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Author Topic: Homebrew analog SWR / Wattmeter  (Read 5023 times)
KC2ZPK
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Posts: 107


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« on: November 07, 2011, 12:28:26 PM »


Homebrew analog SWR / Wattmeter

While surfing the web I came across this meter MJF 400-3084a Which gave me an idea for a quick fall project. I would like to build a SWR/watt meter. The meter in the link is a 300 Watt forward and reflected cross needle meter 200uA (micro amps?). Anyway I have build some electronics kits before, mostly ones with the parts supplied, but now I need to source some parts, and some circuit ideas. I need to find  a rf sensing circuit for the meter and a suitable case for it. I am also thinking about adding an antenna coax switch for routing the rf in and out from 2 or more radios to 2 or more antennas. I would like this to handle 200W +/- . I don't really need finished circuits, but something to get me going in the right direction.

Thanks everyone.
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John
KC2ZPK.com - A work in progress
WD4HXG
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Posts: 186




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« Reply #1 on: November 07, 2011, 04:41:27 PM »

Look in the ARRL Handbook or ARRL Antenna Book or similar text
to find VSWR, SWR Bridges.

You will need to decide if you want HF or VHF or UHF or Microwave
ranges. This will determine the type of Bridge you will need to drive
the meter. The rest you should be able to cookie cutter from the
text in the books or from Google. Be sure to look into the theory of
operation of the way the bridge senses the signal. Most designs
will use a diode detector for both the reflected and forward signal
samples which will provide a nominal 20 to 30 dB or measurement
range. (That will be about a 10 or 15 to 1 ratio between minimum
signal you can measure and the maximum signal.

Enjoy

Chuck WD4HXG
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KA4POL
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Posts: 2028




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« Reply #2 on: November 07, 2011, 10:00:14 PM »

Take a look into http://n2pk.com/RLPmtr/RLPmeter.html
At least this is a starting point for your project.
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KC2ZPK
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Posts: 107


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« Reply #3 on: November 09, 2011, 02:23:00 PM »

OK, small change of plans. I need to make this able to handle a SB-200, so looks like 800-1kw power handling. and like to add a tuner to it as well...... 

Thanks for the direction so far.
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John
KC2ZPK.com - A work in progress
WD4HXG
Member

Posts: 186




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« Reply #4 on: November 11, 2011, 04:49:00 AM »

John

I would design and build the VSWR Meter first.
Johnson Matchbox and other commercial built
tuners in the past were built with a Sensor Head
and connected to the panel meter via a three foot
or so length of wire. Heath took it a step further
by building the Sensor Head in its own housing in
such a manner as the Sensor Head was installed
in the rear of the Meter Display Box but could be
removed from the Meter Display Box for conveniently
locating the sensor head at the transmitter output.

Also I would build the tuner as a second project
and first get the VSWR Meter running. You can
design the Tuner to accommodate the VSWR
Meter Sensor Head and Meter Display.

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