I just noticed in the Feb 2001 CQ mag that LDG is now offering a
weather resistant, waterproof version of this tuner (model RT-11)
designed to be mounted outdoors on a tower etc. I don't think
their price has changed either except that you need a remote
control unit for it. But, that's pretty inexpensive - check it
out. Now, if it would only handle more power ....
----
73, Rich - W3ZJ
> -----Original Message-----
> From: owner-tentec@contesting.com
> [mailto:owner-tentec@contesting.com]On
> Behalf Of Dr. Gerald N. Johnson, electrical engineer
> Sent: Thursday, January 18, 2001 15:00 PM
> To: Sherrill WATKINS
> Cc: EAvila@caiso.com; tentec@contesting.com;
> Bill_Ames@hyperion.com
> Subject: Re: [TenTec] RE: Antenna tuner
>
>
>
> Sherrill WATKINS wrote:
> >
> > Gentlemen: Please be advised that on h.f., it is a
> complete waste of time and money to install an antenna
> tuner at the base or center of the antenna when it can
> be installed easily at the rig. <snip>
> - Corn - k4own.
> >
>
> This not absolutely and completely true. Not at all.
> Consider a couple
> relative common situations:
>
> Situation 1: End fed wire. If fed with a remote tuner,
> the wire need not
> radiate immediately at the ham gear and put RF into the
> microphone and
> the operator. Thus a remote tuner can minimize RFI and
> operator exposure
> to high RF fields. At the same time the wire can be
> more remote from
> domestic RF noise makers allowing for quieter receiving. Triple
> benefits.
>
> Situation 2: Center fed wire using coax, operated as a
> full wave wire.
> This presents a high (~ 1K) feed impedance which causes
> a very high SWR
> on the coax. Worse yet, if the coax is an odd multiple
> of 1/4 wave long
> the impedance at the shack end of the coax will be very
> low (~2.5 ohms)
> which can be outside the tuning range of most tuners.
> FAR outside the
> range of most commercially made tuners. The currents
> required at 2.5
> ohms Z may be far beyond the capabilities of convenient
> coax conductor
> sizes if there's any power involved; will induce more
> than trivial line
> loss; and lead to far more loss in the tuner since the
> tuner has to
> operate at a very high Q (lots of circulating current)
> to achieve the
> large transformation ratios require to match such a low
> impedance if the
> tuner can match such a low impedance. An open wire
> feeder is a far
> better compromise, but it doesn't take well to running
> through metal
> walls or metal conduit to reach the hamshack (other than the
> unobtainable Belden 8290 shielded twin lead for
> moderate powers). Hence
> a coaxial fed remote tuner may be a handier solution.
>
> Beyond these situations (which readily arise since most
> of our HF ham
> bands are harmonically related and that 80 meter dipole
> is just right
> for a full wave center fed on 40, 20, and 10 meters),
> its probably
> expedient to install the tuner where the knobs are in
> reach of the
> operator. On the other hand, the automatic tuner in
> these situations is
> definitely more versatile when located remotely and
> since there are NO
> knobs for the operator to adjust, there is NOTHING
> significantly wrong
> with placing the works of the tuner at the antenna and
> running a flat
> feed line that will radiate less and hear less local
> noise to the radio
> in the more compact shack. Also the impedances the
> tuner will have to
> handle are more reasonable when the tuner is at the
> antenna than when
> the tuner is working through a run of coax, and some
> popular tuners have
> more restricted load impedance (and reactance) range
> than the impedances
> that can be seen at the feed end of a feed line. So the
> remote tuner may
> be able to operated with a lower transformation ratio,
> and hence lower
> loss which may not drastically affect the signal detected at any
> distance, BUT will affect the lifetime of the tuner components
> dissipating that wasted energy.
>
> Seems to me from these arguments that there is NOTHING
> fundamentally
> wrong with a remote tuner at the antenna. Automation makes it a
> worthwhile consideration compared to the automatic
> tuner in the shack.
> There is no doubt that my link coupled series/parallel
> tuned tuner (a
> design that dates from the 30s if not the 20s) is more
> versatile than a
> T or Pi tuner or the L tuner typical of the automated
> tuner but it can
> be a royal pain to change frequency. Sure, the weather
> proof automated
> tuner is not cheap, but the automated tuner in the
> shack can't tune as
> many antennas and is not cheap either.
>
> 73, Jerry, K0CQ
>
> Copyright January 18, 2001 by Dr. Gerald N. Johnson
>
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