(no subject)

[Steve Banks]

Hi Everyone-

I'm looking for any thoughts or suggestions from anyone about some recent
VSWR tests I've made on two antennas.

GAP TITAN BACKGROUND: I've had a GAP Titan vertical antenna running with my
K2 (S/N 1599) for several years.  The K2 and the GAP have served me very
well (QRP WAS, 28 countries, etc.).  The GAP is fed with about 80 ft of RG8U
type coax (Belden 8214).  Its VSWR measurements look completely normal to me
when measured from here in my shack using an MFJ 259B meter.  For example,
typical VSWRs on 20m range from about 1.7 to 2.1 measured directly at the
feedline PL259 connector.  Most of the other seven GAP bands display similar
"expected" VSWR ranges.

Here in my shack the GAP feedline connector is attached to the center
(common) port on a manual (not electronic) Delta-4 coaxial switch.  The K2
and a couple of other rigs (Drake and Heathkit) are connected to the
switchable Delta-4 ports.  That arrangement enables simple rig switches to
the GAP antenna without having to move the feedline from rig-to-rig.  

Measurements of feedline VSWR made THROUGH the Delta-4 switch to the GAP
antenna with a 259B meter produce very similar results to those made
directly at the feedline connector (i.e. with the switch bypassed).
Conclusion: the Delta-4 switch seems completely transparent to the
rig/feedline system.  So far so good.

HEXBEAM RECENT ADDITIONS:  I recently put up a five-band HexBeam (2
wire-type elements for each of the five bands, 20m-10m).  It seems to
perform very well.  The K2's KAT2 tuner likes it, as do the two other rigs
and tuners I have (Drake and Heathkit).  In the process of finishing the new
Hex antenna, and "shaking down" its performance after installing it, I
discovered one defective feedline PL259 connector which I replaced
(naturally, outdoors on a windy day).  

Following that, I measured the HexBeam's VSWR across its five bands from the
shack feedline connector with the 259B; all was well with it.  VSWRs
measured between 2.2 and 1.5 with no strangeness or instability seen on any
of its five bands.  Values on 20m, for example, ranged from 2.2 down to 1.7,
depending on frequency.  Similar measurements show up on the Hex's other
four bands.  (The top of 10m is somewhat higher, but that's not my issue.)

MY ISSUE:  Even though the HexBeam's 20m VSWR measurements appear quite
normal made directly at its shack feedline connector using the 259B meter,
they are VERY DIFFERENT when measured through a Delta-4 switch.  The GAP
antenna's VSWR's are very normal-looking when made through its Delta-4
switch, but the HexBeam and 259B meter are NOT HAPPY with a Delta-4 switch
in place.  (The HexBeam's Delta-4 switch is actually a separate switch, not
the same one the GAP is connected to.)  

For example, instead of seeing a 20m range from 2.2 down to 1.7 on 20m
WITHOUT the Delta-4 switch in place, I see values from about 4.5 or 5.0
across the whole band WITH IT IN PLACE.  The 259B meter also appears quite
"skittish" making measurements through the switch.  It seems unable to
decide on R,X and SWR values that remain reasonably stable.  

Something about the Delta-4 switch seems to have upset the HexBeam's VSWR
applecart when being tested with the 259B.  I see no such strangeness when
measuring through the switch to a dummy load or to the GAP antenna when
connected to the same switch.  The only unexpected results seen through the
switch are those made to the HexBeam.  

Just for jollies I decided yesterday to ignore the apparent problem, and
just let my K2 and other rigs run on the HexBeam, each with its own tuner.
All were happy, with the HexBeam's directivity quite obvious on all of them.

I've disassembled both of my Delta-4 switches, cleaned their contacts,
verified that all of my cable connections to the switches are secure and
correct, and that no other dumb-thumbing factors have been introduced by me.
I've done all the usual loosening-wiggling-tugging efforts to see if I can
find a cable connector that might be in trouble, but nothing has shown up
yet.

MY QUESTION: Has anyone else ever used Delta-4 switches and seen similar
unstable/unexpected VSWR results, either with a HexBeam or some other
antenna connected to it?  It seems obvious that the switch, only when
connected between the HexBeam and a rig, introduces some sort of VSWR
increase, but I've run out of ideas for what to try next.  Yesterday my
granddaughter said, "Just quit measuring and start QSOing!"  Ah, the wisdom
of a 12-year-old, huh?

Thanks and 73 to all for the bandwidth and for any thoughts.

Steve Banks
K0PQ


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[Steven Pituch]

Steve Said:
>>>MY ISSUE:  Even though the HexBeam's 20m VSWR measurements appear quite
normal made
>>>directly at its shack feedline connector using the 259B meter, they are
VERY DIFFERENT when
>>>measured through a Delta-4 switch.  The GAP antenna's VSWR's are very
normal-looking when
>>>made through its Delta-4 switch, but the HexBeam and 259B meter are NOT
HAPPY with a Delta-4
>>>switch in place.  (The HexBeam's Delta-4 switch is actually a separate
switch, not the same one the
>>>GAP is connected to.)  

Steve,
Have you swapped the two Delta-4s to see if the problem with the Hexbeam is
affected by both switches or just the one originally connected to the
Hexbeam.
If just one of the switches has the problem, you've isolated the problem.
If they both have the problem then something unusual is  affecting both
switches.  Perhaps a current imbalance is on the coax for that antenna and
it can not be handled by the switch.  I wonder if a current balum made of 50
ferrite beads would help in that case.  Or you could coil up the coax at the
base of the antenna to made a current balun; six turns 6 inches in diameter
is the usual configuration, but you may need more since it is a stubborn
case.

Sorry I don't know enough to really help you.  An antenna switch is a luxury
I don't yet have.  I still must use the Armstrong method.

Regards,
Steve, W2MY/5
http://users.ev1.net/~spituch/, Corpus Christi, TX, ELl7
QRP/ARCI 8351, FPQRP 1025, NJQRP 25, QRP-L 269, FISTS 3150, ARS 142, NEQRP
281, NWQRP ??, 10-10 61720, NORCAL 691, K2 #402

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[Stuart Rohre]

I agree with swapping the two switches to see of problem is on both.  Is
there any other grounding to the switch chassis?

Other than that, are you using same length coax jumpers, (same jumpers) and
just subbing antennas?  I have seen many problems move with jumpers, even
those you think are good by normal tests.  Still, since you have done the
"wiggle test" , I am surprised you did not find anything.

What is different about feed to Hex Beams?  Any restriction/ limit on
feedline length?  Is the beam pointed toward the shack when you observe high
SWR?

My thinking cap is ON.
72,
Stuart
K5KVH



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[Stuart Rohre]

I looked at the HEX BEAM web site to see if anything special about the feed.

Sounds like it is a simple 50 ohm coax connection.  However, compact
antennas have intense near field, so if there is coupling back to shack thru
its gain direction you may have a weird case going.

Keep us informed of what you find swapping switches.
-Stuart
K5KVH



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[N8LP]

I would put a balun or choke at the feedpoint of the HexBeam for
starters... sounds like
rf on the shield might be causing problems.

Larry N8LP



Stuart Rohre wrote:

>I looked at the HEX BEAM web site to see if anything special about the feed.
>
>Sounds like it is a simple 50 ohm coax connection.  However, compact
>antennas have intense near field, so if there is coupling back to shack thru
>its gain direction you may have a weird case going.
>
>Keep us informed of what you find swapping switches.
>-Stuart
>K5KVH
>
>
>
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>

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