[Antennas] need help with HF mobile mag mount

2002年10月30日 06:19:52 -0500

Dave and All,
I agree that the hustler should work on the roof mount, probably better 
than on the bumper. I use a hustler on 10-40 that I mount on the front end 
of the trunk lid using a heavy duty lid mount. It works better there than 
on the bumper, and I get good results. I am able to tune all bands to less 
than 1.5:1 SWR (it is designed to tune to 50 ohms)and I use it without a 
tuner. An antenna analyzer is helpful to tune it. Plug in the analyzer 
right at the antenna. The 2:1 band width is narrow particularity on 40 
meters, and an antenna tuner does help on that band and on all bands if you 
want coverage on both the CW and SSB portions. I have an 80 meter coil and 
I tried it on 80, but the radiation efficiency was so low that I didn't get 
many contacts. I now use the 80 meter coil on my Hustler 6BTV 
vertical. The Hustler is a good system, but some of the other mobile 
systems are more efficient. The Texas Bug Catcher comes to mind as one of 
the more efficient antennas.
So my advice is to first tune your antenna to 1:1 SWR on your favorite 
operating frequency and use it without the tuner if possible. Or if you 
want to use a tuner to broaden the band width, go ahead and try it and see 
if there is any difference in reports, If you use a tuner, the closer you 
install it to the base of the antenna the better. I used mine with a 
mobile tuner at the rig with RG8 going to the antenna on the bumper in one 
installation and performance was down as compared to using it without the 
tuner and not tuning the antenna. The coax length was short, but it had 
some losses anyway plus the tuner itself has some losses.
I also use a three resonator adapter which will hold three resonators. I 
use my 10, 12 and 15 meter resonators on it, so I have three band coverage 
on these bands without an antenna tuner or having to change the 
resonators. It makes for a heavy installation and really is too much load 
for the trunk lip mount, but I use it while the car is not in motion.
At 03:04 PM 10/29/2002 -0500, Dave Shrader wrote:
>I don't believe the 'ground plane' is the issue!! The radiating portion
>of the vertical antenna is capacitively coupled to the roof [ground
>plane]. The capacitive coupling is the principle means of rf conduction.
>The capacitor is in parallel with the dc path.
>>I've used the Hustler with great success from 10 to 40 meters! [Never
>tried it on 80 or 160].
>>First, get the tuner out of the circuit! Then tune the antenna to
>resonance [not minimum VSWR] by adjusting the length of the upper
>stinger [use an antenna analyzer]. The Hustler is a shortened antenna
>and should have a radiation resistance of 15 to 20 ohms, or a VSWR of
>approximately 2.5 to 1. Use a matching coil [LM-1 or equivalent] to
>bring the impedance up to 50 ohms. Once matched, at resonance you should
>have a bandwidth of 60 to 100 KHz [VSWR 2:1 or less] on 20 meters. Once
>this is accomplished you can re-install the antenna tuner for more
>bandwidth.
>>Note: your antenna system must include a base section, the coil
>installed above the base, the stinger above the tuning coil. I used the
>small spring between the coil and stinger to get some flex into the top
>section.
>>My Hustler installation gave me an antenna about 5 feet in length. The
>antenna pattern is vertically polarized. These points are important for
>two reasons.
>>1) You loose about 3 'S'[~ -18 dB] units due to cross polarization when
>compared to a horizontal dipole. You loose an additional 'S' unit [~
>-5.3 dB on 20 meters] compared to a dipole because of the shortness of
>the antenna.
>>So, if you are comparing the same signal as heard at your home QTH on a
>dipole and the same signal in the mobile a change of -3 to -4 'S' units
>is typical and normal. Or, if a friend is listening to your signal from
>the home QTH and comparing it to the mobile you get the same result. A
>mobile antenna on 20 meters is not as efficient as a full size dipole!
>>In conclusion, all mobile antennas for HF suffer from cross polarization
>losses [~ - 18dB] and shortened antenna losses [smaller effective
>radiating cross section][~ -5 dB on 20 meters].
>>Get it to resonance! Then adjust VSWR! Then have fun!!!!!!!
>>73, Deacon Dave, W1MCE
>Manager, Textron Antenna Range, retired
>>Armin Hachmer wrote:
> >
> > has anyone had good results?
> > I am using a hustler 20m element
> > on 4 big magmount pads in the middle of a minivan roof. a manual tuner
> > reads flat. results are lousy. it hears well but does not get out well. 
> the local radio store told me mag mounts dont
> > couple well enough to give a good ground plane.

73, Chas, W1CG
K2 #462