CHA TD, Broadband Terminated Dipole

Update 03 June 2017

 Some days ago, with help from Carl at Chameleon Antenna, I found the errors I made in the configuration of the CHA TD. Rather than having the counterpoise wires along the ground, I had them terminating above-ground. Allowing the counterpoise to lay along the ground, brought the SWR down on every band, but especially on 40, 17 & 12 meters. On the lower part of 6 meters, SWR increased. This was an incredibly silly mistake to make! Now it’s time to start the tests again.

160-10m SWR
On the wide sweep SWR looked much better. The sweep started to appear more like Chameleon Antennas own plot. Now we know the plot results are attainable by anyone deploying this antenna themselves, provided the engine is deployed correctly.

Band by band SWR
Looking at the results one band at a time they actually look much better than they did in the whole HF band sweep.

WSPR Results 
I must point out that I continued WSPR testing since I corrected the configuration. The new configuration of picked up an average of 600 kilometers on my DX10 results, compared to the incorrect configuration I used previously. Moreover for the first time I picked up North America on 30 meters with this antenna. Something I certainly thought was possible, but wasn’t seeing it earlier.



I hope these new results support the idea of continued testing and fewer assumptions. Some of my regular readers incorrectly assumed the antenna must be bad. The only thing bad about this antenna was the fact that I deployed it incorrectly. So it’s important to continue the testing to ensure the operator himself is not the problem.

Original article
In early January 2017, I received a very nice package in the post from Chameleon Antenna. The package contained things which for the most part, I expected. It also contained things I had no idea about!

In radio communication, a travelingwave antenna is a class of antenna which use a traveling wave on a guiding structure as the main radiating mechanism. Their distinguishing feature is that the radio-frequency current that generates the radio waves, travels through the antenna in one direction.

One of the surprise items was the CHA TD. The CHA TD is a Broadband Tactical Dipole, which in theory, requires no tuner from 80-10M. WTH Julian? Seriously? Yeah seriously! For those of you who have followed www.survivaltechnology.net, you know I’ve had the goal of setting up a broadband antenna systems for somewhat automated Digital comms and band hopping on HF. Think about how simple life would be if you didn’t have to stop and tune each time you require a band change. An operator literally having to push a botton to tune an antenna. This is 2017, and it should be possible to have a high performance antenna, with acceptable SWR on our desired bands, which requires no user interaction. What is acceptable SWR is another question to cover in the future. For now, this will have to do.

Ever since I saw this image from Bonnie KQ6XA I realized I had already been exposed to the Broadband Terminated dipole albeit, in slightly different form. In fact, the ALE HF Link Community has been talking about these type of antennas for quite some time. As I try to focus on one project at a time on the channel, I didn’t immediately make the connection between these two systems. Although this article is about the CHA TD, much can be learned from the work done in HF Link community, so please do check out those pages.
The very first thing I wanted to do was an SWR sweep from 160 meters through 10 meters. There’s no need for me to offer an opinion on the results, they are what they are. In yime i’ll run the tests again, because I’m cutting down a few trees on my property for firewood. Not having these trees in the way, will allow me to deploy the BBTD more effectively. 

Naturally I also did some WSPR testing. First I ran WSPR on individual bands. Then I tried band hopping using  WSJT-X on 5 unique bands, HF band hopping. Finally I am running the  WSPRlite @ 200mw. Here are some non-scientific results.


Initially I thought this was going to be a magnificent antenna for a digital  field station.  In fact I still believe that to be the case,  it’s just not one of those antenna systems, which will be rapidly deployed by one operator. This is definitely the Basecamp system! I know this actually might sound like a complaint, but it’s not and I need to explain why. Testing this antenna with the center at 12 meters on my tower with the legs in sloping dipole configuration, I could swear I was operating QRO when testing using psk31. The system is that good! The things I could hear,  and what happened to the noise!? I immediately sent Carl an email and told him he needs to make a QRP/20W Ultra lightweight version of this antenna. This setup, with a telescoping pole, is something I could get behind for one tool in our comms toolboxes. 

Operating
What I could work with 2.5-5 Watts through my other antennas, I could work with 500 milliwatts with this BBTD. I know I know, this is totally a no-brainer Julian! It’s a dipole, mounted on a tower, extending out to two trees, I get that! One just can’t be prepared for the level of performance when you’re used to operating with normally compromised equipment. It’s no wonder the military, non governmental agencies, aid agencies, … use a similar design concept, for critical Communications.

Practical benefits of this system

  • Broadband
  • No tuner required
  • High duty-cycle digital modes are a non-issue
  • QRP & QRO Compatible
  • Reasonable performance
  • Lots of deployment configuration options

Downsides

  • I deployed this antenna by myself, but would’ve preferred having help.
  • In it’s most effective dx configuration, I lose all NVIS range stations.
  • It is a very big antenna!

I’m going to keep up the testing and come back to this system regularly.

de Julian   oh8stn