Category - M0XXT Archive

Supported Bands

• • 160m
  • 80m
  • 40m
  • 30m
  • 20m
  • 17m
  • 15m
  • 12m
  • 10m
  • 6m

Description

Nearly two years ago, we decided that we needed a better antenna for all band operation to replace our traditional use of wire dipoles. Unfortunatly we do not have the option of putting up many towers with a large quantity of yagi’s so the antenna had to be visually low impact, cheap, all band and allow us to be competative in contests.

Callum M0MCX and James 2E0YOM (now M0YOM) began researching various options but nothing appeared to fit the bill. The basic 1 wavelength loop was the obvious starting point as this provided the potential for all band operation.

After many hours of research, modelling and experimentation we discovered that the use of horizontal triangular loops would provide us with the antenna we needed. Traditionally this shape of loop is used in the “Delta Loop” configuration and is widely believed to be a good NVIS antenna when mounted horizontally and a DX antenna when mounted vertically. We discovered that this is not always the case, when the loop is small <=1 w/l and low to the ground it behaves as you would expect and is a reasonable NVIS antenna, one you start getting to sizes of >=2 w/l at over 1/4 w/l above ground then the loop starts to exhibit some very high gain at low angles.

After building smaller versions of the Megaloop we realised that our location contained 3 tree’s perfect for the support of a full top band megaloop at around 20-22 meters.

The loop is constructed from approximatly 174 meters of 14AWG hard drawn enamelled copper wire and is fed via a 2Kw 4:1 Balun using Aircell 7 coax.

For further details of the Megaloop and it’s construction go to the following links

The basic 80m loop

Firing supports over trees

The 160m Loop

160m Analysis

The megaloop is a little over a full wave length on 160m and only 1/8th of a wave length above ground so as you would expect it behaves as a traditional NVIS loop, this works excellently for inter-G or close in european stations with some occasional DX. The modelled SWR curve shows a slightly high SWR throughout the band however the real Megaloop exhibits a much better SWR of around 2:1 although this is probably due to losses in the balun we are currently using as this is not rated for 160m.

Modelled Properties

Modelled Far Fields

80m Analysis

Performance on 80m is excellent for inter-G and EU with excellent gain for single hop central europe contacts. Low angle gain is also reasonable with similar performance to a high dipole at around 15 degress, NA contacts are not unusual with some occasional other DX. Modelling of SWR shows a fairly usable curve however the real world curve is much sharper than this and the antenna becomes unusable above 3.65, this currently requires a tuner for operation across the whole of 80m and we are working on an auto switching matching network for 80m to remove the need for a tuner. The megaloop starts to exhibit some directivity on 80m, with a slight tendancy towards the side oposite from the corner being fed.

Modelled Properties

Modelled Far Fields

40m Analysis

40m is where the Megaloop really starts to come into it’s own, gain on this band peaks at 10.4dBi with a relativly low angle of radiation. The horizontal pattern shows that although there are some slight nulls in places these are not too deep and still very workable. Contacts to anywhere on the globe can be expected. The modelled SWR shows the curve to be slightly high in the band, in practice the SWR curve is less than 2:1 over the entire band, this is probably due to slight modelling inacuracies. The antenna is excellent on 40m for smaller contests/DX/Special events however for larger contests its omnidirectional pattern and lack of FB can prove problematic and a directional receive antenna may be usefull in these situations.

Modelled Properties

Modelled Far Fields

20m Analysis

The Megaloop performs very well on 20m, with a maximum gain of 13.56dBi at only 13 degrees the DX potential is superb. The modelled 2:1 SWR curve covers the whole band and is confirmed by real world measurements. The far field pattern begins to exhibit some deeper nulls on 20m and it does have some dead spots. It is excellent for smaller contests/DX/Special events however the larger contests can be problematic because of the lack of FB, using a directional receive antenna would be beneficial.

Modelled Properties

Modelled Far Fields

15m Analysis

On 15m the pattern starts to become more unusual with some extremely deep nulls, the SWR curve is good for the whole band however there is some discrepancy between the measured SWR and the software models, probably due to minor modelling errors. When propegation exists in the direction of the lobes performance is excellent offering very low noise levels and giving a high S/N ratio. However due to the deep nulls a small Tri-Bander at 10 meters will sometimes outperform the loop if the propogation falls within its very deep nulls.

Modelled Properties

Modelled Far Fields

10m Analysis

The modelled SWR curve on 10m is slightly high, however in practice the 2:1 curve is good for the whole of the CW & SSB portions of the band. The far field pattern begins to get very messy on 10m, probably due to the size of the antenna, however gain of 14.4dBi is present at only 7 degrees with a double peaked front lobe. The potential for excellent DX is good however not much real world experience of the Megaloop on 10m exists due to poor propogation over the last 18months.

Modelled Properties

Modelled Far Fields

My thanks to Lee (G0MTN) James (M3YOM) Terry (G4MKP) and Aidan (M6TTT, Scout) for getting our new station on the air for a first-time-out on WPX.

We also roped in Chris and Dan, two new foundation student contest Scouts for the spotting on the Mult Station. Barry M0DGQ also gets a big thank you for supplying hundreds of meters of 75 ohm coax for James’s stub-filter project and Charles at Moonraker for sponsoring the large number of required PL259 and T pieces.

We ran a pair of very old Yaesu FT1000MPs (non-Inrad versions) which were completely swamped by QRM to a number of interesting antennas including our new super all-band Mega-Loop (horizontal delta loop at 85 feet) delivering about 12dbi on 20m to US at 10 degrees elevation (more on higher bands). However, it also delivers 10dbi to EU and most of Russia at a very low angle, hence QRM flooding. James’s stub filter project worked but still needs some tweaking. Thanks to K1TTT for helping James get his head around this. Next time, James will have finished Bob Henderson’s filters as well which should sort out any final interference between bands. Poor James soldered nearly 100 PL259s last week. Don’t worry James, fingers should re-grow by CQWW!

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2008 will go down as a wet year. Both VHF NFD and SSB FD was a soaking experience. Luckily, as with most close knit teams, we laughed it off and worked through it, however a tough act all the same. I didn’t take too many photos due to the extreme wet weather however I managed to get a few in the can for the memory box. I uploaded them here:

Arriving at the site on Lunchtime Friday, I got the tent up in a complete hurricane. Stripped to my shorts and a T-shirt in the driving wind and rain and all on my own, at one point I just burst out laughing at my predicament. The only thing that kept me sane was the knowledge that some other crazy people in other parts of Europe were also following my example and getting their stations worked up.

Finally at about 15:30hrs, I had a tent up – and all the tent pegs used up, a sure sign that I had screwed the thing hard into the ground. Sporadic rain continued as Terry and James arrived to part assemble the A3S.

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This year, James and I ran M0XXT at the Scout Hut using a pair of XXT Mega Loops; a full size 160m version and a half-sized one which suited the top end of 80m and 10m. Full-sized Mega Loops don’t work on 10m. I ran out of time to put up a TX vertical for top band, even though I did finally finish making it ready for tuning by Saturday morning during my “off” times at night. Another job for next year.

RF was via one of our FT1000MP radios and amplified by an ACOM. A pair of Dell PCs running N1MM did the logging. We networked the PCs for disaster recovery purposes and used the second copy of N1MM on the spare PC a couple of times when RF shut down the run machine. We were Multi-Single.

The antennas really worked miracles, showing almost unbelievable gain which in the main distil to 6 equally spaced compass fingers or lobes – with the main RF being squirted at around 290 degrees (since it’s slightly twisted off it’s X axis due to the perfect location of the local oak trees for USA propagation). I won’t bore you with the compass bearings, it is suffice to say that these RF fingers cover most high density population areas of the globe. The whole topic of these XXT Mega Loops needs a chapter to themselves and as I write this on Monday evening, I can report that this afternoon I ran a huge pile-up to the west coast US at about 16:00z, at one point switching the amplifier off and continuing to run the pile up with 10 watts (!) which reduced our average incoming signal report to 5 and 7 from 20dB over S9. Even on 40m, the gain figures are healthy with 5dB at 10 degree take off angles to the US. 80m is just a big bubble of RF but with the antenna at 90 feet elevation, at least the bubble has some flatness to it. Same with 160m – hence the idea of a massive vertical.

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Collectively, we have extremely limited experience with VHF. It came as quite a shock to the system to score so few QSOs relative to HF contests that we enter; we are used to scoring 1,500 contacts in a weekend. I must say that the turn-out felt positively low. Is this really the state of VHF contesting in the UK..?

Our location couldn’t get better for a Midland club; 1,000 feet high with easy access on private land (IO91bx [edited, did say IO92bx..!]). The weather was a different story with both the consistent rain and very high winds contributing to some scary moments. Why all three antennas were still standing on Sunday morning, I can’t understand however the guys, stakes or poles didn’t move an inch. Perhaps a testimony to all my recent knot learnings at the Scout Hut!

With limited resources on VHF, most of the gear had to be procured recently to enter this event including a 17 element Tonna and a three element Moonraker beam for 6m. A couple of months ago, we bought a strange X-Quad affair for 70cms which after completely stripping down and rebuilding last week, appeared to work well but we have no way of comparing it to anything else. [Edit: since found out this is a Jaybeam Multibeam, 48 element 12dbd ATV type antenna circa 30 years old]. At 2m long with zillions of elements, I trust it’s as least as good as the Tonna is on 2m. Time will tell. Again, we had to get equipped with rotators so we bought a TV style rotator for 6m and acquired a Hirschman rotator when we bought the 70cms antenna. The Yaesu G450 is permanently attached to the hydraulic tower for the 2m station (normally running an A3S). Coax was also a stumbling block, particularly for 70cms where we only had 50 watts available to us and potentially lots of loss on our standard cut of Westflex, perhaps too lossy for 70cms? A 30m length of Ecoflex 15 was despatched from Diode with matching connectors last week to compensate.

The line-up ended up with FT-2000 on 6m at 100w with a 50m run of Westflex to a 3 element beam at 10m. For 2m, we ran TS-2000 on 100w via 30m of Westflex to the 17 element Tonna at 10m and a pre-amp at the rig end. For 70cms, we ran a further TS-2000 which is factory throttled to 50w through 30m of Ecoflex 15 to our weird X-Quad type antenna at only 9m. Perhaps a small linear for 70cms next year and a pre-amp? A bigger 6m beam will be discussed for next year too.

Logging was exclusively N1MM on Dell Optiplex machines and 15 inch flat-screen monitors without networking enabled due to running separate serial numbers for each band. One Optiplex blew up on Sunday morning after refusing to boot due to condensation we think. We had shut the station at 2:00am for 4 hours to get some sleep and upon waking up and restarting the generator, James discovered an issue of the PSU. Hilarious at the time because when it was plugged in, it sounded like a crunchy plastic pop bottled being scrunched up and I’m shouting at Tim to take the plug out. But like the boy who always cried “wolf”, Tim’s got wise to my practical jokes and really thought I was scrunching up a plastic pop bottle and refused to cooperate. A final “bang” from the PSU convinced him that perhaps this time, I really was telling the truth! Very funny.

Before the off, Tim’s testing proved useful on 6m scoring a number of interesting DX entities, including 7X2RF from Algeria – which enlightened some passers-by who were amazed at what we were doing. I nearly sold two more Foundation tickets!

At 15:00hrs local time we started in anger with myself on 70cms, Terry on 2m and Tim on 6m. Having James and Aidan as rotation operators meant that 70cms didn’t become too onerous (50 QSOs in 24 hours..? Ugh!). Massive thanks to Aidan from the team here; he attracted at least 50% of our score on that band, refusing to give up and logging each contact in a determined and professional manner. This was Aidan’s first time on a contest and he’s just 12 years old. May I take this opportunity to thank those stations that recognised Aidan’s youthful voice and his achievement on this band, you stuck with him to ensure a 100% completion for each QSO. Aidan is currently under guidance as part of his foundation license and to be schooled in contesting so early, we think was marvellous. Thanks to all who helped him. Let’s be clear that he had guidance for each QSO and not left to his own devices.

As a “restricted” entry, we couldn’t use brute force to open any doors and it therefore is a slight embarrassment to only have logged 156 QSOs on 2m, 48 QSOs on 70cms and circa 95 QSOs on 6m.
The “magic” band did prove to house some interesting DX from North Africa through to the deep Mediterranean but 2m and 70cms held back offering us no more than 600 km contacts and then very infrequently. Most QSOs were inside the UK although 21 large squares were worked in the end from Ireland through to Germany.

The weather attempted to dampen our spirits but with such strong characters in the tent, we made our own fun and had a ball all the same. At dinner time, we turned the volume down on all three sets and sat down together for our evening meal. I had cooked a top-line Spag-Boll and Terry had us wash it down with a few bottles of bubbly. Fabulous atmosphere.

We were amazed at some of bad signal quality issues being produced on mostly 2m and 70cms; warbley modulation and severe splatter in the main. In one case, we had a couple of polite conversations over a period of a few hours regarding a particular club’s 60Khz splatter until they finally believed us and turned down the wick. I realise that Open class stations might adopt the AKR attitude, “All Knobs to the Right” but for the rest of us, even stations 60 miles away can still be 30db over S9 and this can spoil the fun when the signal isn’t as clean as it should be. Please check your equipment before the contest.

No real issues materialised bar some water in the 70cms feedpoint which was fixed by a wild guess. Dropping the mast and pouring it out and resealing it for another day had us back to full power. The PSU which blew up the 70cms Optiplex didn’t hurt too bad but dropped the 2m station for 10 minutes while James and I recovered the data by swapping out hard drives – just as Terry finally scored a small run into Northern France! The new tent, “Battalion HQ”, held up well to the weather, only developing a couple of extremely minor leaks after continual battering rain for 24 hours. With its huge side-pods, it really became a massive area to work in allowing a full kitchen in one area and an operations room in the other with a dining room for 6 people. We’ll roll this out again for SSB Field Day. Trust you’ll be there?

Results:

6m            95 QSOs           45,847 points       Best DX UT3UA – 2251 Km
2m          156 QSOs           27,819 points       Best DX  F4CQY/P – 640 Km
70cms      48 QSOs             5,066 points        Best DX  PA6NL – 411 Km

Operators:

M0MCX (Callum, Supreme Commander 4th Quadrant)
G4MKP (Terry)
M0URX (Tim)
M3YOM (James)
Aidan (Foundation student)

There is some mild debate in the team if we’ll do this one again. I’m told that VHF can be fun with some lifts into the continent but maybe Silverstone, Wimbledon and perhaps the rain damped that down – as did lift conditions I think.

I’m amazed that with all those FT847s and TS2000s sold, few operators perhaps even knew to turn on their radios for an hour and work a few of us /P stations on 6m, 2m and 70cms. However, we did work a few vertically polarised stations quite easily who were giving away single digit points and I thank those stations for coming on since we worked hard for every QSO. It’s really quite easy to score a few QSOs from home with a V2000 style tri-bander vertical. Someone, somewhere should fly the flag for this since hundreds of private stations could have helped make this a bigger event.

Cheers-n-beers,

Callum (M0MCX)

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