Review of the Challenger DX Antenna by GAP

This review of the Challenger DX Antenna by GAP Antenna will not be a highly technical review, it will be performance based, using my existing antennas for comparisons  First off, what is the GAP Challenger, and how does it work?  You must be an ARRL member to get the QST article covering that, it is in the January 1995 issue.  I would provide the article, but copyright forbids me from doing so.  You will have to go to the ARRL’s web site and get it.  Once you read that story, you will understand a bit more on the GAP.  Basically it has a very limited number of radials, and still work well.  Why so few radials?  Because it is not the traditional 1/4 wave vertical, it is a vertical dipole, this gives it several advantages over a standard 1/4 wave vertical.  Chiefly the reduced number of radials…  I also have a 30 Meter Mono Gap, (see review here), and it has the same number of radials needed, three, and they are short.

Mounting:

My setup has the Challenger ground mounted, in the middle of a large field with a metal fence running along one side perhaps 30 feet away.  Other than that, there is nothing within 50 feet of the antenna.  It is on the side of a very gentle slope slightly sloping downwards towards the North maybe 20 feet down in the first 100 feet from the antenna, and sloping up perhaps 20 feet to the south at the 100 foot mark from the antenna. It is mounted in a small hole, using the insulating post supplied with the antenna.  It is not on a tilt base, nor does it need a radial field, which is the number one reason I bought it.  I primarily operate on 40 through 10 meters, so any discussion of 80 Meter operation is useless from my point of view.

Grounding:

There is a single ground rod at the base, connected to a bulkhead connector, after four turns of the included yellow coax as an RF Balun.  The recommended three radials are spread out at 120 degrees from the antenna, and tacked into the ground using lawn staples.  The feedline is grounded at a remote switch perhaps 15 feet from the Challenger.

Guying:

I have three non-conducting guy wires, running roughly at 120 degree intervals tied to various objects around the antenna.  The guy point on the antenna is about half way up.  Even though GAP says you don’t need to guy the antenna, it makes me feel better.  I have seen the 30 Meter Mono Gap stand up to 45 MPH winds, with no guy lines, but, I will be adding some in the summer of 2015.

Feed:

The coax feeding the antenna then dives underground into a PVC conduit running about 25 feet to a remote antenna switch, then about 75 feet to the shack.  GAP recommends at least 65 feet of feedline…

Overview:

I operate mostly on 40 and 20 meters, of late, (winter 2013), my 40 meter operations have been severely curtailed by some local RFI.  I have used the Challenger on all ham bands, and a brief report will follow…  First off, I believe that if you don’t guy this antenna it will fall over in a high wind, high being defined as anything over 40 MPH.  Although GAP indicates that you can put it up without guys, I elected to use them, and it makes me feel a LOT better.  If you get any sort of wind, the antenna begins to bend at alarming angles.  Hence why I guyed it.  Guyed this antenna has stood up to 60 MPH winds here in Oregon.  The radials are each 25 feet long, and become invisible in the grass of the field it is mounted in, and can be mowed over after only a few weeks.  One of the reasons I selected the Challenger was the lack of a major radial field to make it work.  I have had several vertical antenna  up, some with a 120 radial field beneath them.  The GAP Challenger outperforms them all on 40 and 20 with ease, mounted in almost the exact same location.

Reference Antenna:

The reference antenna used to compare  the GAP Challenger to is a BWD-90 by B&W mounted about 25 feet off the ground, and in a sharp V configuration, not a really good DX antenna, but great for NVIS.  If you are unfamiliar  with the BWD-90, you should know that it really just a very long dummy load you hang in the air.  It has negative gain…  It is about two S units less in strength than a normal Dipole, in my configuration.

Assembly:

The GAP Challenger DX is not difficult to assemble, but you should be paying attention during the process…  See the GAP Challenger manual here for assembly instructions.  I routinely take mine down and rebuild it every few years, replacing any cable clamps used for the radials, and looking at each connection to be sure all is well.  Although GAP does not recommend the use of Pentrox, I use Pentrox on every connection, the antenna comes apart very easily later on if I use Pentrox.

Use:

80 Meters:

As I said, I do not use 80 Meters much, (as of 2014 I have started using it more on 80), but the little use I have had has been good for DX, and bad for local, which is to be expected in a vertical.  That is not GAPs fault, it is the nature of how antennas work.  The GAP Challenger is about one and one half S unit better than the BWD-90 on DX, and about an S unit and a half worse than the BWD-90 on local, (US), contacts.  I am sure that this is due to the vertical polarization and launch angle of the GAP Challenger.  The BWD-90 is horizontally polarized, so it is not going to do as well as the GAP Challenger for DX.  The GAP Challenger does perform much better than an 18AVQ, ground mounted with 120 radials for DX in my location for both DX and local.

40 Meters:

This is where the GAP Challenger DX starts to shine…  Again, compared to an 18AVQ the Challenger DX easily outperforms the 18AVQ, as well as the BWD-90.  In fact, I would go so far as to say this is the best non-directional antenna I have ever used on 40.

I have had a Bobtail curtain array up for 40.  The GAP Challenger, while nowhere near the performance of the Bobtail, would give the Bobtail a good run.  I run 1500 Watts into the antenna, and have in RTTY contests, so the antenna will take power and not fail.  I believe it takes power so well due to the lack of traps.  The antenna is 39 feet tall, so getting it to resonate is simple…  You trim the radials…  At least as per GAP…  In my case I have NEVER been able to get it to resonate at the bottom of 40, mine resonates on 6.7 MHz.  I just, (2014) shortened the radials in a effort to tune and the resonant frequency went lower!.  So come summer I will lengthen them back again, and try and get it to 7.000.  It likes 6.7 MHz.  I use a tuner on it, and it works just fine…  I could probably contact GAP about this, but to be honest the performance on 40 is so exceptional I no longer care…

20 Meters:

Again the GAP Challenger performs better than anything non directional I have used.  Again, it is way better than the 18AVQ was, and it is way better than the BWD-90.  All as expected.  The GAP Challenger does tune on 20, so I use it with no tuner.  Again, 1500 Watts RTTY and no issues.

15 Meters:

Not so good…  It resonates on 15, but the performance is much worse than the BWD-90 on transmit, and receive, the difference is also not symmetrical, which surprises me.  I would have expected that if I were three sunits less on receive, I would be on average three S units less on transmit– not the case.  The GAP is about on or two s units less on receive, and on 15, about four S units less at the far end of things…  I also would have expected the GAP Challenger to work better than the BWD-90 on 15 Meters in all cases.  I think it is worse than the 18AVQ as well, but I had the 18AVQ up during sunspot minimum.  I am less than pleased with this antenna on 15, and almost never use it there anymore.  It is quieter on receive on 15 Meters than the BWD-90, and it has a much better S/N ratio than the BWD-90, (again a surprise), so much so that you can hear things on the GAP, that are not even hearable on the BWD-90, but there is a marked difference in transmit levels, sometimes as much as three S units better with the BWD-90.  I think all of this is telling me I need to re-address my 15 meter antenna setup, as well as my 80 meter setup.

10 Meters:

About the same as 15 meters, and again this surprises me…  I would expect the GAP Challenger to work better.

6 Meters:

Pretty much useless as compared to a 6 Meter J pole.

Conclusion:

Overall, given that I use 20 and 40 most, with some occasional use on 80, and given that I almost never do local 80 meter work, the GAP Challenger is by far my antenna of choice for day to day operation.  About the only issue I have with this, (and any other vertical), is the RFI pickup.  All vertical antenna pick up RFI much better than dipoles do, so the GAP Challenger picks up RFI really well, except on 15…  Also, given that the sunspots are only going to be around for a few more years, I will revert back to the GAP Challenger for 80-40 operation.  On 20 I will have a beam up soon, so the relative usefulness of the GAP Challenger will be reduced.  I will then investigate a full sized vertical for 40.  I do have a second GAP Challenger I bought to mount on my roof.  I will add an addendum here when that happens.  If I were in a limited space environment, I would pick the GAP Challenger over any other antenna.  It is almost invisible when up, (use thin guys), does not need a major radial field, and in general works well for 80-40-20 meter operation.  Please remember these results are for my installation only.  You may be able to do better, or worse than this…  If by chance you know of a way to tune this antenna on 40 please add it as a comment.  Would I buy this antenna again, yes, diuspite the issues, it performs so well on 40, and 20 that I really don’t think I could get anything to compare to it without a tower.

Addendum:

06/02/13:

I have decided to not roof mount the Gap, but to use it in a phased array for 40 Meters.  I rebuilt my first antenna from scratch.  Over a decade, that antenna had preformed very well, and really had zero issues.  I used at full legal power, and upon disassemble saw no issues whatsoever with it.  Reassembly was a lot simpler than I remembered…  Overall I still like this antenna.

I am considering using a set of GAP Mono band antennas for my 30 Meter four square array.  The concept of a smaller radial field by using these give me great thought as opposed to using a stock 1/4 wave vertical.  I will probably purchase one to test soon…

10/01/14:

I have given up on the idea of phasing a pair of GAP Challengers…  I will be looking at mono GAPS for phasing next…  The antenna is too complex to phase easily, too many ways for things to go wrong in the phasing process with this multiband antenna.  While I could get the correct phase relationships, the RF amplitude at the base of each antenna was wildly different from the other antenna, so rather than try and fix things, I decided to scrap the idea of using a multiband antenna, and work with a more pure antenna, and yes, I was using a Christman Feed.  I think because the Challenger is a multiband antenna phasing simply is not going to work.

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