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FT METER - An Analog Meter for Yaesu FT-857D and FT-897D - The

Homebrew FT-Meter: 

FT-Meter - DIY Homebrew project by MØMTJ 

Yaesu very thoughtfully added an external meter socket to the FT-857 and FT-897

which is excelleint since I like analog S-Meters and connecting a meter to these radios is

child's play. There are no additional circuits required, merely a 100k preset

potentiometer and a small microameter. A meter with a sensitivity of 100µA, 500µA or

1mA should be suitable, the final calibration being done with the small internal preset

potentiometer, setting the meter for Full Scale Deflection using the calibration setting

on the radio.

The menus of the FT-857 and FT-897 allow the radio to output indications of Signal

Strength; Power; SWR; Modulation; Voltage and Discriminator.

I looked at the Bowood Electronics website and found a very nice little 100µA ammeter

measuring about 60mm wide by 50mm high, so I ordered one along with some other

components that were in my basket for the QRP power reducer and power

measurement project mentioned above. 

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 FT Meter schematic circuit diagram drawn by Frank OK2FJ

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FT-Meter - DIY Homebrew project by MØMTJ 

The physical construction of putting a small meter movement into a case should be very

straightforward, but there was the small problem of replacing the 0 - 100µA scale

supplied with the standard ammeter with a suitably calibrated and printed scale.

Producing a new scale for the meter's dial with a professional appearance was more of a

challenge for my graphics / image editing skills! I searched Google for some helpful

images. LDG market two commercially manufactured meters for this job - the FT-

Meter and the much larger FTL-Meter; these retail at about £46.00 GBP and £66.00

GBP respectively - my FT-Meter should cost about £10.00, but I digress! The

photographs of these products illustrated the layout of the graphics, but nothing that

was reproducable for this homebrew project.

I was beginning to think that I might have to draw something by hand - then I

happened across the website of Frank OK2FJ. Frank has produced an excellent meter

scale for his version of the Yaesu FT-Meter. Frank obviously had the same idea as me,

to produce a homebrew FT-Meter for a fraction of the cost of a commercial unit, but

Frank has greater image editing and graphics skills mine. I saved Frank's image fileand then made a few of my own simple modifications to the image file using a basic

image editing program. The result is shown below and can be downloaded and saved,ready to be re-sized and printed to match the size of the particular meter being used:

Above: The image graphic for the Yaesu FT-857 and FT-897 meter scale.Save and print if required. 

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Printing The Scale: The scale can be printed on paper or thin card and possibly laminated,

which is what I did. White paper or card might be the obvious choice, but cream, light green,

yellow or light blue card would also make a good background colour.

When printed, the image will need to be scaled quite accurately to suit the size of the

 particular meter movement being used, otherwise the needle will not line up properly with thescale and the indication will be inaccurate. This can be done by trial and error until the

correct size is found - a bit of a fiddly and a rather wasteful method. Alternatively a bit of

simple math's can be used.

My image editing program allows scaling of the print-out using a sliding scale that shows the

total width of the image when it's printed and the dpi (dots per inch) output to the printer.

Knowing the total image width isn't especially helpful since what is needed in this case is the

dimension that is the distance between the left and right end markers of the S scale - the top

curve. My simple image editor does not allow an accurate measurement of a portion of the

image, so I did a test print, estimating that the resultant image would need to be 50 mm wide,

the output in this case was 920 dpi. I then measured the width of the top curve on the test print, from end marker to end marker - it was 40mm. The scale of the original microammeter

is 34mm wide, so the print had to be scaled down in size.

The magnitude of the size reduction can be found by dividing that measurement, 40mm, by

the required measurement - in this case 34mm.

40mm ÷ 34mm = 1.176 (the scaling factor)

The original test print produced an scale that, at 40mm, was too wide. It needed to be 34mm

wide. The original image width of the test print was 50mm and therefore this needed to be

divided by the scaling factor of 1.176

50mm ÷ 1.176 = 42.5mm

The calculation suggests that 42.5 mm is the width required for the whole image. The image

was printed again at that width and the reulting print measured. It was found that the width

across the top curve from end marker to end marker was, indeed, the required 34mm.

The other way of doing the scaling is to note the dpi output of the original test print, in this

case 920 dpi, and multiply (not divide) that by the scaling factor. The original dpi figure is

multiplied, rather than divided, becuase the dots per inch will increase as the original imagesize is shrunk. In this case the new, and correctly sized print, is 1082 dpi. Whichever method

is used, the second print should produce a scale of the correct size.

Above: The image graphic for a simple analog S Meter scale.

Save and print if required. 

John, G0TEV, emailed with a helpful suggestion for those who want to produce a custommade meter scale: Meter Basic is free and will produce a basic linear scale. Meter is a paid

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for program that will allow more complex designs such as dB, vu, VSWR and S-meter scales.

Both programs are available here: http://www.tonnesoftware.com/index.html 

Felix, ec2alv, writes: Hi, perhaps this may be of interest to you I use GALVA 1.85 to daw all

kinds of scales: variables, pots, meters, etc. for my projects. Just follow the examples and you

will learn to use it fast. Kind regards, Felix EC2ALV

http://www.tonnesoftware.com/index.htmlhttp://www.tonnesoftware.com/index.htmlhttp://www.tonnesoftware.com/index.htmlhttp://www.tonnesoftware.com/index.html