K3 power reduction due to high SWR

[David Stratton]

At what point does the SWR have to rise up to before

the K3/10 output power begins to decrease?

I have been using a TS-830 which is not bothered by

SWR up to at least 3:1. I cannot get the tuner now so

will I be forced to run very low power if my SWR is 2

or 3 to 1? What about the K3/100?

 

My antennas are resonant fan dipoles (80, 40, 20, 17)

fed with 250 feet of 72 ohm cable TV coax.

 

Dave - KO4KL

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[Don Wilhelm-4]

Dave,

The KPA3 will throttle back power at or above the SWR = 2.0 point.  
Actually, I am not certain about the K3/10 - it may or may not reduce
power above SWR = 2.0,. but I would suggest that your goal for antenna
tuning be less than SWR = 2.0.

I you have resonant antennas, then it should be a good thing to tune
them for less than a 2-1 SWR, but if you are using a properly tuned
multiband antenna, you should already have an SWR less than 2-1.
If you are using a non-resonant antenna, you already have a tuner
installed - just set the tuner for the lowest reflected power possible.

73,
Don W3FPR

On 4/4/2012 8:33 PM, David Stratton wrote:

> At what point does the SWR have to rise up to before
>
> the K3/10 output power begins to decrease?
>
> I have been using a TS-830 which is not bothered by
>
> SWR up to at least 3:1. I cannot get the tuner now so
>
> will I be forced to run very low power if my SWR is 2
>
> or 3 to 1? What about the K3/100?
>
>
>
> My antennas are resonant fan dipoles (80, 40, 20, 17)
>
> fed with 250 feet of 72 ohm cable TV coax.
>
>
>
> Dave - KO4KL
>

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[vk4tux]

Dave, Yes well xyl problems can be very tricky to resolve.

If money was no barrier a remote K0/K3 setup may have solved the aesthetics
issue, and cut the feedline length to small numbers.
Not sure how you measured the loss on the 75 ohm coax?

A ocf dipole fed with a Balun designs 4115ocf balun will outperform a fan
dipole any day, and is less obvious apart from the balun.
T Length 41.5m  fed 36% point; 27.5m long leg 14m short leg.

Worked 4A4A & T31A with best VK results using this one antenna for all bands
worked.

Only you would want to go to low loss 50 ohm coax like lmr etc. Of course
balanced line and unbalanced antennas don't mix so coax
 is necessary with the ocf. The dual core choking - true current 4:1 balun
keeps the radiation in the antenna and not the feedline.

The antenna develops gain on the long leg lobes on higher bands and for USA
a long leg to south and short leg to North would suit
your position with some slope to cover nth /sth.


Adrian ... vk4tux

Adrian,

I sent this on the reflector but I thought I would also send it to you
directly.

The 72 ohm coax I am using is what the cable company used to get from the
main line pole to a house. It is about
10 mm or 3/8" in diameter with a "carrier" wire molded onto it.
The coax is not too lossy because I measured the loss when I first installed
it several years ago to be sure. I use a choke balun at the feed point made
with cores slipped over a 3 ft. piece of RG-213.

I must have long runs of transmission line to get my antennas away from my
wife's eyes. When I got back into the hobby in 1989 I put up a center fed
wire in a field 1,200 feet from my shack near the back of my property and
fed it with ladder line and a tuner. Nobody could hear me so I took that
down. I still have plenty of ladder line and some great places to put up
antennas but they are far away and ladder line cannot lay on the ground in
the woods out of sight like coax. Having ladder line in the air hanging off
trees or some other supports on the way to an antenna from my house is not
acceptable.

Maybe I just need to get more creative about placing my dipoles closer to
the house and yet out of sight. I am open to any reasonable ideas.

Dave - KO4KL

-----Original Message-----
From: Adrian [mailto:[hidden email]]
Sent: Wednesday, April 04, 2012 10:51 PM
To: 'David Stratton'
Subject: RE: [Elecraft] K3 power reduction due to high SWR

You have some serious performance limitations with this setup.
If I have to use your antenna, then my move would be to replace the 250' of
75 ohm coax
with 250' of 450 ohm ladder line, check the fan dipole legs are exactly the
same to provide a balanced load.

Get a balun  and short 50 ohm coax section to get from the ladder line back
into the shack, if you can't get the balanced line in to a balanced line
tuner etc.

As it is you are losing 57% @ 20m of your power in that feedline.

A mfj-986 or similar with balanced line is probably the go on a limited
budget.

You will reduce loss from 57% to 9%.

Adrian ... vk4tux

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of David Stratton
Sent: Thursday, 5 April 2012 10:34 AM
To: Elecraft Reflector
Subject: [Elecraft] K3 power reduction due to high SWR

At what point does the SWR have to rise up to before

the K3/10 output power begins to decrease?

I have been using a TS-830 which is not bothered by

SWR up to at least 3:1. I cannot get the tuner now so

will I be forced to run very low power if my SWR is 2

or 3 to 1? What about the K3/100?

 

My antennas are resonant fan dipoles (80, 40, 20, 17)

fed with 250 feet of 72 ohm cable TV coax.

 

Dave - KO4KL

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[WB8ENE]

Adrian,

I've been looking at putting up an OCF antenna to replace my 102' doublet fed with ladder line.  Can you tell me what frequencies on 80 through 10 meters your OCF antenna is resonant?  Also, how much of each band can you cover with less than 2:1 SWR?  I'm interested in the CW portions of the bands.  Any information would be helpful.  By the way, my doublet is currently about 15' off the ground, but I'm considering putting up a 30' center support.

73,
Art  WB8ENE