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Cal AT100 SWR bridge

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Rich McCabe

Cal AT100 SWR bridge

Is there any tricks (or improved techniques) on adjusting the SWR bridge in
the tuner? I just finished a tuner and everything checked out and calibrated
very easy. But I may have a SWR that agrees on my Daiwa in the line 16" away
or it may be as high as 4:1 on some bands even when the tuner says it is
flat or near flat.

I have adjusted C31 for minimum reading (.01 volts) and the null is small so
I really cant center it in the null easily.

I also had a problem with oscillations on 40 meters and I think I read
somewhere it could be a grounding issue. So I am going to go back and do
some more sanding.

Any tips or comments.

Thanks,

Rich

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Geoffrey Mackenzie-Kennedy-2

Re: Cal AT100 SWR bridge

Hi Rich,
Have you tried disconnecting the antenna system and putting a 50 ohm dummy
load at the output of the Daiwa ? If the Daiwa is OK and the tuner's VSWR
bridge is OK both should give you almost the same readings. I say almost
because the additional connectors and line plus the Daiwa that the tuner
sees between it and the dummy load will make the tuner's load something
other than 50 ohms, unless something in the Daiwa - 16" line combo is
compensating. But the diff should be small, increasing with frequency - but
still small.

If that's OK and you reconnect the antenna system and the problem comes
back, then either the antenna system does not look like 50 ohms resistive at
the "problem frequencies" or you have "antenna currents" on the outside of
the feeder - or both - or some grounding problem. If of any help I would be
glad to discuss symptoms / possible cures off list.

When I did the null adjustment with C31 I also found the null to be shallow
and quite broad. But after moving the one wire primary of T1 so that it
passed through the core dead centre, the null became much deeper and
sharper. KAT100 now gives reasonably correct readings.

Good luck es 73,

Geoff GM4ESD

----- Original Message -----
From: "Rich McCabe" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Friday, September 24, 2004 4:31 AM
Subject: [Elecraft] Cal AT100 SWR bridge

> Is there any tricks (or improved techniques) on adjusting the SWR bridge
in
> the tuner? I just finished a tuner and everything checked out and
calibrated
> very easy. But I may have a SWR that agrees on my Daiwa in the line 16"
away
> or it may be as high as 4:1 on some bands even when the tuner says it is
> flat or near flat.
>
> I have adjusted C31 for minimum reading (.01 volts) and the null is small
so

> I really cant center it in the null easily.
>
> I also had a problem with oscillations on 40 meters and I think I read
> somewhere it could be a grounding issue. So I am going to go back and do
> some more sanding.
>
> Any tips or comments.
>
> Thanks,
>
> Rich
>

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Dan Barker

RE: Cal AT100 SWR bridge

In reply to this post by Rich McCabe

Is the Diawa between the K2 and the Tuner, or between the Tuner and the
Antenna?
Is the Antenna resonant?

You should not expect a "flat" SWR after the tuner unless the
antenna/feedline system is a perfect match - That's the purpose of the tuner
in the first place.

To compare apples to apples, check the SWR of the same thing at the same
spot. IE, put the Diawa in the line only, measure SWR, remove the Diawa and
put the KAT100 in line using the same connectors and cables, turn off the
Auto-tuning function (I forget - CALP?), and check again - Same frequency,
Same antenna, Same feeders, Same cables, jumpers, connectors and testing
location.

Let us know what you find.

Dan / WG4S / K2 #2456

<snip>
it may be as high as 4:1 on some bands even when the tuner says it is flat
or near flat.
</snip>

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Geoffrey Mackenzie-Kennedy-2

Re: Cal AT100 SWR bridge

Morning Dan,

Agree with all. My thinking was to remove the antenna system from the
equation so that the "baseline" could be checked out before dealing with any
antenna system induced problems. I know nothing about the Daiwa, but if it
is supplied with mains power any ground loop Power Supply - K2/100 -
KAT100 - Daiwa - mains , or variations of this, might become "visible". I
think Rich has the Daiwa between KAT100 and antenna - but that's for Rich to
say !!

Will standby with interest.

73 Geoff GM4ESD K2/100 #3255

----- Original Message -----
From: "Dan Barker" <[hidden email]>
To: "Elecraft" <[hidden email]>
Sent: Friday, September 24, 2004 12:22 PM
Subject: RE: [Elecraft] Cal AT100 SWR bridge

> Is the Diawa between the K2 and the Tuner, or between the Tuner and the
> Antenna?
> Is the Antenna resonant?
>
> You should not expect a "flat" SWR after the tuner unless the
> antenna/feedline system is a perfect match - That's the purpose of the
tuner
> in the first place.
>
> To compare apples to apples, check the SWR of the same thing at the same
> spot. IE, put the Diawa in the line only, measure SWR, remove the Diawa
and

> put the KAT100 in line using the same connectors and cables, turn off the
> Auto-tuning function (I forget - CALP?), and check again - Same frequency,
> Same antenna, Same feeders, Same cables, jumpers, connectors and testing
> location.
>
> Let us know what you find.
>
> Dan / WG4S / K2 #2456
>
> <snip>
> it may be as high as 4:1 on some bands even when the tuner says it is flat
> or near flat.
> </snip>
>
>

Don Brown-4

Re: Cal AT100 SWR bridge

In reply to this post by Rich McCabe

Hi

I have developed a different technique for adjusting the SWR bridge in the KPA100, KAT100 or KAT2. First I adjust the null as in the manual instructions. I have made up some calibration resistors of 25, 100 and 50 ohms. These are 3 watt MOS resistors mounted into a PL259 connector. The PL259 plug is screwed directly onto the KPA/KAT100 SO239. When doing a KAT2 I use a BNC to PL259 adaptor. Use the 50 ohm first to set the null. Then connect a accurate watt meter or scope to set the forward power out correctly. Disconnect the watt meter and connect the 25 ohm resistor adjust the reflected pot for a 2.0 to 1 SWR reading. Then connect the 100 ohm resistor. If the SWR is not 2.0:1 then very slightly adjust the null cap so the reading is the same with the 25 and 100 ohm resistors. When you get the reading the same then readjust the reverse pot to bring the reading to 2.0:1. Connect the 50 ohm resistor and make sure the SWR is 1:1. All of the measurements are done at about 2-5 watts. The resistors will take up to 10 watts for a few seconds. This is usually long enough to make the settings. If you fill the PL259 void around the resistor with silicone rubber the connector will act as a heat sink and the assembly will take more power. Maybe up to 25 watts for a few seconds. Use GE Silicone II for the fill. It is alcohol based and does not corrode electrical connections like silicone with the vinegar smelling ascetic acid based silicone. You should find GE Silicone II at most hardware stores.

Don Brown

----- Original Message -----
From: Rich McCabe<mailto:[hidden email]>
To: Elecraft Reflector<mailto:[hidden email]>
Sent: Thursday, September 23, 2004 10:31 PM
Subject: [Elecraft] Cal AT100 SWR bridge

Is there any tricks (or improved techniques) on adjusting the SWR bridge in
the tuner? I just finished a tuner and everything checked out and calibrated
very easy. But I may have a SWR that agrees on my Daiwa in the line 16" away
or it may be as high as 4:1 on some bands even when the tuner says it is
flat or near flat.

I have adjusted C31 for minimum reading (.01 volts) and the null is small so
I really cant center it in the null easily.

I also had a problem with oscillations on 40 meters and I think I read
somewhere it could be a grounding issue. So I am going to go back and do
some more sanding.

Any tips or comments.

Thanks,

Rich

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Post to: [hidden email]<mailto:[hidden email]>
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Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
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Rich McCabe

Re: Cal AT100 SWR bridge

In reply to this post by Geoffrey Mackenzie-Kennedy-2

Thanks to all that responded.

Turns out that somewhere along the testing stages I ended up with a bad
connection on a PL-259. Everything looked good on the dummy load, but after
connecting, disconnecting, reversing etc. the problem became apparent.

I also removed panels and did a better job sanding the connections for
ground and do not seem to have the 40 meter problem anymore unless that went
away with the feedline fix.

So all is good :)

73,

Rich

----- Original Message -----
From: "Geoffrey Mackenzie-Kennedy" <[hidden email]>
To: "Dan Barker" <[hidden email]>
Cc: "Elecraft Discussion List" <[hidden email]>
Sent: Friday, September 24, 2004 7:24 AM
Subject: Re: [Elecraft] Cal AT100 SWR bridge

> Morning Dan,
>
> Agree with all. My thinking was to remove the antenna system from the
> equation so that the "baseline" could be checked out before dealing with
> any
> antenna system induced problems. I know nothing about the Daiwa, but if it
> is supplied with mains power any ground loop Power Supply - K2/100 -
> KAT100 - Daiwa - mains , or variations of this, might become "visible". I
> think Rich has the Daiwa between KAT100 and antenna - but that's for Rich
> to
> say !!
>
> Will standby with interest.
>
> 73 Geoff GM4ESD K2/100 #3255
>
>
>
> ----- Original Message -----
> From: "Dan Barker" <[hidden email]>
> To: "Elecraft" <[hidden email]>
> Sent: Friday, September 24, 2004 12:22 PM
> Subject: RE: [Elecraft] Cal AT100 SWR bridge
>
>
>> Is the Diawa between the K2 and the Tuner, or between the Tuner and the
>> Antenna?
>> Is the Antenna resonant?
>>
>> You should not expect a "flat" SWR after the tuner unless the
>> antenna/feedline system is a perfect match - That's the purpose of the
> tuner
>> in the first place.
>>
>> To compare apples to apples, check the SWR of the same thing at the same
>> spot. IE, put the Diawa in the line only, measure SWR, remove the Diawa
> and
>> put the KAT100 in line using the same connectors and cables, turn off the
>> Auto-tuning function (I forget - CALP?), and check again - Same
>> frequency,
>> Same antenna, Same feeders, Same cables, jumpers, connectors and testing
>> location.
>>
>> Let us know what you find.
>>
>> Dan / WG4S / K2 #2456
>>
>> <snip>
>> it may be as high as 4:1 on some bands even when the tuner says it is
>> flat
>> or near flat.
>> </snip>
>>
>>
>
> _______________________________________________
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> You must be a subscriber to post to the list.
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>
>