NØEQ Tests the
AS3900 SINCGARS Vehicle Mount Antenna
as a
Quick Deploy Temporary Base Antenna
|
   
|
A Quick Deploy Center Fed VHF Vertical Here's a standard AS3900 military antenna assembly. It's the center fed VERTICAL dipole that you currently see on every Hum Vee, Bradley, Tank and Patriot Missle Battery in the US Military today (2008 as I type this). Top section of the antenna is sixty-one inches long. The bottom section of the vertical dipole (including mount and spring) is fifty inches long. Should be pretty close to the 6m band. But I measured it on 10, 6 and 2m just to see what happened The Military calls it "Broadband Vehicular Whip Antenna" It is certainly that - Broadband.  Design Specs: Application: Secure Communications Frequency: 30 to 87.975 MHz Impedance: 50 Ohms Nominal VSWR: 3.5 to 1 Maximum Polarization: Vertical Pattern: Omni-Directional Connector: BNC Max Weight: 11.6 lb RF Power Capacity: 150 Watts CW Gain: Dependent on Frequency. Ranges from a minimum of -7.6 dBmp @ 30 MHz to -1.1 dBmp @ 87.975 MHz Not particularly great looking specs with it's negative gain and potentially high SWR. But!...  Rugged as hell! It will survive a 20 kilovolt hit if you drive under a power line. |
|
Designed as a Vertical Dipole... ... the signal is fed like coax up through the spring and bottom half of the vertical antenna. The spring threads, and the female threads on the bottom of the element are both solid brass. Very heavy. Note the rubber O ring and ground screw on spring mount. Missing: Rubber weather cap for use when the vertical element is unscrewed and dismounted from the spring and base.  |
  
|
Hand Assembly Only... ... no tools needed or recommended, once you have the base and spring installed. Unscrew/remove the antenna as social situations dictate. |
 
|
Testing the AS3900 for SWR, reactance, impedance, resonance The tripod stand I use for testing was once some kind of tennis racket re-stringing stand that someone discarded as trash. The mast (recycled of course) is a recycled round landscape timber pushed into the open top of the tripod stand. At the top of the mast, a simple U bolt and one machine bolt hold the metal antenna mount at a height of 8 feet off the ground. The horizontal wires you see in the background are not related to this test setup. They are attached to a separate antenna, which is mounted on the corrugated tin roof behind the test stand. The antenna is a center fed dipole, PROBABLY works independant from any additional counterpoise. And in the interest of rapid setup I did NOT install any kind of radials. Surely mounting the AS3900 on my tin roof or on a metal vehicle will change the pattern/test results of this antenna More vehicle mounting pics elsewhere on these pages. |
|
MFJ Analyzer Readings |
|
     |
Here's the 10m readings from the MFJ analyzer... From 28.0 to 29.7 MHz SWR is - Best case 2.3:1 Worst case 2.8:1 Reactance is - Best case 40 Worst case 59 I try and shoot for a max reactance of 10 for any antenna. The AS3900 is pretty high in reactance Impedance is - Highest at 59 ohms Lowest at 39 ohms. Impedance is acceptable, but reactance and SWR are pretty far away from desirable. |
|
|
|
     |
Here's the 6m readings from the MFJ analyzer... From 50.0 to 54.004 MHz SWR is - Best case 1.7:1 Worst case 1.8:1 Reactance is - Best case 4 Worst case 25 Here too, reactance is pretty high Impedance is - Highest at 83 ohms Lowest at 29 ohms. Not exactly an ideal 6m antenna |
|
|
|
      |
Here's the 2m readings from the MFJ analyzer... From 144 to 148 MHz SWR is - Best case 1.5:1 Worst case 1.8:1 Reactance is - Best case ZERO Worst case 25 Impedance is - Highest at 33 ohms Lowest at 91 ohms. Not bad at all for 2m, a band that it's not designed for Best readings I found seemed to be near the AM aircraft band. |
|
I'm testing as we speak, so to speak. It's making contacts on 2 and 6. More testing tonight. I just finished installing the antenna on my Astro Van. Details and pics of that to follow. Preliminary findings suggest that it doesn't seem to tune up well to any ham frequencies when mounted to the vehicle. It's really resonant around 71-72 MHz. But at 2/6/10m the reactance, impedance and SWR are all beyond what I consider good figures. |
|
The rest of my life?
www.LumpyMusic.com