Stub QTHs - pretty much so a consensus...but
W8JITom at aol.com
W8JITom at aol.com
Thu Apr 18 12:18:17 EDT 1996
Hi Tony,
In a message dated 96-04-18 07:25:36 EDT, you write:
>I'd suggest that if this type of stub doesn't work, you must probably
>have something rectifying or arcing out near the antennas, and no stub
>can cure that problem, because the offending signal is being
>generated downstream from the stub and is in-band. One contest,
>we had all sorts of problems with interstation interference, and tore
>out many things, including hair. Finally the problem was traced to
>a bad barrel connector in the main feed for station 2, which was arcing
>depending on position. Stubs can't fix this problem!
>
>GL-
>
>-Tony, K1KP, fisher at hp-and2.an.hp.com
There are lot's of designs for stub systems, but the design for maximum
harmonic attenuation will always place the stubs about 1/4 wl apart at the
reject frequency, and the first stub 1/4 wl from a low impedance generator at
the reject frequency.
What you say is very true, and there can also be another even more common
problem the stubs won't fix. Most rigs require 25 to 40 dB fundamental
attenuation, and the TX stubs won't help that at all. The only cure is a
passband filter or reject filter in the receive path, or some pretty wide
antenna separation.
Stub away if it's a harmonic problem, things will improve. But I'd bet most
of the time it's a combo problem TX stubs won't completely cure.
73 Tom
>From w2vjn at rosenet.net (George Cutsogeorge) Thu Apr 18 23:37:33 1996
From: w2vjn at rosenet.net (George Cutsogeorge) (George Cutsogeorge)
Date: Thu, 18 Apr 96 22:37:33 GMT
Subject: Auto Switching Stubs.
Message-ID: <M.041896.153733.20 at ppp000.rosenet.net>
A number of people asked for more information on automatic stub switching. The
system referred to was built for a west coast contester who uses it in his
single op, two transmitter station.
A short length of RG214 (needs to have good shielding, length not important)
connects to a tee fitting which is mounted on the input of a six way relay box.
The antenna line connects to the other side of the tee. The six outputs of the
relay box each connect to a stub. The stubs are defined as follows:
A = 1/4 wave shorted 80 meter
B = 1/2 wave open 40 meter
C = 1/4 wave shorted 40 meter (which is also 3/4 wave shorted 15 meter)
F = 1/2 wave open 20 meter (which is also 1 wave open 10 meter)
G = 1/4 wave shorted 20 meter
J = 1/2 wave open 10 meter
One or two stubs are selected with a band decoder and some simple diode logic
as follows:
160 = none
80 = A, nulls 40,20,15,10
40 = B & C, nulls 80,20,10
20 = F & G, nulls 40,15,10
15 = C, nulls 20,10
10 = F & J, nulls 40,20,15
All stubs for one system were RG213 and were coiled up together in a NEMA box
with the six way switch.
Later, more attenuation was required on 40 meters so an additional box was
added that nulled 80,20 and 10. It was connected to the original tee with a
1/8 wave line. The input of the box has a 1/4 wave shorted 40 meter stub.
>From there a 3/8 wave line connects to the output which also has a 1/2 wave
open stub. A DPDT relay selects this box when the band in use is 40 meters and
bypasses it on the other bands. Forty meter performance was:
Unit 80 20 10
Original -28dB -28dB -24dB
W/added -64dB -65dB -41dB
There are many ways to do this type of thing. Other combinations could null
the 15 meter harmonic of 40 meters for example, etc. The relay box was used
while cutting the stub lengths to include it's effect. Performance was
essentially the same as individual stubs.
----
George Cutsogeorge, W2VJN
Umpqua, OR.
>From w2vjn at rosenet.net (George Cutsogeorge) Fri Apr 19 00:28:26 1996
From: w2vjn at rosenet.net (George Cutsogeorge) (George Cutsogeorge)
Date: Thu, 18 Apr 96 23:28:26 GMT
Subject: Fw: Auto Switching Stubs.
Message-ID: <M.041896.162826.46 at ppp016.rosenet.net>
A number of people asked for more information on automatic stub switching. The
system referred to was built for a west coast contester who uses it in his
single op, two transmitter station.
A short length of RG214 (needs to have good shielding, length not important)
connects to a tee fitting which is mounted on the input of a six way relay box.
The antenna line connects to the other side of the tee. The six outputs of the
relay box each connect to a stub. The stubs are defined as follows:
A = 1/4 wave shorted 80 meter
B = 1/2 wave open 40 meter
C = 1/4 wave shorted 40 meter (which is also 3/4 wave shorted 15 meter)
F = 1/2 wave open 20 meter (which is also 1 wave open 10 meter)
G = 1/4 wave shorted 20 meter
J = 1/2 wave open 10 meter
One or two stubs are selected with a band decoder and some simple diode logic
as follows:
160 = none
80 = A, nulls 40,20,15,10
40 = B & C, nulls 80,20,10
20 = F & G, nulls 40,15,10
15 = C, nulls 20,10
10 = F & J, nulls 40,20,15
All stubs for one system were RG213 and were coiled up together in a NEMA box
with the six way switch.
Later, more attenuation was required on 40 meters so an additional box was
added that nulled 80,20 and 10. It was connected to the original tee with a
1/8 wave line. The input of the box has a 1/4 wave shorted 40 meter stub.
>From there a 3/8 wave line connects to the output which also has a 1/2 wave
open stub. A DPDT relay selects this box when the band in use is 40 meters and
bypasses it on the other bands. Forty meter performance was:
Unit 80 20 10
Original -28dB -28dB -24dB
W/added -64dB -65dB -41dB
There are many ways to do this type of thing. Other combinations could null
the 15 meter harmonic of 40 meters for example, etc. The relay box was used
while cutting the stub lengths to include it's effect. Performance was
essentially the same as individual stubs.
----
George Cutsogeorge, W2VJN
Umpqua, OR.
>From Pete Smith <n4zr at ix.netcom.com> Thu Apr 18 17:59:55 1996
From: Pete Smith <n4zr at ix.netcom.com> (Pete Smith)
Date: Thu, 18 Apr 1996 09:59:55 -0700
Subject: Then and now - the cost of contesting.
Message-ID: <199604181659.JAA07214 at dfw-ix4.ix.netcom.com>
This discussion about "first stations" of seasoned contesters really tickled
my nostalgia nerve, but that was about it, until. ...
Quite by coincidence, I ran across a Social Security Administration table
indexing wages over the years, back to 1951, against wages today. A few
examples:
Date Index
1954 (year I got my novice license) 7.53
1964 (year I got married) 5.19
1974 (year we bought our first house) 2.96
1989 (year our last kid graduated from college) 1.18
1994 (year we moved to WV) 1.00
1996 1.00
Aside from telling us that wages have been flat the last 3 years, this table
tells us one amazing thing -- ham radio equipment is cheaper now than it has
ever been. Take an FT-1000MP (yes, gladly!). Today's HRO price is
$2899.95. In 1954 dollars, that's $385! Anyone remember what a 32V3/75A4
combo went for in those days? Around $1200, I think -- or $9036 today.
In 1956, I bought an RME 4350A receiver for $140. That was considered to be
a price breakthrough in those days, to get a good receiver for under $200.
But in today's dollars that RME would cost $940! No thanks.
I believe this same price/performance comparison may be good across the
board. If you could've bought a Create RC5 rotator in 1954 for $100 or
less, would you have messed with converting that prop-pitch, or settled for
the first HAM-M predecessor, with its pot-metal gears and fragile controller?
Where's this going? Noplace special, except to observe that we really have
made a lot of progress over the last 40 years. Now if I could just find
enough 1996 dollars for that second tribander ....
73,
Pete Smith N4ZR (n4zr at ix.netcom.com)
>From w2vjn at rosenet.net (George Cutsogeorge) Fri Apr 19 02:38:51 1996
From: w2vjn at rosenet.net (George Cutsogeorge) (George Cutsogeorge)
Date: Fri, 19 Apr 96 01:38:51 GMT
Subject: Automatic stub switching.
Message-ID: <M.041896.183851.75 at ppp018.rosenet.net>
For some reason the end of my message was cut off, at least on the one I
received. In case it happened to all copies, here is the part that was chopped.
Later, more attenuation was required on 40 meters so an additional box was
added that nulled 80,20 and 10. It was connected to the original tee with a
1/8 wave line. The input of the box has a 1/4 wave shorted 40 meter stub.
>From there a 3/8 wave line connects to the output which also has a 1/2 wave
open stub. A DPDT relay selects this box when the band in use is 40 meters and
bypasses it on the other bands. Forty meter performance was:
Unit 80 20 10
Original -28dB -28dB -24dB
W/added -64dB -65dB -41dB
There are many ways to do this type of thing. Other combinations could null
the 15 meter harmonic of 40 meters for example, etc. The relay box was used
while cutting the stub lengths to include it's effect. Performance was
essentially the same as individual stubs.
----
George Cutsogeorge, W2VJN
Umpqua, OR.
>From Paul van der Eijk <pvander at erols.com> Thu Apr 18 20:43:15 1996
From: Paul van der Eijk <pvander at erols.com> (Paul van der Eijk)
Date: Thu, 18 Apr 1996 19:43:15 +-100
Subject: RS232 cards
Message-ID: <01BB2D5F.4B732140 at as15s50.erols.com>
I'm looking for a PC card with a few (up to four) serial ports. I want =
to use it under Windows and Window95, and preferably the thing uses only =
one IRQ, because my system has not much left. Any suggestions?
Paul, KK4HD
pvander at erols.com
http://www.erols.com/pvander
>From zettel at homer.libby.org (Steve Zettel) Thu Apr 18 23:06:00 1996
From: zettel at homer.libby.org (Steve Zettel) (Steve Zettel)
Date: Thu, 18 Apr 1996 16:06:00 -0600
Subject: Auto stub switching
Message-ID: <v02140b01ad9c62ea069a@[192.0.2.1]>
I've been reading with interest the comments on auto-stub switching, and
the use of shorted stubs in general. Knowing my own propensity for "gross
congitive error" and my intimate acquintance with Murphy, I wonder about
the wisdom of incorporating a shorted "anything" into my transmission line
if it could be switched in when not at the proper fraction of a wavelength
for the frequency selected.
Or am I having another "cognitive error"?
Thanks to all my "Virtual Elmers" out there in cyberland,
Steve Zettel KJ7CH kj7ch at libby.org
Libby, MT USA steve.m.zettel at usace.army.mil
Come visit us at: http://www.libby.org
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