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Sotabeams bandhopper height?


#41

:thumbsup:


#42

Bingo… usually after that I’m more bothered about how to get it to stay up and somewhere nice for me to sit. Portable antennas, always a bit of a compromise. Speed and stability are my biggest factors. We’re not trying to make something perfect that will perform optimally for the next year (or 20). Don’t get too wound up about it.


#43

I’ll wager that this is not something related to antenna centre height, leg angle or leg end height above the ground. If I’m getting high SWR it’s usually something broken. Not antenna positioning. I’ve had moderate SWR levels due to outside influences, such as metal objects or even getting too close to tree limbs.

Of course I could be wrong! I’m a keen SOTA activator, but I’m first to admit that my radio knowledge is pretty basic and just enough to get by on my activations.


#44

Hmm, a thread like this makes convinces me that I am right to have an LDG auto-ATU as part of my set up. I first noticed matching issues when setting up my link dipole above a metal fence, but the SWR was not consistent from one summit to another. I have never had an issue since I started using the ATU and within certain parameters it even allows me to operate on bands other than those the dipole has links for by setting it up as an off-centre dipole. When running a QRP rig (such as the 817) it is essential to get the best match possible, but I agree with Gerald in respect of the temporary nature of portable antennas. Perfection is not required.


#45

Now that really is an interesting observation, Gerald.
Why; because I find pretty much the opposite. :slight_smile:

The tuner in the KX3 is so good that generally the aerial just tunes up and I spent most of our week in The Mournes in 2015 wondering why I was having more trouble qualifying on HF than M6BWA/P was having on 2m.
Then I took out the 857 instead (easy summit) - no tuner and huge SWR with a correctly linked dipole.

I now begin each activation (and QSY if I remember) with the ATU in bypass mode and use the Tune button to check that the SWR is reasonable. If it seems really good ( see below * ) I just carry on; if tweaking looks advisable I reset the ATU and tweak the SWR. I ended up taking the second spare aerial on later summits during the 2017 GI trip.

(Should anyone be curious as to how I manage to break aerials so often I admit to being both clumsy and impatient so the wire gets tangled in my gaiters, in rock cracks and in gorse bushes (other hazards may also be present) all of which are stronger than the wire.)

  • As mentioned earlier in the thread the actual SWR does depend on all sorts of physical features of antenna and summit and that is where the ATU tweak comes in. I test the aerial on the lawn and vegetable patch - just room for a straight inverted V 60m dipole with 5m end strings - using a 5m pole. This patch of ground is flat and bushes and beans are mostly more that 1m from the wire, even on 60m. It is also fairly uniformly damp. Most hills are quite different and sometimes the aerial is actually in contact with vegetation, especially if the wind changes. In GI (apart from The Mournes) most of the wire is often over water which is lower than the foot of the mast! Not surprising if it is a bit off-tune.

73,
Rod


#46

My 3band link dipole shows some SWR indication when operated well from its nominal design frequency but no more than 2 intermittent flashing blobs on an 817 display. Anthing more means I have missed something in the setup and the antenna needs fixing. Letting the ends near the ground affects it, but I keep the ends 1m or so above ground. I can tell at once if the end supports have fallen over by the change in SWR. I can operate it above fences or on its own, in vegeation or above rocks. It is incredibly docile and I seem to be able to have QSOs with it so I don’t think it’s a dummy load (which would have a flat SWR inidcation).

What I’m reading here: (tuners for dipoles when used “in-band”), massively varying SWR indications etc. is just plain wrong. Dipoles are docile, simple antennas. If you are having these issues then there is something fundamentally broken in their setup. Seriously, you have fundamental issues with your equipment if your dipole is not docile when used in band.


#47

Andy: Agreed. I have a LDG tuner that I used to carry for use with the 817. I stopped carrying it because the linked dipole is such a benign and reliable antenna.

My antenna has no brand being home made, but the principle is the same.

Kjetil: As your antenna is new you have no reference point. I think it would be helpful to choose a band and try to find where it is resonant. An antenna analyser (impedance analyser) is the most convenient way of doing that, but your radio and an swr meter should indicate whether the resonance is higher or lower than the intended band. Some radios have an inbuilt swr curve checker.

The other thing worth checking is the antenna length. There is no loading, so the length on each band should be close to 95% of the half wave length. Divide 150 by the frequency in mhz then you have the half wavelength in metres. Reduce by 5% for end effect.

Start at the highest frequency band. The link for that band should be open. Measure the length from that link through the feedpoint and over to the corresponding other link. That length should be within 50mm of the calculated half wave.

On lower bands, all links between the feedpoint and the half wave point for that band should be closed. The same calculation can be done for each band.

A high swr on antenna that is normally perfect, indicates something is broken. The health check on connectors, antenna centre connections and coax damage should be the first resort. Omitting strain relief at the feed point is a way to damage the coax feedline, or damage the connection between cable and connector.

Antenna height: Raising the antenna should have two effects, one is the slightly higher impedance with extra height. The other is reduced ground losses which to some extent reduces the feed impedance, compensating for the height change. I’ve used my linked dipole at various heights and have not noticed any significant change in resonance or impedance. The only times I see high swr is when I have left a link connected when it should be open, or vice versa.

73 Andrew VK1DA VK2UH


#48

Of course, if you’re going to the trouble of carrying a tuner, you may as well forget the linked dipole and carry a vertical. Then you’ll have the opportuniy to work DX too. Certainly for DX in current band conditions, right now, a vertical is the only way to go…

Have fun.


#49

Thanks :slight_smile: I’ll consider that if the next test doesn’t go well.


#50

I have had a Sotabeams linked dipole (80m/40m/20m) for around two years, I also use a Sotabeam 7m pole, running 10w from my Alinco DX70TH, I get very good reports, and the RX signals are normally S9+, even with the antenna laying flat on the ground! ( I have not tried to TX yet, with it in that position !!)
The best orientation for me, seems to be with the legs gently sloping down to ground level, not a tight inverted ‘V’ but with a little slack ?
In windy conditions, I do not fully extend the pole, and there seems little change in reports!!


#51

Agreed. However, mine was set up and trimmed on a relatively flat site with nice damp conductive soil beneath it and the apex at 6m. Cue summit with a rocky pointed top (I need to be up there as I also run 2m), a raging gale so the wire is billowing out, the pole only extended to 3 or 4m and the legs of the dipole not even in alignment as some local feature of the hill prevents that… well, all I can say is, I would rather have the ATU on board than not.


#52

All this confirms me in my decision to stick to the ancient W3EDP antenna. No getting up and stumbling over rocks and heather to mess about with links to change bands, and the simple tuner always gives a low SWR.:grinning:


#53

I was able to do a side by side comparison this weekend with the Band hopper, a vertical antenna and two radios (Xiegu X108G and Kenwood TS480SAT). The Kenwood measured and ran the band hopper perfectly, with a SWR slightly over 1 throughout the bands. My Xiegu gave the exact same reading as it did last time, with a minimum SWR on 20 meters of ~2.7-2.8. I then measured the vertical with both antennas, where both gave identical results (1:1.1 or thereabouts).

As the last tests were with the Xiegu I am inclined to think that this unit is the issue, not the antenna.


#54

Apply a 50Ohm resistor to the Xiegu output and see what it reads.


#55

With a 50 ohm dummy load it shows 1:1.01 over the entire spectrum. As I said I also tested it with my vertical, where both showed identical (the same) SWR on the same frequency…


#56

Well to me then it sounds like the Xiaegu is picking up stray RF when you use the bandhopper and not the vertical. Try a plain SWR meter in series and see if they show the same. Or try winding a few turns (5-10) of the feeder into a solenoid wound coil about 10cms in diameter as close to the radio as possible.


#57

Yeah, that could be the issue. Just a regular coil, or some specific winding type? Could adding a longer feedline also fix the problem?


#58

From Wikipedia:

A solenoid (/ˈsoʊ.lə.nɔɪd/)[1] (from the French solénoïde, derived in turn from the Greek solen (“pipe, channel”) and eidos (“form, shape”)[2]) is a coil wound into a tightly packed helix.

Wind the turns together neatly. If you wind it in an ugly lump the choking effect is reduced and you need more turns. Wind the turns together so there are no air gaps between the turns. We want to use the outside of the coax braid to act as a choke to kill off any RF on the outside of the coax. Don’t forget, coax cable has 3 conductors at RF, the inner, the inside of the shield and the outside of the shield. Different currents can flow on the inside and outside of the shield at the same time. It might have no effect. But if it works, then you’re sorted.


#59

I checked the AARL Antenna book. It appears that the gain of the inverted V antenna increases as the angle is broader. It has the highest gain when the angle is 180 degrees - a straight line. As the antenna is raised above the ground to a higher point, the angle of departure is lowered and therefore, is better for DX signals.

I have been successful using the Sotabeam 40/20 model by putting the antenna up high in a tree and extending the two antenna cords by adding on more string. That increases the angle and tends to take some of the V out of the configuration. Of course, if you are on a bald mountain top, this discussion is not relevant.


#60

Thanks for the tip @MM0FMF, I’ll try that the next time I have the antenna up. If not I learned about a magical item called a ferrite on my HAM radio course last year, that should apparently cure everything from interference to the common cold (I have a feeling that may be exaggerated), so I’ll try one of those if the coil doesn’t work :wink: