Other SOTA sites: SOTAwatch | SOTA Home | Database | Video | Photos | Shop | Mapping | FAQs | Facebook | Contact SOTA

Modifying the portable antennas


#1

:smirk: Morning folks

Hmm sota’s been bit quiet of late, so been brain storming a little bit.

Been wondering the coil I made up to shorten the overall length of 11m of wire to fit nicely on the 8m fibre glass telescopic pole is too close to the ground. So decided to strip it all down again and move it, so its just above the rope support holder and adjusted the wire to suit. Now me shortening length coil is about 4,7m up the pole well away from the ground and on air tests shows its hearing a little more noise than before and you can see its bigger noise drop when you switch to the full wave loop. Just felt to much wire inches from the ground 3m of it. Also feel it may radiate a bit better and looks cooler too. :sunglasses:

Just got to make some inserts so it does not slap around on the pole as pipe is 40mm and the pole is 22m and 20m up there can’t have that slapping around in the wind. :scream:

Now this leads now to a question when I tightly wound the coil it would not tune in on 40m now if i tightly wound it up at height and get it to tune in, getting silly ideas of making a 1/2w vert or even a full wave vert 40m. Reason like to start with the 1/2w version is weight could be an issue up there as be at least 14m of the Sota wire on that pipe of 40mm if it works then move onto the fullwave version vertical which will have 36m of that wire on it. mind you could make the full wave version on 50mm waste pipe prob be better pipe be shorter and fatter take more wire than 40mm version Hmmmmmm.

But this is also leading me to design a smaller better more practical base for the pole to sit in while being erected and more light weight than me currant cross base i have for the ore trick and longer to get to summits.

Karl off back to drawing board yet again LOL 73s


#2

Its all a question of radiation efficiency with verticals Karl. If you coil the wire around the pole it would work, but it probably would not radiate as well as a drawn out wire.
If you are considering making your vertical portable I would suggest as others probably will sticking to 1/4 wave. The amount you “gain” from building a 1/2 wave isn’t worth the trouble. There is also lots of rubbish out there commenting on the correct angle between the loaded element and the CP, you will find this is difficult to maintain exactly in use and makes no difference in practice.

My vertical uses a 15m 1/4 wave CP with an extended top for 20m. Despite not extending the CP with the top it works perfectly (very) well on 20m. Probably one of the best antennas I have made for DX’ing. Good antenna to play with and supports well in high winds.

Jonathan


#3

With a bit of craftiness that loading coil could be made to operate as a trap giving you a quarter wave on 30m or 20m.

Brian


#4

Thanks folks
just get silly ideas in head, just gotta try them out you can learn a lot for this.
Great fun tinkering with antennas and making them work.

karl


#5

Good stuff Karl,

My next crazy idea is to put together a portable 4-square kit. Overnight in the tent on 40m. We shall see :smile:

Zigbee controlled relays from the spare UART port on the KX3.

Jonathan


#6

OHH do tell as it like in a loop for full on 40m

Hmm do tell more

karl


#7

A somewhat simplified description:

If you have a single vertical radiator it has an omni directional radiation pattern.
If you have 2 vertical radiators then if you set them up at random and feed them randomly you get the signals from the antennas interfering with each other.

Now if you select the “right” physical spacing of the antennas and get the feeder lengths “right” then instead of the interference being random, the interference is controlled. For the correct values of “right” you can make the omni become directional. i.e. it has gain.

A 4 square is an arrangement of 4 (identical) vertical antennas arrange at the corners of a square set the correct distance apart fed with switchable feeders. You can then steer the antenna be selecting the correct feeders between the antennas. It is a moderately complex switch arrangement but gives excellent results on the lower bands where beam antennas like Yagis would be physically huge along with the support tower.

Search the interwebs for “4 square antenna” to see the gory details.


#8

Thanks for that info and oh wow very very interesting and park tent in middle LOL or is that NOT a good idea

http://www.k7nv.com/id16.htm

Found this link that explains a lot

So instead of three like i mentioned a while ago ,use four giving off 90’ beam heading would this be interesting.

karl


#9

You can potentially get front to back ratios as much as 30dB in some cases. The classic fish tail pattern can be observed as with a Yagi.

Its something that wouldn’t be worth the trouble to put up for a 1 - 2 hr activation, hence the all-night . Recently the low HF bands have been great on some nights for long skip conditions into the US especially. Spacing them might be interesting that is where the GPS could come in handy. Lots of stuff to bring up as well, and it would be a shame to run QRP :wink:

Jonathan


#10

Karl,

Did you re-measure the resonant frequency of the vertical after moving that coil? You will find that the coil has more “shortening” effect the lower it is, so if it was resonant on 40m at its original height, the antenna will not be resonant on 40m any more with the coil moved to a different location. Instead the resonance will have moved higher in frequency and you need more loading coil.

You suggested adding more coil to make it a different electrical length. The only reason a half wave vertical might perform better than a quarter wave vertical is that it has more straight conductor in the air. Loading a short wire to give it half wave resonance would not make it a better antenna, it would complicate the matching from a simple low impedance antenna that radiated well (if it had a good radial system) to a more complex antenna that radiates no better and is difficult to feed.

BTW what’s with the twisted guy ropes? The two on the other side changed their minds about which direction they were going…

keep experimenting, you are doing it on behalf of thousands of hams who cannot join wire, coax and rope together.

73
Andrew
vk1da


#11

This is a vertical aerial for portable use I built which worked well and was easy to assemble.

A 9 metre squid pole was the basis and the various matching coils were mounted in a lunchbox with SO-239 connectors and banna jacks.

This vertical is multiband 80,40,30,20 and 15 metres, to change band just plug the fly wire from the aerial to the relevant banna jack and SO-239 jack mounted on the lunchbox.

Three or four ground radials say 5 or 8 metres long are spread out on the ground.

This vertical has been used by the motor home and caravaners with good results.

In my usage found it to be more a dx aerial than short range working. Worked quite a bit of dx on qrp cw with the squid pole aerial.

Easy to set up and quite lightweight.

www.philipstorr.id.au/radio/technical/Squid%20pole.pdf

73’s, Nick


#12

Giggle giggle :open_mouth: they got little twisted from up and lowering the pole whilst adjusting the length of wire through the plastic pipe :relaxed: so just got enough to reach the Unun when full up and then all over again after wrapping the antenna wire around the 1ft long 40mm pipe with enough coming off the top to reach the top. So what happens the centre bit takes up the slack of 3m of wire as pole is 8m long and the wire is 11m long…

Had a good look through there and see what your up too. I see your coil is tightly bound wires wrapped next to each other. Mine are more spaced out about 1/2" gap between the wires as when tightly wound it it would not tune on 80 or 40. But this way it does.
Hell must a done something right first contact off Kitt hill straight into VK5 on 10w was just the icing on the cake managed contacts on 40 20 15 and 10m.

Now for ground radials glad you mentioned this mine is a single counterpose of 11m 1/4w thinking of setting up anther 3 making total of four. see how that fairs. But did not on Kitt hill lack of noise level compared to home big difference. Except for 2nd visit to the hill had hell an lightening static on 20m. Must point out mine is ACU controlled with ease.

Just spotted this bit interesting gong have to study this bit a little more and play time I things just had load banana plugs turn up in post. So this is what you call a squid pole a multi tuned antenna liking that idea. Could combine the two here interesting

Stop it brain storming again LOL

Thanks again guys for the information and points of view

Karl