I did a lot of comparisons between my Elk and Arrow II. My results were exactly the same as those of WD9EWK/VA7EWK but I was never sure why the Elk performed better. Comparison tests I have been running between a DIAMOND A430S10R and an Olde Antennas 7CP-70cm have given me an insight as to why the Elk works so much better.

The tests between the Diamond and the Olde were the most inconclusive tests I have ever run until suddenly my ancient grey cells managed to figure it out. The Diamond has a longer boom which gives it more gain. The Olde has a very short boom but is circularly polarized. I had them mounted on opposite ends of the cross boom with a switch for quick comparisons. During part of a pass the Diamond would work better. During other parts of the pass the Olde would work better.

The chart at the top of the SV1BSX web page holds the answer. http://sv1bsx.50webs.com/antenna-pol/polarization.html When the orientation of the sat antenna lines up with the Diamond it works better and continues to work better until the sat rotates to the point where the cross polarization loss cancels the gain advantage the Diamond has over the Olde at which point the Olde works better...

What has this to do with the Elk - Arrow comparison. Since the 2M and 70cm antennas on the Arrow are mounted at right angles to one another we have a problem when working linear polarized sats. If the Arrow is turned to maximize the downlink signal it is automatically turning the uplink antenna to the angle that will maximize the uplink cross polarization loss of up to 30 dB.

I do my testing on the linear sats and listen to my own downlink signal. When the Arrow is rotated to maximize the the received signal my best guess is that it is turned off the angle of the sat antenna. This would spread the cross polarization loss between the uplink and downlink antennas. The exact offset angle would depend on transmit power, receive sensitivity and a ton of other things.

There is nothing wrong with the Arrow II it just can not work as well as the Elk on linear sats unless you have a quick wrist and rotate the antenna between transmit and receive. Even if you have very quick wrists resulting from a miss spent youth playing foosball there still is a problem. Trying to figure out the angle to turn the antenna during transmit is all but impossible. Since the sat is rotating the angle for transmit is not always 90 degrees from the angle for receive. All antennas work to some degree and all this stuff is only important if you are trying to maximize performance.

73 W9KE Tom Doyle

On Mon, Jul 16, 2012 at 3:28 PM, Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb@wd9ewk.net wrote:

Norm,

I use an Elk log periodic for AO-7 and all my other satellite work. I am able to work passes to the predicted LOS time, subject to local surroundings. I was only able to work down to 4 or 5 degrees elevation with my Arrow dual-band Yagi, before I switched to the Elk. You can see this setup in action working satellites - including AO-7 mode B - in some of my videos at: http://youtube.com/va7ewk

For AO-7 in mode A, the Elk is my 2m antenna, and a Buddipole dipole on its tripod and telescoping mast is used for the 10m downlink. Since this requires more setup, and the 10m downlink is weaker than the 2m downlink, I don't work mode A very much.

73!

Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/

On Monday, July 16, 2012, Lizeth Norman wrote:

...

Hi all! Just wanted some comments as to what ops are using for AO-7 portable. More importantly, some info on how they perform near loss of signal. Pictures of antenna arrays would be greatly appreciated. Norm n3ykf _______________________________________________ Sent via AMSAT-BB@amsat.org javascript:;. 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

---

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