Z match versus KAT100

[David Andrews-4]

I'd appreciate thoughts about what I *think* I hear! I normally use K2/100,
KAT100, BL1 (4:1 balun), open wire feeder and 84' dipole - works fine. 80m
is noisy but I get a good match on all bands. I recently connected a Z-match
tuner (old KW Easi Match - like the Johnson Matchbox) to the output of the
KPA100 (bypassing the tuner and balun) and fed the same open wire feeder and
antenna. The contrast between QSOs and the noise on 80 increased (copy much
easier). S meter peaks the same and match is as good.

Am I imagining this, or is there a reason? Thanks.

David G4CWB

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[Don Wilhelm-3]

David,

There is a good chance that you are not imagining things.  Your tuner is
likely a link coupled design which isolates the transceiver side from any
circulating currents on the antenna side.  A balun does not provide the same
isolation.  Antenna currents can be induced from BC stations, wind static,
rain static, etc. as well as the desired signals.

73,
Don W3FPR

> -----Original Message-----
>
> I'd appreciate thoughts about what I *think* I hear! I normally
> use K2/100,
> KAT100, BL1 (4:1 balun), open wire feeder and 84' dipole - works fine. 80m
> is noisy but I get a good match on all bands. I recently
> connected a Z-match
> tuner (old KW Easi Match - like the Johnson Matchbox) to the output of the
> KPA100 (bypassing the tuner and balun) and fed the same open wire
> feeder and
> antenna. The contrast between QSOs and the noise on 80 increased
> (copy much
> easier). S meter peaks the same and match is as good.
>
> Am I imagining this, or is there a reason? Thanks.
>
>

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[Geoffrey Mackenzie-Kennedy-2]

David,

>From what you say I get the feeling that the BL1 is not providing the
antenna plus open wire feeder with a true balanced load, with the result
that the feeder is also acting as an antenna, picking up noise from 'local'
sources which is not cancelled out. Although the KAT100 could provide the
KPA100 with a 50 ohm load, the feeder imbalance remains. A good rule states
that baluns of the BL1 type, current baluns, should not be used with
reactive loads where the load VSWR exceeds 3:1 worst case, not only for
imbalance reasons but also for reasons of stress under power. These are
related. This rule is strictly observed in very high power SW Broadcast
antenna system design, more often 2:1 worst case from what I have heard from
the 'Horse's mouth'.

I suspect that when  you connect the KW Easi Match, which I believe is a
proper balanced tuner, the feeder would be presented with a balanced load.
All other things being right (e.g. routing of feeder), the local noise
picked up by the feeder should be cancelled out.

The antenna itself would be affected to some degree as far as noise
contribution is concerned, but I would think that the feeder would be the
major contributor.

No doubt the same situation exists on other bands, not just 80m, but that
the external noise strength there is less and not noticeable.

73,
Geoff
GM4ESD


----- Original Message -----
From: "David Andrews" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, June 01, 2005 9:29 AM
Subject: [Elecraft] Z match versus KAT100


> I'd appreciate thoughts about what I *think* I hear! I normally use
K2/100,
> KAT100, BL1 (4:1 balun), open wire feeder and 84' dipole - works fine. 80m
> is noisy but I get a good match on all bands. I recently connected a
Z-match
> tuner (old KW Easi Match - like the Johnson Matchbox) to the output of the
> KPA100 (bypassing the tuner and balun) and fed the same open wire feeder
and
> antenna. The contrast between QSOs and the noise on 80 increased (copy
much
> easier). S meter peaks the same and match is as good.
>
> Am I imagining this, or is there a reason? Thanks.
>
> David G4CWB
>

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