Hi,

What would anyone recommend for measuring SWR on a system that has a low
power transmitter (20mW) ?

My meter has lowest range of 3W FSD. I do have a digital power meter and
directional coupler, would it be best to manually measure fwd power and
reverse pwr and calculate SWR ?

Thanks in Advance

Regards

David

David wrote:

Hi,

What would anyone recommend for measuring SWR on a system that has a low
power transmitter (20mW) ?

My meter has lowest range of 3W FSD. I do have a digital power meter and
directional coupler, would it be best to manually measure fwd power and
reverse pwr and calculate SWR ?

Thanks in Advance

Regards

David

20mW is definitely pushing it. QST published a QRP SWR meter at one
point that might go down that far with work. I use an RF noise bridge
and a receiver for establishing feedpoint impedance -- that may be the
way you'll want to go.

IIRC the bridge design came out of "Solid State Design for the Radio
Amateur" by Hayward and DeMaw. I think it's basically what MFJ sells,
only they wrap it all with a fancy computerized controller.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

David wrote:
My meter has lowest range of 3W FSD. I do have a digital power meter and
directional coupler, would it be best to manually measure fwd power and
reverse pwr and calculate SWR ?

On the upstream side of the diodes (if any) in the directional
coupler, you might be able to obtain AC measurements proportional
to the forward and reflected power, depending upon the sensitivity
of your meter. It could also be done using an o'scope.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
. com...
David wrote:
My meter has lowest range of 3W FSD. I do have a digital power
meter and
directional coupler, would it be best to manually measure fwd
power and
reverse pwr and calculate SWR ?

On the upstream side of the diodes (if any) in the directional
coupler, you might be able to obtain AC measurements proportional
to the forward and reflected power, depending upon the sensitivity
of your meter. It could also be done using an o'scope.
--
73, Cecil http://www.qsl.net/w5dxp
===========================================

And having found SWR what would he do with it - calculate forward and
reflected power ?

;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o) ;o)
;o) ;o) ;o)

I suppose then I then should just measure forward power from the
incident port and then tune the antenna while monitoring power on the
reflected port (of the directional coupler) for min. reflected power.

I should have also mentioned frequency is 900 MHz.

I should have also mentioned frequency is 900 MHz.
=========================================

About time too! It could have all been happening on 160 meters. ;o)

On Wed, 22 Mar 2006 10:48:57 +0000 (UTC), "Reg Edwards"
wrote:

I should have also mentioned frequency is 900 MHz.
=========================================

About time too! It could have all been happening on 160 meters. ;o)

I was going to recommend my Oakhills Research qrp wattmeter; it has a
100 milliwatt scale, but it is only rated to 54 mhz. I also looked at
the Bird list of slugs -- they have 100 milliwatt slugs, but not in
the 900 mhz range.

bob
k5qwg