Dear Paul,
Thanks for your informative answer.
Perhaps I may embellish the scenario here.
I operate out of a hotel room.
The antenna is a 300 foot end-fed longwire.
There is 500 feet of counterpoise strung throughout the room.
I use a Palstar manual ATU for the main tuner and am building
a counterpoise "artificial ground" ATU device to match the counterpoise
to the transmit frequency.
My question should have said, " If I first tune the Yaesu with its
internal tuner to a 50 ohm dummy load, and then disable it by
the front panel, does it rtetain the 50 ohm setting or is the tuning
circuit electrically bypassed by the front panel Tuner switch?"
Thanks!
Hal Mandel W4HBM
-----Original Message-----
From: Phil [mailto:phil@kvkantennas.com.au]
Sent: Wednesday, July 26, 2006 7:57 PM
To: ka1xo@juno.com; yaesu@contesting.com
Subject: Re: [Yaesu] FT-1000d / Ft-1000MP MkV Ant. Tuner
Hi Hal,
Your internal ATU has a range to antenna mismatches within which it can
match the load. When you move outside
this range - the ATU will be unable to deal with the high impedances. If
you read the specs for your rig - it will tell you what these are. This
is the reason we often have a large-range external ATU to handle larger
mismatches. Keep in mind the ATU inside the rig is only a very light
duty one. It does not have the 'horsepower' of the dedicated external ones.
The diminished power situation you speak of is normal - and fortunate
for you - it is saving your finals from blowing.
To your ques:
you dont need to use an atu to set the ft to 50ohm. If you have a
50ohm load - you want to be able to switch the atu out when switching
through to the dummy load. With it in line while the 50ohm dummy load is
attached, you risk the possibility of having your atu introduce
additional and unwanted reactance - which will lead to higher SWR's and
artificially so. Your rig provides you with the means of switching it
it/out. The ft920 does, so should the ft1000
The normal course of events are: pick your band, maybe do a test
transmission into your dummy load to make sure your are indeed
transmitting, then switch to the antenna with ATU in circuit and have
it do its work.
If its not getting a match - then it is possible its outside the range
within which it can operate. Keep in mind most auto-atu's built into
rigs can only handle unbalanced feedlines and a very limited range of
antenna Z.
If you carnt get a match - its probably time to buy a decent external
atu with the capacity to handle a wide range of antenna Z' I always
have an external atu attached to my rigs - even the ones with built-in
atu's for this reason.
The skill then is in using the manual ATU quickly and efficiently thats
makes for a speedy match.
Perhaps the following will help. An antenna (all antennas) is(are) an
LCR network. In an ideal world they are just an R network - but we dont
live in an ideal world. An atu is a black box which provides you with
complete control over the L & C values you can add to the LCR network
which is your antenna. The challenge for all of us is to know when and
how to apply that additional L & C so that it cancels out the L & C
reactance in our LCR network, leaving just R.
You may not have enough L or C in your auto-atu to do the job.
Looked upon this way - you can probably answer your own question.
I hope this sheds a little light.
73's
phil vk4kvk
ka1xo@juno.com wrote:
> In attempting to tune up an external antenna tuner sometimes the
> mismatch in getting to a resonance is so extreme the "SWR" illuminates
> on the FT display.
>
> The power diminishes until I go back and switch to a dummy load and
> reset.
>
> My question for the group is if I first use the autotuner to set the
> FT to a 50 ohm dummy load and then disable it, does it remain tuned
> for the 50 ohm load, or is the tuner completely switched out of the
> transmit chain?
>
> What do other forum members do when facing this situation?
>
> Thanks,
>
> Hal, W4HBM
>
> _______________________________________________
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>
>
--
Thank you.
KVK Antenna Systems
Ph: 3216 8060 Fax: 3216 8075
http://www.kvkantennas.com.au
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