GAP Titan Antenna -   A comprehensive review of this product appeared in the UK's premier independent radio magazine "Practical Wireless", July 1998.

We tried scanning the review into our PC, but the definition of the finished article was not good enough. We therefore reproduce it word-for-word below.

Antenna Workshop - PW - Antennas in Action, July 1998.

Straight up !

David Butler G4ASR looks at the GAP Titan DX multi-band Vertical Antenna and asks "Will it replace an antenna farm?"

"How many of us are lucky enough to have a suitable location or are able to get planning (and XYL) permission for a tower adorned with a multi-band Yagi. Some operators might even find it difficult to erect a simple trapped dipole covering the 3.5MHz to 28MHz bands. So, instead of thinking horizontal why not think vertical. Verticals can produce low-angle radiation and will work in a limited space. They make a perfect compliment to a horizontal dipole or any other type of antenna you may be using. However there some significant problems associated with verticals in general and multi-band versions in particular. A ground-mounted vertical antenna ideally requires a perfect ground consisting of an infinitely large, perfect reflector. In the real world however the ground is far from perfect with varying degrees of conductivity. Near the antenna there is a need for a good ground system to collect the antenna return currents without incurring losses. A good earth system normally employs a considerable number of buried wires or radials extending out to at least a quarter wavelength from the base of the antenna. Note that a ground rod or base post, although achieving a good d.c. ground, contributes very little to the r.f. ground system. In the case of a multi-band vertical it is conventional practice to use traps, coils or transformers to achieve auto-switching between the various frequency bands. Traps are problematical insofar that they must have a high Q to operate efficiently. Unfortunately this very process means that they also have a very narrow bandwidth thus restricting the overall antenna bandwidth. No doubt you've heard the stories about the use of trapped antennas during snowy and icy weather. On many occasions users have reported the snow melting from the traps. That's because traps can be lossy and the transmitter power heats them up. Loading coils and transformers also possess similar unwelcome characteristics and of course the more components parts there are in an antenna the less reliable it becomes.

New Design

Recently GAP Antenna Products have implemented a revolutionary new antenna design which eliminates the inefficiencies and losses associated with radials and traps. Ironically, the premise for the GAP principle was the result of an anomaly of a quality assurance test. The test was to determine r.f. leakage from what was supposed to be a "sealed" box. Fortunately, one of the technicians responsible for securing the cover, had failed to fully tighten one of the screws. This resulted in small slit or GAP. Since the box was not tight, when energised, the r.f. literally screamed through this tiny opening.

The President of GAP Antenna Products George Henf  KK4CW remembered this and wondered what would happen if he put a slit in a piece of coaxial cable. He hung the cable, cut for the 14MHz band, from a tree and made a slit where electrically he felt he would find a match at 50 ohms. His thinking was that if the feed point impedance of a full size vertical is 36 ohms and the top goes to infinity, then somewhere in between should be 50 ohms. Thus if the proper elevation is selected, the radiation resistance will be 50 ohms, a perfect match to the feedline. It was also found that elevating the feed point also reduced the earth losses.

Technically, earth loss results from the capacitance of the antenna to ground, from above the feed point. Reducing the earth loss eliminates the need for a radial system. Instead a simple counterpoise system is all that is required. There are no traps in a GAP antenna. The elevated feed and the unique tuner rods enable the GAP to operate as a vertical dipole even though it is grounded. Eliminating traps makes the antenna more reliable and increases its operating bandwidth. This is the principle behind the GAP antenna.

Nowadays, GAP Antenna Products manufacture a range of verticals, however the antenna I'm reviewing is the Titan DX shown in the photograph Fig.1. This is an 8-band centre-fed vertical using the GAP technology and requiring no radials. The antenna covers the 3.5 to 28MHz bands, stands a respectable 8M tall and weighs a little over 11kg. It can handle up to 1.5kW of r.f. on all locations except the 3.5MHz band. But it will comfortably handle the UK limit of 400W on any of the designed bands, no matter what the transmission mode.

As can be seen in the photograph Fig.2 tuning rods are located around the central mast section. Lengthening or shortening these will raise or lower the resonant frequency but there should be little requirement to adjust them from the factory settings. These rods act as vertical dipoles on the bands that the Titan functions on. The only exception to this is on the 3.5MHz band, where a length of coaxial cable is used to compensate for the missing portion of the antenna. This cable is terminated in a capacitor, referred to by GAP as a CAP unit.

Specify Slot

Various CAP units are available, so you must specify in which 100kHz slot of the 3.5MHz band you wish to operate in. For European usage you have to choose between 3.5-3.6MHz, 3.6-3.7MHz or 3.7-3.8MHz. This option only applies to the 3.5MHz band simply because the antenna is not tall enough to cover the entire band. I chose the CAP unit for 3.7-3.8 MHz.

The antenna is designed to mount easily on a heavy gauge steel pipe, has an integral counterpoise system and, as the feedpoint is elevated, you can mount the vertical anywhere you wish. It can be located close to the ground, on top of a tall pole or even above the roof of a house. Although the Titan is designed to withstand substantial winds unguyed it's recommended to use guys as a form of insurance.

If you're going to ground mount the Titan then GAP recommend that the pipe is mounted in a  concrete-filled hole (500 diameter by 1m deep).  But as my QTH is 233m a.s.l. on the foothills of the Black Mountains the use of guys are obligatory on a temporary installation. I laid the four rigid counterpoise rods on the ground to see what physical size they take up. I found that they take a square of 3 metres each side. If I'd had more time I would have mounted the antenna just above the flat roof of my garage but for the purposes of this review I located it at ground level.

The Titan  antenna arrived in a  long, large, flat box.  Inside I found all the necessary aluminium tubing, coaxial cable and associated hardware. The main sections and tuner rods are all made of double-drawn 6063-T832 aluminium tubing. This is an excellent material and much better than the less expensive extruded tubing. All of the antenna components have a real quality feel to them and even the coaxial cable is a special type that is rated for very high power operation. A 14-page installation and assembly booklet is also included. I'm pleased to say that this gives clear unambiguous instructions and contains many line drawings and diagrams to help with the construction.

To get started with the assembly you'll need a large flat space, such as a driveway or patio which allows you to find the screws that you drop! All the holes are factory drilled and all you have to do is simply line up a big hole over a little hole and insert a self tapping stainless steel screw with a  (provided) nut driver. The only other tools you'll need are a flat-bladed screwdriver (and a soldering iron and cutters to connect a provided PL259 plug onto the end of the cable).

The main sections of the Titan are designed to telescope into each other and are simply held in place by a steel screw. The CAP unit which dictates the lowest working frequency on the 3.5MHz band slips inside one of the sections and cannot be changed (easily) once completed. All the plastic tuner rod standoff insulators are pre-positioned on the various mast sections. It's only necessary to loosen their clamps, twist them into the correct plane and then re-tighten. The tuner rods simply slip into holes provided in the insulators and are held in place by a locking screw.

Assembly Straightforward

The assembly was very straight forward and I encountered no problems whatsoever. It took me a leisurely three hours to read through the instruction booklet, identify all components and assemble the antenna. Now it was time to place the Titan onto the ground post. Although the Titan is 8M tall I accomplished this task single-handedly, although another "hand" would be useful.

It's better that the counterpoise hoop assembly, shown in the photograph, Fig.3, is fitted after erection. It's a simple matter of slipping in the four counterpoise rods. A length of copper wire is then threaded through plastic caps placed on the end of the rods to make a large square approximately 3m each side. The exact length of the wire affects the centre frequency on the7MHz band but I just set it to the length given in the assembly booklet and left it at that.

Now it was time to check the voltage standing wave ratio (v.s.w.r. but commonly termed s.w.r) of the antenna on the various bands. The s.w.r. is a measure of how well the feed-point impedance of the antenna is matched to the characteristic impedance of the feed line. (As an aside I should mention that in my opinion the use of s.w.r. as an important evaluation criteria is actually wrong. After all a dummy load will exhibit an excellent s.w.r. match across all frequencies! More meaningful would be measurements of antenna efficiency and radiation characteristics but these are far more difficult to measure.) The s.w.r. tests were very easy to perform and the results are shown in the table Fig.4. On all bands between 7MHz to 30MHz the s.w.r. was no worse than 2:1 and in many cases it was considerably better than this. This is excellent as it allows solid-state transceivers to work from one end of the band to the other without the s.w.r. protection cutting in.

After performing these measurements I then had a completely wacky idea of checking the s.w.r. on the 50MHz band. At the bottom end of the band the s.w.r. was very high (>5:1) however much to my surprise the s.w.r. improved further up the band and measured a comfortable 2:1 between 50.980MHz to 51.780MHz. Co-incidentally this covers all of the f.m. telephony channels centred on 51.510MHz.

This was quite a revelation to me but not as much as the surprise I got when speaking to a GAP engineer about this added feature.He said they already knew about this and asked if I had measured the Titan on the 144MHz band as well! When I checked it showed a very good match across the entire band, with an s.w.r. of 1.5 at 144MHz rising to 1.7 at 146MHz. Of course these were the findings of the review antenna at my QTH so there's no guarantee these are reproducible elsewhere.

In terms of results, it's often difficult to quantify how well an antenna performs during a short review period as there is limited time available for playing with it and of course the state of the sun-spot cycle and the prevailing propagation at the time play an equally important part. At it's lowest frequency of operation (3.5MHz) the performance wasn't really surprising as it's only 8M tall. It gets you around Europe reasonably well but DX signals from much further afield were many S-points weaker compared to my dipole.

However once you move up to the 7MHz band and above the performance really starts to become quite impressive for such a relatively low profile antenna. Using the TS690S barefoot (100W) and resisting the temptation of turning on the amplifier I made a number of contacts on all bands. Highlights are difficult to assess (and possibly meaningless to other operators) but as an example of the antennas potential I made DX contacts on all h.f. bands .

And don't forget that it works on the 50MHz and 144MHz bands as well. A quick excursion onto these bands one evening produced three f.m. contacts on the 50MHz band, the furthest being at 90km. Up on the 144MHz band two f.m. contacts were quickly made, one station being 50km away.

Efficient Vertical

If you need an efficient vertical antenna that takes up very little ground space and covers all bands from 3.5MHz to 30MHz then the GAP Titan DX could be the antenna for you. It uses quality materials, is very easy to assemble and needs no tuning adjustments. Apart from the 3.5MHz band it covers the entirety of all h.f. bands with a low s.w.r. I worked some good DX with it on all h.f. bands and don't forget that although not in the specifications the Titan appears to work on the 50MHz and 144MHz bands as well.

Actually the real bottom line is that I thought it was so good I actually bought the review model and you can't say better than that! My thanks to Ron Stone GW3YDX of Vine Antenna Products for supplying the review model. Ron can be contacted at The Vine, Llandrinio, Powys, SY22 6SH. Tel. (01691) 831111 Fax. (01691) 831386

GAP Antenna Products can be contacted by telephone in America on: 561 571 9922, or for those with Internet access, point your web browser at: http://www.gapantenna.com"

G0CGL makes his comments (among many others who are very pleased......)

"I've had my Titan up just over a year in which time I have worked over 270 countries with it. It seems to perform exceptionally well on 40 through 15 with 10m a little poorer and 80m very poor.

Out of the box it is straight forward to assemble with easy to follow instructions. The one serious omission is any tuning information, GAP seem to think that they aren't necessary. However, having found my 15mtr and 12mtr resonant points were too high, I emailed GAP and got an immediate response with tuning information for all bands.

Being trapless, it handles high power well and isn't prone to frequency changes due to moisture.

I have mine on a 10 foot mast and guyed although GAP claim that guys are unnecessary.

Bandwidth seems fine on all bands except 80m where it is limited to 20kcs at the top end.

Overall I am very pleased with it indeed. "

Table 1 - VSWR - GAP Titan DX

* min value 1.2:1 at 3.745 MHz

** antenna not specified at these frequencies

Fig 1,2 and 3 of the review did not scan well enough to reproduce here - Instead we show a line drawing of the Titan DX below.

(Other antennas are available from GAP - please check out the HF Vertical Page for further info.)

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