The following scans are for a 2 meter/ 70 cm Larson antenna. It was
mounted on a mag-mount base. Measurements were taken
in my office and in my car.This antenna has been in service since "Desert Storm"
when I purchased much of my 2m/440 gear. Everything was going well
after I repaired the coax that had been chewed by the dog. The scans
were looking good - then it happened. I tried to get a better SWR by
"fixing" the antenna. After careful adjustment the unit was completely
destroyed. As shown in the following scans and photographs time,
water, and road salt had taken its toll. The replacement -
Go.
Antenna: Larson NMO2/70 on a mag-mount
Feed: 12 ft
RG/8u
with about 1 foot or RG/8x for repair
2 meter scan - 130 to 170 MHz (This needs to re-scanned for just the 2
meter band after adjustment) The antenna is centered at 139.800 MHz with an SWR of 1.289.
Need to make some adjustments.
Looks good but a little longer should get the resonant frequency to 146 MHz
A little longer made it worse? Let's check what was adjusted and the
base coil threads. This should be better now....
Complete destruction of the SWR and the antenna's center coil as shown
below. There was just a bit of plastic holding everything together and
the metal parts were completely covered with rust. Looks like it's
time for a new antenna.
Jumped on the Ham Radio Outlet's web site and ordered a new coil and whip (.pdf).
This unit has an open coil so there is nothing to break or hold water.
I have the antenna on the trunk lid so I don't beat up the whip in the
parking deck. I also try to do a scan on the roof to see if the band
width changes.
New Scan - At 144, SWR= 1.692, minimum at 148.238. I try adjusting the
whip in the near future and rescan.
If you have any graphs that could be added to
this site please send them along. I'll post and credit your
information.
