Arrow and ELK Comparative Antenna Tests
On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna testing in an attempt to answer the questions about which is the best antenna for portable satellite operation. We only tested the antennas in receive mode to determine their relative gain. Time constraints prevented us from performing additional testing to determine if the transmitted output was consistent with the receive gain of the antennas. For the time being we will assume (and we all know the dangers of doing so) that the transmit performance closely matches the receive performance.
The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a PortaFox configured for 145/435 operation (4 elements), and a Home Brew 4 by 9 element "arrow" antenna. The standard Arrow antenna was the only antenna equipped with duplexer, but not the basic duplexer which is installed in the handle. We did not measure the insertion loss of the duplexer on the Arrow antenna, but this was obviously not a significant factor in the overall performance. A duplexer could still be required depending upon the antenna chosen and the radio(s) to be used.
Using the Arrow antenna as the reference antenna and 145.300 MHz as our test frequency, our measurements indicated that the Arrow and the ELK antennas had identical gain. The PortaFox antenna showed 2db less gain than the Arrow and the ELK. The Home Brew 4/9 element crossed yagi showed 2db more gain than the Arrow and the ELK.
On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db more gain than the PortaFox. The Home Brew 4/9 element had 3db more gain than the Arrow.
Although the ELK antenna shows slightly less (2db) gain on 435.300 MHz, it does have one potential advantage over the Arrow antenna. With the ELK, transmit and receive are in the same plane. With any satellites that have linear polarized antennas, such as AO-27, SO-50, the ISS and maybe SO-67, a crossed yagis can maximize the performance on one band while minimizing it on the other. That does not mean the Arrow won't work, as has been demonstrated by the thousands of satellite QSO's that are made on a regular basis using Arrow antennas. It just means that when you rotate the antenna to maximize the downlink signal, you may be significantly impacting you uplink signal strength in marginal situations.
Even though a satellite may have a circular polarized uplink and downlink, don't assume that the orientation of your station antenna as horizontal, vertical, or something in between won't have a significant effect on your signal strength. My experience operating portable with my home brew antenna has convinced me that my horizontally polarized Qagi should either be remounted vertically polarized or replaced with a circular polarized antenna. That is another ongoing project.
In summary, unless you plan to build your own, the performance of the Arrow crossed yagi antenna and the ELK log periodic antennas are very comparable and should provide lots of solid satellite contacts.
The overall results reflect the adage that bigger is better, but along with more gain, you also get a more bulky antenna that is harder to handle. The home brew crossed yagi I built for portable operation is tripod mounted, can be rotated on its axis, and disassembles for storage in a roll up case. But because of its size, it would be very tiring to attempt to use it hand held for an extended period of time. Pictures of the home brew crossed yagi antenna are on my QRZ page.
John Kopala N7JK
John,
Thank you for your objective, scientific comparison! I eagerly await your article in the AMSAT journal ;-) This is really good stuff. If your test stand is still available there is one more thing I would dearly love to see tested. Antenna guru Kent Britain, WA5VJB, once commented the Arrow seemed to be designed for the elements to be insulated from the boom, and there might be something to be gained from doing just that. Testing the Arrow with the elements in standard convention vs. insulated has been on my to do list ever since but I never seem to be able to get around to it.
Again just a thought, and thanks for your awesome work already!
73, Joe kk0sd
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of John Kopala Sent: Sunday, April 24, 2011 10:50 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Arrow and ELK Comparative Antenna Tests
On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna testing in an attempt to answer the questions about which is the best antenna for portable satellite operation. We only tested the antennas in receive mode to determine their relative gain. Time constraints prevented us from performing additional testing to determine if the transmitted output was consistent with the receive gain of the antennas. For the time being we will assume (and we all know the dangers of doing so) that the transmit performance closely matches the receive performance.
The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a PortaFox configured for 145/435 operation (4 elements), and a Home Brew 4 by 9 element "arrow" antenna. The standard Arrow antenna was the only antenna equipped with duplexer, but not the basic duplexer which is installed in the handle. We did not measure the insertion loss of the duplexer on the Arrow antenna, but this was obviously not a significant factor in the overall performance. A duplexer could still be required depending upon the antenna chosen and the radio(s) to be used.
Using the Arrow antenna as the reference antenna and 145.300 MHz as our test frequency, our measurements indicated that the Arrow and the ELK antennas had identical gain. The PortaFox antenna showed 2db less gain than the Arrow and the ELK. The Home Brew 4/9 element crossed yagi showed 2db more gain than the Arrow and the ELK.
On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db more gain than the PortaFox. The Home Brew 4/9 element had 3db more gain than the Arrow.
Although the ELK antenna shows slightly less (2db) gain on 435.300 MHz, it does have one potential advantage over the Arrow antenna. With the ELK, transmit and receive are in the same plane. With any satellites that have linear polarized antennas, such as AO-27, SO-50, the ISS and maybe SO-67, a crossed yagis can maximize the performance on one band while minimizing it on the other. That does not mean the Arrow won't work, as has been demonstrated by the thousands of satellite QSO's that are made on a regular basis using Arrow antennas. It just means that when you rotate the antenna to maximize the downlink signal, you may be significantly impacting you uplink signal strength in marginal situations.
Even though a satellite may have a circular polarized uplink and downlink, don't assume that the orientation of your station antenna as horizontal, vertical, or something in between won't have a significant effect on your signal strength. My experience operating portable with my home brew antenna has convinced me that my horizontally polarized Qagi should either be remounted vertically polarized or replaced with a circular polarized antenna. That is another ongoing project.
In summary, unless you plan to build your own, the performance of the Arrow crossed yagi antenna and the ELK log periodic antennas are very comparable and should provide lots of solid satellite contacts.
The overall results reflect the adage that bigger is better, but along with more gain, you also get a more bulky antenna that is harder to handle. The home brew crossed yagi I built for portable operation is tripod mounted, can be rotated on its axis, and disassembles for storage in a roll up case. But because of its size, it would be very tiring to attempt to use it hand held for an extended period of time. Pictures of the home brew crossed yagi antenna are on my QRZ page.
John Kopala N7JK _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Thanks John and Patrick. Interesting results and a very nice study.
Question---what was your testing method? I can't glean that from the information below.
Thanks!
Mark N8MH
At 08:49 PM 4/24/2011 -0700, John Kopala wrote:
On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna testing in an attempt to answer the questions about which is the best antenna for portable satellite operation. We only tested the antennas in receive mode to determine their relative gain. Time constraints prevented us from performing additional testing to determine if the transmitted output was consistent with the receive gain of the antennas. For the time being we will assume (and we all know the dangers of doing so) that the transmit performance closely matches the receive performance.
The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a PortaFox configured for 145/435 operation (4 elements), and a Home Brew 4 by 9 element "arrow" antenna. The standard Arrow antenna was the only antenna equipped with duplexer, but not the basic duplexer which is installed in the handle. We did not measure the insertion loss of the duplexer on the Arrow antenna, but this was obviously not a significant factor in the overall performance. A duplexer could still be required depending upon the antenna chosen and the radio(s) to be used.
Using the Arrow antenna as the reference antenna and 145.300 MHz as our test frequency, our measurements indicated that the Arrow and the ELK antennas had identical gain. The PortaFox antenna showed 2db less gain than the Arrow and the ELK. The Home Brew 4/9 element crossed yagi showed 2db more gain than the Arrow and the ELK.
On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db more gain than the PortaFox. The Home Brew 4/9 element had 3db more gain than the Arrow.
Although the ELK antenna shows slightly less (2db) gain on 435.300 MHz, it does have one potential advantage over the Arrow antenna. With the ELK, transmit and receive are in the same plane. With any satellites that have linear polarized antennas, such as AO-27, SO-50, the ISS and maybe SO-67, a crossed yagis can maximize the performance on one band while minimizing it on the other. That does not mean the Arrow won't work, as has been demonstrated by the thousands of satellite QSO's that are made on a regular basis using Arrow antennas. It just means that when you rotate the antenna to maximize the downlink signal, you may be significantly impacting you uplink signal strength in marginal situations.
Even though a satellite may have a circular polarized uplink and downlink, don't assume that the orientation of your station antenna as horizontal, vertical, or something in between won't have a significant effect on your signal strength. My experience operating portable with my home brew antenna has convinced me that my horizontally polarized Qagi should either be remounted vertically polarized or replaced with a circular polarized antenna. That is another ongoing project.
In summary, unless you plan to build your own, the performance of the Arrow crossed yagi antenna and the ELK log periodic antennas are very comparable and should provide lots of solid satellite contacts.
The overall results reflect the adage that bigger is better, but along with more gain, you also get a more bulky antenna that is harder to handle. The home brew crossed yagi I built for portable operation is tripod mounted, can be rotated on its axis, and disassembles for storage in a roll up case. But because of its size, it would be very tiring to attempt to use it hand held for an extended period of time. Pictures of the home brew crossed yagi antenna are on my QRZ page.
John Kopala N7JK _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Hi Mark!
Thanks John and Patrick. Interesting results and a very nice study.
You're welcome!
John and I talked about doing this a few weeks ago while at a hamfest. John called me Saturday morning, and asked if I was free in the afternoon. I went over to his house in the early afternoon, and we turned his front yard into a testing field for antennas for an hour or so. :-)
Question---what was your testing method? I can't glean that from the information below.
On the west end of his front yard, John set up an IFR-1200 station monitor with a long 2m/70cm duckie as the transmitter. The antenna was either a Diamond RH77CA or the MFJ equivalent. I may be able to figure it out from the photos I took, or John can jump in and answer that. On the east end of the front yard, he had his Icom IC-910H satellite transceiver as the receiver along with an RLC Electronics switch attenuator:
http://www.rlcelectronics.com/index.php?option=com_content&view=article&...
between the antenna and the transceiver. John set the station monitor so it would transmit a signal that could be attenuated for an S-9 reading on the IC-910H. We used a large cardboard box to hold the antennas, pointing them toward the station monitor across the yard, and switching levels of attenuation with each antenna to have an S-9 reading on each band.
The PortaFox antenna John mentioned is a log periodic designed and made by Michael Brennan KA6PGN, based on the Elk Antennas log periodics. He had these antennas on display, along with lots of military radios, at the Palm Springs (California) hamfest in late January. He also visited the Yuma (Arizona) hamfest in February, where he sold me the antenna with elements to make it work either as a monoband 2m antenna or as a 2m/70cm antenna. The elements are just like those Elk Antennas uses with their antennas, thicker than those on an Arrow Yagi.
My PortaFox has a length of coax from the feedpoint at the front of the antenna inside the double boom to a BNC connector at the rear. This is similar to how I run coax from my Elk through the PVC handle toward the rear of the antenna, but Michael has done in in a more elegant manner with the PortaFox. Other PortaFox antennas Michael had came with a long length of coax from the feedpoint, and you could put your preferred coax connector on the other end.
I have lots of pictures from this antenna test at home, and will post them somewhere tonight once I scale them down a bit for the web. The photos are 12-megapixel photos from my mobile phone's camera.
As for KK0SD's comment, yes - I remember WA5VJB's article in CQ VHF where he mentioned insulating the elements on an Arrow Yagi from the boom. He also mentioned he had some ideas to increase the gain from an Arrow Yagi, but (as far as I know) this follow-up article has never been published.
73!
Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/
It is commendable to see some direct antennas comparison measurements being made. Computer modeling is one thing. Realizing it in hardware is quite another.
The biggest problem in making field measurements is to reduce and try and eliminate reflections from the ground, adjacent structures and overhead wires and your antenna mount.
The pattern of the antennas under test can be very significant. Two antennas can have the same direct forward gain. But one can have a narrow beam width main lobe but with relatively large side lobes, while the other has a broader main lobe beam width and low side lobes.
While they both can give the same forward gain results the second antenna is obviously the better antenna.
To test for ground reflections raise and lower your antenna and also move it back and forward and see if your signal strength varies.
On a different day and different location repeat the measurements. Your results may well leave you wondering why you made the statements you so confidently did.
To reduce ground reflections raise the antennas as far as possible above ground. Use a high gain directional antenna for the signal source so that little of the radiated power is directed at reflective surfaces. The greater the spacing between the rx and tx antennas the more likelihood of a reflection but the spacing needs to be such that a small change in spacing has little effect on the results. As a rule of thumb spacing about 10 wavelengths.
In actual satellite operating a difference in forward gain of a db or less is hard to detect however the effects of the pattern can be significant in pointing a hand held antenna at a moving target.
Having made hundreds of comparison measurements on 13cm helix antennas I know how much time and effort it takes. However I think it is very worthwhile to actually make real antenna comparison measurements to confirm the theoretical.
Clare VE3NPC
----- Original Message ----- From: "John Kopala" jkopala@gmail.com To: amsat-bb@amsat.org Sent: Sunday, April 24, 2011 11:49 PM Subject: [amsat-bb] Arrow and ELK Comparative Antenna Tests
On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna testing in an attempt to answer the questions about which is the best antenna for portable satellite operation. We only tested the antennas in receive mode to determine their relative gain. Time constraints prevented us from performing additional testing to determine if the transmitted output was consistent with the receive gain of the antennas. For the time being we will assume (and we all know the dangers of doing so) that the transmit performance closely matches the receive performance.
The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a PortaFox configured for 145/435 operation (4 elements), and a Home Brew 4 by 9 element "arrow" antenna. The standard Arrow antenna was the only antenna equipped with duplexer, but not the basic duplexer which is installed in the handle. We did not measure the insertion loss of the duplexer on the Arrow antenna, but this was obviously not a significant factor in the overall performance. A duplexer could still be required depending upon the antenna chosen and the radio(s) to be used.
Using the Arrow antenna as the reference antenna and 145.300 MHz as our test frequency, our measurements indicated that the Arrow and the ELK antennas had identical gain. The PortaFox antenna showed 2db less gain than the Arrow and the ELK. The Home Brew 4/9 element crossed yagi showed 2db more gain than the Arrow and the ELK.
On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db more gain than the PortaFox. The Home Brew 4/9 element had 3db more gain than the Arrow.
I
participants (5)
-
Clare Fowler -
Gary "Joe" Mayfield -
John Kopala -
Mark L. Hammond -
Patrick STODDARD (WD9EWK/VA7EWK)