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

Interesting new SOTA vertical antenna PT2


#1

Just a follow on as the previous thread is full. Finished making my kits from qrpguys today. The tri band vertical and the no tune end fed half wave.


#2

Well done Adrian. I didn’t realise they also had an end-fed - I take it that’s a single band (i.e. change the antenna wire for different bands)?

I’ve just finished re-building the tri-bander to be 20/30/40m. i had built it to be 20/40/60m but I couldn’t get it stable. Stable as in it’s resonant frequencies.
Something else I noticed that even after adding a common mode choke, the length of feed coax changed the resonant frequency of the antenna significantly.
Now I have changed the toroids back to the standard number of windings, I’ll be checking to see if that happens on the standard unit as well - hopefully not.

73 Ed.


#3

This has been my experience as well. On 40m I can’t seem to get it anywhere near good swr except occasionally. It might be useful to me on a relaxed (i.e. warm) summit where I don’t mind fiddling. But I can’t see making it my default antenna.


#4

One solution that I’m considering, is simply to solder a piece of coax to the antenna board, and set-up the antenna over that coax with my antenna analyser and then always only use that coax to attach to the rig.

I think this will work. Perhaps my common mode choke wasn’t right as the problem is RF returning down the shield of the coax I believe.

73 Ed.


#5

If you assume the design works then you need to find where your implementation doesn’t match the design. Or the design has some undisclosed limitations and only works in some situations (i.e. depends on the ground).

Put a good 50ohm load onto analyser and confirm analyser sees a good 50ohm.
Pick a patch lead, 50ohm load one end and connect to analyser, check patch cable is not junk. (You would be surprised how many patch cables are junk!)

Now you have a known good cables. Setup for 20m. This has no loading and is meant to be a 1/4wave.(The length looks long for 1/4wave and the radials are on the ground and the wrong length ISTR). Is it 50ohm on 20m on the analyser. If not, then this needs fixing because the rest of the circuit is designed to make the 20m 1/4wave work on the lower frequencies. So if it’s not very close to 50+0j ohms on 20m it wont be anywhere near 50+0j ohms with those inductors on the other bands.

Till you can set it up so it’s always near as damit a fine match on 20m, you will be chasing your tail trying to make it work on the other bands.

You can tell the design expects it to be near 50ohms resistive with capacitive reactance on 30/40 because you are only adding series inductance. You want the final thing to look like 50+0j ohms. It should be close on 20m. On 30m you hope it will be ~50-Xj and on 40m ~50-Yj ohms. Your inductors will be +Xj on 30 and +Yj on 40m. The inductors in series with the capacitance should cancel leaving somthing close to 50ohms. If the resistance once you have removed the reactance was not 50ohm or thereabouts, you would have the feed tapped onto the coil to change the resistive impedance.

TL;DR - make it work on 20m first!


#6

Hello group,

I have a newbie question . . . how good are those small coils wound on the toroids? Specifically, is it possible to attain a high Q factor with small coil wound on toroids like those in the tri-band kit? Or is there a lot of power being lost with small coils? I’m not doubtful of the quality - just curious since I’ve never worked with small coils on toroids like that.

I’ve been considering building a similar base-loaded vertical antenna for SOTA use. However, from reading the ARRL antenna book and other texts I’ve come to understand that a large diameter coil (2-3" diameter) with a high length-to-diameter radio is necessary to keep efficiency high. (Keep efficiency high = minimize resistive losses and keep the coil as purely inductive as possible.)

What I’ve been reading was all in the context of coils for use in mobile antennas though. Does anyone have a good source for how to calculate the Q of coils on toroids like that? Are small coils on toroids highly efficient? If so, I could use those in my designs and save a lot of bulk in my designs.
Brandon


#7

Hi

Toroids are used because you can get an efficient coil in a small size. Inductors 101. You must chose the right core.

For loading/matching coils an unloaded Q of 100 to 300 should be easy to get. A loaded Q of 4 or thereabouts is desirable. A higher loaded Q gives higher losses. Simple matching circuits that cover more than one frequency would likely have medium loaded Q and hence be less efficient than ideal.

No free lunch. Sorry.

Radial length for this vertical can be optimum for 20 m and will be a compromise on all other bands.

However although involving compromises this antenna is still useful for SOTA.

73
Ron
VK3AFW


#8

Thanks for the advice Andy. I know the analyser (a RigExpert AA-30) is fine as are the three different patch cables that I tried. I went into the modification knowing there was a risk that it may not work - but that’s why we experiment isn’t it?

20m on both the modified design and the standard one works fine - a good trace across wide bandwidth. On part 1 of this thread it was discussed whether tuned radials would be an improvement and whether grouping them together for convenience rather than having the wide apart makes any difference. I have so far just used the 4 x 10’ radials as per the design.

I suspect I will get this working on its standard bands and forget adding 60m to it, then perhaps build Martin DK3IT’s design for 60m.

73 Ed.


#9

Hi Ed, well what happened was i actually only had ordered the tri-band vertical, but what came was the end fed, a few email exchanges later and a week of waiting and i now have both. So far i haven’t cut the radiating elements or countermcpoiseradialthingmybobs yet. May get to that today, Quite interested to try the end fed, see a lot of folks on youtube and here using them. Interested also to try out and see if there is any discernible difference between the 20/40 linked dipole and the 20/40 vertical (30 is a dead band for me right now).
I had thought about making the end fed using one long radiating element and putting it onto a spool or such like and mark it out for each band?

73
Adrian
MM0TAI


#10

Also…want to start using 60m on activations, so will be trying the end fed for that and see how that goes.


#11

Hi Adrian,
The linked dipole will out perform the QRPGUYS 40m vertical as the latter is a 20m vertical with toroid loading at it’s base. It’s a compromise but it’s advantage is that it can be put up on a 6/7m fishing pole with no guys needed as it’s so light. It’s also small and easy to pack. The fact that they decided to make the board also a winder for the driven element and radial wires is brilliant.

I’d be interested to hear how the end fed works out. in that case the toroid is an UNUN I guess?

73 Ed.


#12

I know the dipole is the holy grail to many, but depending on your goal a vertical can outperform a dipole given certain parameters. The vertical generally provides lower angle radiation compared to the dipole and could be a better DX antenna.

My other current 40m antenna is a 20/40 trapped dipole. Those traps add some loss and at an overall height of 20 feet (my telescoping pole’s max height) there is a lot of ground loss and very little low angle radiation.

Then when you figure that I can use 10ft of RG-8X instead of 25ft of RG-174 for the feed, you are getting more RF to the antenna.

Yesterday I was very pleased with the performance of my build of the tri-band vertical. I had plenty of great contacts on all three bands, including 2 S2S on 40m using 10W CW. And this is with

  1. The swr on 20 around 2:1 and around 3:1 on 30 and 40 due to my haste in getting on the air.
  2. I was still using 25ft of RG-174 because I haven’t dug out the RG-8X feeder from the basement.
  3. Still using the bare minimum 4 10’ radials laid on the ground.

With 4, 8, or 12 more radials, a shorter and less lossy feed, and care given to tuning 20m more accurately I’m sure the antenna would be killer.

My point is assuming the linked dipole would outperform the vertical is not a given. Unless the dipole is a half wave above ground, which could be as much as 70ft, the vertical is likely comparable especially for dx contacts.

Add to that the fact that at least on 20m, the antenna is easily made directive with gain by adding another 20ft fishing pole and some wire for a passive reflector design.


#13

I agree evan, theres little chance of me getting my 40m dipole a half wave off the ground. My real thoughts on the tri-band antenna is whilst yes it is a compromise antenna, the small foot print and easy to deploy nature of it justify the £30 experiment. Plus its a bit of fun getting the soldering iron out and making. :slight_smile:


#14

For us in the US of A, its only a 15 “quid” experiment :slight_smile:


#15

Yeah, the shipping from W6 -> GM is the same cost as the item itself :tired_face:


#16

I know where you are coming from Evan, however in the case of the QRP Guys vertical, it is only a “true 1/4 wave vertical” on 20m. On 30 & 40m it is being matched to the rig via series toroids and as such is a compromise antenna on 30 & 40m. There a “real dipole” IMHO will out perform even for DX. I have worked S2S on 5w SSB with the linked dipole at 6 metres AGL in Inverted-V format (a set up that really should be more NVIS than DX - but it works).

As always we have several things to think about with antennas for SOTA, often one is limited space to erect the antenna and there the vertical comes out ahead. I have also tried Inverted-L configuration a couple of times - I’m not sure if that is considered a vertical or a horizontal radiating antenna.

One of the VK5 SOTA activators uses two phased 20m verticals - he puts a great signal out in the chosen direction but of course needs a little more space to do that ( probably onl about the same as one needs for a dipole though.

Agreed on the comments about the coax also - there are some small lightweight low loss coax options as well (for example used by Spiderbeam on their Aerial-51 antennas) but these are more expensive.

Just off to try the QRP GUYS tri-bander again, now that I (hope) I have it built to the standard design. By the way, your SWR values of 2:1 on 20m surprise me, even when I had my modified version I was getting 1.1 to 1.2 across the band. 2:1 on 40m and 60m (now 30m and 40m) OK but on the resonant frequency of the wire without the coils in circuit any over 1.5:1 is unusual in my experience with this antenna.

73 Ed.


#17

Same here in Germany - $15 for the kit, $15 for shipping. However I was surprised that the kit (once actually shipped - I think they were out of stock) got to me in just over a week - I’m used to US/Europe shipments taking a month to 6 weeks.

73 Ed.


#18

I ordered a couple of these from a camping website, meant to be a travel clothes line. I managed to spool on 100ft of wire. Just need to get the analyser out and mark off the length of each band for using as an end fed.


#19

Web reference please, web reference please Adrian - I’ve been looking for something like this for ages to coil antennas on!

Tnx Ed.

OK, found it on German eBay from the US for €7,72 with free shipping??

(scroll down for reduced 2,3,4 & 6 pack prices)


#20

Get 3. 2 for dipoles and one for a counterpoise

They are great for the kit
John ve3IPS