In your message dated Saturday 29, July 1995 you wrote :
> Hi Ron...
> I am facing the same dilemma myself for stacking a 150'
tower.....And I have
> to make a decision in the next few weeks...I am also agonizing
between the
> C3/4 and KT34XA...
>
> First, I think that radiation efficiency is a subject which has been
> overlooked in beams/yagis... I suspect the radiation efficiency of
the small,
> untrapped C3 overcomes the enhanced 'gain' of the TH7...
> The KT34 is a more efficient trapped beam, and therefore better,
than the
> TH7...
> The C3 has a broader main beamwidth (less gain) than the KT34XA... A
stack of
> either will do you just fine... Now, the devil is in the details, as
they
> say...
> A) In contests where the desired sigs may come from many headings
in a
> general direction, you probably will do best with a stack of C3's...
Due to
> the nice fat pattern.... Gain is of secondary importance, i.e. you
need just
> enough gain to be able to hear the desired signals, but ANY increase
in gain
> beyond that merely results in a narrowing of the main lobe
(undesireable)...
> Also, a lower FB ratio may be helpful to snag that occasional
multiplier off
> the back side...
> (FB ratio will be low in any stack, however, so that we need not
concern
> ourselves with this item...It will be what it will be...)
> B) In contests where the desired signals are from a definite
direction, such
> as where you are working just U.S. stations, or just Zed El's, etc.
then more
> gain in the stack, i.e. a narrower main lobe is highly desireable...
Here a
> stack of longer, higher gain antennas is called for... For this the
KT34XA
> will be preferred over the C3...
> C) For working general DX, i.e. non contest situations, a stack of
6 element
> monobanders is exactly what you need...
> D) In all of these scenarios, the TH7 is an also ran....
>
> And, that's my opinion....
>
>
> Rational discussion entertained ( I do a mean soft shoe )
> Flames go to the curb with the kitty litter.....
>
> Denny K8DO@AOL.COM
>
--
----------------------------------------------------------------------
-----
| Ron Stone, GW3YDX - EMail ron@gw3ydx.demon.co.uk
----------------------------------------------------------------------
-----
Well Denny
You will just have to get urself another 150 ft tower. One for the
C3 stack and the other for the KT34XA stack. If only it was as easy as
that !!
I'm still undecided. Dave W6QHS put some mail on the reflector which
is pretty interesting. One of the things that has put me off the 34XA
of late is the prob I have with 15 m SWR. What about if I put another
one together and get entirely different curves. Kinda shoots impedance
matching in the foot from the start.
A couple of guys (including W6QHS) have suggested log periodics. Well
I think poor F/B is an advantage during contests but not when the East
EU is 20 dB over S9 and you're trying to copy a weak KH2 !
The TH6/7 comes out a hot favourite with many people. However that was
before the advent of the C-3. I've heard the results of N7ML' stack of
seven (that was the latest count) C-3s on his rotating tower. Sounds
loud on 20 but havent heard it on the other bands and unlikely to for
a few years.
Dont forget the C3XL - but it is a monster with 3 feedlines.
I may just go for 204BA's to keep it simple. The way 10/15 been of
late it won't be a mistake (for this year !!)
73
Ron
>From Larry Tyree <tree@cmicro.com> Mon Jul 31 19:28:32 1995
From: Larry Tyree <tree@cmicro.com> (Larry Tyree)
Subject: Good callsigns
Message-ID: <199507311828.LAA27753@cascade.cmicro.com>
Just a reminder of my post last year about the "BEST" callsign that
you can have. It was determined using computer analysis by looking
at years of contest results and comparing different callsigns to
other callsigns. Guest ops were factored into the equation as well.
So, the best contest callsign is still (drum roll please)...
the envelope please...
WN4KKN.
Have a nice day!!
Tree N6TR
tree@cmicro.com
>From Marijan Miletic <s56a@ljutcp.hamradio.si> Mon Jul 31 19:26:19 1995
From: Marijan Miletic <s56a@ljutcp.hamradio.si> (Marijan Miletic)
Subject: C3 v. TH again
Message-ID: <66982@ljutcp.hamradio.si>
Hi Contesters, I am having bad luck with this reflector email as I lost part
of my first S50HQ score and PRINT was inserted in above header!
KH6CP/W1/ARRL made some theoretical remarks on "properly designed 2 el. yagi"
versus >20 years old TH6 developed by 3 month of experiments on Hy Gain antenna
range. C3 with ONLY 18 ft boom shared by TWO 2 el. per band beams is surely
inferior to TH6 with 3 or 4 elements spread over 24 ft!
I prefer to talk about db (over dipole) instead of misleading dBi figures when
discribing yagis or other antennas with some gain and directivity.
The main problem with short antennas Zack mentioned is critical tuning which
is largely affected by nearby objects. Other remark about log periodic imunity
is very iluminating in that respect.
I am having lot of fun in that respect with my 78m Windom only 10 ft above the
roof. It was even lower and showed no resonance on 80 & 160 m while now is is
diping atleast at 3775 kHz! I also detect plenty of resonances at lower freqs
but these are NOT of radiating nature.
BTW I sugest software antenna developers to try to calculate Windom impedanse
and after all the meaningless figures they should read VE2CV QST article!
73 de Mario, S56A, N1YU.
>From mraz@maverick.aud.alcatel.com (Kris I. Mraz) Mon Jul 31 20:50:28 1995
From: mraz@maverick.aud.alcatel.com (Kris I. Mraz) (Kris I. Mraz)
Subject: C3 v. TH again
Message-ID: <9507311950.AA24606@maverick.aud.alcatel.com>
Mario, S56A, N1YU, says:
> C3 with ONLY 18 ft boom shared by TWO 2 el. per band beams is surely
> inferior to TH6 with 3 or 4 elements spread over 24 ft!
> I prefer to talk about db (over dipole) instead of misleading dBi figures when
> discribing yagis or other antennas with some gain and directivity.
Just for reader's reference in this discussion here are the gain figures
for the Force12 C3 from their Spring 95 catalog:
Net F/B
Freq Gain Ratio
---- ---- -----
20m 4.6 15
17m 2.5 7
15m 4.8 18
12m 2.1 4
10m 4.4 18
"Net gain is the computed maximum forward gain of the antenna over
real, average ground at a height of 74', as compared to a full size,
resonant dipole also at 74' above real, average ground. This figure
will be fairly constant for antennas 35' and higher".
"F/B ratio is the peak (minimum) difference between the forward and
rearward patterns. The average is higher".
"The C3 is 7 elements on an 18 ft. boom..."
"The driver cell is composed of a 4-element open sleeve, with the coax
attached directly to the 20 meter element".
"All 7 elements work together..."
I don't believe the statement that the C3 has only 2 elements per band is
accurate. However, its not clear to me how many elements there are per band
since I'm not familiar with the "4-element open sleeve" design.
73
Kris AA5UO
mraz@aud.alcatel.com
>From jreid@aloha.net (Jim Reid) Mon Jul 31 22:44:36 1995
From: jreid@aloha.net (Jim Reid) (Jim Reid)
Subject: On or Off?
Message-ID: <199507312142.LAA25515@hookomo.aloha.net>
Hi, The following note came in from Steve this morning.
He adds some information I felt ought to be shared with
all of you on the on-or-off topic.
>Subject: Re: On or Off?
>From: Steve Runyon WQ5G 512-838-7008 <steve@austin.ibm.com>
>
>
>Both are hard on ICs!! I've been designing microprocessors for abt 15 yrs,
>and have some experiance with failure mechanisms - both POH (power-on-hrs)
>and thermal cycles contribute to failures. Failures related to power-on
>hours start high (early life fails) but these are usually screened
>out by burnin at the fab. Then they are very low for a period of many
>thousands of POH, starting to increase at some point. The point at which
>the POH related fails begin to become significant is related to the
>operating temp, i.e., more Watts or less airflow will cause earlier fails.
>Anyway, these fails usually remain very low until at least 40,000 or
>50,000 power-on hours in a well designed system. (That means that most
>IC components will operate 24 hours a day, 365 days a year for 5 years
>or more with less than 1% of them failing!)
>
>Thermal cycles cause mismatched expansion of the IC chip (silicon) and
>module (usually plastic or ceramic). These eventually wear out the
>solder balls or wirebonds. High I/O counts make this worse, of course.
>Also, high power/low airflow is bad - this causes a higher operating
>temp, so there is more expansion in going from room temp to operating temp.
>These type of failures increase exponentially with thermal cycles and
>higher temperature, and on high I/O packages can become very significant
>after only 2,000 or 3,000 thermal cycles. Low I/O counts and wirebonded
>chips tend to be a bit more forgiving.
>
>Of course, you then have to consider the other components in the
>computer or rig. These eventually will wear out as well. Mechanical
>components usually seem more sensitive to power-on hours - that is,
>they wear out. Electronic components tend to die more often from
>thermal shock.
>
>So what do you do? I usually leave my PC turned on unless there
>is a storm in the area or I won't be using it for 12 hours or more.
>However, I do turn off the display if I'm not using it for a couple
>of hours or more - that thing gets really hot!
>
>I usually turn the rig off if I won't be using it for more than a
>few hours.
>
>BUT, DO NOT turn it off every time you won't be using
>it for a few minutes!! (This goes for both computers and rigs.)
>This is worse than just leaving it on all of the time!
>From Ed Gilbert <eyg@hpnjlc.njd.hp.com> Mon Jul 31 22:51:02 1995
From: Ed Gilbert <eyg@hpnjlc.njd.hp.com> (Ed Gilbert)
Subject: C3 v. TH again
Message-ID: <199507312148.AA122597281@hp.com>
> I don't believe the statement that the C3 has only 2 elements per band is
> accurate. However, its not clear to me how many elements there are per band
> since I'm not familiar with the "4-element open sleeve" design.
The open sleeve is a technique of getting a driven element to look
like a 50 ohm impedance at several frequencies without complex traps
or matching networks.
You basically drive the driven element of the lowest frequency with direct
feed, then close-space 1/2 wave elements for the other higher frequencies
in close proximity to the one that the feedline is connected to. By
adjusting the spacing and lengths of all elements involved, you can
get the input to look like 50 ohms at each frequency for which you
parasitically excite one of these driven elements. It's a nice way
to feed a multiband antenna, but all these open sleeve elements are
simply driven elements when you're counting elements per band. As I
recall, the C3 has 7 total elements. 20 and 15m each
have a driven element and a reflector, and 10m has 2 driven elements
(probably to broaden the bandwidth) and a director.
Ed Gilbert, WA2SRQ
eyg@hpnjlc.njd.hp.com
>From mats.persson@mbox2.swipnet.se (Mats Persson) Mon Jul 31 23:54:47 1995
From: mats.persson@mbox2.swipnet.se (Mats Persson) (Mats Persson)
Subject: Contests and good callsigns
Message-ID: <199507312254.AAA10681@mailbox.swip.net>
Hi,
I read some emails debating good and bad callsigns for a contest. Even=20
though I am not a big shot on contests i would think that any callsign=20
should be good for a contest. The most important thing concerning the=20
callsign i think is to make it known in the contests and that the call=20
reaccure from one contest to the next. I base this on my experience with the=
=20
callsign KH8/SM7PKK which has to be one of the worst ones ever used. However=
=20
I managed 4700 QSO=B4s with it on 3 bands in 1989 CQ WW SSB. And as you see=
I=20
have 2 K=B4s at the end of my call which should not be too good on CW but I=
=20
have found that it is a very limited amount of people who get that callsign=
=20
wrong once they got to know it. Also take a look at HG73DX that for sure is=
=20
a mouthfull but people know it.
73 de Mats SM7PKK
>From Fred Hopengarten" <k1vr@k1vr.jjm.com Sun Jul 30 00:32:05 1995
From: Fred Hopengarten" <k1vr@k1vr.jjm.com (Fred Hopengarten)
Subject: TRIBANDER STACKING - MORE FUN THAN "QRL ?" !
Message-ID: <301ac4f8.k1vr@k1vr.jjm.com>
On Sat, 29 Jul 1995 11:38:54 -0400, K8DO@aol.com wrote:
> D) In all of these scenarios, the TH7 is an also ran . .
. . And, that's my opinion....
>
> Rational discussion entertained
K1VR: K8DO puts forth a very good discussion of the
considerations he considers. I'll add two more
considerations: (1) Ability to stay up in the sky, and (2)
Price.
Ability to stay up in the sky
The TH7 is ruggedly built. It stays up in the air
through wind and ice storms in New England, especially if
constructed (or, see below, reconstructed) with stainless
steel hardware. I've looked at KT-34XA's and they seem to
have lots of little plastic parts and small pieces of
tubing. I am prepared to believe that they have more gain
than a TH7, but are they as rugged?
I cannot comment on the construction of the C-3, except
that it seems to be getting the rep of being an antenna
designed to be flexible and thereby stay up in the sky.
Price
Tho somewhat rare, TH7's do come on the used market at
about $300 with SS parts. If you REALLY keep your eyes
open, TH6's come on the market at $100 with rusted parts,
but the HyGain/Telex people will take acredit card order
over the phone for any of the parts you need to rebuild.
You could almost fund 100 feet of Rohn 25 (but maybe not all
of the rotators, guy wires, etc.) on the difference between
three used TH7's and three C-3's.
If you run a $1.98 contest station, three used TH6's
with new hardware are the way to go.
--
Fred Hopengarten K1VR
Six Willarch Road * Lincoln, MA 01773-5105
home + office telephone: 617/259-0088 (FAX on demand)
internet: k1vr@k1vr.jjm.com
"Big antennas, high in the sky,
are better than small ones, low."
|