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Author Topic: SWR/Power meters I built recently  (Read 26401 times)
YU1OXB
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« on: July 25, 2015, 11:41:11 AM »

Hi people!
I was planning for quite some time to build myself reliable and accurate SWR/POWER meter and I am collecting some data and designs through time. About 6 months ago I started to build nice analog meter based on a bit unusual and oldish design from Virgil Leenerts W0INK "Automatic VSWR and power meter" from May 1980. Regardless of years, this is still very usable design if you do not want to go with PIC-s. I am 61, my vision is not any more as it was, so I opted for large 35 uA analog meters salvaged from some old Russian AVO meters. The only departure from original schematics was use of THAT 340P matched transistor arrays in log amplifier as a replacement for LM394BH - to me unobtainable component. There was no PCB-s published (as far as I know?!) so I was forced to develop my own and anyone willing to build this meter can have PDF files from me ... of course for FREE. Unit use three 9V batteries which will last for long time because unit is powering on automatically as soon as transmitter RF appear on input connector and goes off second-two after RF disappear.






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YU1OXB
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« Reply #1 on: July 25, 2015, 11:43:39 AM »

Before I finished this analog meter, I decided that I also need one with digital precision for some precise measurements. It is not because this analog one is not accurate - it is, but some values are not that easy to read on an analog scale. Analog is better for tuning because (for me) it is easier to follow needle movements and moving tendency than to watch digital display for that purpose. I decided to make Steve Drury G6ALU design available from www.radio-kits.co.uk and I manage to obtain some crucial components separately. Steve is a remarkable personality and so willing to help and explain and I was very happy that I chose exactly this design. A friend of mine done PIC programming and as soon as I finished assembling PCB-s, programmed PIC has been pushed into a socket and unit worked smoothly from the first turn on. Following simple instructions for calibration, you will have more than accurate meter even without any additional external reference. Later I compared it connected in series with ubiquitous BIRD43 in my friend shack, and it was spot on following exactly BIRD readings!
It will be hard to beat this meter regarding accuracy, simplicity and reliability (and price!) in that power and frequency class.

Steve, THANK YOU again!





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K8AXW
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« Reply #2 on: July 25, 2015, 08:47:47 PM »

Very good work OM!  It's good to see such quality homebrew work.  Looks like commercial gear.

Is that a burned resistor next to Pin 1 of the (PIC) chip??
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N7EKU
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« Reply #3 on: July 25, 2015, 08:56:49 PM »

Very good work OM!  It's good to see such quality homebrew work.  Looks like commercial gear.

Is that a burned resistor next to Pin 1 of the (PIC) chip??

I think not,

Note the shadows falling on the left side of the tall components.  The dark stripe is just a shadow from the ceramic capacitor to the right of the resistor.

73,


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Mark -- N7EKU/VE3
VK2TIL
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« Reply #4 on: July 25, 2015, 10:59:55 PM »

That is very fine work.

I hadn't seen the Leenerts design so I looked it up; for anyone interested it is US patent 4110685;

www.g3ynh.info/zdocs/refs/patents/4110685_Leenerts1978.pdf

A very interesting design; YU1OXB has made it into a fine finished product.
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G3RZP
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« Reply #5 on: July 26, 2015, 12:12:18 AM »

What is the accuracy, and how does that hold across the frequency range?

Note that 'resolution' and 'accuracy' are not the same.
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DL8OV
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« Reply #6 on: July 26, 2015, 01:20:23 AM »

Nice work! How did you make the meter scales?

Peter DL8OV
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YU1OXB
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« Reply #7 on: July 26, 2015, 04:58:22 AM »

K8AXW:  Is that a burned resistor next to Pin 1 of the (PIC) chip??
N7EKU:  I think not, Note the shadows falling on the left side of the tall components.

>>>Mike N7EKU is right. Nothing is burned so far... thanks God, and I hope to stay that way!

G3RZP:  What is the accuracy, and how does that hold across the frequency range?
              Note that 'resolution' and 'accuracy' are not the same.

>>> I think there is nothing special to “note” here, it is general knowledge and everyone even moderately involved in electronics and measurements will clearly know the difference between  'resolution' and 'accuracy'. I don't have instruments of such class to absolutely determine accuracy of my HM meters, but if we assume BIRD 43 to be sufficiently accurate for any amateur work and needs, than both described meters are as precise as BIRD.

DL8OV:  Nice work! How did you make the meter scales?

>>>  That is easy to ask Peter but not that easy to explain. Drawing scales were harder part of a job believe me. I used INKSCAPE free vector software for that, there were scale examples in the Leenerts article and I dismantle Russian instruments, took scale plates (detachable) and scan them. Then I had to arrange correct size-scale of scans and those from article, put them all in separate transparent layers in Inkscape and than “the show” can start! It will take half of a day for me to describe that all in details but I believe you got coarse picture of the concept. There is beautiful software to draw scales done by some amateur, but it is free just for linear scales and not for logarithmic or special ones, hence I had to do it harder way. All that took me few days, for, I am not particularly skilled for that.  Final work has been saved as PDF in 600dpi and printed on a peal-able MUFLON foil and attached to the back sides of those thin aluminum scale plates.
« Last Edit: July 26, 2015, 02:28:24 PM by YU1OXB » Logged

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YU1OXB
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« Reply #8 on: July 27, 2015, 01:17:17 PM »

Here are layout files of PCB-s I've done for Leenerts SWR/POWER meter. Sorry but I don't know how to upload PDF file of both PCB-s for printing. That file is available from me if anyone needs.





I found the way... http://www.keepandshare.com/doc13/9558/swr-leenert-pcb-s-pdf-34k?da=y
« Last Edit: July 27, 2015, 01:56:55 PM by YU1OXB » Logged

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To have friends, it is to accept that there are more beautiful, smarter and more capable people than you. Who can not accept that - have no friends!
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