[1000mp] Re: Maybe dumb questions ?

[Garry Shapiro]

I believe the problems with tuner use are due to a CHANGING load, rather
than a non-ideal one. The input impedance of some amplifiers varies widely
with drive, and hence with keying, causing the tuner to continually hunt for
a solution.

I guest-opped once at a station using an FT1000 and a homebrew 4-1000A GG
amp with untuned input. My host wanted me to use a footswitch to engage the
amp but I wanted less clutter and we hooked up a relay working off the VOX.
The internal tuner hunted continuously and, after that contest, it failed.
My host blamed me for his repair cost.

Since then, I have been wary of using internal tuners with non-fixed loads.

Garry, NI6T

-----Original Message-----
From: 1000mp-bounces at mailman.qth.net
[mailto:1000mp-bounces at mailman.qth.net]On Behalf Of Rob Atkinson
Sent: Friday, November 04, 2005 3:43 AM
To: All about Yaesu 1000mp
Subject: Re: [1000mp] Re: Maybe dumb questions ?


I've driven my amp with a ts870s using its internal tuner and never had
a problem.   in fact, when the rig sees a 1.5:1 vswr and folds back,
the tuner takes that down to 1.2:1 so the rig is happy, puts out full
power and drives the amp more.   with my mk V the built in tuner
doesn't seem to want to do anything with 1.5:1 so i don't use it and
because it has a 200 w. pa, it can provide plenty of drive anyway.
the mk V tuner seems to be intended to only handle higher ratios, maybe
2:1 on up.

rob / k5uj

On Thursday, November 3, 2005, at 10:18 AM, Scott Manthe wrote:

> Because as you tune the amplifier, the values of impedence and
> reactence the internal tuner in your rig sees are changing, therefore
> changing the output of the rig. I call this "tuner wander," because
> the tuner wanders around trying to find a match and I don't think it's
> good.
>
> Now, if you tune-up fast and don't change values, it's probably much
> better than running the rig into a huge mismatch. But for me, I prefer
> to turn the tuner off. Since my LK-500ZC has a very good tuned input,
> it's not an issue.
>
> 73,
> Scott, N9AA
>
> John Becker wrote:
>
>>> It's never a good idea to use an internal tuner with an amp.
>>>
>> Why is this necessarily a bad idea? The input of my homebrew 4-1000
>> amp apparently isn't close enough to 50 ohms on 15 meters for the Mk.
>> V without the tuner, but I've been driving it successfully by using
>> the tuner.
>>
>> 73,
>>
>> John, K9MM
>>
>
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