The wonderful ME-165 wattmeter

[Opcom]

It is a combined dummy load, wattmeter, and SWR meter. The dummy is twelve 600 Ohm resistors in parallel.

These are fine meters, at least the one here. Good 50 Ohms all the way to 30Mhz. The wattmeter mode looks like just a voltage measurement across the 50 Ohm resistance.

The thing about them is that they do not show the power level when in "Operate" mode. It's a disadvantage I would like to correct.

Explanation; There are four modes, selected by a switch; Power, Adjust, SWR, and Operate. The power meter is used only when the unit is set to "Power", and this is the dummy load position. the circuit and switch setup is more complicated than usual and there are warnings about lead dress so I'd rather not re-invent the wheel.

Has anyone done a good mod to let this unit show the power when in "Operate" mode?

[w8khk]

Patrick,

It appears that the meter is not connected to any input in the operate mode.  Power can be measured relatively accurately when the voltage across a known resistance is measured.  That is, when you measure the voltage across the 50 ohm dummy load, the power can be derived just by measuring the voltage.  It is not possible to measure power accurately by measuring the voltage across a load of unknown  impedance.  I assume that is the reason the meter is not used in the "operate" mode. 

If you wish to measure "relative power" when in operate mode, the RF voltmeter circuit used to measure power in the dummy load position could be used with minor modification.  And the modification would not alter the operation of the instrument when measuring actual power in the dummy load mode.  I would like to suggest two minor circuit modifications that would achieve this goal, but remember that the power reading in operate mode would not be accurate unless the actual impedance of the load is 50+j0. 

Looking at the schematic in the document you posted, disconnect the power voltmeter circuit from the dummy load by removing the connection of R13 and C3 from the dummy load, and instead connect these two components to the input RF connector, J1.  As a result, the voltmeter circuit used to measure power across the dummy load will always receive input from the respective transmitter output.

Next, on S1B rear wafer switch, add a connection between pins 8 and 11.   8 is the pin where output from the RF to DC circuit provides current to the meter in Dummy Load power measurement mode.  11 is the pin that connects this signal to the meter in operate mode. 

There should be no critical lead dress in making these changes.  The signal across the switch is just a DC current to drive the meter.  The signal to the RF to DC meter circuit is not critical in any way, and should not affect the other functions of the instrument.  Hope this helps!

[N8ETQ]

  Hey Patrick,

      I just "Series In" an old Griefkit HM-102
SWR/Watt meter with the output of my ME-165. The
cool part of the thing is that it lets you adjust
your tuner/antenna system without putting out much
signal. Less than a few watts or so.

      I can adjust my Johnson Flashbox for 1:1
SWR on the ME-165 and I don't see any deflection
of the watt meter on the Heath HM-102 or my Diawa
meter even on the 15W setting. Pretty Cool! Put
the ME-165 into the "Operate" position and it's
just a piece of wire and the HM-102 shows power
out and SWR if you want to mess with it.

      Here's a pix of my lash up, I know, pretty
sad. Been meaning to clean it up for years.


      There is a lot of asbestos in the ME-165.
I encapsulated my asbestos with a can of clear
spray lacquer years ago but the 610 can still get
it "Stinking".

GL

/Dan

[W2PFY]

I put one in line a few months back and just love the thing. On a good day, you can be heard with the one watt out feature. Makes tuning up a breeze! Great buy as most of the time they can be had for just over 100 bucks.