The Southern Pacific RR [now Union Pacific] used 160 MHz DDRR antennas
on some of their signalling equipment. Generally on top of a big steel
box beside the track(s). Had a base plate bolted to the box, and a
single 25-30 cm element, parallel to the top of the box, spaced about
6-7 cm above it. The whole antenna looked like it was cast in one
piece. For 20 m, it would be significantly larger, but might be
disguised as, or in, a roof rack. A lot of folks drive around with
stuff piled on their cars these days.
http://www.orionmicro.com/ant/ddrr/ddrr1.htm has some design info
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 7/15/17 8:37 PM, Bob McGraw K4TAX wrote:
Regarding the defrost heat element, there's two terminals, one on
either side. However with the resistance of the defrost wiring in the
window, it might be more like a dummy load. Of course one could just
feed one side against the auto body, unless one drives a Corvette
which is mostly plastic. grrrr
Seems I recall a DDRR antenna which was a low profile, roof mountable
antenna. The 40M version would be a bit large with a diameter of
some 9 ft, although one might reduce the size and still make a 40M -
10M of reasonable dimensions with reasonable efficiency.
73
Bob, K4TAX
K3S s/n 10163
On Jul 15, 2017 7:54 PM, "Wayne Burdick" <[email protected]> wrote:
I’m dealing with one of the last unsolved problems in amateur radio:
how
to operate HF mobile without an antenna. At least not one that,
according
to some vehicle co-owners/spouses, would defile your new sedan.
For 10 bonus points that have only philosophical value, your
challenge is
to create an invisible mobile antenna and actually make a QSO on it.
For
practical purposes (i.e., not frying the car or passengers) let’s
say the
maximum power level is 10 watts. The bands of interest are 40-10
meters.
Here are some ideas I’m considering:
- mag loop in the rear window
- thin wire loop on a roof rack
- gamma match to the entire roof
- surface acoustic waves
- prayer
Other ideas?
Yes, I know this violates the laws of physics and bioethics. And I
fully
expect the car to generate debilitating levels of RFI. But isn’t
this the
least you’d expect from an unsolved problem?
Thanks in advance,
Wayne
N6KR
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