Cushcraft X7 Tri-bander Review
As more than five years have now passed since
the X7 was first installed, I thought this would be a good time to pass on any
further comments on the antenna.
As you can imagine, I have had a great deal of feed-back from owners of both the X7 and X9. I will pass on a summary of this, along with any further tips on installation and operating experience that I have gained to date. For convenience, the update is concentrated at the end of the article.
The article was originally written for the Aberdeen Amateur Radio Society news letter but, due to the interest generated, I decided to place it on my home page. I have no connection with any manufacturer or dealer, so you can be certain that the content is an honest reflection of my experience with the X7. The original article generated a lot of e-mail which I am more than happy to answer but please, if you have questions, be patient and don't expect an instant reply.
Early November with the wind howling outside and the first touch of snow blowing against the window, definitely a day for being in the shack. I was feeling pleased with myself, having completed all my antenna maintenance during the summer and thinking that for another few years, I could now enjoy the fruits of my labours. Funny how it is at times like this, when things seem to be going so well, that things start going wrong. "Murphy's law" it's called! My trusty tri-bander suddenly developed a very high SWR on 15 meters and a much higher than normal SWR on 10 and 20. It looked as though I had a faulty 15 meter trap on the driven element, but I would now have to wait until the weather improved to confirm this.
Over the past thirty years of operating, I had lost two tribanders, both
having failed through faulty traps on the driven element. As I rarely run more
than 200 watts of power, in both cases it would appear that moisture ingress
had been the cause of the failure.
I remember thinking to myself, wouldn't it be nice if someone could produce a tribander without traps on the driven element. As I was confined indoors because of the weather, I now had time to consider what action to take. If a faulty trap was confirmed, I had the option of repairing the possible faulty trap, or alternatively, replacing the existing antenna. As I was a bit out of touch with the latest models, I had a look through my Radcom to see what was available. By sheer coincidence, there was an advert from Cushcraft, offering just what I had dreamt about. The new "Big Thunder" beams, a triband 7 or 9 element antenna, with no traps on the driven elements and suggesting a performance close to that of a mono band antenna. I just had to know more about this and decided to have a look at the Cushcraft web site. It all looked good and I made up my mind then, that if the existing antenna was faulty, the X7 model would be the replacement.
It was the following week before the weather had improved enough to venture on top of my 45 foot Versa Tower. Replacing the antenna with a dummy load quickly confirmed that the feeder was good and the high SWR was being produced by the existing antenna. Despite the thought of all the work ahead, I was secretly glad that I had the excuse to go for the Cushcraft X7. A few phone calls later confirmed that Waters and Stanton could match any price I had been quoted and as I had always had excellent service from them, my order was duly placed. Jeff Stanton did state that it could be February before they had a shipment from the USA, but as Christmas and New Year holidays were just around the corner and the weather was anything but nice, a few more weeks would allow me to plan the change-out properly. At the end of January I decided to give Waters and Stanton a call to receive an up-date on anticipated delivery. It appeared that they had just received a shipment and my antenna would be dispatched that day. True to word, 48 hours later the carrier arrived and I took delivery of two rather large card board boxes. One 85 inches long and one 63 inches long marked A and B respectively.
Now the fun could begin! Find the assembly instructions and spend the
evening reading all about it. The X7 antenna as you might expect has seven
elements, one trapped director, followed by four driven elements acting as a
log periodic and finally two reflectors. The feed is via a four to one balun to
the matching straps feeding each driven element. Let me stress here that if you
decide to go for this antenna, assembly should not be rushed. There are in
excess of 500 bits and pieces and the first thing is to identify all the parts.
A permanent marker pen should be an essential part of your tool box, along with
two small adjustable spanners, a heavy duty screw driver and a measuring tape.
This is all the tools that would be required, although a small ratchet / socket set would make life much easier. After unpacking the parts, my first impressions were of quality. I am a mechanical engineer by trade and believe that if you are going to expose metal to the extremes of the Scottish climate, then the mechanical construction has to be of the highest standard. No one could fail to be impressed by the quality and precision fit of the components supplied. The Cushcraft X7 is constructed entirely with .058 inch wall tubing, heavier wall thickness than that used in any antenna I had previously owned, but the weight had still been kept down to 60 pounds. The element and boom brackets are constructed from extruded 6061-T6 aluminium. All the hardware is stainless steel and all nuts have a nylock insert. The instructions come in a ten page leaflet which is clear and precise and no one should have any problem with the assembly, providing time is taken to identify and mark the various tubes. The only minor problem I had was of my own making. I had talked my XYL into allowing me to assemble the boom in the living room but an 18 foot boom is not the easiest of things to get out the patio window!
Time for the assembly of the antenna was three days, without rushing. It could probably be built in a weekend if two people were involved, but I would strongly recommend a "one man" operation. It is so easy to get confused as to who has done what, and the last thing you want is to have the antenna up in the air and discover that there is confusion over who did what. The finished assembly is a sight to behold! My first impressions on quality were confirmed when I saw the completed article. As far as I was concerned, the assembly was the easy part. Tower mounting was not going to be quite as simple.
Although my Versa Tower will tilt over, this is not an easy task at my QTH.
The tower is attached to the house and the eaves of the old croft house are only 6 feet above ground level. This rules out the use of the normal winch and involves the use of a two ton chain block, attached to the house, should tilting be required. I have never been concerned about the strength of the chain block, but with the pivot and loading points being only four feet apart, the force exerted on the wall of the house can well be imagined. In the past, I have had visions of the wall of the house coming down! I had already removed the faulty tri-bander by mounting a gin pole on the top of the mast and this was going to be the method used for installing the X7. In my case this operation was going to entail the services of three people. One to do the raising and two to keep the antenna clear of the house and other obstructions. This operation could be the subject of a complete article on its own, so I will not get into it too deep at the moment. Suffice to say that the X7 eventually made it to the top of the tower without mishap.
Now comes the time when we can decide if the antenna works as good as it looks. When the article was written, I did not have the chance to do a full comparative evaluation of the on air performance, as that was going to take several weeks, if not months. However, I was in QSO, working the States, with a local amateur, Sandy, GM3BCL. Sandy is one of the few stations in the UK to have worked all USA counties and he has an excellent take-off to the West. In the past both using Cushcraft A3S antennas, Sandy was always two "S" points better than I was. We were now receiving similar reports, which suggests that the X7 is better than the previous tribander by one, or even two, "S" points. Sandy was soon on the phone to Watters and Stanton to check on the delivery of an X7!
So what happened over the next few weeks? Well for a start, Sandy now
has an X7 on top of his tower!
I was roped into assembling the antenna for Sandy and this time, I assembled the antenna in two, rather than three days. They do say that practise makes perfect. The comparison between the standard tribander and the X7 is probably still the best test to give an indication of forward gain. Sandy of course is totally delighted as he has regained the distinction of being a full "S" point up on me! I have taken a full set of front to back comparison figures over all five bands - yes I did say five bands. Although the X7 is advertised as a tribander, with the aid of an ATU, it appears to offer some gain over a dipole on 12m and 17m. Certainly being able to reduce signals off the back of the beam on 12m and 17m can be very useful indeed. I have measured the front to back readings as carefully as possible, using fixed attenuation and the station of GM3BCL as the source. Sandy is exactly 10 miles from me as the crow flies and was able to give me a steady tone on all five bands for the tests. The front to back readings obtained were as follows: 10m - 33dB, 12m - 15dB, 15m - 33dB, 17m - 9dB, and 20m - 27dB. Cushcraft suggest a maximum of 30dB and I have no doubt that their equipment would be more accurate than mine, so these figures could be slightly on the high side. There could also be some distortion of the figures from ground wave, but you can take them as a general guide. As I said previously, it was not possible to give any clear indication of forward gain and that has been judged to a large extent on the reports received, along with the comparison against the standard tribander antenna. VSWR readings were all within specification, except on 15 meters. There the readings ranged from 1.4/1 up to 2.1/1. I was pretty certain that this would be the result of the close proximity of my 14 element 2 meter yagi, mounted only five feet higher on the same mast. Cushcraft have a technical support service which will assist with tuning and a fax sent to them resulted in a reply within two hours. They more or less confirmed what I had been thinking and suggested inserting a short length of additional feeder prior to checking the SWR again. They also offered further help if the extra feeder did not do the trick. A few trial attempts brought the matching within specification across all three bands.
I have now had the opportunity to compare DX signal reports with other GMs
using standard tribanders and to say that I am delighted would be an
understatement. I received a 5x9+ report from a VK7 who stated that I was by
far the best signal coming out of the UK and I certainly never had this type of
I have had excellent reports from Japan, North and South America, Canada and even New Zealand, which I always found very difficult to work in the past. I have also worked KP2AD on 12m and received 5x9+ reports from USA on 17m, where being able to reduce the signal off the back of the beam was very much appreciated. I would say that the claim made by Cushcraft, suggesting virtual monoband performance on 10m, 15m and 20m has to believed. As I said before, if you invest in this antenna you will not be disappointed. It is not cheap, retailing at just under 500 pounds, but that is only about 100 pounds more than a standard tribander with traps. Having trapless driven elements, to my way of thinking, makes it worth the extra money, even more so when you throw in 12 and 17m bands for good measure. The quality of construction is such that I have no doubt that the 100 M.P.H. survival figures quoted by Cushcraft could be exceeded, without damage to the antenna. I have been asked if I found anything that I did not like about the antenna but the truth is that I can't find anything bad to say, and Sandy is of the same opinion. The only thing I would recommend is fixing the telescopic sections with self tappers or pop rivets. An anti-oxide compound is supplied with the parts and this makes it quite difficult to fix the telescopic sections securely with the hose clips alone. I would also recommend opening up the holes in the mast fixing "V" blocks. They have very little clearance and an extra sixteenth clearance makes all the difference. Cushcraft Technical Support have sent on an optional set of wider feeder straps, which they suggest should further improve the VSWR. The only bands where this would be required would be 12m and 17m, where the SWR is 1.8/1 and 2.2/1. This is well within what could be handled by an ATU, but it would be nice to further improve the SWR if at all possible. I will try to get time to experiment with these straps over the next week or two, but to be perfectly honest, I'm having far too much fun working with this antenna to take it off the air!
Five years have now passed and I felt that now would be a good time to supplement the original article with the experience gained to date. I did change out the feeder straps as suggested by Cushcraft but found little, if any, change on the SWR readings. As the readings I have on 10, 15 and 20m are now all within specification, this did not really come as a disappointment. From communications I have had with other owners of the X7 it would appear that the initial higher than normal SWR on 15m was not unique to my antenna. However, if required, in all cases the addition of a few extra metres of feeder brought the SWR within specification across all three bands. Feeder length seems to have a dramatic effect on 15m which does not show up on 10m and 20m. The surprising thing is that the performance on 15m seems to be exceptional! Please note that the changes to element lengths and the replacement traps now supplied by Cushcraft on later models has eliminated any SWR problems
I have now learned that there was a mistake in the original manual. The metric measurements provided did not match in with the imperial dimensions shown. The imperial measurements provided were the correct measurements at that time. Having said that, there is a new manual now supplied for the X7 which also shows a small change in element lengths and there are also alternative 15m traps available, as mentioned above. The changes are as follows: Element No.3 measurement 207" should be changed to 205.5" and element No.7 measurement 77" should be changed to 75". If desired, the TB 15m traps could also be exchanged for T6 15m traps. These element lengths may have been altered further for later models, so it is wise to check on the latest information form Cushcraft. I am assured that these changes have no effect on the performance of the X7 apart from improving the SWR. If you are happy with the SWR readings that you have, there would be no point at all in changing anything. I would stress this point, as the changes mentioned may raise the SWR on 12m and 17m to around 4 or 5/1. As I have not tried the new dimensions I can not be certain about this, but these higher readings on 12 and 17m were obtained by Peter Hart, G3SJX, after he carried out a review for RadCom, incorporating the new dimensions and traps.
If you are prepared to run low power you will find that the X7 matches very
nicely on 40m. without the additional 40m. add on option and second feeder.
This would not be recommended by Cushcraft but I have found no problems without
an ATU, running 200 watts with an SWR of 1.7/1. The beam seems to offer
no gain over a rotary dipole on 40m. but will provide a deep notch off the side.
Forward gain was measured within 3 dB of that obtained with a full wave delta
loop at 40 feet.
I have received feed-back from other owners of the X7 and X9 beams and all seem to be delighted with the performance of the basic antennas. I am aware that there was a problem with the 40m option but as this was never contemplated at this QTH, I can not pass on further details. A note from Dave, KC7DM, mentioned that the feed straps feeding the driven elements tend to buckle as the boom droops. I did not encounter this problem, as in my case the feed straps were fitted after the beam was on the tower and I have not noticed any deflection of the boom since it was installed. The only other point worth noting is that some owners had problems with high SWR readings across all bands. The reason was traced to the connections inside the balun, which had only been tightened finger tight. Well worth taking the lid of the balun and checking these connections, before you mount the beam on the tower.
Have I found any problems? Well yes, I did have to go off the air for a few
days, but this was to change out the rotator! My 20 year old Diawa rotator
decided it was past it's sell by date and has now been replaced by a Yaesu
G-1000. Hopefully it will last for the next twenty years! The only other work
that the X7 has entailed was the addition of guy wires to the tower. My free
standing Versa tower looked a little slim when supporting the X7 and I decided
that caution rather than valor was called for.
As a matter of interest, the highest wind speed experienced to date has been 75 m.p.h.
Turning to the on air performance of the X7, I can only say that I am
totally delighted in all respects. I have worked mainly SSTV on 15m, with
regular skeds to Japan on 15m and 17m. Calling in to pile-ups on 20m these
days, nearly always results in an instant reply. It's truly amazing the
difference a few extra dB can make to your operating pleasure. Although not
vastly different in size compared with the previous beam, performance is very much
superior and Cushcraft certainly seem to have come up with real winners with
the "Big Thunder" series.
John Cramond - GM4NHI Any questions? Just send me an e-mail.