2008 KØS, Strange Antenna ChallengeSM

Hosted by Erik E. Weaver nØew and Dwayne T. Walker wb5plj,

Event Dates: May 24-26, 2008


UPDATED: June 7th, 2008

 


Vertical is up

It's up!

 


      ...If it is metal...

                     ...If you can tune it...

                                    ...If you can load enough power into it...

...You too can make contacts!


2008 Recap

This year Dwayne and I remained inside the 20-meter band the entire time we operated. We used an aluminum multi-task ladder as the primary radiator, which is one of those ladders that can be bent into a variety of configurations. It is approximately 15-feet long when fully extended. It seems to work quite well as an antenna! We found it to be very wide-banded as well, which given it's girth is to be expected. Once tuned on 20-meters we were able to graze anywhere within the General Class of the 20-meter band without needing to retune the transmatch.

    ( 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.

Basic Connections

We connected to the Strange Antenna with a short length of wire using hose clamps to press the tips of the wire against the metal. The opposite end of the wires lead to a home-made 1:1 current balun. This is used to help insure the RF is kept off the outside of the coax shielding. We do not wish the transmission line to become a radiating element of the antenna system. The coax used was 78-ft, 4.5-inches, of LMR-400 (measured from the base of the PL-259's tip, to the base of the opposite PL-259's tip). The coax was then connected to a MFJ-969 "Deluxe Versa Tuner II" transmatch. This model uses a roller inductor going to ground with two air-variable capacitors completing a "T" configuration.

Why Use a Manual Transmatch?

We have found a manual transmatch is much more flexible, and offers a wider range of impedance matching ability, than auto-tuners we have tried. It is also very convenient to observe the dual-needle display while tuning up the antenna system. Strange Antennas can be especially delicate in their tuning, so a fine touch is helpful. Also, auto-tuners are often "Go/No-Go" black boxes. If they don't find a successful match, you can't use the antenna system. With a manual transmatch even when you can not find an optimal impedance match you can often make use of a less-than-perfect impedance match. This will not allow one to transmit at full power, but one can in fact transmit at a reduced power output. During an emergency this may be a critical difference.

How Do We Use a Manual Transmatch?

Generally we start tuning a Strange Antenna by placing each capacitor in it's mid-position, and then place the roller inductor at one extreme of its range. Shorting out the entire coil, so the smallest amount of coil will be used when we find a successful impedance match, is best. ( If you haven't used this specific transmatch before, open the case and observe which knob settings produce minimum and maximum settings of all the critical components. ) At this point double-check all your connections and ensure you have the transceiver (XCVR) and transmatch properly connected, and that the proper antenna is selected, and that you are in the "tuning" mode vs. "by pass" mode. If any questions remain as to the proper operation of any of your equipment, find the answers before transmitting!

    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. )

AIM-4170 Antenna Analyzer

This was the first year we used the AIM-4170 Antenna Analyzer to record the complex impedance of the antennas we employed. This is reported to have an accuracy of +/- 3% which is much more accurate than the MFJ antenna analyzers which are reported to be approximately +/- 10% at HF and on the order of 20% for 2-meters and 30% at 440 MHz.

    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.

 


 

Antenna Rules:

  1. KØS stations* may not use wire antennas;
  2. KØS stations* may not use metal pipe antennas.
  3. NON-KØS stations use whatever antennas they wish!
* 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....

 


Vertical Ladder over Trailer

    We used this Strange Antenna both Saturday and Sunday. It seemed to work quite well on 20-meters.

Vertical Ladder with Trailer

Vertical Aluminum Multitask Ladder with 16-Foot Trailer as Ground Plane
K0S Strange Antenna Challenge Special Event
May 24 & May 25, 2008
Springfield, MO

  Analyzer Scan

AIM-4170 Antenna Analyzer Scan 2.0 MHz - 30.0 MHz
Vertical Ladder over Trailer Ground Plane

 

 

A-Frame Ladder

    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!

A-Frame Vertical Ladder over Step Ladder Ground Plane

Aluminum Multitask Ladder in A-Frame over Step Ladder/Metal Folding Chairs as Ground Plane
K0S Strange Antenna Challenge Special Event
May 26, 2008
Springfield, MO

  Analyzer Scan

AIM-4170 Antenna Analyzer Scan 2.0 MHz - 30.0 MHz
A-Frame Ladder over Step Ladder Ground Plane

 

 

For comparison purposes, below is the AIM-4170 Antenna Analyzer Scan of the Commercial Buddipole


The Buddipole was only used as a reference antenna during the special event, and never to contact any of those we worked as the special event station K0S.
This is a commercial antenna designed primarily for portable operations by Budd W3FF. More information may be found at their web site: www.buddipole.com
Please note, no effort was made to optimize the Buddipole. We simply transformed the complex impedance with my LDG Z-11 Pro automatic antenna tuner.

Analyzer Scan

AIM-4170 Antenna Analyzer Scan 2.0 MHz - 32.0 MHz
Buddipole Dipole on 16-Foot Mast

 

  Buddipole

Buddipole Dipole on 16-Foot Mast
Each side of the dipole: two 22" arms; "red" coil (no taps); "black" whip fully extended;
One 22" arm extended above dipole serving as a truss support;

 

  Buddipole

These are the sand bags, which worked very, very well.
We found "pea gravel" actually worked better than sand. Each bags weighs between 10 and 15 pounds.
It would take an extremely strong wind to blow this over!

 

  2008 Log

2008 K0S LOG 1 of 5 -- Ladder Vertical

 

  2008 Log

2008 K0S LOG 2 of 5 -- Ladder Vertical

 

  2008 Log

2008 K0S LOG 3 of 5 -- Ladder Vertical

 

  2008 Log

2008 K0S LOG 4 of 5 -- Ladder Vertical

 

  2008 Log

2008 K0S LOG 5 of 5 -- A-Frame Ladder

 

 

 

  n0ew reflected in screen

Erik NØEW reflected in computer screen

 

  n0ew

Erik NØEW

 

  wb5plj

Dwayne WB5PLJ

 

 


Run Your Own K0S Satellite Station!

Running your own "Strange Antenna Satellite Station" is tons of fun!

    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?


Do you see the rabbit

Do you see the rabbit?
He came by to inspect our operation, and finding it carrot-free idled along shortly.


"KØS Field Manual"

 


    73 ~ Erik n0ew



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73 de Erik, nØew
© 2002 - 2007 Erik E. Weaver, n0ew
 
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