Vortex Q82 (Sigma IV for the 21st Century)
Well a few years of occasional dabbling and trying to resuscitate the old Hustler 5-BTV (to no avail) since moving to Brittany as well as enthusiasm to get a better antenna for 10m prompted ordering a new vertical.
Back in the day the Avanti Sigma IV was THE antenna for 11m SSB or 'Freeband' and worked pretty well on 10m as well! Sirio have produced a Sigma IV imitation for quite a while but with a poor reputation for strength and build quality is a concern with the worst that a Brittany winter can throw at a fairly tall antenna on occasion so I took the plunge and ordered the new Q82 from highly regarded Vortex Antenna Systems in Peterborough. Early reports suggest this to be a damn fine bit of kit and as an 'old sidebander' from 11m days it'll be fun to try this out on the under used 10m band.
The antenna is currently ground mounted near some trees (far from ideal I know) but fed with Westflex and I will doubtless continue to 'dabble' with set up, radials, earthing etc. for best results.
Well the Q82 arrived in a pretty big box, arrangements had been made with Steve at Vortex for the antenna to be shipped to my folks house in Cornwall while I was visiting so I could then take it back on the roof of the car to 'belle France'. Despite the efforts of the courier (who delayed things and damaged the box!) everything went to plan and a large selection of high quality aluminium and stainless steel components arrived and were duly re-packed onto the roof bars and taken back via Brittany Ferries. There was a slight delay in proceedings due to work commitments but at last the build got under way and my its a beauty!! The antenna is now ground mounted at the top of the garden and guyed! Only one or two minor issues were experienced with good old nylon lock nuts (which I have always hated!!) one of which jammed (lower mounting clamp) and no amount of heating, twisting and cursing would free so in the end was cut off and replaced with a conventional nut and lock nut of the appropriate size to the remaining U bolt tail, sorted! The antenna is a big old unit but clears the nearby trees and judicious help from a couple of 'chums' (thanks Eddy and Kevin!) got the aerial vertical and secured in place. We have not had any winds of note since but with the three way guying in place I don't see it moving! So far so good, I guess its in the eye of the beholder but I think he looks superb, JJ calls it 'the pylon'!! Initial tuning and fettling to start now :-)
Well at long last a gap between working silly hours and having the "outlaws" to stay has allowed the tuning in of the new Q82 and connecting into the shack with Westflex (and the appropriate connectors) and at last give the 'pylon' (as it has been christened by my wife), a run on 10 metres. After a couple of 'local' contacts in Switzerland and Croatia it was time to venture a little further afield with a good 59 into Florida, closely followed by 56 into Uruguay and then spend a little time to break a monster of a pile up for VP8VPC Bob McLeod in Port Stanley in the Falklands, by my reckoning that's over 7600miles across the equator with my splendid new vertical! For a first outing on 28MHz it has acquitted itself well and more than surpassed expectations. In direct comparison to the G5RV the wire is quieter in terms of background noise but generally the Q82 is pulling signals in better, doesn't need a tuner and on 10metres at least seems to be getting out better. As the old adage goes, there's no substitute for getting plenty of metal up in the air!!
Further experimenting and 'tinkering' has moved the 'sweet spot' further up the frequency (I listen but seldom transmit on CB frequencies so AM/FM/SSB on CEPT and even FM on MPT1320 is not a big issue for me). Being ground mounted it seems the antenna likes wet weather best the band spread and SWR being lower in wet and wintry weather, which suits Brittany pretty well for a lot of the year!! Other than that though the antenna is currently tuned as follows (readings from Yaesu FT1000MPV internal SWR meter):
SWR without radials: AND SWR with radials (see below)
- 24.950MHz (12m SSB!) => 1.70 SWR (well thats not too bad!!!)
- 26.965MHz = 1.80 SWR => 1.70 SWR
- 27.405MHz = 1.95 SWR => 1.75 SWR
- 27.555MHz = 1.90 SWR => 1.75 SWR (naughty!)
- 27.601MHz = 1.80 SWR => 1.70 SWR
- 27.991MHz = 1.50 SWR => 1.25 SWR
- 28.350MHz = 1.45 SWR => 1.35 SWR
- 28.500MHz = 1.30 SWR => 1.30 SWR
- 28.580MHz = 1.30 SWR => 1.50 SWR
- 29.100MHz = 1.55 SWR => 1.55 SWR
- 29.600MHz = 1.55 SWR => 1.55 SWR
Well, one very soggy June day (!) in 2019 and finally got around to installing some radials. These comprise base mounted heavy gauge copper wire 1/4 wavelength each based on 28.5MHz and installed diagonally/at 45 degrees due to site limitations (its installed near a hedge!). One thing that seems to have come about though is that the SWR has generally reduced giving a yet greater bandwidth! It probably helps as I've already mentioned that the weather has been very wet this year (2019) and being ground mounted it increases the effective ground plane efficiency (or maybe I'm just imagining it!). What I didn't expect though was that I no longer needed to use the tuner to get decent tune on 24MHz, yes the band width really does seem to be that wide!
Without the radials this amply bears out the manufacturers indicated 1.80MHz bandwidth, in fact more than..., unofficially I had tested down to 25.650MHz and up to 30MHz with sub 2.00 SWR (Thats better than 4MHz..., the SWR peaks and dips once or twice in that range but never goes over 2.00). Which has to beg the question if I moved it lower down the band how low it could go.
There is now a 'new improved' Q82 mk2 which will genuinely tri-band for 12m, 11m and 10m and that would be interesting to try! It is claimed to have a massive bandwidth of 4.37MHz ..., I have a sneaking suspicion subject to mounting and testing it could do even better, especially when the ground is wet!! Adding the radials gives a yet further improvement in bandwidth and state of tune and this equates now to something in the region of 5.7MHz!!! It will go down to 21MHz but only with the tuner.
There has been a temptation to put the Q82 onto a scaffold pole and lift it higher but I somehow suspect with the surrounding trees I'd only find a significant improvement if I put it onto the house gable but access is difficult and it would expose it to some pretty significant wind loadings so maybe not! Also referring to the article mentioned above by PG0DX (see below) it may give marginal improvement but less of an enhancement relative to any other similar vertical.
Anyway there is a copy of the original Avanti Sigma IV advert below as well as one from a period Dutch CB magazine. Also a photo of slightly windswept roof mounted one! I wish I had a photo of the neighbours I used to have in 1982 who had a Sigma IV mounted on the roof eaves just downhill from our house, also Mick, Cockney Rebel who had one on the roof of his bungalow! Now if only I could track down a 6 foot Avanti Moonraker mobile antenna...!!
There is an excellent article giving an assessment of the Sigma IV and its successors online by Henry Poelman PG0DX / 19PA348 which gives a lot of very technical information on the design and performance of the antenna and gives a few interesting suggestions. These include doing away with the Gamma match and direct feeding the antenna (?) also that being ground mounted using four radials will offer an improvement (see above) and, of course, including an RF choke wound out of co-ax to prevent the feeder becoming a radiating element (already installed on mine). He indicates as well that as you add height the gain or improvement over a conventional vertical becomes less so mine will remain ground mounted; after all the original advertising actually suggests it (see above)!
PS. Here was a temptation (mid 2019), an original boxed Avanti Astro-Plane advertised on Charlie-Tango with couple of other bits and bobs for £60 but with a really good Sigma IV replica already in the garden rather difficult to justify!! Incorrectly dubbed by CB friends in the 1980's as a Sigma 2 (which is actually something different again - see Dutch advert above) but by all accounts a good aerial. I hope someone gives it a good home and enjoys it!