My R7 Restoration Project
I had previously owned a R5 for 4 years and enjoyed it so much, but it was lacking bands I needed an antenna for, they were 40 and 30 meters. Seeing as I already have a double bazooka up for 80meters and it does well enough, and already owning a Hygain 18AVT, I did not really like the thought of mounting it on my tower especially seeing I also have a Cushcraft ATB-34 on my main tower, it would be quite difficult to maintain the turning abilities of the triband yagi while having ground radials on the Hygain vertical above it. So After a wee bit of searching I decided on a Cushcraft R7. Now it was to find one, seeing they have not been made for more than a decade they are getting quite rare. So my journey begins with a posting on the “Tower Talk Reflector” After a couple of days I finally netted myself a used R7. While I awaited for its arrival, I started with some research and found there is not a whole lot of information regarding the setup of these antennas, there are a few great sites with repair/maintenance information, but when it comes to the actual setup of one, other than the manual on Cushcrafts website, I was not able to locate much information.
Well about 4 days later it finally arrived, and to my dismay it was not as advertised, the seller had told me it was cleaned and then put away after he had decided to purchase a different antenna, what he did not tell me was that when he had taken it apart to clean it, he never bothered for what ever reason to take accurate measurements of the traps and details on how it was assembled. None of this was apparent at first, but I soon came to this realizeation once I had followed the manual and installed it on a test site in my back yard, man talk about a major disappointment. Not one of the bands loaded up anywhere near the edges of the bands. So down it came and I brought it back into the shack, I checked and double checked my measurements and all were within ¼” so where did I go wrong? Next thought was did I use the wrong traps in the wrong location on the radiator, So after a close examination of the manual and the lengths cushcraft has listed it did not take me too long to come to the realization that I had a much more serious problem on my hands. So Back to the PC and Google. I entered in “Cushcraft R7 trap Information”, the very first link took me to a past posting on the tower talk reflector, and low and behold it was posted by the same person I had purchased the R7 from. And in detail he went into how he had attempted to clean the antenna and failed to make any recorded information how the traps went back together. Oh boy was I in a tight spot now. I could literally feel my heart race and my stomach sink to my knees. So back to the tower talk reflector with my next question, I was hoping someone out there had a R7 spare or complete one that they could take some detail measurements for me. A few days went by, and then I finally heard from Dave K1HT
He had an R7 he bought for parts and the traps were all there, so he then offered to take the measurements I needed, I quickly opened up Windows Paint, yes the cheap drawing program that comes standard in Windows XP. I made some real crude drawings of the traps along with some areas I was considering to be very vital to the assembly of the traps. Within a few days Dave had gotten back to me and provided me with dimensions he said was accurate to 1/16” and he was not kidding, man they were so good that once I re-setup the traps with his dimensions , BINGO !!! Suddenly I went from totally nonresonate antenna to one that loaded up on almost all bands, not completely where I wanted them to but close enough to work with. The only band that was still causing me grief at this point was 17meters no matter what I did it still would not load anywhere near legal transmission on that band. I know most may have quit at having 10-40 without 17M but not me I wanted it to work and work right and would not quit there. I then sat down and tried to think like someone who may have made the booboo of taking this antenna all apart and not knowing how it went back together. At this point I was really stumped. Until it hit me like a ton of Bricks, the traps are comprised of a coil, and a capacitor made up of a length of aluminum tubing with insulative tubing inside of that then a smaller rod that slides in and out of the insulative tube to create a variable capacitor. Simple enough if all the parts are in the right place I guess, wait a minute I have been so obsessed with the measurements of the cap tubes, I totally ignored the fact that the trombone sections or the sliding part of the variable caps could be in the wrong trap assembly. Not wanting to pester poor Dave any more than I have already. I got to thinking, if 10-15 is fine SWR wise, and 30 and 40 are acceptable but not quite what I wanted , what possible combination could be mixed up and how would they go in order to make it right again. Well I pulled the trombone from the 30M trap, No way; it is way too long to go inside any other trap than this one so back it went. That then left just the 20M and 17M traps being mixed up, could it really be that simple? Oh yes it could as soon as I swapped the two trombone sections, I now had a HF vertical that not only was designed for 10-40M but it loaded up SWR wise right exactly where I wanted it to… Man what a stroke of luck.
Well now that I have it operating well with an excellent VSWR, I then asked myself, how can I a) prevent this from happening to myself again, B) hold these settings while I mount it on my tower without disturbing them should I bump it on the way up and on top of the tower as well as c) possibly eliminate the problems some people have mentioned about the problem with rain getting into the traps and raising the SWR.
Well here is what I did …
1- To start with the heat shrink tubing on mine had been replaced some coax seal, or self amalgamating tape, not my choice to keep the weather out for long periods of time, So I removed the tape and got my mitts on some high quality Heat Shrink Tubing, The stuff I used has a substance that melts when it is heated and adds to the sealing of the item in question, I have used this product on the coils of My ATB-34 and that was many years ago and it is still holding and sealing very well.
2- Ok phase one was taken care of, now if you know anything about the R7 at all, u will know some traps are mounted in reverse to others , what I mean for example the 30M trap the 2 capped ends face upwards, while the 20m and 17 meter as well as half of the 15M trap all have points where the trombones face upwards and no amount of heat shrink tubing will seal this joint 100%, so I then proceeded to make use of some Silicone Sealant, being I am a window installer by trade I have access to some real quality stuff, So once all my traps were tuned and set where I wanted them and after I had redone all the heat shrink tubing on the spot where the main cap tube and the trombone meet I then went one step further and injected a small amount of silicone sealant into the ends of a second layer of heat shrink tubing and proceeded to heat and shrink then up. After a day or two the silicone had setup, and being UV resistant stuff I feel I know have the best water tight seal against rain and weather related moisture possible by me.
3- After that about the next thing for me to do was to ensure no part would come loose by way of wind vibration, so here I used a small amount of lock tight (I used a very light grade product here) In the event I ever have to dismantle the unit I can still do so with a wee bit of effort.
About the only other step I took to lengthen the life of this antenna was to put a couple light coatings of Epoxy resin on the fiberglass insulator at the base of the antenna and painted in with Black UV resistant paint.
That’s it for now, I will advise how well it works after the next contest, I was able to do all of this and get it ready to test at the 5 foot level in time for the last hour of the BARTG HF RTTY Contest, and it seemed to work quite well, with only my Hygain 18AVT and my 80M bazooka to use as a comparison, it out heard all of them, keeping in mind my HyGain is ground mounted , less than 1 foot off the ground and it is 4 feet deep in snow… HiHi!!! So it is not working very well at the moment, but I did manage to work some England on 20m and USA stations on both 20 and 40M I also was lucky enough to work a station in Uganda on 40M which made me feel quite good about the antenna and how it should perform once it rests at the new tower location. But that will have to wait as I messed up my back struggling to get the R7 on top of the temp mast one night in high winds.
I will update this page once I have it installed and have had a chance to work some real dx…
Until next time 73 and CU on the bands…
de Marc Tessier – VE3TES