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

Resonant Antenna tuner needed in field

As we all know environments change sometimes when we get on the mountain. Everything looks good at home, but orientation and configuration can change based on what we have to work with once setup in the field.

Have you ever been in a situation where your once resonant antenna, became unusable on the mountain? What did you do about it? (Obviously this is referring to where you don’t have access to a tuner)

3 Likes

Hi A.J.

Always I’ve a tuner (mAT-10) even if i don’t use it MAT-TUNER Antenna Tuner
and an antenna analyzer RigExpert Stick 230 Specifications | RigExpert™ which does not weigh heavy (185g), but which will allow you to correct your aerial very easily.

73, Éric

4 Likes

I’ve never had a problem with a normal centre fed dipole on hundreds of activations on different types of ground. No tuner needed. I’ve never had a problem with 1/4wave GPs on different types of ground. I have one antenna that is dependent on the ground. But it adjustable by design, so on deployment I check the match using the SWR meter in the radio and tweak the antenna for best match (SWT <1:1.7).

5 Likes

I’ve only ever had one issue with my linked dipole from SOTA Beams.

I QSYd from 20m to 40m and immediately sent CQ etc., . The SWR was very hight indeed but I was immediately answered by Eric/F5JKK - It was only then did I realise I’d forgotten to change the link. (This was some time ago Eric!).

Otherwise no issues of working near rocks, undulating ground, cliffs or even with a large portion of the dipole very near my campervan :smiley:

(I wish my radios were as well mannered.)

3 Likes

In fact, I explained myself badly. :yum:

The advantage of a small analyzer is that you don’t have to use the SWR meter in the radio.
I use an 8m coax for my multi band vertical or a 10m coax for a dipole. I just have to disconnect the coax on the TX side, connect the analyzer and I can walk and adjust the length of the dipole strands or the position on the vertical coil.
Otherwise, you would have to go back to the TX to ensure that the setting is correct for each tweak.
I had an EFHW at first that worked fine in my backyard but not once on the summit, not sure why !
You had to go to the end of the antenna to adjust the length and it took a lot of time, hence the tuner.
The coil of the vertical is not marked from the start, hence the use of the analyzer.

73, Éric

3 Likes

Yes, my antenna is the same, adjust far end, walk back to radio, check SWR, walk to far end, adjust far end. Repeat until match is OK.

4 Likes

For my 30 m QCX I built myself an endfed: BNC - coax - antenna wire is connected in one piece. Everything was tuned at home with the NanoVNA. During the activities it always worked wonderfully.

Once I just threw the antenna wire into the bushes where it rested on leaves. The performance was not very high… and when I touched the balun, it was surprisingly warm.

I didn’t get to measure the SWR with the QCX, but sure enough it was horrible and I’m glad the PA survived it all.
After that I threw the antenna wire more freely over a branch, and everything was quickly better.

73 Armin

2 Likes

If you use antennas like the MP-1 or HF-P1 things like that can happen, e.g. the peak is in the middle of the forrest with many trees or you have a contact issue with one of the parts. Then some bands can be tuned easily while with others (like the 40m band) you might have problems.

However, with this type of vertical antenna, ATU cannot be used. To be more precise, you cannot use the ATU to bring down an SWR from 1:30 to 1:1, but you can bring down 1:3 to 1:1.

73s
Ingo

2 Likes

If the VSWR is less than about 5:1 and I can’t improve it I ignore it and reduce tx power by half.

Of course I investigate if the SWR is very high. A pocket knife can remove a faulty connector and help bodge up a connection.

A tuner can reduce SWR but not fix faults.

73
Ron
VK3AFW
Edited to say what I meant to say

3 Likes

Here in the Northeast USA, there are trees available to use.

There have been times when I’ve run my EFHW antenna and gotten a terrible match >4:1 on a previously “resonant” antenna.

Most of the time it’s due to one of the legs making the antenna elements bending and wrapping around a branch or branches and or the tree is wet.

2 Likes

Reduce your overall way by tuning by noise. Set the rx audio to loud, adjust the atu to maximum band noise, walk back, check swr and cq.

Ahoi
Pom

2 Likes

When out /P, I always have the FT817 with me & sometimes the G90. Although it would be easier to always use the G90 with it’s inbuilt ATU & 20w, I do prefer the excitement of seeing how far I can get out with the FT817 and it’s 4w. With such low power all 3 of my homebrew antennas (20m dipole, 20m EFHW & 20/40m linked EFHW) are designed to be resonant but, as you say, their sweet spot often moves around when set up on the summit. Of the 3 of them, the dipole is tuned to 14.210 and is the most reliable as I have ‘fixed’ the geometry, i.e. a fixed marked point up the 10m pole to suspend it and along with defined lengths of string to tie off the ends of the elements to keep them a known distance off the ground. The only variable left is the slope of the ground which appears to only have a marginal effect on the SWR. When the situation does not permit use of the dipole then my next go to antenna is the 20m EFHW. I usually have this tuned to 14.285 however it can be way off when set up on a summit. This is where the Nano VNA comes into action as the wire can sometimes require adjustments as much as 300mm (12") in either direction! Needless to say, the Nano VNA is now an essential part of my kit as it’s possible to ‘tune’ a wire dynamically and monitor the ‘dip’ move along the band until it reaches the preferred frequency along with the Smiths Chart reading. The whole ‘tuning’ process takes about 8-10mins max and is worth it. For example, whilst activating G/SC-005 Selworthy Beacon on Monday, I only made 8 QSOs but the 5th was with Alfred WX1S in New Hampshire… I mean… that just made me break out into a huge great big smile whilst doing that QSO on just 4w :slight_smile:

73, Lea M0XPO

3 Likes