Tag Archives: Dale (N3HXZ)

Chameleon MPAS Lite: Using the coax shield as a counterpoise and how this might affect directionality

Many thanks to Dale (N3HXZ) who shares the following guest post:


Portable Operation Using a Vertical Antenna Without a Counterpoise Wire!

by Dale (N3HXZ)

In a previous article that Thomas was kind enough to post, I ran experiments to determine if the counterpoise wire orientation of the Chameleon MPAS LITE antenna system in the vertical configuration in any way shaped the antenna pattern.  The configuration of the antenna is shown below.

The system consists of a 17’ telescoping whip antenna, a matching transformer, a 50’ coax cable with an in-line RF choke, and a counterpoise wire (60’ long, but unwound to only 25’ for use in the vertical configuration).

Subsequent studies I performed have reinforced my earlier conclusions that the positioning of the counterpoise wire in this setup does not appreciably shape the antenna pattern. One of the comments from my post came from Stephan (HB9EA). He commented on the fact that the coax cable is indeed a counterpoise via the coax shield and that in fact my system set-up had two counterpoises.

It was Stephan’s comment which led me to contact Chameleon Antenna to discuss counterpoises with the MPAS LITE antenna in the vertical configuration. I communicated with the Director of Research and Development group at Chameleon and found out some interesting information that I wanted to pass on.

He mentioned that the system can be used with the coax cable acting as the lone counterpoise as long as the coax cable is at least 25’ long, and preferably 50’ long.  The coax should be spread out and not coiled along any portion of its length. It was stated that the counterpoise wire provided with the product should be used with short-length coax cables.

With regards to a counterpoise orientation shaping the propagation direction, he stated that it is generally accepted that using only the coax as a counterpoise tends to have the antenna pattern slightly favor the direction in which the coax is laid out. Adding the counterpoise wire in a direction opposite to the coax would tend to balance out that pattern. Having the coax and counterpoise wire at some angle to each other introduces variables that make it difficult to determine the antenna pattern.

My initial study had the counterpoise wire oriented at an angle to the coax cable.  I mentioned that my initial study showed that orientation of the counterpoise wire did not seem to appreciably shape the antenna pattern, and he agreed. What is unknown is the overall degree to which the coax cable shapes the antenna pattern with or without use of the counterpoise wire.  This is an area I am currently investigating.

Operating the MPAS-LITE vertical configuration with only the coax cable as a counterpoise was an intriguing thought.

To test it out I teamed up with Jim (KJ3D) for a SOTA activation on W3/PT-003 (Seven Springs). We both deployed the MPAS-Lite with only the supplied 50’ coax cable attached. Coax cables were laid out in a straight line. One cable was oriented southeast, the other one oriented east. We operated on 10 Watts in CW mode. The activation successfully worked all bands from 40M to 10M. I operated an Elecraft KX2 and Jim operated a KX3. The internal tuner of both rigs easily obtained a 1:1 match across all bands.

A map of the QSO’s is shown below. Note that despite the coax cables facing to the southeast and east, we easily worked stations in the opposite directions. Hence any minor shaping of the antenna pattern by the coax orientation does not appear to impede successful communication in all directions.

In summary, the MPAS-LITE antenna system in the vertical configuration utilizing the 50’ coax cable with an in-line RF choke as the single counterpoise has been demonstrated to perform well in the field.

For portable operation where fast deployment and simplicity is paramount, using the furnished coax as a counterpoise is a quick and dirty way to get the antenna erected and on the air with reliable communication capability. Eliminating the counterpoise wire allows for quicker set-up and tear-down, and one less thing to put in the backpack!

N3HXZ: SOTA and POTA in the San Juan Islands!

Many thanks to Dale (N3HXZ) who shares the following guest post:


SOTA and POTA in the San Juan Islands

by Dale Ostergaard (N3HXZ)

My wife and I like to take educational tour vacations from time to time. The outfit we mostly use is Road Scholar.

The tours are geared around education and immersion in local cultures and experiences. In addition, you meet a lot of like-minded people on the tour and make new friends.  Last summer we wanted to take a vacation to the pacific northwest. We had never been there and came across a tour through the San Juan Islands. The islands are located north of Seattle and east of Vancouver. Touring the islands is made easy on a guided tour as they arrange for all transportation between islands and on land.

Washington State has an excellent network of ferries serving the island which makes for easy connections to the islands.

After we booked the vacation I began wondering if there were SOTA and POTA opportunities on the islands. I quickly looked up sites on the SOTA Goat app and the POTA website.  Low and behold there was a treasure trove of parks and summits!

SOTA Map
POTA Map

Realizing the opportunity, I cross checked our itinerary with the parks and summits. The difficulty of course is that when you are on a guided tour, you have very little flexibility in the schedule, let alone transportation to go off on your own. After researching, I found 4 opportunities that included 3 parks and 1 summit. The parks were K-0061 San Juan National Historic Park, K-3223 Lime Kiln Point State Park, both on the island of San Juan, and K-3232 Moran State Park and summit W7W/RS-065 Mount Constitution on Orcas Island. The Summit lies inside the park so I had the opportunity to grab both with 1 activation. Continue reading N3HXZ: SOTA and POTA in the San Juan Islands!

Dale uses WSPR to test counterpoise orientation

The CHA MPAS Lite

Many thanks to Dale (N3HXZ) who shares the following guest post:


Does your antenna counterpoise orientation matter?

by Dale (N3HXZ)

I am an avid SOTA and POTA activator and love field operation. I use a portable vertical whip antenna with a single counterpoise for my antenna system and have always wondered if orienting my counterpoise would provide some signal strength gain in a particular direction.  I decided to run a series of tests using WSPR to gather field data, and use statistics to answer the question:

Does one counterpoise orientation favor another in terms of average signal strength?

WSPR is a great tool for antenna testing. You can study various antenna configurations by making some WSPR transmissions and then checking the data on the WSPRnet database to see how well the signal was received at various stations located all over the world. You have to be careful in interpreting WSPR data though as receiving stations have different antenna and radio configurations, and the band propagation can vary rapidly at times. So how do you take advantage of all the data you receive from stations and draw some meaningful conclusions? I have found that using proven statistical theory in analyzing the transmitted signal strength received from individual stations can provide you results that you can confidently trust.

So what statistical algorithm is helpful?

For antenna signal strength comparison between two configurations, you can use an independent two-sample t-test with a one-tailed t-test evaluation. It sounds like a mouth-full, but it is quite simple. For our purposes, the t-test compares the average signal strength at a given receiving station from two different antenna configurations. The one-tailed test validates or invalidates the hypothesis that one antenna configuration produces an average signal strength greater or less than the other antenna configuration.

The testing requires that you run WSPR long enough to gather multiple reports at a single receiving station for both antenna configurations. Using the signal strength reports, you compute the average signal strength and the standard deviation of the signal strength over the sampled data points. Excel can easily provide that data.  With this information and the number of sample points for each antenna configuration (they can be different), you then run a calculation by hand or in Excel to compute the ‘t’ value.

This ‘t’ value is then compared to a critical value for the number of sampling points from a ‘Students t table”. If the ‘t’ value is less than the critical value you can confidently conclude that the hypothesis is false and therefore conclude that there is no significant difference in the mean value of the signal strengths between the two.  If the ‘t’ value is greater than the critical value you can accept the hypotheses that one antenna configuration produces a greater or less average signal strength than the other configuration. Continue reading Dale uses WSPR to test counterpoise orientation

Dale’s solution for enhanced CW field ergonomics

Many thanks to Dale (N3HXZ) who shares the following guest post:


Ergonomics of Operating CW in the Field

by Dale (N3HXZ)

About a year ago I started getting active in Parks On The Air (POTA) and Summits On The Air (SOTA). I had always been an avid hiker and backpacker, and though I am getting up there in years (recently retired!) these amateur radio opportunities were just the medicine I needed to rekindle my passion for the outdoors and amateur radio.

Thanks to Thomas (K4SWL) and his blog post and videos I was able to quickly come up to speed on the basics and get out into the field for CW activations.  I quickly discovered that operating CW in the field is quite different from operating at home. The creature comforts of a good chair, a level and spacious operating table, and isolation from the weather makes for a great experience in the shack, but is not available in the field, especially if you are backpacking to your destination. My early activations were sitting on a rock, or the ground, and using only a clip board to mount my rig (Elecraft KX2), locate my CW paddle, and place a notepad to record QSO’s.

While simple, this operating setup poses problems. Attaining and maintaining a flat workspace is tough in the field in order to keep things from shifting or falling off the clipboard, especially if you are not firmly seated. There is not enough space to set your wrist in order to steady your CW operating, and the notebook pages can flap in the wind, or the wind can blow your logbook clear off the table while operating. I realized I needed to upgrade my mobile station! Continue reading Dale’s solution for enhanced CW field ergonomics