Back to Antenna’s

I think I have found the antenna for me going forwards. After playing with the half wave coaxial vertical antennas for some time, the only one that really worked consistently was the 10/11m version.  I could not get rid of the CMC’s on the 20m version no matter what I tried so have given up for now.  I went back to the inverted V but it was a hassle having to erect it and tear it down all the time. it was also a visual eyesore. The SWR would change based on height and angle and any nearby objects. I was always getting it tangled up so deployment took quite some time, not to mention needing 2 points to tie it off in addition to securing the base. But when in the air, it worked nicely and received quietly and transmitted well. Tried to add a 20m wire to the feed point of the 40m inverted V but neither antenna seemed to work as well, so gave that up. Consequently band changes meant antenna changes and more time wasted.

I was convinced a half wave vertical was the way to go for ease of deployment. The 12m telescopic poles stay up very well with just a light wire taped to them, I just needed to feed it correctly. Enter the 49:1 un-un.  This is what I bought.
10-80m 1kw no tune on the various bands it is resonant on.
There are many other designs using a 9:1 un un but they require a tuner to get usable SWR to the radio. I didn’t want to rely on a tuner so did not look any further at them.
A European company making similar antennas using a 49:1 un-un can be found here:
Half wave verticals have always worked well on 10 and 11 meters and most did not incorporated much in the way or radials, so it stands to reason they would also work well on 20m (if we could get them up high enough.)

For 20m we can easily attain this with a 12m push up telescopic fibreglass mast. Half wave verticals do not require a complicated ground plane system like 1/4 verticals. It is not to say they won’t benefit from an extensive ground plane but they do seem to work well without much in the way of counterpoise or radials. They also work in all directions. No need to rotate.

The 80m wire (40m long) that came with the 49:1 Un Un feed box was way too long to use so I cut a 5.5m length of light weight 2mm insulated wire and started playing around with that on 20m. To get a low SWR I ended up trimming it back 9.15m. The SWR at 14.2mhz was 1.3 and did not rise above 1.5 at the band edges. According to the antenna analyzer the resonant frequency was 14.6mhz despite the lowest SWR at 14.2mhz. I also used 2 ea 2m radials and I think if I play with  these I can change the characteristics to bring the resonant frequency and the minimum SWR a bit closer together.

I noticed several things while using and testing this length of wire on 20m with the “My Antenna” 1kw 49:1 Un-Un. It is not a balun. Everything to do with this antenna is unbalanced! The performance improved remarkably once we got the feed point up in the air a few meters and out in the open. It does not like to be around other metallic structures or antennas or feedlines. It is also susceptible to noise and nearby radiation sources. I noticed a lot of bleed over from nearby AM transmitters when in AM mode. Fortunately there is a lot of information on the internet about these type of antennas: from those maintaining it doesn’t and can’t work, to those that swear by it. The truth is they do have their problems and one needs to be aware of them. Common mode currents is the big issue. I got rid of most of the noise by installing a 2″ round toroid choke at the feed point. Wound 15 or so turns of RG58 around it. That quietened things way down. Allowed me to stop using the attenuator to reduce the noise and got rid of the AM broadcast bleed over in AM mode. One website recommended a counterpoise of 0.05 wavelength. That comes to 1m for the 20m band so I need to play more with that to see what changes it actually makes.
I might also ground it at the Un-Un seeing it has a ground/radial lug and see what that does.

Another advantage is that it is resonant at any frequency that is a multiple of a half wave. So the 20m version should show resonance somewhere in 10m which it does. Unfortunately; just over 29mhz which ties in with the measured resonance at 14.6mhz.
So with a bit more work I should have a dual band no tune vertical.

Which has go me thinking…Spider beam do have an 18m push up telescopic pole advertised on their website. That is pretty well a half wave on 40m! Soo..40, 20 and 10m on one pole. I think I can do that. Just need to make a suitable mounting point against the house that I could strap the bottom section of a 60′ of tapered fibreglass pole to. A length of 6″ x 3″ treated pine should be enough.  20200117_091649[1]20200117_091723[1]20200117_113612[1]20200117_113716[1]20200118_164312[1]

About David Donaldson

66 and Live in New Zealand now. Hiding from Covid 19! I like to ride my bicycles.
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s