Hi all, I have some spare time inside today (joking I hope you are all well)…
I use a 9:1 on a fishing pole with around 49ft of wire. badly setup inverted L.
I wanted to keep the RF away from the room so I added a choke (240 with RG58 turns) around a ft from the 9:1 so I though I need to test some counterpoise as the feed-line is no longer part of the system.
This is what I got! Let me know what you think?!?!?!
As you can see, from this table, the length of a counterpoise can be quite long on the lower bands. Where do you put 66 feet of wire? Before I answer that, lets look first at a suggestion for making the counterpoise for multiple bands.
A multiband counterpoise consists of several separate wires, each cut to the proper length for a single band. You may be able to eliminate some counterpoise wires for bands that are harmonically related in odd multiples. 15 and 40 meters or 80 and 30 meters are examples.
The ARRL Antenna Handbook is a great reference for antenna theory and practice for radio amateurs. I recommend studying it.
If you add a quarter wave radial/counterpoise at the low end of the 9:1 transformer you will be putting a low impedance point there to “collect” the current that otherwise goes along the outer of the coax.
The length will depend on whether it is on the ground or elevated. Probably longer than your estimates.
I would consider laying a 42 ft counterpoise under the radiator on the ground to stabilise the ground reflection. I would have at least one radial per wanted band.
I am unable to comment on the SWR curves as I do not know for certain which is which.
Good SWR on this sort of antenna is not necessarily what you want. For example last Saturday I was pleased to see the VSWR go from 3.5 :1 to 6.8:1 on a backyard vertical.l The resistive component reduced with each radial and that meant reduced losses. The ATU took care of the mismatch and I got good reports.
Look at the Rs value and see how it varies. A lot of the measured resistance is going to be loss resistance.
This is never going to be a great antenna but you can try to make it as good as it can be.
Elevating the radiator is the best thing you can do. Adding radials and a coax choke are both positive things to do.
Hi Tasos,
Thanks for the clarification.
As a general rule for verticals two radials per band is considered the minimum. For each pair they should be in a line so for example if one 20 m radials goes east the other should go west.
More radials make a better approximation of a perfect ground.
Twenty radials 0.2 wave long is considered good for ground mounted verticals.
So for your inverted L system the more radials the better with one per band being a good idea and two per band even better.
I think you are mainly interested in 20 and 40 m in which case I suggest a vertical section of 16.5 ft and a horizontal section of 34 ft with the far end elevated if possible.
do counterpoise on random wire help in receive?
with no counter my S noise reduced 3S at least! (and strongest signal property by 2S, tested on ft8 10m)
Hi Tasos,
My first trial of a 10m long wire endfed antenna for SOTA was without a counterpoise because I had a 5m length of RG58 coax feeder and the written theory was saying that the braid of such coax length would be acting as a counterpoise and therefore a dedicated counterpoise wasn’t needed. The truth is that I felt that antenna quite deaf and low performer compared to the vertical wire antenna with 4 wire radials I had been using up to that moment and I felt the urgent need to try something…
When I connected a random length of wire I had around as a counterpoise, I noticed the antenna started performing much better both RX and TX.
Later (some other day) I even changed the 5m of RG-58 to nearly 0.5m of RG-58 and the antenna works great, having allowed me to work several DX with just 5W.
The only problem I’ve noticed is that I can’t always tune it on 17m, but appart of that, it works fine from 10 to 40 and I have even managed to tune it on 60m.
That random length of wire I connected as a counterpoise, turned out to be about 6.5m long. I have always used it since then on all my SOTA activations with the endfed antenna. I usually try to have it horizontal and elevated from the ground, but I have sometimes left it laying down on the ground and the antenna kept performing great.
Good luck with your testing.
73,
well!! thank you for the info! helps my brain a lot!
Im almost on the same page! I have used the coax as the counter for years but I;d like to limit the currents from the house and I used a choke near the UNUN. So no coax radiation hopefully.
So without adding extra counter my RX was very low (and Im in the super noise central London) even noise was super low…
Now Im now sure which length is better, or maybe use multiple together.
Hi,
In general a good transmitting aerial is a good receiving antenna. But sometimes it receives a noise source as well as the DX so no better s/n . So sometimes a poor antenna that does not “see” the noise source can give a better s/n on receive but be poor on tx.
I hope you are all well)…
no ideas or comments of what seems better or what I could test more?!!? 