The TransWorld compact vertical antenna is a multi-band dipole with capacity end loading and inductive loading. It does not require any radials or ground system, and is very suitable for a restricted space or stealth antenna system.
It is also very useful for portable operation, and is supplied with a convenient base and carrying bag suitable for commercial aircraft baggage holds.
It is supplied in two possible configurations, the BackPacker is a manually switched antenna covering 20, 17, 15, 12 and 10 metres, band switching being effected by the user plugging in two U-links into the appropriate frequency selection slots.
The Traveller, on the other hand, whilst electrically identical to the Backpacker, and covering the same bands, has its frequency selection performed by relays selected remotely via a control box. Since the radio frequency aspects are identical, their communications performance is similarly identical.
The mechanical and electrical construction is to a very high order.
The BackPacker is probably more suitable for portable operations, as it does not require any power, whereas the Traveller requires a source of 12V to operate on any band other than 20 metres, which is its default state.
TransWorld have recently changed the design of the Traveller. In the previous version, the relay controller was a micro-processor controlled switching unit with momentary action pushbuttons for band selection, or, via an accessory interface cable, a Yaesu or Icom transceiver could control the antenna and switch its frequency of operation depending upon the band selected on the transceiver itself, giving completely automatic band selection.
The present version is simply a rotary switch for band selection, the chosen band being indicated by a LED, there is no capability for a transceiver to control the antenna as before. In addition, the previous micro-processor equipped controller also offered the option of a user-supplied 5-wire control cable being connected by means of terminal blocks at both the antenna and controller end, unfortunately this option has also disappeared, so that the custom control cable and its special plugs are the only means by which the connections can be made.
I had originally ordered a Traveller for use as both a base station antenna as well as for portable operation, but because of some production difficulties this version was temporarily unavailable, and so I settled for the BackPacker. Some months later TransWorld resumed shipments of the Traveller, and also offered the centre section, with its controller and control cable, for those wishing to convert a BackPacker to the remote control version, and I availed myself of this option.
I had made quite some use of the BackPacker for both fixed station and portable operation, and so was quite familiar with its setup and tuning procedure by the time I received the Traveller centre section. When its tuning was checked, it was found that although not resonant at exactly the centre of the various bands, its SWR was sufficiently low that it could be operated from almost any modern transceiver capable of tolerating a 2:1 SWR.
I decided to improve its tuning and it was when I removed the cover that I discovered what to me seemed to be an unfortunate design choice.
The relays used for the band switching were 24V, whereas most amateur radio equipment operates from a nominal 12V supply, typically 13.8V. I checked the relay manufacturer's data sheet, and the worst-case pull-in voltage is specified as 70% of the nominal supply voltage, or, in this case, 16.8V. Worse, as there was a diode and a 10 ohm resistor in series with the relay coil, in fact to ensure that there is at least 16.8V across the coil meant that the actual worst-case supply voltage was now 17.7V to allow for a 700mV drop across the diode as well as that across the 10 ohm resistor.
It has to be admitted that this is a worst-case scenario, and in practice many 24V production relays will actually close with only 12V applied. I measured a few 24V relays of this type, and found that most would close with as little as 10.7V applied, but this is taking unreasonable liberties with the manufacturer's design tolerances, and it means that unless production relays are specially selected for low voltage closure characteristics, there may be some that will simply not close under the worst case conditions.
Bear in mind that the nominal supply voltage of a modern Yaesu, Kenwood, or Icom transceiver is specified as 13.8V +/-15%, meaning that the lowest guaranteed operating voltage is 11.73V, and you will appreciate that as this is significantly below the guaranteed operating voltage of the worst-case relays, then unreliable operation can result. I queried the manufacturer's, but they did not respond.
For fixed station use, a typical nominal 12V unregulated plug-in AC adapter often provides as much as 18V open circuit, and, having a large filter capacitor, this means that it can supply more than enough voltage to positively close even a worst-case relay, especially as the band selection switch has a positive break before make action.
For portable operation from a 12V lead-acid battery the situation is more problematic as the voltage is now definitely below the worst-case threshold.
In my case, I ordered a replacement set of nominal 12V relays from mouser.com and changed them. This certainly increased the total current drain, from approximately 43mA at 13.8V to approximately 110mA. (The LEDs used to indicate the band draw 17mA.) This increase is hardly of significance when one considers that the transceiver draws about 850mA - 1.2A in receive, and up to 20A in transmit. I am quite happy with this, as the increased reliability is worth the trouble.
For others wishing to change their relays, the actual replacement type is: JW1aFSN-DC12V, and is a form-A single contact closure relay. Note that this is the high capacity relay, there is another with the part number: JW1aSN-DC12V which is a lower rated relay and should not be used. The high-capacity relay is rated at 10A, the low capacity at 5A. Make sure you specify the JW1aFSN-DC12V, the F in the part number indicating the high-current option.
Removing the relays is not particularly difficult using a 48W soldering iron and solder-wick. With all the solder wicked up, using a thin bladed screwdriver, gently prise the relay from the board at the contact end of the relay whilst heating the pads with a soldering iron. The relay should lift off its pads quite easily, and then by alternately heating the coil contacts and wriggling the body the other end can be released. Gently clean the pads and holes with solder wick, then remove the flux residue with denatured alcohol prior to inserting the replacement relays and soldering them in.
So much for its design, what about its performance? It is a quite remarkable omnidirectional antenna system, especially considering its size. I had originally intended for fixed-station use to mount it about 2 - 3m off the ground, but when its SWR was checked, it was very high. In fact, the lower element should be no more than 1metre off the ground for optimum SWR.
The antenna is somewhat affected by nearby objects, as one might expect, but provided it is at least 3 - 4 metres clear of any sizable metallic objects, then its performance seems to be relatively unaffected.
The manufacturer's give a complete description of how to adjust the antenna, but it must be emphasised that an antenna analyser is essential. Ad-hoc adjustments without such test equipment will almost invariably degrade its performance. I used a RigExpert AA-230 Pro analyser, which made the job very easy and straightforward.
Once optimised, in my case I can achieve an SWR of 2:1 at the band edges of 20m, falling to 1.25:1 at the centre. The bandwidth between the 1.5:1 points is 180KHz. All the other bands have similar centre-band SWR, on 15m the SWR is 1.4:1 at the band edges. The 17m and 12m bands, being so narrow are 1.2:1 across the entire band. On 10m, it is 1.0:1 in the centre of the band, and 1.4:1 at the band edges. In my case, I have no need of an antenna matching unit when using either my Yaesu FT-857D, or my Kenwood TS-140S.
The manufacturer's recommend that the co-ax feeder should be "at least 65 feet". I have experimented with a variety of feeder lengths, and can find no real difference in performance or SWR with a feeder as short as 4m (12 foot) or as long as 30m (100 foot). Indeed, as the antenna has an internal balun, the coaxial cable should not be part of the radiating system.
The manufacturer's also recommend that the feeder be positioned so that it makes at least a 45 degree angle from the antenna to avoid parasitic coupling. In practice the SWR does not appreciably alter even when the angle is as little as 30 degrees, but the best results are certainly obtained when the angle approaches 90 degrees.
The contacts obtained, mostly on 20m SSB, using 100W, show that 5-7 to 5-9 signals can be obtained for stations within a radius of about 3,500km, 2,174 miles. Basically, if you can hear them, then they can hear you.
I took the antenna to a friend's QTH to compare it with his setup. On 20m he uses a 3-element beam on a 60' tower, but despite the gain of this antenna, the receive signals were only about an S-point lower on the TransWorld antenna. Obviously the directivity of the beam will also help, and of course the omni-directional characteristics of the TransWorld make it somewhat noisier, but even so, given the wide disparity in size the difference in signal strengths means that for a restricted environment the TransWorld is still quite capable of giving an excellent account of itself, and is certainly one of the better compact antennas available.
Overall, I am very impressed with the quality of construction of this antenna, and its overall performance both as a fixed-station and a portable antenna. I would certainly recommend it to anyone looking for a compact, reasonably efficient antenna that is very easy to set up; does not need radials or a good ground; does not need nor requires a high elevation; readily matches to almost any modern transceiver; and is highly effective from a communications standpoint. My only criticism is the choice of 24V relays rather than 12V. Those relays having closure voltages towards the upper end of the tolerance range may not work properly on a typical 12V supply.
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