When Rugby Radio in the centre of the UK was operational at two megawatts
(antenna current of 800 amps!) there were many engineers frequenting the
station and in close proximityto a very high level of radiation at 16
kilohertz. The point is that none of them reported any individual heating of
body parts and apart from one elderly engineer with two heads, they all gave
the appearance of being normal. Well, normal for radio engineers and a lot of
them were licensed as amateurs as well! One of the main trunk roads of the UK
passes within half a mile of the station and at no time were any notices
displayed about a radiation hazard. Now sadly shut down and all the
transmitters gone, the site is to be developed for industrial use. So much for
any museum commemorating a fine piece of history.
Regards and all good wishes.
Cliuve GW3WEQ
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Today's Topics:
1. FS: Motorola PT9730 PT9731 PT9732 transistors (jimmoci)
2. Thoughts on half-wave dipole (Dr. David Kirkby)
3. Re: Damage? (Rob Atkinson)
4. Al80A problem (Georgens, Tom)
5. Re: Al80A problem (Carl)
6. Re: Damage? (Roger (K8RI))
7. Socket source for Valvo TBL2-300 (Randall, Randy)
8. Cooler....GI-46B.. (robert briggs)
9. Re: Damage? (Carl)
10. Re: Thoughts on half-wave dipole (kenw2dtc)
11. Re: Thoughts on half-wave dipole (Steve Cook)
----------------------------------------------------------------------
Message: 1
Date: Sun, 27 Jul 2008 13:43:30 -0400
From: jimmoci
Subject: [Amps] FS: Motorola PT9730 PT9731 PT9732 transistors
To: amps@contesting.com
Message-ID: <2E1CC9AE.40CB.432D.952A.13712A8A0807@aol.com>
Content-Type: text/plain; charset="iso-8859-1"
All are motorola
N.O.S. (5) available PT9730 @ $15 each
N.O.S. (5) available PT9731 @ $15 each
N.O.S. (4) available PT9732 @ $15 each
Or make me an offer on the whole lot.?
+USPS priority shipping $5
Tnx & 73!
Jim
------------------------------
Message: 2
Date: Sun, 27 Jul 2008 20:10:42 +0100
From: "Dr. David Kirkby"
Subject: [Amps] Thoughts on half-wave dipole
To: 'AMPS'
Message-ID: <488CC832.9010706@onetel.net>
Content-Type: text/plain; charset=windows-1252; format=flowed
I know this is a bit off-topic. but possibly someone here has some
thoughts. I've posted it to rec.radio.amateur.antenna and
sci.electronics.design, but someone here might know. I've corrected a
couple of typos that appeared on the newsgroup post.
--------
I wish to know if the reactance of a dipole that is physically 0.5000
wavelengths in length depends on the diameter of the wire or not.
I know a dipole 0.5 wavelength long is not resonate, but inductive so
you need to shorten it a few percent to bring it to resonance. I know
the length at resonance depends on wire diameter.
But I'm interested if the reactance does very with wire diameter when
the antenna is physically 0.5 wavelengths long, which means it will be
somewhat inductive.
A book published by the ARRL by the late Dr. Laswon (W2PV)
Lawson J. L., ?Yagi Antenna Design?, (1986), The American Radio Relay
League. ISBN 0-87259-041-0
has a table of reactance vs the ratio K (K=lambda/a, where a is the
radius) for antennas of 0.45 and 0.50 wavelengths in length. I've
reproduced that table below.
The first column (K) is lambda/a
The second column (X05) is the reactance of a dipole 0.5 wavelengths in
length.
The third column X045 is the reactance for a dipole 0.45 wavelengths in
length.
K X05 X045
-------------------------
10 34.2 23.1
30 36.7 6.4
100 38.2 -14.1
300 39 -33.6
1000 39.6 -55.5
3000 40 -75.7
10000 40.4 -98.1
30000 40.6 -118.6
100000 40.8 -141.1
300000 41.0 -161.8
1000000 41.1 -184.4
What one notices is:
1) Reactance for 0.45 lambda is very sensitive to radius, varying by
more than 200 Ohms as K changes from 10 (fat elements) to 1000000 (thin
elements).
2) The value for a dipole 0.5 lambda in length changes much less (only 6
Ohms), but it *does* change.
3) For infinitely thin elements (K very large), the reactance of a
dipole 0.5 lambda in length looks as though it is never going to go much
above 41.2 Ohms. Certainly not as high as 42 Ohms.
Now I compare that to a professional book I have:
Balanis C. A., ?Antenna Theory ? Analysis and Design?, (1982), Harper
and Row. ISBN 0-06-0404458-2
There is a formula in Balanis' book for reactance of a dipole of
arbitrary radius and length, in terms of sine and cosine integrals. It's
hard to write out, but the best I can do gives:
Define:
eta=120 Pi
k=2 Pi/lambda
reactance = (eta/(4*Pi)) (2 SinIntegral[k l] +
Cos[k l]*(2 SinIntegral[k l] - SinIntegral[2 k l]) -
Sin[k l]*(2 CosIntegral[k l] - CosIntegral[2 k l] -
CosIntegral[(2 k a2)/l]));
where 'a' is the radius.
(It's in Mathematica notation)
What is interesting about that is that for a length of 0.5 lambda, the
reactance does not depend on diameter at all - it is fixed at 42.5445
Ohms. So two different books give two quite different results.
Numerically evaluating the above formula gives this data.
K X05 X045
-------------------------
10 42.5 35.7183
30 42.5 15.5269
100 42.5 -6.79382
300 42.5 -27.1632
1000 42.5 -49.4861
3000 42.5 -69.8555
10000 42.5 -92.1784
30000 42.5 -112.548
100000 42.5 -134.871
300000 42.5 -155.24
1000000 42.5 -177.563
Does anyone have any comments? Any idea if Balanis's work is more
accurate? It is more up to date, but perhaps its an approximation and
the amateur radio book is more accurate. (The ham book seems quite well
researched, and is not full of the voodoo that appears in a lot of ham
books).
BTW, I'm also looking for an exact formula for input resistance of a
dipole of arbitrary length. I know is 73.13 Ohms when 0.5 wavelengths
long, but I'm not sure exactly how much it varies when the length
changes (I believe it is not a lot).
Dave G8WRB.
------------------------------
Message: 3
Date: Sun, 27 Jul 2008 17:54:15 -0500
From: "Rob Atkinson"
Subject: Re: [Amps] Damage?
To: amps@contesting.com
Message-ID:
Content-Type: text/plain; charset=ISO-8859-1
<<drive past any
50kW AM BC stations, which are often set up right alongside major highways.
-WB2WIK/6>>>
You all make it sound like the 1-A stations were all built after the
expressways. Here in Chicago, the four 1-A stations' transmitter
plants were all sited back in the 1930s but curiously, they all did
wind up being near interstate highways, with the 670 station the
farthest away from one at about 2 miles. So the question should be
what about the tx sites attracted those highways? : )
rob / k5uj
------------------------------
Message: 4
Date: Sun, 27 Jul 2008 16:09:58 -0700
From: "Georgens, Tom"
Subject: [Amps] Al80A problem
To:
Message-ID:
<273FE88A07F5D445824060902F70034430E373@SACMVEXC1-PRD.hq.netapp.com>
Content-Type: text/plain; charset="utf-8"
I turned on my AL80 today and while the hv looked fine, it was drawing grid
current and had negative plate current while idling. I had nothing connected to
it and it was in standby.
Anything easy that I should check first.
Thanks and 73
Tom W2SC
------------------------------
Message: 5
Date: Sun, 27 Jul 2008 19:20:22 -0400
From: "Carl"
Subject: Re: [Amps] Al80A problem
To: "Georgens, Tom" ,
Message-ID: <021801c8f03f$59e7d2b0$6500a8c0@KITTYMA123>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
The safety diode from the PS board to ground is shorted, probably from a
tube arc. Might also have taken out the bias zener.
Carl
KM1H
----- Original Message -----
From: "Georgens, Tom"
To:
Sent: Sunday, July 27, 2008 7:09 PM
Subject: [Amps] Al80A problem
>I turned on my AL80 today and while the hv looked fine, it was drawing grid
>current and had negative plate current while idling. I had nothing
>connected to it and it was in standby.
>
> Anything easy that I should check first.
>
> Thanks and 73
>
> Tom W2SC
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
------------------------------
Message: 6
Date: Sun, 27 Jul 2008 19:29:55 -0400
From: "Roger (K8RI)"
Subject: Re: [Amps] Damage?
Cc: amps@contesting.com
Message-ID: <488D04F3.4040202@rogerhalstead.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Rob Atkinson wrote:
> <<> drive past any
> 50kW AM BC stations, which are often set up right alongside major highways.
> -WB2WIK/6>>>
>
> You all make it sound like the 1-A stations were all built after the
> expressways. Here in Chicago, the four 1-A stations' transmitter
> plants were all sited back in the 1930s but curiously, they all did
> wind up being near interstate highways, with the 670 station the
> farthest away from one at about 2 miles. So the question should be
> what about the tx sites attracted those highways? : )
>
Just South of Alma MI, there is a broadcast array situated between Old
US27 and the expressway. IOW it is *close* to both (I could throw a rock
far enough to hit the closest and I am not a good pitcher) but at least
it's relatively low power. What the ERP is in the favored direction? I
don't know.
Roger (K8RI)
------------------------------
Message: 7
Date: Sun, 27 Jul 2008 19:40:43 -0400
From: "Randall, Randy"
Subject: [Amps] Socket source for Valvo TBL2-300
To: "amps@contesting.com"
Message-ID:
<5CBCD439080F744F966BB2815C060775054BDECC@MAIL-B.healthall.com>
Content-Type: text/plain; charset="us-ascii"
This is a euro external anode triode with a coaxial base. Are there sockets
available for this tube? I have 3 sealed NOS in the box that I would like to do
something with or trade them off for something I can use.
Thank you,
Randy AB9GO
Tube data here: tubedata.tigahost.com/tubedata/sheets/030/t/TBL2-300.pdf
Confidentiality Notice: This e-mail message, including any attachments, is for
the sole use of the intended recipient(s) and may contain confidential and
privileged information. Any unauthorized review, use, disclosure or
distribution is prohibited. If you are not the intended recipient, please
contact the sender by reply e-mail and destroy all copies of the original
message.
------------------------------
Message: 8
Date: Mon, 28 Jul 2008 09:50:07 +1000
From: robert briggs
Subject: [Amps] Cooler....GI-46B..
To: amps@contesting.com
Message-ID: <488D09AF.7070300@bigpond.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi all....I'm on the "bot" again...I am looking for a spare cooler for a
GI-46B tube...Situation is this >>>>
I am presently constructing another GI-7B amplifier...I intend replacing
the existing coolers on the tubes with GI-46B coolers for more efficient
cooling..
I have 3 new GI-46B tubes with coolers set aside for a later project,,I
have taken two of those coolers off the 46B tubes for the GI-7B
project..This leaves me with 3 GI-46B tubes but only one cooler...
I would be happy to either pay for another cooler or swap one GI-46B
tube W/O cooler for a spare cooler...
I can buy another complete tube but that's a bit expensive for the sake
of 1 cooler..
Reading this, it looks cool....
Wonder if anyone can help....
73 all.......Bob VK3ZL..
------------------------------
Message: 9
Date: Sun, 27 Jul 2008 20:02:10 -0400
From: "Carl"
Subject: Re: [Amps] Damage?
To: "Roger \(K8RI\)"
Cc: amps@contesting.com
Message-ID: <023701c8f045$3082b060$6500a8c0@KITTYMA123>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Better yet whats the field strength at ground level at that distance?
Carl
KM1H
----- Original Message -----
From: "Roger (K8RI)"
Cc:
Sent: Sunday, July 27, 2008 7:29 PM
Subject: Re: [Amps] Damage?
> Rob Atkinson wrote:
>> <<>> drive past any
>> 50kW AM BC stations, which are often set up right alongside major
>> highways.
>> -WB2WIK/6>>>
>>
>> You all make it sound like the 1-A stations were all built after the
>> expressways. Here in Chicago, the four 1-A stations' transmitter
>> plants were all sited back in the 1930s but curiously, they all did
>> wind up being near interstate highways, with the 670 station the
>> farthest away from one at about 2 miles. So the question should be
>> what about the tx sites attracted those highways? : )
>>
> Just South of Alma MI, there is a broadcast array situated between Old
> US27 and the expressway. IOW it is *close* to both (I could throw a rock
> far enough to hit the closest and I am not a good pitcher) but at least
> it's relatively low power. What the ERP is in the favored direction? I
> don't know.
>
> Roger (K8RI)
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
------------------------------
Message: 10
Date: Sun, 27 Jul 2008 20:10:37 -0400
From: "kenw2dtc"
Subject: Re: [Amps] Thoughts on half-wave dipole
To: "Dr. David Kirkby" , "'AMPS'"
Message-ID: <19BE5EBC838D4AB2B57D86773F1899E0@ownerqmjm9l00k>
Content-Type: text/plain; format=flowed; charset="Windows-1252";
reply-type=original
Dr. Kirby,
You mathematical dissertation on the dipole, with footnotes no less, has
embarrassed me. I feel like an antenna novice. Hope you get your answers.
73,
Ken W2DTC
------------------------------
Message: 11
Date: Sun, 27 Jul 2008 17:22:30 -0700
From: "Steve Cook"
Subject: Re: [Amps] Thoughts on half-wave dipole
To: "Dr. David Kirkby" , "'AMPS'"
Message-ID: <002301c8f048$07233ac0$61caab46@youro0kwkw9jwc>
Content-Type: text/plain; charset="Windows-1252"
By the time you figure this one out mathematically, you could already have had
the answer with an antennalizer and a pair of wire cutters.
-S
----- Original Message -----
From: Dr. David Kirkby
To: 'AMPS'
Sent: Sunday, July 27, 2008 12:10 PM
Subject: [Amps] Thoughts on half-wave dipole
I know this is a bit off-topic. but possibly someone here has some
thoughts. I've posted it to rec.radio.amateur.antenna and
sci.electronics.design, but someone here might know. I've corrected a
couple of typos that appeared on the newsgroup post.
--------
I wish to know if the reactance of a dipole that is physically 0.5000
wavelengths in length depends on the diameter of the wire or not.
I know a dipole 0.5 wavelength long is not resonate, but inductive so
you need to shorten it a few percent to bring it to resonance. I know
the length at resonance depends on wire diameter.
But I'm interested if the reactance does very with wire diameter when
the antenna is physically 0.5 wavelengths long, which means it will be
somewhat inductive.
A book published by the ARRL by the late Dr. Laswon (W2PV)
Lawson J. L., ?Yagi Antenna Design?, (1986), The American Radio Relay
League. ISBN 0-87259-041-0
has a table of reactance vs the ratio K (K=lambda/a, where a is the
radius) for antennas of 0.45 and 0.50 wavelengths in length. I've
reproduced that table below.
The first column (K) is lambda/a
The second column (X05) is the reactance of a dipole 0.5 wavelengths in
length.
The third column X045 is the reactance for a dipole 0.45 wavelengths in
length.
K X05 X045
-------------------------
10 34.2 23.1
30 36.7 6.4
100 38.2 -14.1
300 39 -33.6
1000 39.6 -55.5
3000 40 -75.7
10000 40.4 -98.1
30000 40.6 -118.6
100000 40.8 -141.1
300000 41.0 -161.8
1000000 41.1 -184.4
What one notices is:
1) Reactance for 0.45 lambda is very sensitive to radius, varying by
more than 200 Ohms as K changes from 10 (fat elements) to 1000000 (thin
elements).
2) The value for a dipole 0.5 lambda in length changes much less (only 6
Ohms), but it *does* change.
3) For infinitely thin elements (K very large), the reactance of a
dipole 0.5 lambda in length looks as though it is never going to go much
above 41.2 Ohms. Certainly not as high as 42 Ohms.
Now I compare that to a professional book I have:
Balanis C. A., ?Antenna Theory ? Analysis and Design?, (1982), Harper
and Row. ISBN 0-06-0404458-2
There is a formula in Balanis' book for reactance of a dipole of
arbitrary radius and length, in terms of sine and cosine integrals. It's
hard to write out, but the best I can do gives:
Define:
eta=120 Pi
k=2 Pi/lambda
reactance = (eta/(4*Pi)) (2 SinIntegral[k l] +
Cos[k l]*(2 SinIntegral[k l] - SinIntegral[2 k l]) -
Sin[k l]*(2 CosIntegral[k l] - CosIntegral[2 k l] -
CosIntegral[(2 k a2)/l]));
where 'a' is the radius.
(It's in Mathematica notation)
What is interesting about that is that for a length of 0.5 lambda, the
reactance does not depend on diameter at all - it is fixed at 42.5445
Ohms. So two different books give two quite different results.
Numerically evaluating the above formula gives this data.
K X05 X045
-------------------------
10 42.5 35.7183
30 42.5 15.5269
100 42.5 -6.79382
300 42.5 -27.1632
1000 42.5 -49.4861
3000 42.5 -69.8555
10000 42.5 -92.1784
30000 42.5 -112.548
100000 42.5 -134.871
300000 42.5 -155.24
1000000 42.5 -177.563
Does anyone have any comments? Any idea if Balanis's work is more
accurate? It is more up to date, but perhaps its an approximation and
the amateur radio book is more accurate. (The ham book seems quite well
researched, and is not full of the voodoo that appears in a lot of ham
books).
BTW, I'm also looking for an exact formula for input resistance of a
dipole of arbitrary length. I know is 73.13 Ohms when 0.5 wavelengths
long, but I'm not sure exactly how much it varies when the length
changes (I believe it is not a lot).
Dave G8WRB.
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
------------------------------
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Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
End of Amps Digest, Vol 67, Issue 41
************************************
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