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| Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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4th Aug 2016, 10:36 am
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#1 |
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Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,995
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A little RF test-meter.
A few years back, at the Didcot radio rally I picked up an old 250-microamp meter whose previous owner had hand-added a SWR scale.
This sat in my "useful bits" box until a couple of weeks ago when I decided to do something with it. An old Eddystone-type diecast box, a couple of chromed ex-filing-cabinet handles, a BNC socket, a DIN socket, a micro-switch-with-push-button and a 10KOhm linear pot and knob were soon found. Time for a bit of engineering, in my usual "1940s/early-1950s military-industrial" style. I'm getting good at applying crackle-finish paint. The BNC socket feeds through a 50pF 1Kv capacitor to a voltage-doubler pair of AA119 diodes, then to the top of the pot. The DIN socket has 2 inputs, the push-button selects between the two. The pot acts as a sensitivity control. Feeding RF into the BNC socket either from a probe or a coupling-loop, it's ideal for 'peaking' low power oscillator/multiplier/driver stages. With a 90-degree BNC adapter and a 3-foot antenna plugged in I can put it at the bottom of the garden and watch it through a 'long-range visual coupling device' - a.k.a. a telescope - while tuning my transmitter for maximum RF. The 2 chromed handles protect the front when the 3-foot-whip wobbles and the thing falls on its face. I'm in the process of building the next part: a forward/reverse coupling 'head' for SWR measurement - it'll connect to the DIN socket and the green push-button will switch between forward and reverse. |
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4th Aug 2016, 10:45 am
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#2 |
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Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: A little RF test-meter.
Very pro, proper job.
Lawrence. |
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4th Aug 2016, 11:56 am
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#3 |
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Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,931
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Re: A little RF test-meter.
Love it!
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G8JET BVWS Archivist and Member V.M.A.R.S |
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4th Aug 2016, 12:25 pm
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#4 |
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Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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Re: A little RF test-meter.
I could have sworn that meter had GWR on it when I first looked.
Must have been some mental association with Wiltshire....... 
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....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
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4th Aug 2016, 6:28 pm
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#5 |
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Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,995
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Re: A little RF test-meter.
If it was a GWR-meter, its units-of-calibration would be Brunels.
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4th Aug 2016, 8:30 pm
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#6 |
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Guest
Posts: n/a
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Re: A little RF test-meter.
Ah, from the days when people could write, today it would take a CAD programme and hours rather than a bit of india ink and a pen!
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1st Sep 2016, 11:34 am
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#7 |
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Pentode
Join Date: Jul 2014
Location: Bangalore, India
Posts: 132
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Re: A little RF test-meter.
Real professional, G6Tanuki!
Regards, Nandu.
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https://nandustips.blogspot.com |
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1st Sep 2016, 5:39 pm
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#8 |
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Octode
Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
Posts: 1,270
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Re: A little RF test-meter.
This thread reminds me of my younger days when I placed an article in the Short Wave Magazine on how to mark up a meter scale for use as a SWR Bridge.
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Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way! 
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1st Sep 2016, 10:33 pm
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#9 |
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Dekatron
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,748
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Re: A little RF test-meter.
Nice work, and a lovely pseudo-ex-WD appearance!
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Phil Optimist [n]: One who is not in possession of the full facts |
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