Hi All,
Looking for some advice on HF antenna setup at my QTH. Currently have an Icom 718 working directly into a 40/20 fan type dipole and whilst RX is excellent, not having a lot of success getting out. I have invested in a basic ATU (LDG 100) and looking to revamp my antenna setup. I would like to be able to work 80/40/20 as a minimum.
My shack is a 50SQM colourbond shed in one corner of the block. The adjacent corner (about 10m away) has a very large tree I can use as an anchor point up to about 12m AGL. The roof of the house is at about 10m AGL and the distance between the tree and the house is about 33m so there is room for a fairly large antenna but the 80m dipole I have is just a bit too long. I suspect that part of the issue I am having on 40m is that the centre feed on the dipole is too low.
Hopefully the group will indulge me with some opinions about the following questions!
1) Given I have a fair bit of room to work with, should I stick with some sort of multiple band dipole arrangement?
2) Is a end-fed type antenna through an ATU ever going to be as effective in this situation as a dipole?
3) Can an ATU on a resonant long dipole also tune for lower bands? I've never used an ATU before so not sure what their capabilities are and whether this is a silly question!
The other option might be a vertical but I am limited in room to run radials. Can the 50sqm colourbond roof of the shed be used as part of a counterpoise in this setup?
Cheers
Marcus
I am sure others will also provide suggestions but I will get in first, provide my impressions against your questions and also a couple of links for you to follow.
"
I suspect that part of the issue I am having on 40m is that the centre feed on the dipole is too low." The height will affect the takeoff angle BUT it should still work ok. Something to try : assess the signals from within VK to those outside VK on receive. That may provide you with an idea as to whether it will work on transmit - i.e. reciprocity. Maybe your 1:1 balun is saturating on transmit, getting hot and lossy.
1) Given I have a fair bit of room to work with, should I stick with some sort of multiple band dipole arrangement?
Have a look at my article at https://www.vk4adc.com/web/hf-projects/4...d-v-dipole but contemplate it for 80 / 40 /20 in lieu. It's short enough to fit the distances you mention.
2) Is a end-fed type antenna through an ATU ever going to be as effective in this situation as a dipole?
End fed antennas will work if they are fed against an effective ground - and - there is a reasonable impedance match in place via an UN-UN device. The UN-UN is mandatory but might be one of 4:1, 9:1 or 16:1.
3) Can an ATU on a resonant long dipole also tune for lower bands? I've never used an ATU before so not sure what their capabilities are and whether this is a silly question!
A dipole is usually only efficient at its basic resonant frequency and any odd harmonics of that frequency. It is also where it will reflect a low impedance making it suitable for coaxial feed. An ATU (eg LDG Z100) will synthesise a match as far as the radio goes but will do so by consuming some of the RF (component losses) BUT the antenna efficiency drops if not at resonance. Lower bands - ATU-matchable ? probably. Efficient ? definitely not.
The other option might be a vertical but I am limited in room to run radials. Can the 50sqm colourbond roof of the shed be used as part of a counterpoise in this setup?
Have a read of post #4 in the topic at
https://www.ahrdf.net/forum/showthread.p...50#pid3250
The 50SQM roof is big enough to act as a reasonable ground plane even on 80M, without adding extra radials.
I have successfully used the Z100 with a combination of Icom transceivers (718, 706..) over a number of years and it is amazing how well it will provide a match to the transmitter to enable it to produce maximum power output. It does not resonate the antenna and that relates back as actual efficiency- i.e. how well it actually works.
I have a set of ray dipoles up in the air at the moment, 160/80/40/30 with a second set for 80/40/30 at about 90 degrees to the first. The height is far less than desirable but I still worked most of VK and a ZL during the JMMFD over the weekend on 40M. I also have various homebrew trapped dipoles too that go portable eg 80/40/20/15/10/6 with a companion set that adds 30/17/12M (this was used for my VK9NU operation in 2016), then the one in the link provided earlier for 160/80/40. You can probably find more details in other articles on the VK4ADC web site.
I have done quite a bit of antenna experimentation over the last 5 years and have plenty still in operation today. I posted the count the other day : 17, and that counts the above multiband ray dipoles as one each ray dipole set. (One of the advantages of a 1.1 acre block - space.)
Cheers Doug - I heard you on 40m on the weekend and tried calling but couldn't ever seem to get through. That was with the dipoles I had setup at a temp field location. I think I have a bunch of options at home, its just a bit bewildering with all the choices!
Marcus
Don't be concerned if I didn't hear you on Saturday. The local static crashes were up to S9 and over for quite a bit of the afternoon, and much of the east coast was similarly being battered by the storm noises. In the brief pauses when there weren't crashes, my s-meter was down around S2-3. Some stations were easy to work, others quite hard.
I was running my IC7400 - so 100W PEP with internal ATU - into my full-size 160 / 80 / 40 / 30 ray dipole set maximised for North-South (where most of the stations were) while the East-West set would have been better to work you. Otherwise our stations were fairly equivalent.
If you were hearing well but not transmitting well then I would harp back to your balun behaving poorly. I had that effect when running FT8 last year while portable - the raw SWR was rising with transmit time as the ferrite core got hot. The heating of the core was such that the ABS enclosure box was reasonably warm and the toroid was mid-air inside. The fix was a bigger toroid that didn't saturate, re-wound and (just) housed in the same balun box. The FT240-61 cores are good up to about 1KW SSB but lower powers on the likes of FT8. Search for FT240-61 on my web site.
One of the best things about AR : you get to experiment.
For wire antennas, check out the September 1984 issue of "Amateur Radio" article titled "Wire Antennas".
AR Mag
I use the one on page 17 under "My Recommendations" A. Multiband General purpose array.
I can't quite fit the whole top section horizontally between two trees. so at each end a metre and a half or so hangs vertically.
My shack is at the opposite end of the house, so I use an SGC remote antenna coupler under the eaves where the antenna is to feed the open wire line. The antenna works well on 80/40/30/20m but lesser so on the higher bands due to the additional lobes.
Wow lots to read and making headway through it all now. Got the laser out today and measured the trees and distances. If I run a standard dipole (unsupported in the middle) I can get each end of the dipole to about 9m AGL and I can support a maximum length of ~ 30metres. If I bend (drop straight down) the last 5m of the dipole closest to the shack then I can fit a 80m dipole but it will be unbalanced - one end will be turned down and the other end flat.
I was thinking of building a 80/40/20 fan dipole and just folding one end of the 80m element but with no centre support for the balun this tends to sag a bit and the centre is sitting at about 6m instead of 9m so it isn't ideal.
If instead I centre support the balun I can get it up to 13m in the tree and use an inverted V approach but the centre point would not be in the middle of the 30m length I have to play with - the tree is close to the end of the block so no way I can fit the 20metre legs for the 80m element. I can probably fit the 15m legs of a G5RV though and this would seem to be a good compromise option.
Q: With an inverted V (either dipole or G5RV) I know the included angle in the V needs to be greater than 100 degrees but how critical is it that the angle is even? Because the tree I am using is close to the back of the block, I would need the northern leg of the dipole to be a fair bit steeper than the southern leg. The included angle would be about 120degrees but it wouldn't be symmetrical.
Is that likely to work?
It will work, and on 80 & 40m you don't need much to put out a good signal for local use.
The usual thing, get the antenna as high as possible and ideally symmetrical i.e. if the horizontal section won't fit, have the same amount hanging down at each end, but on 80 & 40 I suspect you won't notice much if any difference.
There is also the Carolina Windom to consider, which is an off centre fed dipole, which may be a better fit for your block.
Welcome to the world of antenna experimentation! My XYL asks me when will all this playing with wire stop? Probably the day after the guys in black suits put me in the van with dark windows and cart me off to the chiller!
You should also consider a horizontal loop in a triangle shape (sort of is OK). Can be fed with coax with a 2:1 balun at the feed point, but I got the best results using home made open wire line down to a 4:1 balun just out side the shack wall with a short length coax through the wall to an external tuner. Mine was only 8m high and a full wave length long on 40m. Worked very well on all bands between 40-6m and reasonably well on 80m. Shorted the feed line and loaded it against ground for 160m. Much lower noise than a vertical. If I had the right configuration in my present yard it would still be my HF antenna of choice.
Have fun, but remember there is no cure for becoming a TAWAN.
73
Wayne VK4WDM
OK I will bite Wayne.
Whats a TAWAN?
Wayne...
And I thought you were TIWAE
( Totally Into Wire Antenna Experimentation )
Far from being a Novice / Newbie..
(21-03-2019, 06:05 AM)VK4ADC Wrote: [ -> ]Wayne...
And I thought you were TIWAE
( Totally Into Wire Antenna Experimentation )
Far from being a Novice / Newbie..
Totally Addicted Wire Antenna Nut. Anybody need useless lengths of used wire there are plenty in my shed.
(19-03-2019, 07:35 AM)VK3RX Wrote: [ -> ]For wire antennas, check out the September 1984 issue of "Amateur Radio" article titled "Wire Antennas".
AR Mag
I use the one on page 17 under "My Recommendations" A. Multiband General purpose array.
Thanks Damien,
Unless I am reading it wrong, that multiband array looks a lot like a variant of the G5RV. The total length is 25m compared to the ZS6BKW variant's 28m and the original G5RV length of 30m. The feeder length is 12.5m compared to 11.7m for the ZS and 10.3m for Louis' original design. So it is, in effect, shortening the length of the horizontal component and lengthening the vertical component of the ladder line.
The smaller 3m in total length would be helpful but I only have 14m below the midpoint for the feeder to hang so @ 12.5m in length it means the transition to coax is happening at head height which isn't ideal!
Bob lost me at 'Hey, what's up?"
I have built a multi-band dipole arrangement like KK4DVs in the past, using a similar spacing wire to wire ( 4" / 100mm) and the greatest issue is that the wires are too close and the interaction while tuning each dipole is enormous.
My current multi-wire dipole set(s) arrangement is a hang-down style. The lowest frequency dipole set supports the next lowest by allowing it to hang down below it. The next band hangs from it etc.. and you can adjust the hang-down connection distances to set the amount of droop for each dipole set. The ends have 100mm spacing to the wire above and a tensioning arrangement to keep this end spacer basically vertical. Mine are made from 3mm stainless steel wire (so no stretch) and the wire goes through the hole in an egg insulator and is then clamped back along the incoming wire with a 3mm wire grip. The S/S wire is not trimmed off at all during trimming to frequency - only the wire grip(s) are released and the wire foldback is adjusted, also resetting the hang-down point as needed.
You
must start with the lowest frequency (the supporting dipole set) and then work up in frequency (so hanging sets) as you tune the antenna
at the final working height. The values available from my web page (
https://www.vk4adc.com/web/hf-projects/4...na-lengths ) will give you a good idea as to how much to adjust the wire fold-back length once you have measured an initial resonant frequency for any particular dipole set.
By adjusting for more dipole droop (ie. spacing) , the interaction is reduced band by band.
A final note is that select which bands you want dipole sets for with care. Do NOT pick directly ODD-harmonically related ones. Don't forget that dipoles will work at odd multiples also.
So picking 160 / 80 / 40 / 30 is ok (even multiples) but avoid 40 / 20 / 15 (mix of odd and even) as the tuning interaction makes it hard to solve.
For odd plus even go to trapped dipole arrangements.
@ Doug VK4ADC - any issues with using the stainless wire? I have a 40/20 dipole constructed basically the same way as you describe but with 2mm wire. The 20 is suspended beneath the 40 using 8" lengths of 15mm conduit to provide a standoff. VSWR on the 40 is about 1.4:1 and VSWR on the 20 is about 1.6:1 so not perfect but tunes up easily.
A few people have expressed surprise that I used SS wire - apparently it is the source of all my woes? I reckon the lack of height and a bit of a messy installation is more likely the culprit but curious to hear your experiences with the wire?
Marcus
Back before I moved semi-rural I used copper wire for my HF wire antennas, mostly insulated and of varying wire gauges. One of the things that became apparent over many HF antennas over the last 40+ years has been wire stretch - particularly during storms and high winds.
I used to keep a page with the SWR minimum frequencies and I would update it from time to time and note the frequencies slowly dropping - except after a storm, when the drop was more noticeable. None of the copper wire was hard-drawn and varied from hookup wire to building wire. The stretch factor applies to all of them.
Every so often I would either shorten to re-tune or replace the wire completely figuring that it was likely to snap eventually.
I put up the existing sets (160/80/40/30 and 80/40/30) about 5 years ago now and have not noticed any frequency shift. I was using my East-West mounted set when you heard me on Saturday so it must work.
I can't quote minimum SWR values but I typically aim for 1835, 3610, 7110, 14190, 18135, 21190, 24920 and 28470 when I am tuning my HF antennas and try for minimums at those frequencies.
The final SWR is not critical as when you analyse the height above ground scenario, your antennas are usually lower than optimum to get the 50 ohm centre-feed impedance that results in a 1:1 SWR. Different bands = different optimum heights so SWR is usually never perfect on every band. One maybe, others will be variable. Unless, of course, you can get the whole array more than 10 wavelengths above ground at the lowest frequency.... ( let's see : 800 metres above ground at 3.5MHz
)
Stainless may not be optimal as a conductor but it does have the other physical advantages as mentioned. The 3mm as a 7x7 is what I use most now.
A postscript about using s/s wire: make sure you include a "weak link" in the supporting arrangements. The wire won't break if a large branch flies through the air and lands on it (or a tree falls over !) but you don't want the antenna supports to be damaged, particularly if one (or more) end(s) or centres are at a house or tower. I use a length of 3mm 'handycord' on my dipole-set centre-support halyards as a mechanical 'fuse' and it becomes the purposeful weak link.
VK2BT published an article about why Stainless is a no-no for dipole antennas here:
http://www.mwrs.org.au/2011/06/23/antenn...vs-copper/
As with everything in this hobby, it seems you can find diametrically opposed (and well argued) points of view on just about any subject and its hard to know whom to believe unless you have done extensive experimentation yourself!
I really like the idea of using stainless, it solves a lot of mechanical issues for me and has the added bonus of being cheap and easily found. I had been working on the assumption that the stainless was a big part of the poor antenna performance largely due to the article above but if that isn't the case then I need to look elsewhere.
I think what I am going to do over the weekend is put up a pure 40m dipole using 14AWG copper in parrallel to my stainless 80/40. Using identical baluns and cabling, I am going to do some A/B comparisons and see if there is an actual noticeable difference in performance before I go any further with this...
It is worth noting that almost all the commercially-made ham and military antennas currently being produced use SS wire.
Wayne VK4WDM