> 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.
I would think that weatherproofing wouldn't be that difficult or
expensive. Some of the plastic containers made for outdoor storage
or even a good quality cooler made by a number of manufacturers
used together with some readily available marine sealant would be
inexpensive and do the trick. This could be used at the base of a
vertical or on the ground below an antenna fed with open wire
feeders. The more easily handled and now nearly perfectly matched
coax would make the possibly long run from the tuner into the
shack. Makes sense to me.
---
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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