QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940340.txt

Internet Message Format | 1994-11-13 | 15KB

Date: Tue, 11 Oct 94 04:30:14 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Ant Digest V94 #340
To: Ham-Ant


Ham-Ant Digest              Tue, 11 Oct 94       Volume 94 : Issue  340

Today's Topics:
                         Antenna Rotor Wanted
           does anyone have the phone number for heathkit?
        does anyone know anything about the HM-2102 swr meter?
                      Enough already! i want 80
                     Enough already! I want 80m!
                    How does a depolarizor work ?
                           Isoloop mobile?
                   Newbie questions...and then some
                                Quad's
                        Superior coaxial line?
                       Tiger Tail (HT antenna)

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Archives of past issues of the Ham-Ant Digest are available
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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: 10 Oct 1994 14:08:38 -0400
From: [e-mail] (Ed Humphries)
Subject: Antenna Rotor Wanted

Perhaps of net.interest:

Can someone tell me what the windload rating is
for the readily available Radio Shack antenna
rotator? The local sales-droids don't even know
what I'm talking about.

Anyone have the real figures instead of "it
turns a really big tv antenna"?

Cheers & 73
Ed Humphries
Hewlett Packard Atlanta GA
[e-mail]

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

Date: Mon, 10 Oct 1994 16:44:52 GMT
From: Mike Lyon <[e-mail]>
Subject: does anyone have the phone number for heathkit?

i heard that heathkit still sells parts for there products. if anyone out
there has the phone number for them it would be appreciated if you could
e-mail it to me or just post it.


                                thank you,
                                [e-mail]




--
Mike Lyon <[e-mail]>

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

Date: 10 Oct 94 17:25:55 -0400
From: [e-mail] (Kenneth Grimm)
Subject: does anyone know anything about the HM-2102 swr meter?

In article <[e-mail]>, Mike Lyon <[e-mail]> writes:
>
> i recently purchased a heathkit hm-2102 swr meter. i would like to know
> how to calibrate it and what the knob that says "pull to set swr sens."
> means. i can't figure out how to measure forward/reflected power with it
> so basicall i want to figure out how to align it. also if anyone out
> there knows what bands this thing will work on that will also be
> apprecciated.

> Mike Lyon <[e-mail]>

Not sure about your model number, but have had a couple of Heath bridges
and homebrewed a bunch like them over the years.  The following worked in
all of those.  Your mileage may vary....

With the knob pulled out and with a signal going through the bridge to
the antenna, set the sensitivity to full scale.  Push the knob in and
read swr.

73,

Ken
--
___________________________________________________________

       Kenneth D. Grimm                 K4XL
       [e-mail]
___________________________________________________________

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

Date: 10 Oct 94 21:03:11 GMT
From: [e-mail]
Subject: Enough already! i want 80



Quoting ham-ant: [e-mail] (Sean E. Kutzko)

H>Honestly, I want a DX performer for a SMALL city lot. Knowing that
H>this is a HUGE order to ask for with the limited space I have, I got
H>to thinking about an 80m horizontal loop. It would probably be no more
H>than 30' off the ground, fed with twin lead. DX would be faint, but a
H>possibility.

H>1) Would this antenna have an EXTREMELY high angle of radiation?

Elnec suggests this antenna would have a radiation pattern resembling a
tall barrel cactus. I think this is often referred to as a "cloud
warmer". But on the positive side, as with most loop designs, it should
hear less of the biggest problem that 80m has to offer - QRN. And, it is
an inherently balanced antenna, which should minimize another big 80m
problem, RF in the shack. Good luck.

Igottago, 73 de KF0IA   ..
[e-mail]
---
│ CMPQwk #1.4│ UNREGISTERED EVALUATION COPY

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

Date: Sun, 09 Oct 94 11:34:00 -0800
From: [e-mail] (BOB ALBERT)
Subject: Enough already! I want 80m!

You might try a loaded dipole, a dipole that is shorter than a half
wave, with inductors added to make the electrical length greater.
Thus, a 40m dipole can be converted to make a mediocre 80m dipole.
The impedance will be different so it should have a matching device
as well.

73 DE K6DDX

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

Date: 10 Oct 1994 16:25:29 GMT
From: [e-mail] (Marcin Skubiszewski)
Subject: How does a depolarizor work ?

I have heard of a device called "depolarizor". It is included in all
European "full-band" (10.7 - 12.75 GHz) Ku LNBs used for satellite TV
reception. It allows your LNB to get both linearly and circularly
polarized microwave signals. Allegedly, this is a piece of teflon able
to convert circular signals into linear. It is placed before the
ferromagnetic polarotor.

Could somebody please explain to me (and to these newsgroups in general)
how this thing works ? I have a theory about it, but I believe that
the theory is flawed; here comes my theory anyway, please correct me as
appropriate.

I hope that hams in radio.amateur.antenna won't find my posting
inappropriate. After all, it is a technical question about radio
antennas, event if is not exactly a kind of antenna used by hams.

                                Marcin.

======================================================================

Every radio wave can be viewed as a sum of two components:
one horizontally polarized, one vertically polarized. We will use here
the receiver's, rather than the satellite's, definition of
"horizontal". Then, we can have among others

    - a horizontal wave (in the receiver's coordinates; this
      corresponds with a horizontal transponder of a
      satellite having the same latitude as the receiver): the
      vertical component of the signal is zero.

    - a diagonal wave (this corresponds with a horizontal or a vertical
      transponder of a satellite placed on a lattitude much
      different from the receiver's one): here the vertical and
      horizontal components are of equal strength and are in
      phase. It is easy to see that the total signal is diagonal:
      it is the sum of two perfectly identical signals, one
      vertical and one horizontal.

    - a circular wave: the vertical and horizontal components are
      of equal strength, but one is delayed by period/4 wrt the other.
      Intuitively, in this case the signal is "circular" rather
      than "linear sinusoidal" because the electrical field
      vector goes in circles: instead of keeping a constant
      direction and having its value change sinusoidally, it
      keeps a constant module and keeps changing direction.
      Sorry, I won't get into more details here (the
      trigonometrically callenged can mail me for a more complete
      explanation).


My idea is that the piece of teflon (the depolarizor, that is) is
anisotropic and introduces an extra delay of period/4 into one (say,
the vertical one) linear component of the signal. This would

    - keep vertical signals vertical (and delayed by period/4, but
      this has no importance)

    - keep horizontal signals horizontal

    - transform circular signals into linear, diagonal. The
      direction of the diagonal (left to right bottom up or left
      to right top down) corresponds with the direction (left or
      righ) of the circular signal.

      Explanation of this: In a circular signal, the vertical
      component comes to the antenna either delayed or advanced
      by period/4 wrt the horizontal one. After the depolarizor,
      it is delayed by either 0 or period/2. Putting it
      differently, it is always delayed by 0 and is or is not
      inverted (or "put upside down").

    - transform linear, diagonal signals into circular.
      Explanation: the vertical component, received in phase
      with the horizontal one, is after the depolarizor
      out-of-phase by period/4.

This is partly OK: to get a vertical signal, we just set the polarotor
for 0 deg, for "horizontal" it is 90 deg, for the two circular
polarizations it is respectively + 45 deg and -45 deg. But for a far
away satellite, whose H and V transponders are viewed by the receiver
as + 45 deg and -45 deg diagonal, we have no reasonable way to get
linear signals: these are seen by the LNB as circular. There is a 3 dB
signal loss and no separation at all between H and V transponders.
For a satellite whose tansponders are seen as, say, -20 deg and 70
deg, the situation is intermediary: there is some signal loss (say 1dB), and
the channel separation exists, but is quite weak.

So, either

    I missed something
    Or my explanation is OK, and depolarizors do have serioous
drawbacks.

Please enlighten me.

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

Date: Mon, 10 Oct 1994 11:10:13 GMT
From: [e-mail]
Subject: Isoloop mobile?

Russell Gore ([e-mail]) wrote: : I am thinking about getting
the MFJ isoloop thinge... [ deleted ]

   I suspect that AEA would be very upset if MFJ was selling an
antenna named the "Isoloop".

:-)

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

Date: 10 Oct 1994 16:07:24 GMT
From: [e-mail]
Subject: Newbie questions...and then some

In article <[e-mail]>,
Mark Hemlick Ph. D. <[e-mail]> wrote:

>This is gospel, and one is advised to NEVER use steel wire as the radiating
>element of an antenna.

Hi Mark, a little common sense goes a long way. If you were in an emergency
situation and all you had for an antenna was steel wire, would you use it?

>If steel radiators are so
>bad, especially at higher frequences (VHF & UHF), why are the radiators of
>virtually all mobile antennas...stainless steel!!!?

Assuming steel has 10x the resistance of copper, An 8 ft steel whip has
approximately the same resistance as an 80 ft copper wire. The current is
higher at the base of the whip and so is the diameter so the resistance is
lower at the base. The base of the steel whip is typically larger in diameter
than the wire in a copper dipole. For 100w into the base of a 50 ohm whip,
the current is only 1.4 amps and the base of my RS steel whip is about one
half inch.

Incidentally, the ballpark radiation resistance of a coat hanger is something
like 0.1-j4000. The power you can stuff into a load like that is approximately
(v/4000)*(v/4000)*0.1    Figure up how much voltage you need to warm up
the coat hanger. 40,000 volts will give you 10 watts, but most of that power
is probably radiated as RF and not dissipated as heat.

--
73, Cecil, KG7BK, OOTC   (All my own personal fuzzy logic, not Intel's)

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

Date: 11 Oct 94 02:50:41 GMT
From: [e-mail] (Lynn Geitgey  KB0LRB)
Subject: Quad's

Hi All,

The other day, while browsing several Antenna books, I came across an
interesting, but unexplained idea.  Is there some Quad Guru out there,
who can explain the reasoning behind locating the feed point for a Quad
in a corner, instead of the middle of a loop?  I understand the positioning
of the feed point, on the bottom, for Horizontal polorization.  An on the
side, for Verticle Polorization.

What advantage/disadvantage's are there to the feed point being in a corner?

Any help is appreciated.

73 de KB0LRB
Lynn Geitgey
[e-mail]

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

Date: 10 Oct 1994 18:43:20 -0400
From: [e-mail] (David M. Roseman)
Subject: Superior coaxial line?

>
>One can even get this coax for free by visiting ones local cable TV provider.
>Ask them if they have any leftover chunks from the giant spools they use. Ive
>gotten some nice sections (as much as 100feet) this way. The connectors for
>Heliax are, however, more valuable than gold.
>


i'd like to thank you for saying that...next time i'm near chan.39, i'll try!


DAvid
:)****************************************************************(:
          David Roseman                  [e-mail]
       SysOp of NODE 3 BBS               The Flying HAm - BBS
      Running OBV/2 Software             KBR-9318 - CB
          HAmmy in IRC                   N3SQE/SVARC - Ham
                                 [e-mail] - Packet

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

Date: 10 Oct 1994 20:10:20 GMT
From: [e-mail] (Bob Levine)
Subject: Tiger Tail (HT antenna)

There have been several posts about the Tiger Tail.  I
distribute Antennas West gear and before I agreed to carry
the TT, I got a freebie to check out as I was skeptical
also.  I used a signal strength meter by Nye Engineering,
the little cube with 2 antennas sticking out the sides.

I discovered that in the plane of the HT (my FT530), the signal strength
is greatly increased with the TT.(>2x) The signal strength directly
above the HT goes way down.  The TT seeems to increase the lobes
in the horizontal plane and reduce the amount of energy going
vertical.  I did these tests the best I could with the HT in
a plastic holder and keyed up from about 5 feet away with a
speaker mic so I would interfere as little as possible.

Is it worth $7.95?  Well you can certainly make it with a piece
of wire.  What you are paying for is the nice rubber coated wire
painted yellow with a custom connector that slips over the BNC
of the HT properly.  You are also paying for someone else's time
to make it, package it, advertise it, buy flea market tables to
sell it, etc.....

Bob


Not to debate the $ value of it any further, just wanted to tell
you that my simple tests certainly did show a significant field
strength increase in the horizontal plane around the HT.

M


---
------------------------------------------------------------
Bob Levine  KD1GG 7J1AIS VK2GYN               formerly KA1JFP
[e-mail]   <--Internet email    Phone[phone] x247
[e-mail] <--Packet Mail         FAX[phone]
------------------------------------------------------------

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End of Ham-Ant Digest V94 #340
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