

We did attend a few local special events such as the fish fry, the progressive dinner and the re-enactment drama based on the voyage of the Bounty, the eventual mutiny led by Fletcher Christian and the exile of the mutineers at Pitcairn Island. This history is a proud aspect of the Norfolk Island culture today.

A great event and a fun filled 10 day trip for me.

Here are some photos at Flickr:

Here is one photo of the EME antenna.  Remember  it is 12 metres long.  There are 19 elements.  Click the photo for a larger view. The long “element” in the centre of the boom is just a truss boom – the antenna has vertical and horizontal stabilisation to prevent it flexing and losing gain. EME antenna at VK9NA