Hi Bill,
Several have already responded saying "go with the K3 ATU. I would probably
suggest the same, but we really don't have much data to go on with regard to
your Cobra antenna. I can tell you that the K3's ATU is excellent, and
probably will do the job nicely. Presumably your antenna is relatively
closely matched on the bands you use it on, but there can always be
problems. Multiband antennas tend to have narrow bandwidths on lower bands,
like 40 and 80. Trying to work those bands from one end to the other can be
a stretch for many ATU's. So I'm not sure anyone can say with 100%
confidence that you won't have an issue somewhere.
What SWR readings do you get without using a tuner? That might be helpful
to know in order to make a more informed judgement on how the K3's ATU would
respond.
I get full band performance with my K3 or 40 through 6 meters using an R8
vertical. The K3 ATU has no problem. In fact, I can even get a match on 80
meters, which the antenna isn't even supposed to cover! Moreover, I can get
a 2:1 match on 160 meters! Having said that, I don't think I'm very
efficient on either 80 or 160, and the ATU is not going to make any magic.
But it does tell me that the K3 ATU is very, very good at finding a match on
difficult situations. In fact, I doubt you will find an internal ATU that
works better.
So, I think you would be making a good bet by adding the internal ATU. It
certainly won't disappoint you provided you give it something "reasonable"
(or maybe even slightly unreasonable) to match. But you have the
responsibility of making sure the antenna is within realistic reach of
resonance, and not so poorly designed (or installed) that it presents
something just too complex for the ATU to deal with. I'd say if you see 5:1
or better without a tuner you are probably safe. And that probably
understates the ability of the K3's ATU. But if you see much more than
that, you might really need a better antenna! Even though I can get a 2:1
match on 160 with my R8, I'm not going to press my luck by operating there.
Clearly the ATU isn't particularly happy, and it's probably struggling
excessively. Besides, even though the match seems "acceptable", the antenna
still sucks on that band.
So, bottom line is, get the K3 ATU. If it doesn't deal with your antenna
with relative ease, change antennas!
Dave W7AQK
----- Original Message -----
From: "KB1PXD" <[EMAIL PROTECTED]>
To: <elecraft@mailman.qth.net>
Sent: Thursday, April 10, 2008 3:41 AM
Subject: [Elecraft] K3 ATU specifications
Greetings everyone,
I'm trying to debate whether or not to pickup an external LDG tuner or
just
go
with the K3 built-in ATU. Does anyone know the tuning specifications of
the
ATU? I need a tuner that will hopefully tune every band to <= 1.5:1 on a
Cobra
multiband dipole antenna. The built-in ATU in my TS-850 has difficulties
with
certain frequency ranges within a couple of bands. Should I go with the
built-in
K3 ATU, or remove that from my order and just pickup an a decent external
LDG tuner? Any advice would be greatly appreciated.
Thanks!
- Bill, kb1pxd
--
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