[TrunkCom] Outside Antennas - A Rambling Epistle

[JEFFREY MICHAEL KENYON]

One system that uses 420 MHz LTR that I am really interested in is known
as Repeater Systems.  Not sure if it allows the users to roam, but Detroit
Schools use it for security operations, but I can get this system rather
well with what I have now with the exception of the sites that are far from
me.  There are quite a few LTR UHF systems around here and from what I
have been able to gather it is mostly business.  Why are they placing
these systems on 400 MHz rather then 800 or 900?





On Wed, 1 Jan 2003 scannerman6@juno.com wrote:

> The 70 Centimeter Ham antennae might work for trunking in the 400 -425
> band.  Then again alot of people do NOT listen to that portion since the
> trunking in the area of the spectrum ii usually Business Band L.T.R..
>
> Then again, from what I undestand, by logging onto
> http://www.trunkedradio.net, one of the municipalities from this area
> actually uses a bbusiness band LTR for their Snow Plows.
> On Mon, 30 Dec 2002 09:45:09 EST W5HLMNEWS@aol.com writes:
> > As way of background, I live in Harris County, Texas and have been
> > monitoring
> > various agencies here for over 20 years.  I've also been a ham radio
> > for over
> > ten years (W5HLM), and am active on the UHF/VHF bands.  To answer
> > your
> > question, I'd like to share some of my experiences with various
> > antennas over
> > the years.  Please keep in mind that this information is based
> > strictly on
> > empirical observations, and reflects what worked best in my
> > particular
> > situation.  Your mileage (and opinion) may vary.
> >
> > First, I've yet to find a single antenna that would do everything I
> > needed
> > for just scanning, much less scanning and ham use.  The closest
> > thing I've
> > found is the Radio Shack discone.  As I recall, the RS discone has a
> > power
> > limitation of something like 25 watts, so it's not an ideal antenna
> > for
> > transmitting with the full power available to most mobile rigs.
> > There are
> > numerous discone antennas on the market, but the Radio Shack antenna
> > is the
> > only one I've experimented with.  Some other brands also employ a
> > vertical
> > whip on top to increase effectiveness on the lower bands.
> >
> > I've found discone antennas to be reasonably good monitoring
> > antennas, but
> > their main drawback is that they have no gain.  Also, they tend to
> > work
> > better on some parts of the spectrum than others.  On a positive
> > note, they
> > seem to work relatively well for aviation monitoring.  On the
> > downside, they
> > are less than ideal for monitoring 800 MHz systems--especially weak
> > signals.
> >
> >
> > Through experience, I finally came to the realization that I was
> > never going
> > to get a single antenna to do everything I needed, so I sought
> > alternative
> > solutions using multiple antennas.
> >
> > I used to live in a home in the suburbs, and had a house with a huge
> > attic.
> > I had six UHF/VHF antennas up there, and this arrangement worked
> > very well.
> > Now, I live in an apartment (third floor) and my antenna options are
> > much
> > more limited, so I've had to come up with more creative solutions.
> >
> > For amateur use, I've found a good dual-band mag-mount on a metal
> > surface is
> > pretty effective.  I have a gun safe in the closet of my study, and
> > have a
> > Larsen dual-bander on a mag-mount on top of the safe.  This gives me
> >
> > reasonable range--comparable to what you'd get in a mobile.  And if
> > you are
> > having trouble finding a metal surface to mount the antenna, an old
> > ham trick
> > is to set it stick it to a pizza pan in the attic.  A hot water
> > heater also
> > works very well as a mag-mount base.
> >
> > I've found 800 MHz scanning to be the biggest challenge.  I live a
> > considerable distance from the main county trunked system
> > transmitter, and
> > have a very difficult time receiving the signal consistently.  I
> > think I've
> > tried almost every antenna/amplifier solution known to man!  What
> > seems to
> > work best are highly directional, high-gain commercial antennas.
> > Two that
> > I've had good luck with are Yagi (beam) antennas tuned for the
> > mid-800 MHz
> > band and "corner" antennas designed for commercial cellular use.
> > Both pop up
> > on eBay from time to time.  The main drawback to these antennas is
> > that
> > unless the signals you are attempting to monitor at lower
> > frequencies are
> > pretty strong, they are fairly ineffective outside of the 800 MHz
> > band.  They
> > are pretty much a one-trick pony, but for distant 800 MHz systems,
> > they can
> > be highly effective.
> >
> > The other problem with 800 MHz signals is that the coax and
> > connectors
> > designed for use on lower frequencies tend to attenuate the signal
> > significantly.  This is especially true when using cheap coax.
> > Also, PL-259
> > connectors can impact the signal adversely, since they are not
> > recommended
> > for use above around 500 MHz.   As a matter of fact, any modest
> > gains
> > achieved though a good antenna are quickly negated with a long run
> > of s
> > ubstandard coax or multiple connectors.  What has worked well for me
> > is a
> > good grade of commercial cable TV coax.  Yes, I know it's 75 ohm as
> > opposed
> > to the 50 ohm impedance of the radio.  But as long as you don't
> > attempt to
> > transmit on it, it seems to work well.  Since finding a BNC
> > connector to fit
> > this type of coax may be a challenge, I just leave the original "F"
> > connector
> > on the coax and use an "F" to BNC adapter (available at Radio
> > Shack).  Both
> > types of connectors work in the 800 MHz range with no significant
> > signal
> > degradation.
> >
> > Another trick I've used for 800 MHz, especially where I have limited
> > outdoor
> > options, is a mag-mount cell phone antenna.  These antennas usually
> > have
> > about 3 dB of gain, which is less than ideal, but is often enough to
> > do the
> > job.  Also, because you don't have a long run of coax to contend
> > with,
> > coax-induced loss is kept to a minimum.
> >
> > If you are limited to mounting a single antenna outdoors, you will
> > need to
> > assess which is band or requirement is most important to you, and
> > use that as
> > your primary outdoor antenna.  If you consider the amateur band to
> > be most
> > important, then you may wish to mount a dual-band base antenna
> > outdoors, and
> > use a discone and Yagi in the attic for the scanner.  Unfortunately,
> > this
> > will require that you swap antennas, depending on the band you are
> > monitoring.  And this will be dictated by the strength of the
> > signals on the
> > various bands.
> >
> > If you are most interested in scanning UHF/VHF, then you may wish to
> > mount a
> > discone outdoors and use an amateur mag-mount antenna indoors.
> > However, if
> > you use an antenna for transmitting indoors, remember to observe RF
> > safety
> > rules and make sure no one comes in contact with the antenna while
> > transmitting.  Also, don't discount the usefulness of dedicated 800
> > MHz
> > antennas.  I simply sat a corner antenna on the shelf of my closet
> > and it
> > provides good coverage of the 800 MHz system that I wouldn't
> > normally be able
> > to monitor.
> >
> > As you are evaluating your monitoring options, consider using one
> > scanner for
> > trunked monitoring and one for conventional UHF/VHF systems.  This
> > makes the
> > antenna decisions less of a hassle, and you can apply the right
> > antenna
> > solution to each scanner.  Since a typical UHF/VHF scanner is now
> > relatively
> > inexpensive, this multiple scanner approach is now in financial
> > reach of the
> > average hobbyist.  Also, this arrangement allows you to monitor
> > multiple
> > agencies more effectively during a significant event or emergency.
> >
> > Finally, don't be afraid to experiment.  Some of the best solutions
> > I've
> > found were the result of trying things out of the ordinary.  Have
> > fun, and
> > share your solutions with your friends on the message boards!
> >
> > For more information, and to read some of the articles I've written
> > for
> > Monitoring Times, please visit my web site at: <A
> > HREF="http://home.houston.rr.com/w5hlm/">
> > http://home.houston.rr.com/w5hlm/</A>
> >
> > For more monitoring tips and trips, refer to the article at this
> > URL: <A HREF="http://home.houston.rr.com/w5hlm/mt1.html">
> > http://home.houston.rr.com/w5hlm/mt1.html</A>
> >
> > Another great source of information is the fantastic Strong Signals
> > web page.
> >  The antenna evaluations can be found at:
> > <A
> >
> HREF="http://www.strongsignals.net/access/content/antenna.html">http://ww
> w.strongsignals.net/access/content/antenna.html</A>
> >
> >
> > Regards,
> >
> > Haskell Moore, W5HLM
> >
> > In a message dated 12/29/2002 6:49:21 PM Central Standard Time,
> > at649@tcnet.org writes:
> >
> > > Hi everyone.  I am finally going to be putting up and outside
> > antenna in
> > > the near future.  Although it will mainly be for ham use, I have
> > always
> > > wanted something that will do well on 800 MHz for scanning distant
> > trunked
> > > systems, and systems that I am just on the fringes of.  The ham
> > bands that
> > > I will be using this for is 2-meters and 440, but I figure that if
> > I am
> > > going to do something I had might as well look into what will help
> > also
> > > with scanner use as well.  Any help would be good, and thanks and
> > happy
> > > new year.
> >
> >
> >
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>
> Wesolych Swiat, Bozego Narodzenia, I Sczclwego Nowego Roku -
> Polish for Mery Christmas and a Happy New Year!!!!
>
>
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