The 13 element LFA RPOL antennas polarity is rotated using simple and inexpensive TV rotators. The control of these polarity rotators must be sync’d.
Bill Ockert, ND0B built this RPOL controller.
The controller uses a CLICK PLC to control both rotators in a syncronized fashion.
The software is written in C# and has a really cool feature. You can select an option to do a “Noise Scan” this will rotate the polarity of the antennas a full 360 degrees and show graphically the lowest noise angles. This really comes in handy in a a very noisy urban environment.
Notice that the lowest noise is at 0 degrees “H” pol and that +90 is lower than -90 degrees. This tells us for this particular Az/El of the antenna, use the “+” side of the antenna polarity rotation.
See KK6FAH for additiona information.
For more information on the RPOL controller, contact Bill Ockert, ND0B
My 2 meter Amplifier is an M2 1K2 SSPA.
The Amp Requires 50V at 40A to make a KW output. The typical solution is to use an HP Server power supply which can be picked up on EBAY for $30.
The HP server power supplies work well, but have high fan noise, and are pretty bad EMI generators. You must take extra measures to reduce the EMI emissions. On EME, even one or two dB of extra noise is not acceptable. The best solution would be to mount everything in a metal cabinet. I have a nice wood shop, so I built a wooden roll-around box and lined it with radiant barrier material. This worked great, but xyl complained that it was ugly.
I was browsing EBAY and ran across a seller who has a bunch of Kepco/TDK RKW 15-22K power supplies. I bought six of them for $37 each.
The RKW 15-22K is adjustable from 10 to 18V and delivers 22A. These power supplies are designed to be run in parallel with provisions for master/slave and current balance. So with a pair you have 44A. If you put three pairs of these in series you have 53V at 44A. Viola!!!
These Kepco RKW power supplies are extremely well made and meet the very strict EU emissions requirements. No noise emissions from the new power supplies for the SSPA.
I have sold the 4X7 EME antennas and picked up a pair of 13el RPOL antennas.
These antennas were designed by Jimmy KK6FAH.
The antennas are 13 element G0KSC LFA’s. These antennas are monsters, the boom length is 35ft. They are rear mounted to allow for full polarity rotation.
The polarity of the antennas is controlled by a pair of inexpensive TV rotators
These antennas are incredible. I often work single yagi modest power stations.
A typical Q with the old 4X7s would yield decodes of -24 to -28dB. With these RPOLs, I see the same class of stations at -15 to -19 dB. The signal loss due to Faraday rotation can be as high as 20dB. With the ability to rotate the polarity, I can bring a signal from “not even there” to a strong -20dB trace. The Polarity of the returned echo is by far the largest variable in working EME. It makes the degradation rather insignificant.
I often hear audible echoes, and have recorded several QSOs at below -10dB. The best being -6 dB from one of the big stations. This is easily within the “CW” category. I have yet to try on cw, but will do so soon.
The rotation of the antennas is synchronized by a controller designed and built by Bill, ND0B.
See info on the controller box here.
Jimmy uses three of these antennas. See his really cool video .
See Jimmy’s video on construction of the RPOLS.
Seeing my own echoes!!!