QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940208.txt

Internet Message Format | 1994-11-13 | 19KB

Date: Sat,  2 Jul 94 04:30:16 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
Errors-To: [e-mail]
Reply-To: [e-mail]
Precedence: Bulk
Subject: Ham-Ant Digest V94 #208
To: Ham-Ant


Ham-Ant Digest              Sat,  2 Jul 94       Volume 94 : Issue  208

Today's Topics:
                        A Question on Yagi's.
                           DB .vs. Celwave
                   extending "ladder line" (2 msgs)
                            Here's KLM ...
                 Is LArson a good brand of equipment?
                     More on the QST compact loop
            More on the QST compact loop antenna (3 msgs)
    Where is the best place to install a low pass filter? (2 msgs)

Send Replies or notes for publication to: <[e-mail]>
Send subscription requests to: <[e-mail]>
Problems you can't solve otherwise to [e-mail].

Archives of past issues of the Ham-Ant Digest are available
(by FTP only) from UCSD.Edu in directory "mailarchives/ham-ant".

We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: Fri, 1 Jul 1994 22:35:38 GMT
From: taligent!taligent.com![e-mail]
Subject: A Question on Yagi's.
To: [e-mail]

In article <[e-mail]>, [e-mail] (Jon Tara) writes:
[ antenna design question... ]
> There is only one dipole. There is normally one set of "directors" in the
                                                          ^^^^^^
> front, and multiple "reflectors" in the back. The short end points toward the
                       ^^^^^^^
> station.

Hmm...  This antenna wouldn't be made by BOSE would it?  :-)

(Just kidding.)

Adios,
  Logan

--
The genius of France can be seen at a glance
And it's not in their fabled fashion scene
It's not that they're mean, or their wine, or cuisine
I refer of course to the guillotine
(the French knew how to lynch)
                T-Bone Burnett, "I Can Explain Everything"

------------------------------

Date: 1 Jul 94 20:51:17 GMT
From: [e-mail]
Subject: DB .vs. Celwave
To: [e-mail]

     A few weeks ago I requested comments reqarding dual-band antennas for
repeater usage on repeaters in very harsh environments.  The results of that
survey lead me to the conclusion that no suitable dual-band antenna exists
for longevity in harsh environments.
   The time has come for our ham club to replace our repeater antennas
(after 15 years of service, current antennas are both db-220 and
phelps-dodge super-stationmaster).  We are again discussing the db products
4 bay vs the Celwave PD-200 antennas (VHF 146 range).  My local enquires and
combined experiences have taugh me that the 4 bay (or more) antennas work
very well, but need frequent cleaning (yearly).  The phelps-dodge antennas
seem to be more reliable over years of neglect.  We would like to make a
good decision.

Has anyone else traveled this path that could offer some opinions?
I'd also appreciate comments from users of small phased beam arrays for
repeater antennas (what type of beams, how many, what pattern you were
trying to achieve, etc.,etc.)

Thanks

/*

Terry Bartholomew               NQ4Y
Jr. Programmer/Analyst          ERC, Inc.
205 Research Park Dr.           Email: [e-mail]
Tullahoma, TN  37388            Wk: 615-455-9915   Fax: [phone]

*/

------------------------------

Date: 1 Jul 1994 14:26:45 GMT
From: ihnp4.ucsd.edu!swrinde!howland.reston.ans.net!wupost!crcnis1.unl.edu!unlinfo.unl.edu![e-mail]
Subject: extending "ladder line"
To: [e-mail]

 I have installed a new operating position in the 'ole shack and the
450 ohm "ladder line" or twin lead feeder doesn't make it all the way
to the table. Are there any considerations to take into account for
extending the cable/twin lead about six feet? I assume I should keep
the spacing between the conductors and make sure the soldering on the
splice is very well done. Is this enough or should I replace the line
all the way to the antenna?? The antenna is a center fed zepp......

                 Thanks de Dan [e-mail]
                               OR
                       [e-mail]

------------------------------

Date: 1 Jul 94 15:27:09 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!vixen.cso.uiuc.edu!aries![e-mail]
Subject: extending "ladder line"
To: [e-mail]

[e-mail] (daniel wright) writes:

> I have installed a new operating position in the 'ole shack and the
>450 ohm "ladder line" or twin lead feeder doesn't make it all the way
>to the table. Are there any considerations to take into account for
>extending the cable/twin lead about six feet? I assume I should keep
>the spacing between the conductors and make sure the soldering on the

I use double bananna plugs. Stick the ladder line wire into the part on the
side where you screw down onto the wire, and you have a male or female,
your choice, to plug into the next piece. Great for adjusting the length
also.
.....NO USER SERVICEABLE PARTS INSIDE.....
Chuck Hawley, KE9UW in Urbana, Illinois
[e-mail]
School of Chemical Sciences, Electronic Services
University of Illinois, Urbana-Champaign

------------------------------

Date: Fri, 1 Jul 1994 16:42:22 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!cs.utexas.edu!convex!news.ssc.gov!fnnews.fnal.gov!gw1!nntpa!bigtop!longs![e-mail]
Subject: Here's KLM ...
To: [e-mail]

Just to set the record straight, KLM and Mirage seem to have parted ways.

The current (7/1/94) address for KLM is:

KLM Antennas, Inc.
14792 172nd DR SE #1
Monroe, WA 98272

[phone]
FAX: [phone]

------------------------------

Date: Fri, 01 Jul 1994 14:54:00 PST
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!europa.eng.gtefsd.com!newsxfer.itd.umich.edu!nntp.cs.ubc.ca!mala.bc.ca!epaus!ham![e-mail]
Subject: Is LArson a good brand of equipment?
To: [e-mail]

[e-mail] (Scott Van Nostrand) writes:

>Comments?
>
>Thanks.
>
>Scott
>[e-mail]

If you're talking about Larsen Antennas and their line of VHF/UHF mobile
(mostly) antennas, I'd say yes. They're competively priced, work well, and
are rugged. I've also found Larsen a good company to deal with.


[e-mail] (Robert Smits Ladysmith BC)

------------------------------

Date: 1 Jul 1994 20:42:46 GMT
From: ihnp4.ucsd.edu!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!psgrain!news.tek.com!tekgp4.cse.tek.com![e-mail]
Subject: More on the QST compact loop
To: [e-mail]

[e-mail] (Andy Domonkos):

>. . . A local ham siad he made a high voltage cap
>from PVC and copper sheets glued to the pvc tubing (small tubing
>rotating in larger tubing). W/the high voltage in the loop I wonder if
>the PVC will breakdown?

I dunno about the voltage breakdown, but using this capacitor for a small
loop would be disastrous from a loss standpoint.

Here's what we're talking about with these small loops:

Some numbers from a quick ELNEC run of a 6 foot diameter loop made
from 2" dia pipe at 3.8 MHz (one which I had on file), using a capacitor to
resonate it:

With 100 watts in, and a lossless capacitor, the current in the loop is
over 40 amps RMS. The voltage across the capacitor is 6.3 kV RMS. The loss
due to the RF resistivity of the copper pipe is 2.8 dB or about 48 watts.

With this amount of voltage across the capacitor, the dielectric loss is
critical. Polyethylene and PTFE (Teflon) have a dissipation factor of
<.0002. If you made a capacitor with a dielectric with DF of .0002, the
capacitor loss in this antenna would be 1.8 dB, or 18 watts of the 52
remaining after copper loss. PVC has a dissipation factor of about 0.01.
Using this for the capacitor dielectric gives a loss of 14.3 dB, or about
50 of the 52 watts left after copper loss. With air, the dielectric loss
is negligible.

As pointed out earlier in this thread, there are no laws of physics which
dictate that small loops have to be lossy. But you can bet your joules that
if you don't pay *very* careful attention to losses, they sure will be!

73,
Roy Lewallen, W7EL
[e-mail]

------------------------------

Date: Fri, 1 Jul 1994 12:21:01 GMT
From: ihnp4.ucsd.edu!library.ucla.edu!csulb.edu!csus.edu!netcom.com![e-mail]
Subject: More on the QST compact loop antenna
To: [e-mail]

In article <[e-mail]> [e-mail] (andy domonkos) writes:
>
>I plan on using the loading var. cap. (200pf) I stripped out of an old
>Heath DX60b, do you think that will handle a full 100 watts?

The DX60B was rated at 90 watts INPUT thus maybe 50 out, CW. The loading
cap was probably rated for about that.

Add to that that a loop is a high-voltage, low-current beastie.

In other words, NO!

Greg

------------------------------

Date: Fri, 1 Jul 1994 12:56:12 GMT
From: ihnp4.ucsd.edu!swrinde!howland.reston.ans.net!noc.near.net!usenet.elf.com!rpi!psinntp!arrl.org![e-mail]
Subject: More on the QST compact loop antenna
To: [e-mail]

andy domonkos N3LCW ([e-mail]) wrote:

: I am planning on building the 40M loop. Could you give the exact dimension
: you used on the Loops and the ratings and value of the tuning cap. Also,
: are you using a motor to remote tune it?

: I plan on using the loading var. cap. (200pf) I stripped out of an old
: Heath DX60b, do you think that will handle a full 100 watts? I have an
: AEA Isoloop 10-30 and it's tuning cap is HUGE. Thanks for your work on
: the 40M version...

I'm not sure that tuning capacitor will work properly--a difficulty
is that you typically need a very high quality capacitor with low
loss to get the claimed efficiency.  The easiest way to find out may
be to just go ahead and build it.  Ideally, the tuning should be
real sharp, just like the equations (like those in the Antenna book)
say it should be.  If it is much broader than it should be, you are
probably losing a lot of power someplace.  Interestingly, QST initially
reported that the loops really didn't work well, since they failed to
use sufficiently low loss components (in the 1960s).  Of course, back
in the 60s people mostly designed high voltage, high impedance circuits,
which didn't need parts with extremely low resistive losses.  Working
with these loops is more like working with 30 amp power supplies....


circuits.



--
Zack Lau  KH6CP/1           2 way QRP WAS
                           8 States on 10 GHz
Internet: [e-mail]   10 grids on 2304 MHz

------------------------------

Date: Sat, 2 Jul 1994 02:17:48 GMT
From: ihnp4.ucsd.edu!sdd.hp.com!col.hp.com!srgenprp![e-mail]
Subject: More on the QST compact loop antenna
To: [e-mail]

Andy Domonkos ([e-mail]) wrote:

: A local ham siad he made a high voltage cap
: from PVC and copper sheets glued to the pvc tubing (small tubing
: rotating in larger tubing). W/the high voltage in the loop I wonder if
: the PVC will breakdown?

PVC is a high-loss dielectric at RF frequencies.  To get a high-Q
capacitor, use air dielectric or at least some low-loss material
like polyethylene.

AL N1AL

------------------------------

Date: 1 Jul 1994 17:22:38 GMT
From: ihnp4.ucsd.edu!library.ucla.edu!europa.eng.gtefsd.com!news.msfc.nasa.gov![e-mail]
Subject: Where is the best place to install a low pass filter?
To: [e-mail]

[e-mail] writes:


>Can someone tell me where the best place is to install my
>Drake 1KW low pass filter?

>    1) Between my HF transceiver and my 1KW RF amp
>    2) Between my 1 KW RF amp and my 1KW antenna tuner
>    3) Between my 1KW antenna tuner and my antenna
>    4) Sell it at the next ham fest
>    5) Anywhere after the transceiver

>Thanks, 73s Tom WB7ASR...

>[e-mail]

The answer is 1.  The reason is as follows:

The transceiver is solid state and thus generates the most harmonics due to non-
linear characteristics (this applies to all amplifiers).  So if the
the filter is between the rig and amp the harmonics from the rig will be
attenuated and thus not have any chance to be amplified by the amp.

The second reason is (assuming a tube amp) that the amplifier basically has a
matching network on both the input and output of the amplifier, what you are
doing when you tune the amplifier is matching the output impedance of the
tubes (the amplifier) to the antenna (50 ohms).  Since this tuning process has
a small operating range (also known as bandwidth) the harmonics never make it
out of the amplifier.

Hope this helps.

Herb


--------------------------------------------------------------------------------
W. Herb Sims                                        [e-mail]
NASA/MSFC/EB56                                      [e-mail]
Huntsville, AL 35812                                [e-mail]
KU0C                                                Voice [phone]
PP-ASEL-IA                                          FAX   [phone]
--------------------------------------------------------------------------------

------------------------------

Date: 1 Jul 1994 19:40:03 GMT
From: ihnp4.ucsd.edu!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!yeshua.marcam.com!news.kei.com!ssd.intel.com!chnews!scorpion.ch.intel.com![e-mail]
Subject: Where is the best place to install a low pass filter?
To: [e-mail]

[e-mail] (Tom Boza, WB7ASR) writes:

>>Can someone tell me where the best place is to install my
>>Drake 1KW low pass filter?

>>    1) Between my HF transceiver and my 1KW RF amp
>>    2) Between my 1 KW RF amp and my 1KW antenna tuner
>>    3) Between my 1KW antenna tuner and my antenna
>>    4) Sell it at the next ham fest
>>    5) Anywhere after the transceiver

In article <2v1jcu$[e-mail]>,
Herb Sims, KU0C <[e-mail]> wrote:

>The answer is 1.  The reason is as follows:

>The transceiver is solid state and thus generates the most harmonics
>due to non- linear characteristics (this applies to all amplifiers).
>So if the the filter is between the rig and amp the harmonics from
>the rig will be attenuated and thus not have any chance to be
>amplified by the amp.

I don't think it is necessarily true that solid-state -> higher harmonics.

Regardless of this, though, modern transceivers have a bank of
low-pass filters that are switched into the output line dependent on
operating frequency.  These filters assure that the transceiver
exceeds Part 97 requirements over the entire spectrum.

>The second reason is (assuming a tube amp) that the amplifier
>basically has a matching network on both the input and output of the
>amplifier, what you are doing when you tune the amplifier is matching
>the output impedance of the tubes (the amplifier) to the antenna (50
>ohms).  Since this tuning process has a small operating range (also
>known as bandwidth) the harmonics never make it out of the amplifier.

Well, imperfect components rear their ugly heads.  The tuning networks
you describe are made out of solenoidal coils and wire-connected
capacitors that become something else at VHF.  These components don't
supply the rejection you might think they do up there at the 23rd
harmonic.  And he *was* asking about a TVI filter. Those are designed
with a 41 MHz corner, at least an 80 dB/decade roll-off, and shielded
compartments between sections.

However, in this era of zero-bias triodes, most amplifiers run class
B (linear), even for CW.  So the prime culprit in amateur-caused
TVI cases, the over-driven, class-C operated, plate-modulated final
tube sitting on a breadboard has, thankfully, faded into history.
Today's HF rigs, even the max. power jobs, are pretty clean well
up through VHF.

I still opt for 2), although it's more of an insurance policy.

Jim Bromley, W5GYJ  <[e-mail]>

------------------------------

Date: 1 Jul 1994 12:50:34 -0400
From: ihnp4.ucsd.edu!swrinde!howland.reston.ans.net!news.intercon.com!news1.digex.net!digex.net![e-mail]
To: [e-mail]

References <2usnbp$[e-mail]>, <[e-mail]>, <[e-mail]>.n
Subject : Re: More on the QST compact loop antenna

In article <[e-mail]>, Greg Bullough wrote:
> In article <[e-mail]> [e-mail] (andy domonkos) writes:
> >
> >I plan on using the loading var. cap. (200pf) I stripped out of an old
> >Heath DX60b, do you think that will handle a full 100 watts?
>
> The DX60B was rated at 90 watts INPUT thus maybe 50 out, CW. The loading
> cap was probably rated for about that.
>
> Add to that that a loop is a high-voltage, low-current beastie.
>
> In other words, NO!
>
> Greg

That's what I suspected. A local ham siad he made a high voltage cap
from PVC and copper sheets glued to the pvc tubing (small tubing
rotating in larger tubing). W/the high voltage in the loop I wonder if
the PVC will breakdown?

Andy

------------------------------

Date: 1 Jul 1994 18:18:22 GMT
From: ihnp4.ucsd.edu!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!yeshua.marcam.com!news.kei.com!ssd.intel.com!chnews!scorpion.ch.intel.com![e-mail]
To: [e-mail]

References <2usnbp$[e-mail]>, <[e-mail]>, <[e-mail]>co
Subject : Re: More on the QST compact loop antenna

In article <[e-mail]>,
Greg Bullough <[e-mail]> wrote:

[ Commenting on using a DX-60 loading capacitor to tune an ]
[ electrically small loop antenna.                         ]

>Add to that that a loop is a high-voltage, low-current beastie.
>
>In other words, NO!

Just a nit, but it really is a high-impedance, high-current beastie.
Which means you get the worst of both worlds, high voltage across
the reactances due to high circulating currents flowing through
them.  So you have to have a high-voltage, high-current (high-Q)
capacitor.

The way the loop obtains its radiation efficiency (such as it is)
is by causing a large circulating current to flow through its small
radiation resistance.  The circulating current comes from resonating
the loop's inductance with a capacitor at the frequency of interest.

Jim Bromley, W5GYJ  <[e-mail]>

------------------------------

End of Ham-Ant Digest V94 #208
******************************