It's up!
...If you can tune it...
...If you can load enough power into it...
( We did not attempt to stray beyond the General Class band limits because we prefer to remain within the General Class segment of any band we may utilize so as to maximize the number of stations that have the opportunity to work us. )
Configurations used:
Saturday and Sunday we used the ladder rigged straight up in the air as a vertical antenna. It sat on a 16-foot trailer which served as the ground plane. On Monday we moved the ladder into the side yard, and set it up in an A-Frame configuration for the primary radiator, separated from the ground plane by 2x4 lumber. It's ground plane was a closed aluminum step ladder, which in turn sat upon the seats of two metal folding chairs used as saw horses. We figured if the metal-to-metal contact between the step ladder and chairs was conductive enough to matter, fine, and if not, also fine. Provided we were able to tune it up and make contacts with relative ease we don't really care.
Having double-checked our connections, we then reduce power and transmit in RTTY mode while slowly rotating the roller inducting so as to slowly add more inductance to the tuning solution. Watching for a "dip" in the reflected power needle (we are seeking a minimal value of reflected power with a maximum value of forward power) once we see the reflected power drop, we then ever-so-slowly adjust the capacitor's to further produce a reduction in reflected power, while causing an increase in forward power (up to a maximum value equal, or nearly equal to, the current user-selected transmitted power of the XCVR).
Slowly is the operative word here! If you madly swing the knobs hither and yon you very likely will never see the dip!
Once we achieve the best result we can find (defined as minimal reflected power and maximum forward power) we increase the transmitted power, and repeat the above steps. Once that results in the "best tune" we repeat again. Increase power, adjust the coil, adjust the two capacitors. Repeat as needed.
Generally, we start with very low power. Perhaps 5-watts to 10-watts when using a 100-watts XCVR. The second step may have the transmitted power increased to 20- to 25-watts. The third step will bring us up to the order of 40- or 50-watts, and the net step will bring us to approximately 75-watts. From 75-watts, if the tuning process has been smooth and fairly easy, I'll go to 100-watts (my maximum power) but if the tuning has been difficult, or is very sensitive to small changes, I'll increase power to the maximum in smaller increments. Once you have matched the impedance ("tuned" the antenna system) transmit an inquiry: "Is this frequency in use?" a couple times. If you still hear nothing, go ahead and start calling CQ.
If you observe this "tuning up" process while seeking an impedance match between the antenna system and the XCVR, you will note that you are seeking two simultaneous results: (1) lowest reflected power; and (2) maximum forward power. By observing the dual-needle display it is obvious that a low swr is generated anytime the reflected power is very low. I generally find the reflected power is first reduced, and then the capacitors are tweaked to produce the maximum forward (transmitted) power while retaining minimal reflected power. This is to say, during the above tuning process I am most concerned with maintaining a low-level of reflected power, and not overly concerned about the forward, until I reach the final tune. However, if you are not able to incrementally increase the forward power throughout the tuning process there is a good chance something is wrong or in need of adjustment.
For those of us using a 100-watt transmitter, any swr value of 1.5:1 or less is quite good. Further, there is so little power difference between 1.5 and 1.3 or even 1.0:1 swr there is very little reason to seek a "perfect" swr. Also consider that our amateur radio equipment is not lab-quality. For example, when we read a 1.3:1 swr, we have no way of knowing whether that is really a 1.5:1 or perhaps a 1.1:1 swr. Nor does it really matter. Most late-model XCVRs have a self-protection circuit to protect the finals from excessive heat. When I find a difference between my MFJ swr meter and that on my Icom XCVR, I trust the Icom's meter.
When I transmit I want to see the XCVRs power output reaching the maximum (for which I have set it), the swr to be acceptable (anything 1.5 or lower), and the ALC to remain near the top end of it's reading, without exceeding it's maximum suggested limits. (Check your manual for your XCVRs recommended settings.) If the ALC isn't fluctuating in the upper 1/5 of the recommended range I adjust the mic gain until it does.
Given a sheet of paper and pen to log, now we're ready to play radio!
( Usually one of us is working the mic, with pen and paper at hand, while the other enters the log information in the laptop. )
One of its nicest features was the ability to sweep a user-defined range of frequencies at the touch of a button. Sweetness itself I assure you! A comma separated file is also generated at the same time, so once saved under a unique filename, we are able to refer back to this sweep at a future date. Very nice! The only trouble we experienced was getting the device to recognize which com port was needed. That was very clunky and was the most time consuming part of using this device. Still, a great time-saver compared to using the MFJ-269 as we had in the past. And as already mentioned, about 3-times as accurate.
In the following scans taken with the AIM-4170 Antenna Analyzer:
The various screen shots shown below were generated by capturing a "screen print" in Paint, importing that JPEG into Adobe Photoshop, and then cropping and reducing the filesize.
* This includes all satellite stations as well as the official K0S special event station.
To clarify somewhat by example, if one of us were to bring a large tent, we could fly the entire tent as an antenna, but we would not just pull out its longest metal poles and use them as antenna elements. You have to use your common sense. We cannot identify every possibility out there... just don't use plain ol' wire or pipe. Otherwise we'd just be able to go buy long lengths of copper pipe and use them as an antenna (which would work great, of course, but it wouldn't be strange it'd be quite normal). And what's the fun in that? We're after strange antennas!
Please, note that mobile stations are not in and of themselves "strange" nor are maritime mobile stations. Now if you are using the transport itself....
We used this Strange Antenna both Saturday and Sunday. It seemed to work quite well on 20-meters.
We only used the A-Frame antenna for about an hour on Monday. It seemed like it was getting out about as well as the other one, but on Monday it just didn't seem people were interested in talking very much. We had difficulty in engaging in QSO's because it seemed like everyone kept saying "73" before we filled in the log. So we gave up. It was too much like pulling teeth! Besides, it was getting about time to start tearing down the antennas and station anyway. If we missed you, hope to work you next year!
There are many benefits to participating in, and promoting, The Strange Antenna Challenge. It provides a unique "hook" to help secure media attention, it provides learning opportunities to share you rknowledge of antennas systems and impedance matching techniques limited only by your imagination, is a wonderfully intreiging means of engaging the public, and demonstrates the extreme flexibility of the amateur radio service.
Unfortunately, not everyone that participates as a Satellite Station sends us pictures and tells us about the fun they are having, but the following fine folks have! Please, take a few minutes and see what fun some of your fellow hams had this year. And why not consider using this special event to promote your ham radio club next year?
Have we mentioned how much fun this is?
73 ~ Erik n0ew
Having trouble finding something? Use Control F on your keyboard!
73 de Erik, nØew
© 2002 - 2007 Erik E. Weaver, n0ew
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