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Mobile GP antenna for SOTA success


#1

Dear all,
As I explained in a recent post, I’ve recently acquired a set of 5 monoband vertical ECO antennas for mobile with the aim of using them when on holidays, but also when activating SOTA as a fastly deployable antenna.

As many of you know by now, every Saturday morning I hike Mount San Cristóbal (EA2/NV-119), near Pamplona, while my 2 daughters are taking their weekly rockclimbing training at a close place.
I have always activated this SOTA on 2m FM on those Saturday morning ocasions because of the lack of time to deploy the whole set-up I used to have for HF activations.
The rock climbing training lasts 90 minutes and the hike takes me 35 minutes up and about 30 minutes down. Plus about 5 minutes drive from the training place to the hiking start point and another 5 minutes for the drive back, lets me just 15 minutes to be in the Summit, so the set-up has to be really fast if I want to have some QSOs in the log.
During Christmas holidays I designed and built a wooden rack as to have my FT-817ND, the ATU, and all cables (microphone, paddle, headphones, 12V) connected inside this wooden rack.
This has been tested successfuly in previous activations and definitely spared a valuable amount of time for not having to do all the connecting work at the beginning and the disconnecting at the end plus putting it back tidily to the handbag I had for that.
With that improvement, plus the new fastly deployable ECO antenna I brought with me this morning, I managed to activate Mt. SanCristobal on 20m CW for the first time on one of my Saturday morning ascents.
My new ECO mobile antenna was elevated about 2.5 m above the ground and one single radial about 5m long sloping gently down with its end tied to a extension cord which was tied to a wooden pole so the radial end remained about 1m above the ground. The radial was sloping down towards the North.
With this simple set-up, I managed to collect 16 QSOs in just 12 minutes operation. One of which, the very last one, was a S2S with HB9BIN/P from HB/NW-022.
I felt very satisfied with this morning experience but, given that the operation time was so short, I felt like giving it a new try this afternoon. So I did and activated Mt. Erreniega (EA2/NV-092)
This time I brought with me the 10, 15 and 20m band antennas. I installed the set-up as you will see in the following picture with 2 radials of nearly 5m long each this time, both sloping down gently but keeping their ends above the ground with the help of extensión cords trapped by stones on the ground.


With this very simple set-up I was delighted with the following QSOs logged.
On 10m: 8 QSOs in 9 minutes, 7 of which were DX with USA East Coast stations.
On 15m: 11 QSOs in 9 minutes, 1 of which was DX with a W7 station from Arizona.
On 20m: 19 QSOs in 22 minutes, 2 of which were DX, one was N7UN and the other JA4FKX.
After this last 2xQRP QSO with Nan JA4FKX I was starting to feel cold as the sun was very low and it was getting a bit dark, so I decided to call it a day and proceeded quickly to pack everything up for descent.

You can see how a small mobile antenna and 5 watts can do great DX!

Thank you very much and best 73 de Guru.


Mt. San Cristobal EA2/NV-119 by EA2IF/P on 23/05/2015
#2

Thank you for sharing your experience. It is always nice to have a quick deployment antenna. Sometime I hike with my non-radio-amateur friends and I try to activate during their Photo/snack/rest break :smiley:

How long is the vertical element ? it has some coil at the bottom ?

73
Petronel


#3

Hi Petronel,
The antennas I’ve got are monoband. They don’t have any coil at the bottom.
They all have different legths, being the longest one for 80m with something like 175 cm and the others decreasing in length to about 150 cm the shortest.
I didn’t measure the ones for 10, 15, 20m, as I have them in the boot of my car, but the ones for 40 and 80m are nearly my length and I’m 175 cm short :wink:
Best 73 de Guru.


#4

Hmm, seems a bit short for a vertical antenna :slight_smile: I wonder what is inside that box…
Are you using an ATU ?


#5

The blue box is not part of the antenna made by ECO antennas, it’s an old, broken 3 ways antenna switch I had which I have refurbished to use it as a mecanical support for the mobile antennas connected to the central SO-239 and the feed line to TX connected to the opposite SO-239. The other 2 SO-239 at the sides are used to connect the wire radials, of course they only have electrical contact with the external part of the SO-239 to the switch box, not the inner conductor.
I’ll take a picture and post it later.
Best 73 de Guru


#6

The coax is RG213 and I introduce it inside the PVC blue tube you can see in the picture of my first post.
I first tried RG-174 for weight reasons, but given that the PL-259 doesn’t fit perfectly the PVC tube inner diameter, I changed to RG-213, which is thicker and far more robust helping to keep the antenna switch and therefore the mobile antenna in vertical position.
Should you have any questions, don’t hesitate to ask.
Best 73 de Guru.

P.D. the blue PVC tube is also something I’ve had for years in some of my several junk boxes waiting for some useful thing to serve to. Now it does :slight_smile:


#7

What puzzle me is the short vertical element. For 1/4 L on 20m it should be around 5m , that’s why I supposed it has a coil at bottom similar with the one used in CB car antenna.

73,
Petronel


#8

Well, the antennas have the active wire helically wrapped around a former but I don’t know and can’t see whether they have put some coil at certain point. It definitely doesn’t seem to have any coil at the bottom.
Best 73 de Guru.


#9

Thanks Guru,
That makes sense. I wanted to make a similar antenna using MFJ-1979 telescoping whip, but too expensive with shipping to YO.

73,
Petronel


#10

Guru,

your antenna looks quite the same as mine. :wink:
I always use a short vertical for 20 m - 10 m SOTA activations. The obvious difference is the radials, as I have three bunches of radials, each bunch consisting of four resonant radials for 20 m, 17 m, 10 m, and 6 m.
The aerial is a center-loaded quarterwave and measures approx. 2.5 m on 20 m, 1.8 m on 17 m, and 1.4 m on 10 m. Makes nice signals through Europe and I’ve worked North/South America, Africa, and Asia, also.
In addition, I have a 10 m monoband aerial. It’s a short 5/8 lambda, approx. 1,7 m and I hope to lower the radiation angle and gain some DX-db’s with this aerial when it comes to the 10/6 m challenge. :smile:

Ahoi,
Pom


#11

Very interested to see this guru, I’ve a half finished helical wound antenna I am planning to experiment with as a quick way of getting on air. It looks like I am making a HB version of yours


#12

Hi Pom and all,
I initially prepared the 5m long radials for 20m band, which is the one with best chances to provide lots of chasers and good pile-ups at almost any time of the day.
However, thinking on the coming 10m challenge, I thought about preparing either a separate set of about 2,5m radials with PL-259’s as to put them instead of the 5m long ones or adding these second set of 2,5m radials to the same conector used by the 5m long ones.
The same 2 possible options for 15m with another couple of about 3,25m long radials.
However, this would add more weight to my rucksack and will complicate and disturb the rapid deployment of the antenna. Since I always carry an ATU and given the good DX worked on 10 and 15m last Saturday while having connected the only 5m long radials for 20m I have so far, I wonder whether preparing a separate set of radials cut for 1/4 wave of 10 and another one for 15m is worthwhile.
What do you guys/lads think?
In case you think they are necessary, what would you do, 3 different sets to have intalled only the 2 specifically cut for the band of use which would have to be replaced at the time of changing the vertical antenna for each band change or all 3 different length radials tied together, as they were whiskers, so only the vertical antenna but no radials change would be needed when changing bands?
Best 73 de Guru.


#13

I recommend resonant radials.

This is what I did on my first activations. Later i de-twisted them and fixed each end of a radial at a longer radial. Couldn’t spot any difference. I change bands within seconds by changing the steel top of the aerial and the antenna works well on 20, 17 and 10 m.
Have you thought about linked radials?

Ahoi,
Pom


#14

Yes I thought about linked radials but I forgot to mention it in my previous post.
I think this is the best to minimise weight and band changing time.
Best 73 de Guru


#15

… maximise efficiency. But in changing bands you will be some seconds behind me and my GP. :wink:
To be honest, I’ve been thinking about linked radials, too, for a short while.


#16

Hi Pom,
I finally prepared last night a linked wire radial to be used with my mobile whips.

I used it today on 10, 20 and 40m during my SOTA activation of Mt. Monjardin and it worked fine, although I only worked one single QSO on 10m. I think it wasn’t the right time of the day for 10m.


#17

Hi Guru,

in the morning the condx were lousy, too, on DM/NS-122 and -123. ES* barely above the noise level and a local qso via groundwave. But around 1230 utc, all of a sudden EA8, VU, 4X and PY gathered in my log.
You still have to be patient to get your qso’s on 10, but this is only the beginning of the season. Four weeks ahead things will look different. Looking forward to having s2s with you and your loaded vertical in the summer.

Your work looks good. That’s the same way I would have done it. But at the time I’m very satisfied with my bunch of radials, so I won’t change anything.

Ahoi
Pom

*: Estonia, not sporadic e. :wink: