VE6AB Mobile Ops
RPR HF APRS 30 Meter Digital Antenna
What your looking at is an antenna that I built for working RPR (Robust Packet Radio) HF APRS on the digital portion of 30 meters.
This dedicated digital 30 meter monobander consists of the Cal-Av spring at the mounting point, followed by a 3/8" X 30" 304 stainless-steel mast, then one of my 17 meter really rugged coils, and then the 3/8" OD X 72" 6061 T6 high tensile aluminum tube whip, topped off with a 36" closed loop caphat with 304 SS elements and a 6061 aluminum hub.
All stainless steel fasteners hold it together.
I already run a dedicated 30 meter monobander that I built to use exclusively with RPR HF APRS on the top end of 30 meters, but I felt I could improve on it by eliminating as much of the coil as possible, and adding more whip up top for better radiation resistance.
While I was trying out various coils that I made up especially for the top end of 30 meters, at one point I wondered what would happen if I placed on of my 20 meter really rugged coils in place with a whip that loaded the antenna properly.
http://www.jerryclement.ca/HamRadio/HamRadio/i-2DCG4ZB/0/XL/6N4A2345-001-XL.jpg
I did just that, and the RF Network on the Smith Chart of my Rig Expert analyzer looked good, so I decided to try one of my 17 meter really rugged coils and eliminate more of the coil yet for 30 meters.
So far its looking good, and I will continue to run tests with this antenna mounted on my mobile.
Its interesting to have this monobander antenna mounted on my mobile with a caphat up top, as up until now I have only used a caphat with my gearmotor antennas.
The interesting thing is that this digital 30 meter antenna weighs a about a 1/4 of the weight of my smallest gearmotor antenna.
I fully expect this monobander 30 meter antenna to out-perform my gearmotor antenna set in the 30 meter position, as the whip on this monobander is a full 12" longer in length with the same caphat mounted up top and less coil required to load the antenna.
The aircraft high tensile aluminum tube .3/8" (.058" wall) X72" whip is proving to handle the wind well while going down the road at 110K, and is also proving to be a good performer.
Since designing and building a really rugged monobander antenna system for a number of different bands, I have discovered that a monobander will out-perform a gearmotor antenna used for the same band if designed properly for said band http://www.jerryclement.ca/HamRadio/HamRadio/i-84xzb43/0/XL/1-6N4A3746%20copy-XL.jpg
Gearmotor antennas no matter how well they are designed, still have that large metal mast assembly in close proximity to the coil degrading the Q of the coil that resides within the mast.
Even with Delrin used for the upper endcap on the coil form, you cannot get away from the mass of metal that makes up the bottom of the antenna.
Hustler antenna coils designed for the lower bands have a reputation as being poor performers due to their large metal caps.
Well guess what, most gearmotor antennas suffer from the same malady as a large Hustler 80 meter coil, metal in close proximity to the coil degrading the Q of the coil.
My 30 meter digital monobander as mounted on my mobile does not suffer from this malady.
Now there is no doubt that a well designed and built high performance gearmotor antenna is a joy to use and very convenient for changing bands while going down the road, but for ultimate performance on a single band, a well designed monobander is where its at.
How high is that antenna you ask.....13' 6" to the tip from the blacktop.
I could shorten the antenna by increasing the diameter of the caphat and still retain the performance that this antenna has, but then the wind loading on the whip increases while going down the road as well as the diameter of the caphat.
Click on the photo for a closer look....
