[TowerTalk] 2 radios & Stacked Tri-banders??

[Barry Kutner]

Hi Dan,
I went through a series of similar questions a few years ago.
I started with 2 TH7s at 40 and 76 ft phased with a DX Engineering 
phase box. I wanted to enable the station for SO2R, but didn't want 
to split the stack, as it is an excellent performer.

I looked into replacing the TH7s with C31XRs and use separate 
feeds. At the time I looked into it, F12 alluded to the possibility of 
using a single C31XR in SO2R, but had nobody that had done it. I 
wanted to make sure that while using one C31XR on 2 bands/2 
radios would not fry one or both radios with excessive field 
strength. F12 was not able to give me firm numbers on the field 
strength between bands (for example, if on 20m, how much RF is 
seen at the PL259 on 10 or 15). For that reason, I ruled out the 
C31XRs.

I put up a Hygain DX-77 40-10m vertical abt 200 ft from the tower. It 
was in the clear, mounted 10 ft above ground. It was a terrible 
antenna (though better than a neighbor's Butternut, when we did 
head to head comparisons). The SWR was fine, but I couldn't work 
anything on it (in a contest, that is). Even on the WARC bands 
(which it supposedly covers), my 40m beam and 80m slopers 
worked better than it.

After doing a lot of modeling with EZNEC, my final solution was 
adding a third TH7 at 22 ft on the same tower, on a separate 
feedline.  There was no advantage on any band to phase it with the 
top two, if using one radio, and interactions were minimal. I also 
modeled the C31XR in place of the TH7, and interactions were 
terrible.  The TH7 at 22 ft was an average of 6 S-units better than 
the vertical into Europe! If you want to see some pics, go to
http://www.ticgen.com/NT/gallery/ticphotos.htm

In your case, I believe 50 ft spacing is too far apart for phasing, 
except maybe on 20m. If you can space them closer, you could 
phase them with Stackmatch with the second feedline option, and 
split them between radios when needed. Otherwise, if 50 ft apart, 
put separate feedlines on them, one for each radio. You definitely 
will need stubs and/or bandpass filters in either case (I have both 
here).

Let us know what you wind up doing.

73,
Barry W2UP


On 31 Dec 00, Dan Levin wrote:

> I am in the process of installing 2 C-31XR's stacked 50' apart on a crank-up
> tower.  Both are rotatable (the lower one on a Ring Rotor).  I want to run 2
> radios for contesting.  There are two obvious options:
> 
> 1) Rig the tri-banders for use with 2 radios.  That means separate feed
> lines, 3 StackMatches (or equiv)., and a SixPack (or equiv.).
> 
> 2) Rig the tri-banders for radio 1 (with 1 StackMatch), and put up a
> separate antenna (probably either a low C-3 or a tri-band vertical) for
> radio 2.  I can put the second antenna about 400' away from the main stack.
> 
> Any thoughts on which way to go?  Seems to me that if the separate feedlines
> on the C-31's really works, then the upside of using them for both radios is
> excellent performance on radio 2.  The downside is money (or time to build
> un-un's), and a complicated cabling harness.  The much simpler approach is a
> separate antenna, and I will also get much better isolation (esp. if I use a
> vertical, neh?).  Decisions, decisions...
> 
> Thanks for your thoughts!
> 
>             ***dan, K6IF
> 
> 
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com
> 


--
Barry Kutner, W2UP              Internet: w2up@mindspring.com
Newtown, PA         FRC         alternate: barry@w2up.wells.com

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com