Well thanks to advice from Dan, N5AR and Tom, W8JI, I've weeded out the bugs
in my mobile array and am now using a DPDT
switch to toggle in and out my 180degree 1/2WL phase line instead of
shorting it out with a SPST switch. Each antenna gets
equal lengths of 3/4WL RG8X, then the 180degree line is introduced in the
front antenna.
Rough gain at 3/8WL spacing is 2-3dB or so, but , hey, ANY gain in the
mobile is a LOT when you're only running 90w on the most difficult DX band
there is. (HF is for sissy's! Did I say that out loud?) heh heh
Now, I have a question. I used a DPDT (actually a DPTT) (center off position
switch, triple throw?) switch, so I could actually
(hopefully) have available to me the following 3 arrangements:
"broadside/endfire/single antenna."
I haven't had a chance to drive around and check out various signal sources
as it's dark and rainy here right now and dangerous to drive and watch the
S-meter in hte middle of a mild storm, right @ the freezing point 32F,
but......
My question is, with my switch in the center (off) position and only the
rear antenna connected, do you guys think that the pattern
will be more or less omnidirectional? IE: Will the other vertical, 7' away,
with a 3/4wl of open coax attached to it, act like a reflector, or be far
enough away (3/8WL almost) to not make much difference.
On the same (crowded) car rooftop I also have a 10m 1/4WL (shorty) whip and
a 2m 5/8WL whip (which I have already determined makes little difference if
it's there or not.)
73 all and thanks for the tips!
Happy 6m DX-ing,
VE9AA 109DXCC worked on 6m from FN65rs.....who know how many also worked
mobile...maybe 20?
Michael, Coreen & Corey Smith
(VE9AA, VE9AAA & Baby-VE9)
271 Smith Rd
Waterville, NB
E2V 3V6
Canada
http://members.tripod.com/~ve9aa/index.html
http://www.geocities.com/RainForest/Vines/2174/
----- Original Message -----
From: Tom Rauch <w8ji@akorn.net>
To: <towertalk@contesting.com>; Mike Smith VE9AA <ve9aa@hotmail.com>
Sent: Monday, November 05, 2001 12:44 PM
Subject: Re: [TowerTalk] phased verticals on 6m HELP!!
>
> > I am running 2, 1/4wl verticals,spaced 3/8WL apart (my car roof is
> > only so big) and feeding each antenna with an equal length of RG8X
> > (116" I think) I have a spdt switch with a jumper across the common
> > and one side(to make it a spst in actuality), so one antenna is ALWAYS
> > connected direct to a short length of RG8X to the rig. I then have a
> > 1/2WL of rg8x (77" aprox) which I short out or open up, introducing a
> > 180degree phase shift. No matter how many times I check and double
>
> If you short the ends of the 1/2 wl of cable together with a perfect
> short, you should have what appears as a short across the main
> transmission line! What that does is form two 1/4 open stubs that
> parallel the main transmission line, and each open 1/4wl line acts
> like a short between the shield and center at the connection point.!
>
> I don't see how that ever worked on any band.
>
> What you need to do is switch that line out, and that takes a DPDT
> switch.
>
> It also doesn't sound like the line is correct, because it looks like
> you used solid poly dielectric velocity factor of .66. A free-space
> half-wave is about 118 inches on six meters, and the Vf of most
> RG8X I've measured is about .75. .75 times 118 is 88 inches, not
> 77 inches! That still is a small error, unless the particular RG8X
> you have has a lighter foam than most RG-8X cables I have seen.
> In that case the error is larger.
>
> By the way, while it is true that solid poly cables are about .66 Vf,
> foam cables vary widely in Vf. I have cables as high as just above
> .9 Vf, and as low as .75 (the RG-8X I have)!
>
> Another problem is a 1/4 wl vertical over a reasonably good ground
> is about 35 ohms, and so there are usually standing waves in the
> system. With mutual coupling the antenna base impedances will
> be different than for a single antenna...but you have a BIG problem,
> because of the switch wiring.
> 73, Tom W8JI
> W8JI@contesting.com
>
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>
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