[TowerTalk] Duo band 20/15 meter beam

Mon Nov 7 13:55:49 EST 2016

Would be interesting to know the answer to your remark, apparently they are 
selling enough that they continue to offer it in their catalog.

I have two (one up and one down which I use for spare parts). One I 
purchased In Portland OR new as a TH7DX back when they first came out, the 
other came with a crankup tower I purchased in Portland in the late '90's, 
so was probably 4 or 5 years old then. It also was a TH7DX.

When I moved to the OR coast in 2003 I put the older TH7DX I'd been using up 
on the crankup. After some 12 years of salt air exposure, I began to notice 
some intermittent SWR and later full SWR issues with the TH7 and made a few 
inquires on this reflector. The common response pointed to corroded trap 
screws. Over the summer I pulled each trapped element and began the 
inspection process.

One input suggested that the trap covers could only be removed after the 
dimples (4 per side) were drilled out. I did this on the first two 15 M R 
traps using a number 43 drill. The first problem encountered was the screw 
holding the trap cover to the element, so badly corroded that a 1/4 in 
socket just spun on the hex heads. This necessitating getting my Dremel out 
and doing some grinding, enough to pop the head off. Once the covers were 
removed I could use a long strong channel lock to grab the remaining screw 
part and back it out. I bypassed the dimple drilling on the remainder of the 
trap covers, finding I could pop the covers off without the necessity of 
drilling the dimples out. In summary, it is not necessary to drill the 
dimples out of a TH7 trap to get the cover off. I did find the plastic 
spacers (4) holding the trap covers rigid over the element tubing chock full 
of 'creatures' and debris which had to be washed out. When reinstalling the 
cover it is best to leave the two outer plastic supports off so the inner 
ones can be driven securely against the coil screws, adding the end trap 
supports later. This is important since the 4 plus the trap cover give the 
rigidity needed to support the element tubing.

Next step was inspection of the coils and screws. As had been suggested by 
many I found significant corrosion between the hex head screw with 
refastened star washer, the coil wire and the element itself. I did not find 
any coil problems. After removing the old screws (these heads were still 
OK), cleaning the wire and element surface, I covered the mating surfaces 
with a bit of copper based antiseize and refastened with SS screws and star 
washers. Note - the 10 M coil wires just wrap around the screws, the 15 M 
coil wires are terminated in side solder lugs.

NOTE - the manuals (I have 3 iterations produced over a long period of time) 
all show different PN's between the 15 M traps used on the DE's and those on 
the R. After examination and some correspondence with MFJ/HyGain I learned 
that replacement 15 M traps sent today are identical in construction for the 
DE's and R regardless of the PN shown. MFJ/HyGain obviously has little 
information on the earlier models or the general TH7 history. One tech 
thought earlier R 15 M traps had an extra or missing turn, but could confirm 
this. Why the manual has not been corrected is anyone's guess. I did not see 
any difference between my 15 M DE and R traps except for the label on the 
trap cover.

Once the other antennas on or using the tower are checked out I'll tilt the 
tower back up, raise it and see what happens. Hopefully, all will work!!!! 
Gets harder and harder to do this in your 80's. Tnx to all who offered me 
advice on this antenna.

I may be slow, but I'm not very fast.

Don W7WLL

-----Original Message----- 
From: Steve Baughn
Sent: Monday, November 07, 2016 4:58 AM
To: Jim Thomson ; towertalk at contesting.com
Subject: Re: [TowerTalk] Duo band 20/15 meter beam

Hy Gain still uses the dual DE on their TH-7DX but not sure how many of
those they are selling these days with all the other choices out there.

73, Steve, WD8NPL

-----Original Message----- 
From: Jim Thomson
Sent: Sunday, November 06, 2016 11:34 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Duo band 20/15 meter beam

Date: Sun, 6 Nov 2016 01:51:06 -0500
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk at tm.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Duo band 20/15 meter beam

The KLMs came out in the late 60s or early 70s.  They worked well for
antennas of the day. I had 5L on 20 and 6L on 15.  Mine "appeared" to
have gain, or were at least directive.  IIRC they used dual DEs and were
quite broad banded.  I had a 7L Wilson on 10 that played very well.
Even on that cycle low, I could hear JAs on an apparent dead band. It
was fed with a quasi air core coax.  It had a spiral dielectric that
looked like layers of thin polystyrene. .They didn't use software as
there wasn't any except on mainframes and mini computers and it was
EXPENSIVE as was computer time.  Programs, even at the college level
were input with punch cards.

73

Roger  (K8RI)

##  The dual de KLMs had a flat swr  vs  BW...but thats about it.   The FB
vs
bw....  and gain vs bw was none too great.  Most of those ants back then did
not hold
a good pattern across the band.  These days nobody uses dual DEs, except on
40m,
like optibeam, jk, and m2.  Even those, with their dual 40m DEs,  dont hold
a
pattern across the band, only the swr is fairly low across the band.

##  But still, the old yagis worked reasonably well.

Jim  VE7RF

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