I just found out that business travel is going to require me to be in
Singapore over the CQ WW Phone weekend. (Oct. 28th/29th) This got me to
thinking, "Hey it would be fun to try operating the contest from there!"
Does anyone out there have a line on any multi-operator contest stations in
Singapore that wouldn't mind having another operator drop by for awhile. If
I remember right, last year there was a multi-op station in the contest from
Singapore. Maybe they have the same plans again.
Thanks in advance for any leads you might have.
Scott Tuthill/AA7TF stuthill@micron.net
>From Tony and Celia Becker <becker@shell.portal.com> Tue Sep 19 01:03:09 1995
From: Tony and Celia Becker <becker@shell.portal.com> (Tony and Celia Becker)
Subject: Addition of weak signals (was Cryogenic Radio)
Message-ID: <199509190304.UAA25770@nova.unix.portal.com>
This thread is related to my work as well as near to my heart, so being the
pushy person that I am, I asked a professional contact of mine, Jont Allen,
to comment. Jont is a noted, published researcher at Bell Labs in the field
of acoustics and the auditory system of mammals, esp. humans. He is not a
ham and generally dislikes e-mail correspondence on technical subjects, so I
feel privileged that he took the time to respond.
If any of you wants to correspond with him, send the response directly to
me. I will summarize for Jont and the reflector, so as to keep the
irritation level to a minimum.
AE0M, Tony Becker - becker@shell.portal.com - Silicon Valley, U.S.A.
######## begin forwarded message
There was a report in Nature a few months ago (Jan?) that reported this
effect, and it got a lot of press. It then showed up in Scientific American
in the amateur exper. column, with a circuit that demonstrated it.
It is a property of a 1 bit A/D that adding noise (dither) expands its
dynamic range. In the mathematical literature it is called Prices theorem.
As far as I know, it does not apply to the auditory system, but has been
used as an explanation of why the auditory system works as well as it does.
They claim that the internal noise of the auditory system is expanding the
dynamic range of the binary channels in the stereo cilia of the inner hair cell.
If you have a threshold device, and a signal below threshold, then adding
noise can dither the signal to randomly bring it above threshold. This
effectively linearizes the response. In dither systems, they usually
subtract out the dither noise to recover the signal.
jont
######## end forwarded message
>From Joe Subich" <subich@ramlink.net Mon Sep 18 15:22:01 1995
From: Joe Subich" <subich@ramlink.net (Joe Subich)
Subject: Rohn 25 capacity?
Message-ID: <9509190035.AA0034@localhost>
>
> I can't find my Rohn book. What's the maximum height that Rohn 25G can be
> self-supporting with a load of about 10 sq. ft.? I think I remember 30
> feet, but I'm not sure. I'd like to put up about 30' for the winter and
> throw a big tribander (with a 40m add-on kit) on it as the antenna
> system for the second CONTEST radio.
>
> 73, Greg
>
> Greg Becker NA2N
> gb546@bard.edu
>
//------- no ice --------\\ //------- 1/2 " ice -------\\
Ht. 70 MPH 80 MPH 90 MPH 70 MPH 80 MPH 90 MPH
10' 19.7 14.3 10.5 22.8 15.5 10.5
20' 14.2 9.0 6.9 14.4 7.1 2.1
30' 6.4 3.7 1.7 2.5 0.0 0.0
35' 3.6 1.4 --- 0.0 --- ---
40' 1.5 --- --- 0.0 --- ---
Notes: 1) Tower designs in accordance with ANS/EIA-222-E
2) All towers must have fixed bases. Pinned bases must not be used
3) designs assume transmission lines symetrically placed as follows:
#25 tower - one 5/8" line on each face (total 3)
4) antennas and mounts must be symetrically placed at tower apex
5) allowable antenna areas assume all round member antennas
6) for wind speeds with ice, areas shown include 1/2" radial ice.
antenna areas without ice must not exceed the areas shown for
the no ice condition.
This information from Rohn drawing number A871266RI dated 9/24/87
>From oo7@astro.as.utexas.edu (Derek Wills) Tue Sep 19 05:48:21 1995
From: oo7@astro.as.utexas.edu (Derek Wills) (Derek Wills)
Subject: Addition of weak signals (was Cryogenic Radio)
>>If you have a threshold device, and a signal below threshold,
>>then adding noise can dither the signal to randomly bring it
>>above threshold. This effectively linearizes the response.
I think this is why students say they study better with the TV on.
The TV jiggles one of the brain thingies just enough that something
they read causes a response and they remember it, for a while anyway.
Derek AA5BT, G3NMX
oo7@astro.as.utexas.edu
>From n3rr@cais.cais.com (Bill Hider) Tue Sep 19 05:59:18 1995
From: n3rr@cais.cais.com (Bill Hider) (Bill Hider)
Subject: October QST
Message-ID: <199509190459.AAA18187@cais.cais.com>
Dave Sumner, Billy Lunt and the ARRL Contest staff:
The attached message from AA6KX says it all. The contest coverage in Oct
QST really deserves an award itself. The contest coverage in the issue is
given right-hand-page emphasis, no-clutter authority, and the most
significant presentation in recent memory.
Thanks for getting it all together, guys, with great editorial content and
management space allocation ("news-hole" as we say in the business) to allow
it to happen.
73!
Bill Hider, N3RR@CAIS.COM
At 12:27 PM 9/15/95 -0400, AA6KX@aol.com wrote:
>The mailman finally brought my October QST yesterday, days after I had heard
>comments from the east coast that led me to believe the ARRL DX contest
>results were burried in the back under a footnote. Instead, what I see is an
>issue with more emphasis on contesting than I have seen in years. That can
>only be due to your efforts to raise the visibility of contest activities in
>QST and gain greater prominence for the contesting community. My personal
>and sincere thanks for your efforts, and my compliments on what I see as
>excellent results.
>
>What absolutely jumps out at me in this issue is--
>--A cover photo of every ham's dream station. This picture is art,
>gentlemen. REAL antennas like that make my heart throb.
>--An announcement on the cover that this is the DX Contest issue.
>--A full page (p.13) of color glossy photos giving some background for that
>gorgeous cover photo.
>--In the contest results themselves, a whopping total of 25 different "top
>ten" and "top five" boxes to highlight the high scorers. I know that you
>have had people long argue the case for more of these kinds of boxes in order
>to give recognition to the little guns, and the fact that the granularity you
>use is now so fine that I can even find my call in one of them indicates that
>you indeed have succeeded in reaching down to the little gun! Good work.
>--Space is included in the contest results for 13 different photos of
>contesters in action. Not only that, but I observe an intelligent mix in
>this presentation--domestic/DX, individual/group, returning big gun/newcomer,
>etc.
>--A writeup for the contest that indicates you really were a part of the
>event yourselves. Yes, the CW weekend was a genuine surprise, with
>conditions far better than most people expected. Conversely, just as you
>stated, the phone weekend was slow and tedious but with some surprising 10m
>opportunities. It may be just a matter of personal preferences, but I
>thought the writing conveyed interest and excitement in the topic, was lucid
>and well-organized, and gave encouragement to the people who almost (but not
>quite) made it to the top.
>--The results listings contained a new column for "hours worked", a first for
>this event. I know this is of great interest for the part-time contesters,
>and I'm sure they appreciate your efforts in their behalf.
>
>In summary, I think you did a great job with this issue. We can't expect to
>see a focus on contesting in every issue, but it is nice to get a break from
>the steady diet of newcomer-oriented issues and see some open encouragement
>for those newcomers to upgrade their skills and join the contest next year.
> The October issue of QST definitely accomplished that.
>
>73...Bruce Sawyer, AA6KX
>
>From kf3p@cais.cais.com (Tyler Stewart) Tue Sep 19 06:04:26 1995
From: kf3p@cais.cais.com (Tyler Stewart) (Tyler Stewart)
Subject: ARRL DX results
Message-ID: <199509190504.BAA18664@cais.cais.com>
>>> Reply to: RE>ARRL DX results
>>>
>>>Or how about turning in the best score in the world, 13M+ pts, one of the top
>>>five all time scores regardless of category and meriting only a single
>>>sentence. AND no plaque. VP2MFM (multi-two) beat All multi-op categories, DX
>>>and W/VE. Hell, we made more Qs on 15m than W3LPL did in the entire contest
>>>(no insult intended). We are wondering who's punch bowl we pissed in. Maybe
>>>that explains why the volcano is erupting and hurricanes are threatening the
>>>island, the Gods are angry....
>>> 73, Cliff KO4FM/VP2MDI
>>>------------------------------
>>
>>I agree, Cliff. I've heard this complaint before about the SS contest as
>>well...
>>
>>I think all that is need to correct this is to have Stan or Billy get on here
>>and tell us what plaques need sponsors.... no doubt, as K1AR knows, this
>method
>>works extremely well!
>>
>>QSL Stan?
>>
>>TU de KF3P
>>
> Who is Stan? You mean Warren? Is Stan his nickname?
>73! Dick
>>
>
awwww SHOOT! Well, at least I didnt call him Johnson.
(I've got to stop doing this at 2AM!)
Tyler KF3P
>From Tim Coad" <Tim_Coad@smtp.svl.trw.com Tue Sep 19 06:11:16 1995
From: Tim Coad" <Tim_Coad@smtp.svl.trw.com (Tim Coad)
Subject: FWD>Black hole defined!
Message-ID: <n1400660058.98717@smtp.svl.trw.com>
Mail*Link(r) SMTP FWD>Black hole defined!
I got some good answers to how big the black hole is,
here's my favorite sent in by Dave, K5GN.
>>Hmmm... just how big is that black hole anyway?
>I think it looks something like this:
.------------------------------------------.---------.
| | |
| | |
| | NEW |
| | ENGLAND |
| | |
| THE | |
| BLACK |---------'
| HOLE |
| |
| (THE REST OF US) |
| |
| |
| |
| |
| |
'------------------------------------------'
>Dave K5GN
BTW: In my original message when I said:
>Isnt that kinda like saying WA7NIN in Nevada is not a west coast station?
I was not trying to reduce the significance of K3LR accomplishments in anyway!
(Really Tim I wasnt! :-) ) From all accounts Tim has done a great job!
It just sounded real funny to me. You got to realize that when I am trying to
work Europe, EVERYONE else calling seems like they ARE on the East Coast!
73 & Gud Luck!
Tim - NU6S
>From w7ni@teleport.com (Stan Griffiths) Tue Sep 19 09:54:26 1995
From: w7ni@teleport.com (Stan Griffiths) (Stan Griffiths)
Subject: Rohn 25 capacity?
Message-ID: <199509190854.BAA10494@desiree.teleport.com>
>
>I can't find my Rohn book. What's the maximum height that Rohn 25G can be
>self-supporting with a load of about 10 sq. ft.? I think I remember 30
>feet, but I'm not sure. I'd like to put up about 30' for the winter and
>throw a big tribander (with a 40m add-on kit) on it as the antenna
>system for the second CONTEST radio.
>
>73, Greg
>
>Greg Becker NA2N
I think that if you find your Rohn book, you will wish you hadn't! I have
lots of Rohn books and quite a lot of experience with them since I used to
be a Rohn dealer from about 1977 to about 1982 and I just re-established my
Rohn dealership last month so I have the old books and the latest which, by
the way, do not say quite the same things on this specific question. I have
experienced extreme frustration in trying to follow Rohn's guidelines for
tower installation. Let me expand on this a little and I am sure it will
start a long and interesting thread.
First, let me tell you what I find in the very latest Rohn book to address
your specific situation. In the "Consumer Catalog" that they sent me, 25G
is not even mentioned as a tower that you can have freestanding at any
height. (See, I knew you wouldn't like it, and this is just the beginning!)
They might say something different in a different catalog that I don't have.
25G can be used "bracketed--no ice"! (That is probably a good trick in
2-land.) They do tell you how far above the top bracket you can extend the
tower. You might consider that as the "allowable height above ground" for a
self-supporting 25G since that is the non-supported height above the top
bracket. Since Rohn does not seem to address 25G as a free-standing tower
at all, I am not sure it is valid to consider the allowable height above the
upper bracket as an acceptable free-staniding height. There may be no
acceptable free-standing height today for 25G. The reason I have not come
right out and given you the number for allowable height above the top
bracket is that you have to get it from a chart with a lot of numbers in it
and the actual real number depends upon several factors we have not yet
discussed. The most important one is the velocity of the expected winds in
your area and the resulting wind pressure on the tower and antenna.
So, to get at the expected wind velocity, the usual way is to refer to an
EIA wind map of the U.S. The newest Rohn catalog I got inconveniently
leaves this map out so I had to dig into my old books to find it. (I assume
the old map is still valid, dated April 1960.) Anyway, almost all of the
U.S. is in "Zone A" which is the lowest wind velocity zone recognized by the
EIA. "Zone B" is for moderate winds and includes various areas of the U.S.
like the Bay Area, Pudget Sound, the Gulf Coast, Eastern Maine, and some
areas in the the Mid-West. You should get your own map and study it.
Anyway, in 2-land, just the extreme east coast of New Jersey is in Zone 2.
Zone three, the highest wind aone, is southern Florida and the coast of
North Carolina. We will assume you are in "Zone 1" which has the lightest
winds.
Next, we consult another chart and find out that for the parts of your tower
under 300 feet in height in Zone A, we must use a loading number of "30"
which is the smallest number in the chart and this is as good as it gets.
No where do they tell us what units are attached to the number "30" but I am
90% certain they mean a wind pressure of "30 pounds per square foot".
Putting it another way, the EIA thinks there is no place in the U.S.A. where
any tower should be designed for less wind pressure than 30 pounds per
square foot. I think that is good advice. Consulting yet another chart
(again, in the old Rohn book and not the new one), we see the relationship
between wind velocity and wind pressure and we see that it is not linear. I
will reproduce a few numbers from the chart so you can see how it goes. By
the way, 70 MPH is the lowest number on the chart and that almost makes
sense since the EIA thinks the lightest wind area in the U.S. should assume
30 pounds per square foot which translates to 86.6 MPH:
Wind Velocity, MPH Impact Pressure Lbs./Sq.Ft.
70 19.6
70.7 20.0
80 25.6
86.6 30.0
90 32.4
100 40.0
111.5 50.0
122.5 60.0
132.3 70.0
141.4 80.0
You can see what is happening here. When you double the wind velocity from
70 mph to 140 mph, the loading goes up by a factor of 4, from 20 pounds per
square foot to 80 pounds per square foot. That means if you try to fudge
these numbers a little bit, the stresses on the tower go up very fast!
Let's see, where were we. Oh yes, we were about to take a number off of a
chart to tell us how high above the top bracket we could go for a bracketed
tower. Notice in the chart below, that there are two bracket elevations:
upper and lower. Rohn apparently assumes there will always be two brackets
on a bracketed tower. Here is the chart straight out of the latest Rohn
catalog:
Tower Bracket Elevation Allowable Antenna Areas (Sq. Ft.)
Height Upper Lower 70 MPH 80 MPH 90 MPH (for various wind speeds)
Feet Feet Feet
40 30.0 15.0 15.3 11.3 7.7
50 36.0 18.0 14.6 10.0 6.8
60 46.0 23.0 14.0 8.9 5.9
70 56.0 28.0 13.5 8.3 5.5
80 66.0 33.0 13.1 7.7 5.0
90 66.0 33.0 6.8 4.9 ---
100 66.0 33.0 1.7 --- ---
I don't think I have ever lived in a house that could have a bracket at 30
feet much less 66 feet! It is hard for me to imagine a tower installed
according to this chart.
Since we have assumed that you are in Zone 1 (30 pounds per square foot, or
86.6 MPH), and you want 10 sqare feet of antenna, that will put you on the
top line about midway between the 80 and 90 MPH columns on the chart above.
The chart tells me you can go 10 feet above the top bracket. (The tower is
40 feet high and the top bracket is at 30 feet, or ten feet above ground if
the tower is free-standing and you assume you can go the same distance
free-standing as you can go above the top bracket.) If you want to be safe,
don't go over 9 feet. Obviously, there must be something wrong with this
analysis. What is it?
So let's abandon this approach and look in the old books where Rohn actually
recognized 25G could be used as a free-standing tower. They give a chart
there too:
SELF-SUPPORTING HEIGHTS FOR 25G TOWER
Wind Load Factor of Safety-1.5 Factor of Safety-2.3
No Ant. 2 Sq.Ft. No Ant. 2 Sq.Ft.
10.0 psf (50 mph) 72.4' 64.8' 58.4' 50.9'
14.4 psf (60 mph) 60.4' 52.9' 48.7' 41.3'
20.0 psf (70.7 mph) 51.3' 43.8' 41.4' 34.1'
This entire chart seems to be in direct conflict with the EIA map in that
this chart only goes up to 70.7 MPH and the EIA map only goes down to 86.6
MPH. So I guess this chart is for installing Rohn 25 inside of the
Astrodome . . . Besides that, they only recognize 2 square feet of antenna
and give you no clue as to how this might translate to a larger load like 10
square feet. My guess is that if you really ran this chart to 86.6 mph and
really ran the load up to 10 square feet, it would show you a maximum
self-supporting height of 9 feet, just like we found out in the first
example above.
Well, I guess you can always call your Rohn dealer and ask. No, wait. I'm
a Rohn dealer and I don't have a clue. Maybe you can try the factory. Yes,
that's it. Call and talk to one of their consulting engineers but be
careful if they ask for your VISA number. In my previous life as a dealer,
I asked what their consulting fees were for tower installations that were
not easily extrapolated from their published charts. They were
astronomical, as you might guess, since they are legally responsible for the
answers they give you. I didn't think you would be happy if you found your
Rohn book. So where does that leave us?
There are hundreds of Rohn towers up so at least some of us must have been
successful in getting around this mess some way. In all of my 43 years as a
ham, I have sold dozens of Rohn towers, put up two dozen or so, and have
closely inspected a hundred or more. I can remember only one tower out of
all of them that totally met Rohn's suggested installation recommendations.
That tower is 100 feet of Rohn 45 which is guyed to the hilt and the largest
antenna on it is a medium sized 6 meter beam. The rest are VHF and UHF
antennas. Since virtually all of these Rohn installations are grossly
overloaded (according to Rohn) and most of them still seem to stand there, I
can only conclude that Rohn is extremely conservative in their installation
advice. It doesn't take a genius to know why they are so conservative given
some of the ridiculous monetary awards given to stupid consumers by the
court system these days. Rohn's advice has to be almost impossibly
conservative so that they can always take the position in court that their
advice was not followed to the letter. This is the "CYA" approach and I
would not expect anything different from a tower company.
Here is another interesting observation about Rohn towers. BX towers are
heavily advertised in QST, CQ, and anything else that hams read. They are
free standing, relatively cheap, and support lots of surface area, up to 20
square feet according to one drawing for HDBX (Heavy Duty BX) tower in my
latest Rohn catalog. What may not be obvious to you (since it is never
advertised) is the fact that the "Typical Tower Analysis" that Rohn supplied
in my catalog assumes a wind pressure of 20 pounds per square foot which
translates to 70.7 mph. According to the EIA wind chart, there is no place
in the U.S. where it is accaptable to have a tower designed for less than
86.6 mph or 30 pounds per square foot. So how many square feet of antenna
can you put on it if you want to be safe at 86.6 mph? Rohn gives no hints
(at least for free).
If you continue to read the fine print, you will see that Rohn strongly
recommends limiting the boom length of any antenna on a BX tower to 10 feet
or less because the tower is not designed to take the heavy twisting forces
of larger arrays. Imagine, if you will, a ham antenna with 18 square feet
of area and a boom less than 10 feet! I suppose a boomless quad would
qualify, technically, but we all know that a boomless quad would still have
large twisting forces and Rohn is really warning us about keeping the
twisting forces low and you can generally (not always) do that by keeping
the boom short.
The ARRL takes great pride in their advertising policies and they claim they
would not allow anyone to advertise something dangerous in the pages of QST.
I think BX towers are dangerous if you care to believe what the manufacturer
publishes about them and, yes, I think the publishers of QST should refuse
to accept ads for BX towers without publishing "the rest of the story".
So, is there any light at the end of the tunnel? Maybe so. We have several
great antenna modeling programs now and we no longer have to rely on gut
feelings and guesses about what will work. I think we are ripe for a tower
modeling program which will allow us to do a sound mechanical analysis of
the tower itself including things like the stresses on elevated guy posts
and the effects of torque bars. What, for example, are the effects of
guying steeper than Rohn recommends in order to keep the guy anchor on your
property and still go up 100 feet? What, as another example, are the
effects of moving one of your guy points a couple of degrees around the
tower to miss your driveway and not have them precisely 120 degrees apart?
We all make these decisions all the time when we put up towers. I don't
know about you, but I use "gut feelings", put it up, and cross my fingers!
I have been lucky so far. Why should we depend on luck when we could have
the real answers to all of these questions with a well done software
program? Unless I am way off base, the principles involved here are those
of standard mechanical engineering design and should lend themselves very
well to computer analysis.
You might recognize me as the guy who recently asked for your experiences on
torque bars. I feel I can get better answers here than I can from Rohn
although I still intend to phone them, too, and ask just to see what they
tell me. I will soon summarize the torque bar info.
Thanks for letting me vent this stuff here. (Not that I gave you a choice!)
I have been thinking about these issues for at least 25 years.
Stan W7NI@teleport.com
|