A Tank For An Antenna

ORIGIN At one of the meetings of the Tynemouth Amateur Radio Club in the spring of 2006 somebody brought along some a few bits and bobs to pass on if any body could make use of them and at the end of the evening there was a green rod left.

I picked it up and was examining it when one of the members told me that it was a section of a Tank Antenna and I needed 4 sections to make an antenna for use on the Amateur bands. He told me to take it and to hold onto it as I would only need three more sections to be up and running.

A short while late I received a call from the same club member to say that he had a complete Tank Antenna and if I was interested in it I could have it for a donation to club funds. 

I hot footed it around to his house and made a donation in exchange for it, the Tank antenna as previously outlined consisted of four rod sections, a top, middle and two bottom sections which measured about 4.9 metres when fitted together. The sections are constructed out of sprung steel (so I’m told), given a copper coating and painted green. They have a short broad thread on them and are pushed together and given a quick twist to join together.

MOUNTING Having bought my Tank Antenna, I now had to figure out how I was going to mount it. Another club member had a spare mount which he gave me. This consisted of a short metal tube that the Antenna fits into, a metal collet that tightens to secure the Antenna, and all this is mounted onto an insulator which is about three quarters of an inch in diameter and a couple of inches long.

For several weeks I pondered on how I was going to mount the Antenna with or without the mount that I’d been given. While looking at mounting options in my garden one thing that really struck me was that it has a low impact visually. Looking on the internet you will see vertical antennas on the market that are mounted close to ground level so that was an option. There is also a lot said about Stealth Antennas and I thought that it might be a good antenna to mount at the top of the fence and couple it to an auto ATU.

In June 2006 a couple of us from the radio club decided to go out for the day and play radio, it was planned to go to a local farm where we have been lucky to gain permission to use for our various field days. With this planned I worked a bit quicker to sort out a way of mounting the Antenna. Looking at the insulator there is a hole underneath and I wondered if it would sit on top of a section of fishing Pole. It would, but there would be too much flex and it would probably fall to the ground. However, the insulator would fit inside a Swaged pole and also inside a section of fishing pole. I had a couple of spare sections off a fishing pole that was broken as a result of my son using the pole to retrieve his Frisbee out of a tree, he took it apart and put it back together again the wrong way around and trying to sort it out damaged a few sections of the pole, so I now had two spare sections.

In June 2006 a couple of us from the radio club decided to go out for the day and play radio, it was planned to go to a local farm where we have been lucky to gain permission to use for our various field days. With this planned I worked a bit quicker to sort out a way of mounting the Antenna. Looking at the insulator there is a hole underneath and I wondered if it would sit on top of a section of fishing Pole. It would, but there would be too much flex and it would probably fall to the ground. However, the insulator would fit inside a Swaged pole and also inside a section of fishing pole. I had a couple of spare sections off a fishing pole that was broken as a result of my son using the pole to retrieve his Frisbee out of a tree, he took it apart and put it back together again the wrong way around and trying to sort it out damaged a few sections of the pole, so I now had two spare sections.

I decided to mount the antenna at ground level and cut one of the poles down and fitted the mount inside. I had a Ground Spike from another manufactured Portable Antenna, so I decided to use that, and the Pole fits nicely inside the tube attached to the ground spike. The Antenna was now mounted and supported.

RADIALS The next thing that the Antenna needed was Radials. The Antenna is about 4.9 metres long, so you don’t have to think too hard to work out that it was around a quarter of 20 Metres. Thinking back to a talk given by the Chairman of the club at the time on ground planes and radials I remembered various points discussed and using these principles I made up 12 radials. In the talk given to the club it was mentioned that a good number of radials to use was 120. I couldn’t manage 120 so I decided on 12.

I mounted the radials on a bolt that was connected to a short earthing strap and that would then be attached to the Spike or Pole. I have a SOTA beam which comes with a length of coax with a BNC connector on one end and lengths of wire soldered to the centre core and outer braid of the coax cable with crocodile clips attached to clip onto the antenna. I had made up another similar length of coax with a PL 259 plug on the end, so I used this and connected the centre core of the coax to the metal collet on the antenna mount and the outer braid to the earthing strap which was connected to the radials. I made the radials slightly longer than the antenna with the intention of folding them back until I got the SWR correct and I would then cut them to length. I attached automotive connectors onto the radials in order to thread them onto the bolt.

OPERATION On the 8th June 2006 along with other  members of the club we went to the Farm to play with our Radios and Antennas. Three of us have Yaesu FT 817’s and we were going to have a QRP day. I took along the Tank antenna, my 817, an SWR meter, an ATU and a small amplifier because my previous attempt at portable QRP operating I didn’t have any success with SSB and I had other people nearby using higher power. To power the entire set up I also took along a Leisure Battery, over the top I know but I wasn’t going to take any chances and if I wasn’t successful with the QRP I was going to use the amplifier, so the extra power would be handy.

I set the Antenna up, connected it to the radio and switched on. Immediately I was receiving good clear strong signals. I hooked up my SWR meter and checked the SWR and it appeared to be spot on, the needle only moved a fraction on the meter. I called the others over and checked the SWR again to show them how good it was (I expected to be fiddling on with the radials for some time to get the SWR right). When the needle hardly moved there was a comment that “It’s broken”. I kept the SWR meter connected to the radio, but I could have actually removed it. I made only made 12 contacts but at a fairly leisurely pace, it was also a social event with plenty of chat. My first contact came after a couple of CQ calls and was with Ian G3PHD in Tilbury, Essex who gave me a 5 & 7. I had one 59 report, a couple of 57 and a lot of 55 reports which when you actually take time to understand the RST system of reporting 5 by 5 reports are perfectly satisfactory. On this first outing I contacted a German station DQ2006S who gave me a 55 report and he obviously found it hard to believe I was running only 5 watts, he kept asking me to confirm I was QRP I confirmed it and he came back to tell me that he was transmitting 500 watts.

At a fun club event on the 15th of July that year a few of us organised a QRP Barbecue come QRP competition. The basic idea was that we would have a day out at the farm, do some operating and have a barbecue. The competition side of events was a wire dipole for 40 metres verses the Tank antenna for 20 metres and Yaesu 817’s as transmitters. Competitors would have a 15-minute slot on each antenna and the person with the most contacts was the winner. There was an adjudicator sitting with each competitor to verify the number of contacts. It was a great day out with fantastic weather, good food (if I do say so myself), good company and overall it was good fun.

DEVELOPMENT Since that first outing and success with my antenna I have made another coax lead with automotive connectors on to tidy up the connection between the coax and the antenna, I have also tidied up the connection with the radials. I have also shortened the section of fishing pole which sits inside the ground spike, it was initially too long and one windy day with it moving about it split the fibreglass tube and fell over. Lowering it takes away that strain on the tubing.

During another day out on the farm in mid-February 2007, my first contact of the day was with PT7CB in Brazil! Wow I was over the moon; this was using the internal batteries on the 817. I also had a contact with CN8PA in Casablanca which was a first for me, so I was also very pleased with that.

Initially the Antenna was not intended to be used solely for QRP and it could certainly be used with more power or as a home base antenna, but I get such a buzz from making a contact using it on QRP that I am now totally hooked, and I would always keep sure that I have a Tank antenna for portable work.

Coming up to date in August 2018 twelve years on from when I first used the antenna.

I still have the antenna; the connections and radials are still working perfectly, and it has been used on many occasions at various power levels. The only further development that I have made with it is a tripod mount for use when I’m on a hard surface and cannot hammer the ground spike into the ground. It is a camera tripod that I was given with the tilt/mounting head on a central pillar that can be raised or lowered in the tripod. I simply took the tilt head off and the section of fishing pole with the antenna mount attached slides over the top of the pillar.

Give the Tank antenna a go, you’ll be very pleased with the results.

Enjoy your radio…

Graham M0GAE