[BC] mounting whips on vehicles

[Mike McCarthy]

From: Tom Spencer<Radiofreetom at gmail.com>

>>108" whips are usually fender or bumper-mounted, BTW - anyone who would put one on the roof of a VAN ought to have their head examined; it's not practical; definitely subject to damage 

On 11/28/2010 11:55 PM, Broadcast List USER wrote:

>First of all, NO antennas are bumper mounted today.  Today's cars don't have that kind of pumpers!
>
>Even mounted on the top of a van, while the antenna would be high, we make allowances in order to get the job done.  The antenna may have to have it's top coupled back to another point on the van, just like on the "Andy Griffith Show."
>
>PLUS, Diamond and other companies make mounts that will remotely and electrically fold down the whip.  Why not?

 1) The Sheet metal of today's vehicles is so much thinner that there is a tear out threat even under highway driving conditions. Never mind the low overhang or tree branch.  There are kits made for "bumper" mounting antennas.  And most cars bumpers have bolting which can be adapted for attaching antennas.  but as with any offset mount the nulls to the rear will be rather deep. (which is why bumper mounts made for great DF'g)

2) Pneumatic masts compress into a MUCH smaller vertical profile than a whip can. While the wind loading can and often does increase with a mast, the extended profile is greatly reduced.  Also, there are kits now available with a 20ft. mast which completely tilts over flat to minimize the profile even further. I saw this on a ENG Pick-up truck in Toronto recently. (Part of the TV stations garage is a relatively low ceiling.)

3) HF was popular before super tall towers became available which then enabled VHF and now UHF base station antennas to be placed high enough allowing 100 mile line of sight capability.

4) VHF and UHF radios at the time were exceedingly large and heavy...and expensive compared to today's relatively micro sized systems.  And then there are mobile repeaters which are now little more than a couple HT's back-to back with a duplexer for those super long shots.

5) In the LMR world, the issue generally isn't the base station being heard in the field.  It's the field radios not being "seen" by the base station. As such, this is where the extending masts came into play.  Get the field antenna up even 20 ft. and the LoS extends by another 10 miles.  That's hard to execute with a 10ft or longer antenna without some serious hardware which would be time consuming to erect and deconstruct for any remote event. The latter is necessary for the HF RPU band at distance.

MM