The HF antenna…

Posted on 19/11/2016 by Andrew G0RVM

So, most members should be aware by now that the old 40m dipole has been removed and replaced with a new 40m dipole! The feedpoint 1:1 balun was also changed for good measure and sealed thoroughly for the winter.

But this is not the end of the work on the HF antenna, that was just task 1 😉 Task 2 consists of two activities and is planned for Spring 2017 once it dries and warms a little 🙂

Activity 1 will add elements for 30m and 20m expanding the 40m dipole into three parallel dipoles. This will result in a tri-band antenna that is resonant on 40m, 30m and 20m giving us a very useful antenna.

Activity 2 will replace the coaxial feeder between the radio room and the antenna feedpoint.

Today we have approximately 2.3dB of loss at 7.1MHz between the radio room and the antenna feedpoint. Assuming the coax is in the very best condition (which its not) and it’s RG-58C (Its an RG58 of some sort) this equates to about 54m of coax. That’s a 40% power loss on Tx and Rx. Replacing this with RG-213 reduces the loss to 0.9dB or a 19% power loss. An improvement of 1.4dB or 20% doesn’t sound much and its not but consider the situation at 14MHz. With RG-58C there is 3.2dB / 53% loss but using RG213 the loss is 1.3dB or 26%.

Frequency	RG-58C	RG-213/U	Ultraflex-10
7.1MHz	2.2dB	0.9dB	0.5dB
10MHz	2.7dB	1.1dB	0.6dB
14.2MHz	3.2dB	1.3dB	0.8dB

Coax loss per 54m

To put this differently. The transmitter places 100W max into the feeder at 7MHz, 10MHz and 14MHz. With RG-58 the antenna receives: 60W, 54W & 47W respectively. Replacing with RG-213 results in: 81W, 77W & 74W. Using a better coax and one that does not cost much more than RG-213 the situation can be improved further. The overall difference of using something like Ultraflex-10 over RG-58 is definitely worth having and that is why activity 2 is so important.

The completed parallel dipole antenna will remain in its current location supported by the trees at either end. But supporting the end of the antenna elements will require two attachment points instead of the one we have today. Investigation has showed this is not a significant obstacle.

Thanks to Peter, G3LDO for the above diagram taken from his excellent book Backyard Antennas.

Antenna Maintanance

Posted on 06/11/2016 by Administrator

Yesterday myself, Andrew, Graham, Rex, John and John spent the day at the Chantry renovating the club’s antenna systems.

Our plan for the day was to inspect the existing antenna systems, replace a section of coax between the attic and balun and to install and tune the new 40m dipole.

Condition of existing antenna systems

Existing 40m dipole balun

The overall condition of the existing HF antenna was good, but clearly the self-amalgamating tape has suffered from UV degradation. This doesn’t appear to be a major problem however the antenna has only been up roughly 4 years, so the problem would get worse over time.

A photo of the existing co-linear VHF antenna

Existing VHF Co-linear

While on the roof we also inspected the existing VHF antenna. It is clear that it is not ideally placed, being blocked by the chimney stack as well as the Chantry’s satellite dish.

Replacing the coaxial cable

One of the jobs for the day was to replace the RG-58 coax run between the attic space and the existing balun with some superior Westflex 103. In order to do this, Andrew and myself had to climb into the attic in order to cut the existing cable and solder new UHF connectors onto it. This allowed us to replace the cable between the attic and the antenna. On completion we measured the loss through the cable using a 50Ω dummy load and power meter.

New Westflex 103 cable run

We measured the loss at just under 3dB at 7mHz. We measured 60W at the end of the cable with a 100W input. Currently we plan to improve this loss further by replacing the rest of the cable to the shack

Andrew holding a dummy load and power meter

Andrew getting ready to test the loss through the new cable

Installing and tuning the new 40m dipole

With the new coax installed, we now set to work installing the new antenna. Before we could putt the new dipole in place we had to let down the existing antenna. As the two ends were attached to trees, I volunteered to put my tree-climbing skills to use and lower the existing elements

Rex giving us a hand getting up the trees

With the antenna on the ground we attached the new dipole and hoisted it into the air. Following some tests with Andrew’s MFJ antenna analyser we deduced that the elements were too long. Following several rounds of tuning we reached a state where everyone was happy with the performance of the antenna.

New balun installed

We sealed the connections with self amalgamating tape and headed to the shack to have a listen to the band.

40m dipole

Performance

Frequency (mHz)	Resistance (Ω)	Reactance (Ω)	SWR
7.0	60	8	1.2
7.1	78	0	–
7.2	112	0	1.5

We also tested the SWR in the shack and measured an SWR of 1.4 at 7.2mHz. A quick sweep of the band picked up some loud and clear Morse, although this may be due to a contest that was running at the time.

Conclusion

We hope that the new 40m dipole continues to deliver excellent results. There are still improvements that need to be made to the club’s antenna systems, including:

Adding the two other elements (30m and 20m) to the fan dipole array
Replacing the coax run between the attic and the shack with lower loss cable
Deciding on an effective way to relocate and improve the VHF antenna system.

I’d like to thank Andrew G0RVM, Graham, Rex G4RAE, John M3EQQ and John M0HFH for giving up their time yesterday to help the club. I had a great day and learned a lot throughout the process.

Peter Barnes
2E0UAR

Antenna Horizon

Posted on 12/07/2016 by Andrew G0RVM

Have you ever wondered what it would be like to sit at your antenna and see what it ‘sees’? Well, this evening I attached a camera to my antenna and shot the following short video as the mast was raised and rotated.

The video starts with the antenna pointing at 45 degrees. Once elevated its rotated to the following directions where it stops momentarily: North, West, South, then back around to East, South, back to North then to 45 Degrees before the mst is finally lowered again.

What this little experiment shows is that the horizon looks pretty flat in all directions – no big hills evident. It also gives a good feel for how well the antenna clears the surrounding houses.

Andrew
G0RVM

Strange problems….

Posted on 05/04/2016 by Andrew G0RVM

So, for a couple of months I’ve had a growing suspicion that I’m not receiving as well as I am transmitting. I first noticed the problem when observing the strength of signals from GB3VHF which after one winter storm seemed much weaker than it had been. However, there seemed to be no impact upon transmit as SWR remained negligible and stations some distance away where still receiving me well even when my transmitter was generating about 0.5W PEP!

Since first noticed I’ve worked many stations and the signal reports always seem to identify that I’m not receiving as well as the remote station. Establishing this pattern has taken some time. It should be said at this point that its the same antenna and feeder used for both transmit and receive.

Its been a wet Winter and not really suitable for removing weather proofing from exterior connections and outdoors work. But now Spring has arrived things are finally starting to get dryer and warmer. Alongside this I’ve taken down the mast and antenna for work to support an new PRO.SIS.TEL 641D rotator. This has enabled a detailed inspection and test of feeder and antenna.

Before starting any work I thought about and identified the following possible causes:

failure of the receiver, possibly signal amplifer
damaged feeder, possibly a connector problem or water ingress
damaged feeder at the antenna feed-point. possibly also water ingress.

Problem (a) seemed possible but without a second receiver its very hard to be sure. But its a quality Transverter (Kuhne TR144H) and I’d be surprised if that had partially failed – remember signals are only 2 – 3 S points down on what I think they should be.

So, (b) or (c) seemed much more likely.

So with the mast down and everything removed back to a dry, warm environment I removed weather seals – no sign of water or even the slightest amount of moisture ingress. The coax was tested with a DC Ohm meter – no shorts or higher than expected resistances; with an antenna analyser and dummy load – again this looked perfect.

So attention shifted to the antenna feed-point, pictured before it went outside for the winter and before the connections where weather sealed. Note: Grey plastic tape overlays amalgamating tape. Again, there was no signs of moisture ingress into the coax, but there where signs of galvanic corrosion between the aluminium driven element and the stainless steel (A2 grade) machine screws to which the feeder connected. Actually, to be more precise between the aluminium driven element and the flat washers on each machine screw. It was clear that the liquid rubber sealant which I’d applied had not sufficiently covered these connections and thus water had been in contact between the different metals acting as an electrolyte.

To be clear, the machine screws where not showing any significant signs of corrosion, just the washers. So the feed-point was thoroughly cleaned and reassembled without using the washers then liberally coated in liquid rubber to seal against contact with water.

Now, at this point I don’t know if this was the problem, but it does make some sense. Any transmit signal would be of a much higher voltage/current than a received signal so would probably cross a mildly corroded junction with marginal attenuation. But marginal attenuation of a much weaker signal would be more noticeable. That’s my reasoning anyway.

The acid test will be when I erect the mast and antenna again in a few weeks and see if received signals such as GB3VHF have returned to their earlier strength. When doing this I will also use new feeder, so if signals are stronger I’m never going to be absolutely sure the problem was galvanic corrosion. Of course the problem may still be present and it could be another cause such as the receiver!

For information, the antenna is an 8-element LFA Yagi from InnovAntennas.

Andrew
G0RVM

Back to the Future…

Posted on 20/10/2015 by Andrew G0RVM

Back in the 80’s I received my first amateur radio license, a ‘B’ license as it was back then entitling me to use, if I recall correctly, bands above 30 MHz only. We didn’t have 6m and 4m band allocations then so it meant 2m and 70cms were the bands of choice for me and the majority of other ‘B’ license holders.

So I started with 2m and 70cms SSB and my interest was soon peeked by space communications with Oscar 10 etc. Those early Oscar’s were excellent as, if I recall correctly, they where in elliptical orbits which meant that they appeared to hang in the sky for some time, not shooting overhead as do satellites in lower more circular orbits. Their transponders were just like big SSB repeaters in the sky and I worked all over Europe. Happy days. But working those Oscars was not that easy especially at Acquisition of Satellite (AOS) as they were pretty far from the Earth so a good station was needed. My station grew to a 2m, 9 element crossed Yagi; a 70cms, 19 element crossed Yagi, both circularly polarised; azimuth plus elevation rotators and mast head preamplifiers. The radio was a Yaesu FT-736 which I only sold last year…It was a wonderful radio.

Of course with those antenna’s it was perfectly possible to work terrestrial communications too. I made contacts across the UK and Europe using sporadic E and Tropospheric propagation. Those were exciting times indeed as not only was amateur radio new, to me, but it was such fun learning about different types of propagation, satellite communications and having great fun talking to people.

Ok, so by now some of you will be asking – what is the point of this article? Well, bear with me… I learnt Morse code and in the early 90’s received my ‘A’ license. Soon afterwards the world changed as I started doing radio professionally for a few years. This removed all interest to do amateur radio stuff when I got home from work. Anyhow, time passed and I started to operate on HF talking to people all over the world – it was fascinating – I learn’t lots more.

With solar cycle 24 rapidly fading and with the real possibility that cycle 25 may be no better, probably worse, I’ve been looking back and found myself comparing my V/UHF experiences with those of HF.

My conclusion is that HF is fun, its pretty easy to work stations across the UK, Europe and further afield depending on your station. Take a minute and think about that, especially the ‘depending on your station’ bit. Do you have the space to erect, for example, a 9 element Yagi for the 20m band? I’m seriously impressed if you do 😉 I bet most of us are using simple HF antenna’s and we are constrained by space, interference and the cost of erecting a high-performance HF station. But move on up to VHF and things get so much easier. I bet many of us could erect a 9 element Yagi for the 2m band and mount it several wavelengths above ground too…. Such an antenna will cost a tiny fraction of its HF equivalent; its small, light and easily rotated too. Interference does certainly exist above HF but its nowhere near as bad. But, FM repeaters and modes such as D-Star aside, VHF is dead these days I hear you say? I cannot deny that it is much quieter than in the 80’s and 90’s but its still a happening place… Its perfectly possible to work stations using phone and data modes across the UK and into Europe when propagation is flat. All those exotic data modes are present and in active use too, people are exploiting Tropospheric propagation, meteor scatter, satellite communications, auroral propagation to name a few.

So its back to the future for me, the HF antenna is now down and until I receive my new VHF antenna I’ve elevated one of my original 9 element Yagi’s. Already I’m hearing beacons GB3ANG in Scotland, GB3VHF in Kent and GB3SSS in Cornwall. I even worked an old friend towards London using CW (RST:559) and Olivia with 20 watts. Who says VHF is line-of-sight. 🙂

I guess you realise the message by now…. V/UHF is lots of fun, you can work DX, high-performance stations are much more achievable than on HF and you learn lots. Amateur radio is so much more than HF, FM, repeaters, D-Star etc. So, why not explore our higher bands?

Andrew
G0RVM

Fox Hunting with a TDOA Antenna

Posted on 03/08/2015 by Administrator

In preparation for the pedestrian fox-hunt that happened a couple of weeks ago, I decided to take a look around for some antenna designs that I could build at home. I came across a blog post which showed off a Time Difference of Arrival (TDOA) antenna that someone had designed and built.

A simple and effective fox-hunting antenna

How it works

The antenna relies on a timer, in my case a 555 timer, to generate an audible signal. I have mine calibrated to a frequency of 1kHz. This signal is level-shifted so that it goes between -4.5V and 4.5V. The use of a set of diodes causes the circuit to quickly switch between the two dipole antennas mounted to the unit (tuned to 145mHz). When the signal received by the two dipoles is out of phase, the receiver emits a tone. When the RF source is equidistant from both antennas (when you are pointing at the “fox”) the signals are in phase, causing the tone to disappear.

This design is fully functional regardless of how close you are to the source, providing an advantage over other antenna designs. The audible tone also provides a clear indicator of direction. However, the main issue is the fact that you get two readings, at 180° to each other.

Parts List

The list of components required is quite simple, so I had most of them laying around.

555 Timer
4.7K Resistor
100K Resistor
2x 470Ω Resistor
2x 0.01uF, 50V Capacitor
10uF, 25V Capacitor
0.001uF, 50V Capacitor
4x 1N4007 RF Pin Diode
2x 10uH Inductor Coil
RF Choke, 8 turns (salvaged from a motherboard)
SPST Switch
9V Battery
9V Battery Clip
Antenna wire (single core) or 4x Telescopic Antennas
1.5M of RG-58 Coax

Build

When building the antenna, I used two blog posts for reference. You can find them here(pdf) and here. For some reason I ended up combining both of the designs, using the Bryonics.com design for the dipole circuits, and the 146970.com design for the rest of the circuit. This probably isn’t advisable, but it worked for me. Here is the circuit I used:

You can test the 555 timer circuit by hooking the output pin up to a speaker. You should hear a tone when power is supplied to the circuit. I started by breadboarding the timer circuit, and then moved it to veroboard for the final build. Once the circuit was complete, I zip tied the PTT button down on my PMR446 Walkie-Talkie, plugged the antenna into my Wouxun KG-UVD1P reciever, and tuned into the 446mHz signal. The antenna worked perfectly first time, providing a clear tone that faded out when I pointed the antenna at the radio.

For the physical construction of the antenna, I used some thick, single core, cable to make the dipole antennas, and mounted the whole thing on a 60cm long piece of wood. Lots of glue gun was used as I couldn’t be bothered to find some screws. I also drilled holes in the ends of the wood to poke the coax through. The dipole elements were attached using screws, and can be bent between a folded and deployed position.

Evaluation

I took the antenna out for the pedestrian fox-hunt that happened a few weeks ago. The antenna picked up the first signal very well, and the audio tone allowed me to find the direction of the transmission to quite a high accuracy. Unfortunately for me, I headed off into the wrong direction, as the antenna will give you two readings at 180° to each other. I had it running all evening, without the battery flattening. The RF choke fell off quite quickly, as I had not done a very good job with the soldering. I was also worried that the connection between the RX input coax and the board would break, so I would consider using a small connector in the future (such as an SMA socket). Overall the antenna worked very well, albeit sending us in the wrong direction! In terms of improvements, I would also like to mount the circuit board properly, and put it in an enclosure.

If anyone has any questions, or wants me to bring mine with me on a club night, just let me know.

-Peter Barnes

Cobwebb resonating. Part 2

Posted on 01/08/2015 by Andrew G0RVM

Last week I wrote about recent work that identified where my G3TPW Cobwebb antenna was resonating on each of its five bands (20m, 17m, 15m, 12m and 10m). Following on from that work G0MGM and myself spent a day recently adjusting my Cobwebb so that it was resonant around the SSB sections of each band and this article summarises that work.

The instructions supplied by G3TPW for his Cobwebb are excellent and identify the tuning effect of shortening/lengthening each dipole leg. For reference I have identified these below:

Band	Change
20m	40kHz/cm
17m	50kHz/cm
15m	75kHz/cm
12m	100kHz/cm
10m	120kHz/cm

What the instructions omit is whether the dipoles interact, whether they should be adjusted in any sequence (e.g. 20m before 17m) and the impact of extending/reducing the gap between each dipole leg (spanned by the string) upon resonance. These were all questions that were going through my mind prior to starting adjustment work and which drove the approach adopted.

The reactance, resistance and impedance data presented in Part 1 was collected using my MFJ-259b antenna analyser. The MFJ-259b is a basic analyser and does not have any capability for data logging or data export necessitating the collection of data at multiple manually sampled frequencies. This process was laborious and constrained the number of samples it was practical to collect and thus the accuracy of the overall result. As I foresaw the need to resample each of the five bands for each single adjustment, it clearly, was not going to be practical to use the MFJ analyser. Fortunately, a good friend, G0MGM, has a miniVNA analyser that can auto-sweep a band, log the results and export them in a CSV formatted file, which we later imported into Microsoft Excel. This capability made it practical to capture data samples, visualise and analyse the impact on each band of every change.

All graphs in this article may be enlarged by ‘clicking’ upon them.

Baseline

Because a different analyser was used, two new sets of baseline data were captured with the antenna at 3m and 8.5m above ground. The lower height represents the height of the antenna when my mast is retracted. The baseline data presented in this article is that sampled at 8.5m. Measurements were taken in the radio room at the end of the RG-213 coax feeding the antenna.

It is interesting comparing the baseline results above with those captured previously using the MFJ analyser and presented in Part 1. It should be noted that the comparison was performed with the antenna at the same height, with the same coaxial feeder, but on different days, that the weather was similar and that on both occasions the antenna and its surroundings were completely dry. Furthermore it should be noted scales and colours vary thus some interpretation is required.

Adjustment

Based on experience of adjusting a Butternut HF-6V antenna, now made by DX Engineering, and a need to start somewhere, the decision was made to sequence adjustments from 20m, progressing to 10m.

After analysing baseline results it was decided to adjust the 20m, 17m and 15m elements. Starting with the 20m element we reduced the length of each leg by 2cm and resampled data across each of the five bands. Results showed that the change had a positive impact, raising the 20m resonant frequency by the amount expected with little or no change on any of the other bands. This was good news and was the first indication that there was little interaction between the five elements. We then repeated the process removing a further 2cm from each leg. Again the results were the same. i.e. the change on 20m was that expected and there had been little or no change on the others. The graph below is the final result of the two changes.

Next the 17m dipole element was adjusted, reducing each leg by 2cm. The process of sampling across all five bands was repeated and again it was found that the change had no significant effect upon the frequency of resonance for the other bands. This really gave confidence that each element could be adjusted independently and that no sequence of adjustment was necessary.

Only one change was necessary and it raised the resonance point to the frequency required.

Sticking with the original plan, although it was almost certain by now, the 15m element was adjusted reducing each leg by 1cm. This raised the resonant frequency to that required. This time some minor changes were noted to the point of resonance on the other bands, however, the change was very small.

The changes to 20m, 17m and 15m had necessitated the retying of the string between there individual leg elements. The string between the unchanged elements had remained unchanged and it was now observed that there was noticeably more slack in the wire at the leg ends for those elements. It was thought that this additional slack may be causing the very small changes observed.

With changes complete the results from sampling each of the five bands were analysed and found to be acceptable so again the antenna was lowered and the length of string on the unchanged elements reduced so as to tighten the wires slightly. The change in string length was small but afterwards it was noted the resonant frequency had raised a little on those band elements. This was expected as reducing the gap between each leg end adds capacitance.

The results for 12m and 10m are shown below.

Conclusion

Adjusting the Cobwebb proved to be much simpler than expected. Results showed that each dipole element could be adjusted without impacting other elements and that adjustment need not take place in any particular sequence. It was also found that frequency change per cm as specified by G3TPW in his instructions was accurate.

In writing this article it was realised that it would have been useful to capture the length between the ends of each element leg. i.e. the string length. When these can next be measured I will update this article with the information. Describing the tautness of the elements is difficult. They are neither taut nor slack, but ‘just right’. i.e. there is a little movement of the wire. Perhaps it is better to describe by stating that their tautness does not deform the cross shape of the fiberglass spreading arms.

Key to the success of the adjustment work was the miniVNA analyser and its ability to visualise and log sampled data. Without it, what took approximetly 5hrs would have taken much longer.

Finally, thanks to Rob, G0MGM, for his assistance and his miniVNA and enjoy the bottle of sake 😉

Andrew
G0RVM

Cobwebb resonating. Part 1

Posted on 25/07/2015 by Andrew G0RVM

I’ve had a G3TPW Cobwebb for almost a year but recently its moved location and is now on the top of a Total Mast Solutions 11m pneumatic mast. Because previously it was in a temporary installation I didn’t think much about ensuring that resonance on its five HF bands (20m, 17m, 15m, 12m & 10m) was where I wanted it to be. I just used a manual coupler (aka ATU) to ensure its match to the transceiver was close to 50 Ohms.

The antenna has been performing very well considering its very small size and has yielded worldwide contacts but I decided recently it was time to do some investigative work to see just where it was resonating and thus whether it could be further improved. I have an MFJ-259b antenna analyser which lets me identify the resistive and reactive components at a given frequency. However, and annoyingly, it doesn’t support any sort of automated band sweep or result logging capability. Therefore its necessary to take and record multiple individual measurements then manually enter these into a graphing tool (MS-Excel in my case) to visualise the results.

To provide a reference baseline I captured the resistive and reactive components both with the antenna at 3m and 10m above ground. As the results were similar I’ve included only those results when at the greater height and these are shown below.

Select each for a larger size.

In the coming days a good friend G0MGM who has a MiniVNA analyser has agreed to help. His analyser has two of the key capabilities my MFJ-259b lacks: Band sweep and result logging. The intention is to adjust each dipole individually to achieve resonance just where I want it. However, I’m not clear how the five dipole’s interact, I assume they must to some degree as they are closely spaced, or whether its best to adjust them in any sequence. i.e. 20m before 17m.

In part 2 of this post I hope to report what we found, the adjustment methodology and importantly the results.

Andrew
G0RVM

Field weekend (3)

Posted on 02/06/2015 by Andrew G0RVM

This is the third post in a three part series regarding the late May field weekend of the Thornbury and South Gloucestershire Amateur Radio Club (TSGARC).

So Tuesday arrived. Four days on site had passed very quickly. The final day was set aside for taking everything down, packing it away, clearing the site and getting home. No radio operation was planned. This proved a good choice as it was mid-afternoon when John finally left.

Just like the setup day, we had a good attendance and it didn’t take long for the tents to come down and packing to start. What took time was all the little things like tables, chairs, food etc not to mention the coax, antenna masts and guys… Anyway, by mid-afternoon everything was packed and the only evidence we had been there was the trampled grass. 🙂

The objective of the weekend was not just to setup a station and make contacts but to try things that we could not try at home where space or equipment are constraining factors and to facilitate the exchange of skills and knowledge between club members. Measured against these objectives, the weekend was a great success. Everyone who attended had a good time and the English bank holiday weather was kind to us.

The club was active on 2m, 6m, 12m, 15m, 17m, 20m and 80m making contacts around the world. In total we spoke to 19 countries excluding the UK. We did not generally participate in ‘rubber stamp’ contacts, most lasted several minutes, some significantly longer. The countries worked were:

America
Argentina
Aruba
Austria
Bulgaria
Canada
Israel
Japan
Kenya
Kuwait
Russia
Spain
St. Helena Is
Svalbard
Sweden
Turkey (maritime mobile)
Ukraine
United Arab Emirates
Uzbekistan

The event had 2 x 2kW and 2 x 1kW petrol generators. The intention was to operate 1 or 2 of the 2kW units and the others would be used in case of failure. As it turned out one of the 2kW units failed but the other worked flawlessly so no others were needed. But just having one of the primary generators fail proved how important it was to have backups. The amount of petrol consumed was surprisingly low (approx. 40 litres) considering almost full day/evening use.

Almost everything went well but things of special note are:

site access incl parking
the site location was close to home
excellent member turnout, especially on setup and tear-down days
the chemical toilet
separating the radio tent and social/domestic tent
trailer tower
G-600RC rotator.

Of course there were some things that didn’t go to plan or that could be done better next time:

catering – bring your own food & drink failed
conversations still occurred in the radio tent and were hard to limit
disappointingly low use of VHF despite having some excellent antennas
failure of a primary generator.

As organiser of this event I would like to express my special thanks to the following:

John’s friends for the use of their field (We have bought them a bottle of Pernot and some flowers)
John Laney for the tents and cooking
Graham Clark for petrol
Rob Dodson for his TS-2000
Shirley for the wood burning stove.

Final thoughts

The message from those who attended was that this sort of event is something the club should do again before the year is out. We will have a rethink about catering and try something different next time. Possible options have already been identified, discussed and sound promising.

When we do this next? Well almost anytime is possible, but there is the RSGB VHF Field Day on the 4th and 5th of July and the RSGB SSB Field day on 5th and 6th September. We should also not forget the ARRL Field Day on June 27th and 28th….

Andrew
G0RVM

Field weekend (2)

Posted on 02/06/2015 by Andrew G0RVM

This is the second post in a three part series regarding the late May field weekend of the Thornbury and South Gloucestershire Amateur Radio Club (TSGARC).

The trouble with camping during May is it gets light early! Setup had been a long and busy day but the birds knew nothing of our endeavours and were chirping their happy, annoying song at first light. John (M3EQQ), despite slumming it at the house, was up just as early as the birds and made sure everyone was awake also 😉 To his credit he woke people with a cuppa but it was clear there was to be no sleepy lie-in… Mind you, it was going to be a busy day as there was food, rotor cable and plugs to purchase not to mention the completion of tasks outstanding from the previous day, delayed due to the extended time working upon the trailer tower.

Generally speaking the noise floor at field/portable sites is very low so you can hear almost everything, but making yourself heard is harder. For this event I wanted to make the club heard. I’d heard many good stories and good signals from stations around the world using hex beams, so I purchased a Hexbeam from Anthony (MW0JZE). This was fed with 400w from an Ameritron AL-811XCE amplifier. The result was fantastic, not only could we hear the DX but we could also work it 🙂

A large part of Saturday morning was spent assembling the hex. Yes, it took a while as I was careful to assemble it correctly and as per the YouTube video instructions. The antenna does not come with instructions which is a nuisance but the video instructions are excellent – just accessing them from a remote field is a little challenging… Next time, however, assembly will be much quicker.

After the hex was on the tower, John (M3EQQ) and I went to get the much needed food and cable to replace the damaged rotor control cable. The little castle town of Berkeley has some good shops so food was not a problem, but cable needed a drive further afield. Fortunately there is a branch of Attwoolls not far away and they were able to supply 30m of cable and new connectors. On our return it was clear the other members had been equally busy as we now had a full sized vertical 80m loop and a Beverage receive only antenna for the 80m band. Both the 80m loop and Beverage were connected to Rob’s (G4RNK) Kenwood TS-2000.

The Beverage was the creation of John (M0HFH) who had read much about its ability to overcome noise on the lower frequency bands; the field weekend gave the ideal opportunity to try a 1.2λ, 80m Beverage. Researching the many methods of construction John (M0HFH) came across some old papers published by the BBC research team at Crowley. This gave in-sight into the height of the antenna from the ground and some surprising information, higher is not always better!

The Beverage in various designs has been around since inventor Harold H. Beverage developed the antenna design based on designs used by Edmond Bruce at the Otter Cliffs US Transatlantic listening station in 1919. The antenna used during our field weekend was the simplest form of this design and consisted of a 9:1 home-made balun feeding a long wire (120m galvanised steel electric fence wire) terminated at its far end with a non-inductive resistor into a copper earth stake with 4 x 15m radials. A similar ground plane earth system was set up at the feed end to be the earth point for the coax feeding the radio. The antenna was set at 1.5m above the ground.

We attempted to match the Beverage terminating resistor to the earth system using a method adopted by W8JI which involved measuring the range (not the value) of SWR indicated on an MFJ-259 antenna analyser sweeping a frequency range from 1.8HHz to 7MHz and varying the termination resistor until the variation in SWR was minimised. Kyle (M6KBP) recorded the values of SWR in the form of a table whilst John (M0HFH) varied the terminating resistance using a switched resistance box; communications from one end of the Beverage to the other by 2m handheld. We settled for a termination resistance of 640 Ohms after some discussion of the results.

Listening to weak signals on the lower frequency bands, in particular 160m, 80m, 40m, the Beverage revealed a substantial reduction in background noise and an increased signal to noise ratio as compared to the TSGARC vertical with radials.

Rob (G4RNK) was responsible for the 80m loop. It was made from hard drawn, PVC coated, copper wire about 265ft in length. Its matching stub was made from 75 Ohm coaxial cable a quarter wavelength long, (66%). This matching stub was then connected to 50 Ohm coax which ran back to the TS-2000 transceiver in the radio tent. With a view to working stations to the East (Europe) and the West (USA and beyond!), the loop was orientated to face East/West with its nulls to the North and South. The feed point of the loop was 1ft above ground, the top of the antenna was at 30ft, suspended between to masts, so the mean height of the loop was 15ft for 80 the 80m band. This sort of antenna can be tuned for use on other bands with a transmatch antenna tuner.

The hexbeam replaced the 2m beam on the trailer tower as at 12kgs it needed a strong support. The tower will support something much heavier but the other masts would have been overloaded. It was raised to about 13m above ground where it pretty much remained for the rest of the weekend. Feeding the hex was an Icom IC-7200 and the aforementioned amplifier. The system worked faultlessly and some nice contacts were made, my personal favourite being Tokyo. Lots of contacts were made by myself and the mic was shared with John (M3EQQ) and Kyle (M6KBP). This gave John and Kyle the opportunity to see a capable station in operation and to talk with stations further afield.

Around 20:00hrs GMT about S3 of pulse type interference was observed from the West, this continued till we shutdown just after midnight. Interestingly the interference seemed to start around 14MHz and spread across all higher parts of the spectrum up to 50MHz. Higher frequencies were not checked. The interference was not observed on lower frequency bands – nothing was heard on 3.7MHz using the 80m loop. Swinging the hex to the East also greatly reduced the interference. In the adjacent field on the Western side there is a large overhead power line, but we understood this was not in operation… If the interference was emanating from the power line I would have expected it to hear it on 80m. A mystery, but there was speculation that it may be some farm machinery in the big shed located to the West.

Sunday morning dawned with another early call, cuppa and breakfast from John (M3EQQ). The remaining 10m masts were erected. With these we now had an impressive selection of antenna’s and the site looked great in the sunshine. In total there was the 12m trailer tower, 2 x 10m masts supporting the Tonna 2m and 6m antennas plus 2 x 12/10m masts supporting the 80m loop. With this selection of antennas it was a shame that we didn’t have more radio’s and operators. However, Rex (G4RAE) made use of the 5-element, 6m Yagi making several Morse contacts.

HF propagation was superb, strong phone contacts were had with Aruba on 20m, 17m and 15m, St. Helena and numerous other stations in the USA. It was clear that the hex, amplifier combination was delivering good performance. Band conditions remained excellent till shutdown soon after midnight. The mic was again shared with John and Kyle allowing them to make some excellent contacts. The interference noted the previous evening was not present till a similar time when it returned with exactly the same characteristics.

Shirley, John’s (M0HFH) partner, lent the club her wood burning fire. Its an excellent piece of kit that burns wood exceptionally well and provides lots of surface area on which to cook. So late in the afternoon, John (M3EQQ) started to barbecue chicken and sausages. Whilst we ate the food a friend of Rob’s (G4RNK) arrived with his quadcopter. The quadcopter had a small camera attached and despite it being a little windy good photo’s of the site were captured.

Monday was very different, the HF bands appeared to be in good shape for a few hours in the early morning when we had some great contacts, but soon after deteriorated leaving signals either well down on preceding days or non-existent. Andrew (G0RVM) took the opportunity to run an antenna workshop with Kyle (M6KBP). The workshop started with the basic principles of the dipole then progressed to calculating its size, construction and finally adjustments for resonance and on-air testing. The dipole was made for the 17m band and it clearly worked when compared with the hex. Another Foundation class member, Derek (M6xxx) got involved, helping Kyle with the physical construction of the dipole.

Nighttime arrived and conditions appeared to improve greatly. Again many contacts were made culminating with an excellent conversation between Kyle (M6KBP) and Ray (N4LEM) using his Collins HF-80.

Andrew G0RVM, John M0HFH and Rob G4RNK

Thornbury & South Gloucestershire Amateur Radio Club

Amateur Radio, Ham Radio, TSGARC

Tag Archives: Antenna

The HF antenna…

Antenna Maintanance

Antenna Horizon

Strange problems….

Back to the Future…

Fox Hunting with a TDOA Antenna

Cobwebb resonating. Part 2

Baseline

Adjustment

Conclusion

Cobwebb resonating. Part 1

Field weekend (3)

Field weekend (2)