Quick question, and hope it hasn’t been done to death in previous threads, but not that I could find by doing a search…SOTABeams BandSpringer counterpoise length.
I have a BandSpringer which I wish to press into service and apart from a short play with it I have done nothing serious with it as yet. I intend using it with my IC-705 and an EMTECH ZM-2 matching unit. Now SOTABeams quote the length of the radiator and the counterpoise as both being ‘approximately 42 feet’. I haven’t measured the exact length of the two wires as yet but intend doing it tomorrow. However, when looking at random wire lengths in use here and from other forums the most popular lengths appear to be 41’ radiator and 17’ counterpoise. Why is this? Has further science come out since the introduction of the BandSpringer suggesting 41’ and 17’ a better performer? Should I be using a shorter counterpoise on the BandSpringer and maybe trimming a foot off the radiator? I am just trying to understand the logic behind the choice of the two lengths.
I have just moved QTH yesterday and as such have no permanent antennas set up and am still struggling to find sufficient radio gear to even set up a portable station from all of the unpacked cartons…apparently setting up the radio shack is the lowest priority according to my dear wife…enlightenment has yet to touch her Tomorrow night I would like to participate in Go QRP Night on 80 meters and Sunday I would like to activate a summit. I am thinking my chances on the summit are getting pretty slim.
Anyway, if anyone could throw some light on the disparity of lengths between the BandSpringer and the more commonly chosen lengths of recent times I would be very appreciative.
Hi,
The Hitchhiker’s Guide to the Galaxy clearly states the answer is 42. The 17 ft thing is an approximate quarter wave on 14 MHz. It is likely a fail on other bands.
Use whatever you tuner is happy matching and let the propagation take care of the rest.
One of my favorite subjects the band springer. I used one for quite a few activations in early SOTA days. The ZM-2 will tune it for you I was messing with one the other day. But as you may know Richard came up with the design on the band springer and did a lot of his summits with that antenna. The 41 foot ops usually have a 9 T 1 balun in the circuit as well and have great success with them and internal tuners on there radios. I have tuned the 41 footer on my ZM-2 with no balun and with a balun in line also but did not make enough QSO to compare. The thing to remember when you see guys on You Tube making contacts their chasers usually are with in a closer in foot print than we have in VK for instance and there are more of them. You might be ok in ZL and have lots of chasers as well that is why I mostly use a link dipole for SOTA to put out the bench mark signal as apposed to a random wire as the band conditions slowly died down during the last cycle. Give it a go is all you can do and if everyone can hear you thats great. I would have my link dipole in the bag with me though HI.
Hope I can chase you when you go out.
Regards
Ian vk5cz …
Yes, that’s true. I don’t think I’ve used my 41’ EFRW with any other tuner. I found out yesterday when I forgot my 9:1 that it will work without one (but only just on 40m).
So that makes the antenna a random (length) wire doublet. Which can be tuned on many bands.
If you use a much shorter counterpoise then it’s starting to look like an EFHW (End Fed Half Wave) on some bands and will have a very high impedance so you will need either a really good tuner or a 7:1 feed point transformer which some people call a balun but it isn’t really (technically a balun doesn’t change the impedance it just converts from balanced to unbalanced).
You could wind a feedpoint transformer (search this reflector for EFHW) and then try the bandspringer on each band both ways.
When Wayne introduced the KX2 during my annual SOTA lunch, he used a 13’ CP. When he introduced the KH1 at last years lunch, he used the same length. I have seen 17’ cited many times, and that’s what I use with my 41’ EFHW, 4:1 balun and KX-3. Never a problem from 80 to 6m.
I’ve used a Bandspringer with an IC-705 on many activations, using the Icom AH-705 tuner. I agree the length of the “counterpoise” seems a bit odd but I’ve been heard in VK and VE and elsewhere with 10W so it works.
I read somewhere that it isn’t a traditional counterpoise but I can’t remember what term was used to describe it.
OK, I did a little test today. Not definitive but possibly informative.
Setup: BandSpringer in L-configuration on a Spiderbeams 7 meter mast.
Counterpoise aligned under the radiator:
Band
SWR (KH1)
SWR (KX2)
40
1.5
1.1
30
2.2
2.9
20
1.7
6.5
17
2.5
1.1
15
1.5
3.3
Counterpoise 90 degrees from radiator:
Band
SWR (KH1)
SWR (KX2)
40
1.3
1.1
30
2.2
1.0
20
1.0
6.7
17
2.4
1.2
15
1.7
2.5
Counterpoise 180 degrees from radiator:
Band
SWR (KH1)
SWR (KX2)
40
2.2
1.3
30
1.9
1.0
20
1.2
4.9
17
2.5
1.0
15
1.7
2.9
I’m suspicious of the KX2 20M tuning and am going to check to see if all my tuning relays are working.
As a last experiment I set up a plain old random wire that started at 40 feet in length, using a 25 foot counterpoise. I kept trimming off bits of wire until it was 35.5 feet long. This turned out to work really well for the KH1 as I got 1.3 or better on 40, 20, 17 and 1.8 on 30 and 15. An SWR of 1.8 is still about 92% efficient, so I’m happy with that.
Addendum: I tried the same radiator with the counterpoise that comes with the KH1 and the results were even better. 1.3:1 or better on all bands excepts 15M, which was 1.7:1.
That’s brilliant @AJ6KZ . I take that those SWR’s are what each transceiver managed to tune the individual configuration to? KX2 surprised me a little given the reputation of their tuners, 4.9 to 6.7 on 20 meters was not what I would expect. The inverted ‘L’, was that straight up the pole and then 90 degrees horizontal or did the second leg slope back down to the ground in what I believe is called a ‘Shark Fin’ configuration?
I was to busy trying to find radio gear to enable an activation attempt tomorrow so didn’t get out to play with my BandSpringer, but when I do I shall try all the same bands with the SOTABeams recommended configuration and see what SWR I can achieve with the Emtech ZM-2 matching unit.
Colin,
Once you measure a wire’s length it’s no longer a random wire. It may be a non-resonant length. I have my own idea as to how this misuse of the word came about but I would upset 300 million people if I voiced it.
Or you could have a trunk full of wires of different lengths. If you blindly reach into the trunk and pull out a wire it has been chosen at random and could be called a random wire, regardless of its length.
If two equal length wires are raised above the ground and fed at their centre junction, then yes they become a doublet.
Almost anything will work now given our high sunspot count and the proliferation of tuners.
I have used two 82 ft wires, one inverted Vee and one on the ground underneath it. It worked well enough from 160 m up.
That’ll be a nice comparison! That ZM-2 tuner looks pretty neat.
My configuration was sloping up to the top from the radio at approximately a 45 degree angle and then the short leg on the other side sloping down at approximately a 45 degree angle. I think that is the SotaBeams suggested set up.
Yes, those SWRs are what was achievable by the tuners in the radios.
My best results for this type of antenna using my KX3’s ability’s to tune it seemingly easily was 51 foot wire up my 7m pole and 12 feet counterpoise along the ground. Like someone else on this thread I made up a scrap piece of wire and cut it a few times making it shorter or adding to it at times. Once the kx3 seemed happy to tune it without going through a long tuning cycle I ended up with those lengths and made a “good” one out of new wire. My KX3, ZM-2 and You Kits LC tuner would all tune this antenna so I figured I had arrived at a suitable combination for the tuners to match. I used it quite happily with good results until the down turn and needed 80m to hit my more local chasers then I went back to the link dipole with extensions for 80m.
Regards
Ian vk5cz …
Hi Kelly,
Is there a reason why you haven’t listed 10 metres? With all the activity there at the moment (and the SOTA 10m challenge) it would be interesting to operate super-light with this antenna simply thrown in a tree.
73 Ed.
Ah OK, understood.
As the Bandspringer is listed as a 60m - 10m antenna (but not 80m Phil @ZL3CC), I’m hoping it should be fine on 10m with a simple Z-Match.
If the weather stays fine on Monday (so variable at the moment, no promises) I’ll be out testing it (with the standard, as supplied length counterpoise) on 10m for my super light travel kit with the “baby” G106.
73 Ed.
UPDATE,
I have just checked the antenna on my Rig Expert analyser in the garden - here’s what I found:
60m - 2:1
40m - 2.5:1
30m - 2.5:1
20m - 1.8:1
17m - well over 3:1 - not usable without some kind of matching unit
15m - 1.5:1
12m - 2.5:1
10m - 1.1:1
(I even tried it on 80m and it gave a 2.5:1 reading) - so you may be fine after all Phil @ZL3CC
Those readings were all measured using the standard antenna with no changes. I wonder if changing the counterpoise length would make 17m better?
The end of the antenna was run up the (wooden) flagpole and the counterpoise ran out on the ground roughly underneath the antenna (over grass and concrete).
Considering this is an end-fed random wire antenna with no UNUN supplied, I am somewhat surprised at the relatively good SWR achieved on all but one band. I think I’ll leave the counterpoise wire length as is and not use it on 17m. It is clearly stated that the antenna must be connected directly to the radio (or atu) and not coax-fed, hence the lack of the need for a UNUN I presume.
I have used a SOTABEAMS Bandspringer Midi for some years now, which is still on sale. I believe there was a Maxi version, which was twice the size, but hasn’t been produced for many years now.
I initially used it with a Yaesu FT-817ND and Emtech ZM-2 ATU, and then latterly with the Elecraft KX3 and built in ATU.
My experiences with the KX3 are that it will nearly always tune any of the bands from 60m to 10m, and the SWR is usually 1:2.5 or better. I use a 6m fibreglass pole.
I find the SWR varies dependent upon the location, probably due to ground conductivity and landscape (i.e. walls, buildings, masts etc.).
Over the years I have read that the:-
Aerial/counterpoise length was arrived at with the aim of producing the lowest impedance on a wide range of amateur bands;
Aerial is not a perfect match on any band.
I have on occasions used it as a vertical, and counterpoise.
I like the aerial because of its frequency band coverage, simplicity, compactness, and light weight.
Having spent the last few years trying to research this question and the distinction between a counterpoise and a radial, I think this is as good an answer as any. Choose your own unit of length from nanometres to light years. Many writers conflate the two terms, confusing the rest of us, and making any sensible discussion of CPs or of radials (and how to optimize either) meaningless.
There are so many different opinions, answers and contradictory information on this subject in AR literature and online. What I’ve concluded is:
A counterpoise is part of a ground plane to replace the ‘missing’ pole for antennas like EFHWs and bottom-fed monopole verticals
It forms the top ‘plate’ of a capacitor and the ground on which it is lying forms the bottom plate
(Unlike a radial) it is not tuned for the operating frequency(s)
However, its minimum length (to be effective) is somewhat related to operating frequency and I’ve read mostly a recommended total length of the wire(s) between wavelength/4 and wavelength/5
Given a total length of wire, multiple shorter counterpoises are more effective than one long one, e.g. I cut my original 16m-long CP wire (as supplied with my Cha MPAS Lite vertical), first into two 8m CP wires, and more recently into four 4m CP wires. This is more hassle and time-consuming to lay out. I’ve no objective way of judging any improvement but it comforts me because people say it should be better
I never bother using a CP with my three EFHWs. I get good performance (i.e. reports given/received) with 10W of CW on mostly rocky summits. IMO I use EFHWs coz they’re a bit quicker to deploy. If I had to use a CP with them, I might as well erect one of my inverted-V linked dipoles instead
Conclusion: don’t bother with a CP with the BandSpringer unless it comforts you or have time to spare
Tomorrow night I would like to participate in Go QRP Night on 80 meters and Sunday I would like to activate a summit. I am thinking my chances on the summit are getting pretty slim.