[NLRS] Questions on the LOW end of the spectrum
John P. Toscano
[email protected]
Sat, 16 Aug 2003 17:36:17 -0500
I know that many of you have your attention devoted to 10 GHz and up
these days, but I'm sure that I can still find plenty of expertise to
tap in the group concerning the other end of the amateur spectrum.
My old 1992 GMC Safari Van (AWD, extended length model) is gone,
replaced with a much smaller 2000 Lexus RX300 SUV. So I have to re-do
all the radio mounting and antenna mounting on the new vehicle.
In the old van, I had built a wooden console that held a Yaesu FT-5100
(dual-band FM rig) and an Icom IC-38a (222 band FM rig) for everyday
use, and had an additional shelf that could hold either my Yaesu FT-847
or my Icom IC-706MkII. For long trips, I liked to slide in the 706MkII,
plus an LDG Electronics AT11-MP autotuner.
( http://www.ldgelectronics.com/at-11mp_description.html
in case you aaren't famililar with that particular tuner.)
I had three holes drilled in the roof of the van, lined up front to back
down the center of the roof, with SO-239 connectors peeking out of them.
The center and rear held a dual-band vertical and a 220 band vertical.
The front SO-239 went to a PL-259 Tee, and from there, cables ran to
the four corners of the roof rack, to which I had attached four
clamp-mount Hamstick connectors. One of them was drilled out and the
Hamstick bayonet connector was replaced with an SO-239 barrel connector.
Onto these four corners, I mounted a 15-meter, 20-meter, and 40-meter
Hamstick, plus a Comet 6-meter/10-meter dual-band vertical that screwed
into the modified bracket's SO-239.
It looked a bit like this (will only make sense with a fixed-width font
such as Courier, etc.):
6M/10M 15M
on Bayonet
SO239 Hamstick
|--------------------------------------------------------------|
| | |
| | |
| ||| |
| SO239 |
| Thru |
| Roof |
| |
| |
| |
| 220 FM |
| ||| |
| SO239 |
| Thru |
| Roof |
| |
| |
| |
| 2M/70cm FM |
| ||| |
| SO239 |
| Thru |
| Roof |
| |
| |
| |
| |
20 M 40 M
Bayonet Bayonet
Hamstick Hanstick
With this setup, I could work 2M/70cm FM on one vertical, work 220 FM on
the second vertical, and could work 6, 10, 12, 15, 17, 20, and 40 meters
on the array of four HF antennas, by just switching to whatever band I
wanted. (I know, none of the antennas was really resonant on 12 or 17M,
but with the help of the autotuner, it actually worked pretty well.)
My new vehicle definitely does not have room for three radios up front
for day-to-day operation. (Roving is a whole different matter, since it
is a short-term thing!) And though there is a (much smaller) roof rack
on the new SUV, I'm not so sure that the array of four HF antennas is
the way to go again. I'd also like to refrain from drilling lots of
holes in the roof of this pretty vehicle. I might be willing to have a
few holes put in and have SO-239's mounted in them, but I'm still
somewhat undecided.
I really miss having the FM radios with me all the time for my short
trips around town, but if I was to consider replacing them to save
space, something like a Kenwood tribander comes to mind. But they are
so expensive (over $1000 new, pretty rare used) that I could buy a
compact all-mode HF through 70cm radio for less (and love it a whole lot
more!) Besides, I am one of the control operators for TCRC, and we are
going to have a 6M repeater going sometime soon, so I want to be able to
access it also. So I need a quad-band radio! (Yaesu makes the FT-8900,
but the fourth band is 10M, not 135cm! And it's still FM only.)
So my first thought was about the radio(s). If I replaced both FM rigs
with an IC-706 MkIIG, it would fit OK in my limited space. I could also
possibly squeeze in a W1GHz 222 transverter somewhere, and have 5 watts
for day-to-day use, and it would actually be more than enough to drive
my 110 watt brick for rover use (it makes full power at 3 watts in!).
That would give me all the bands from HF to 432 in one radio, limited
mainly by antennas. The 706MkIIg came to mind first because I am very
used to using my existing, older IC-706MkII, but the MkIIg adds 70cm.
And the older MkII is (soon?) going to spend a lot of its life as an IF
rig for 902 and up (it is already my IF rig for the 222 DEMI
transverter), and I could certainly MAKE a spot for it in the vehicle
for roving purposes to cover 50 - 2304 MHz with two radios.
Then John Hoaglun (KC0LBT) suggested I consider the Yaesu FT-857 and the
ATAS-120 automatic screwdriver antenna. The one ATAS unit could cover
all of my HF bands from 40 Meters up. It appears to be small enough
that it could mount to the roof rack with a clamping bracket like the
one I modified for my 6M/10M SO-239 vertical. This has some appeal to
me, but I'd probably prefer the FT-897 to the FT-857, since it looks
like it might be a bit better ergonomically with the extra space
available for its display and controls. On the other hand, there is a
"remote control DTMF mic" available for the FT-857 that might overcome
some of that objection, and I don't know if it works with the FT-897.
I asked Dan at Radio City for a suggestion, and he basically suggested
either one of the Yaesu solutions mentioned above or, if I wanted to
stay with the IC-706MkIIg, using Icom's AH-4 autotuner plus a 102" whip.
Then I got to thinking, if the AH-4 can tune a 102" whip from 40 Meters
through 10 Meters, why couldn't my existing AT-11MP do the same? And
how should I mount the 102" whip? Mount it to the roof rack? (Gets the
whole antenna above the vehicle body, which is good for the radiation
pattern, but now it is around 15 feet tall.) Mount it to the trailer
hitch? (Gets the total height below 12 feet, but now the first few feet
of the whip's radiation are pointed right at a big mass of steel car
body. And then there's the issue of minimizing the length of the coax
between the tuner and the non-resonant antenna radiator. Is it OK to
have a few feet of such coax, or would I be much better off trading out
to something like the LDG RT-11, which is in a weatherproof box that is
designed to be mounted at the antenna? The old setup had about 12 feet
of coax from the AT-11MP to the SO-239 in the roof, and from there
another 3 to 10 feet to get to any of the four antennas. But presumably
the fact that each of the four anteannas was tuned manually (via its
whip length) to resonate near my usual operating frequencies made it
easier for the autotuner to extend their bandwidth (and in the case of
12 and 17 M, to work on another band adjacent to them).
John was also surprised that I had good luck with my old setup, since
the antenna shields did not connect to a good ground plane until the
coax penetrated the roof, which was 3 to 10 feet away from the base of
each antenna. If I were to mount another antenna to the roof rack, it
would have a similar grounding issue because the roof rack is DC
insulated from the body of the vehicle. At least with a trailer hitch
mount, a grounding strap could be added easily.
So I'm open to advice, comments, suggestions, etc., on all of the above.
73 de W0JT