Heath Cantenna

[John Farrington]

On 9/3/04 Jim K8DHC wrote on the Heath list:

 >Can anyone pass on to me what the DC output voltage to power is for
 >the Cantenna dummy load?
 >Thanks  Jim K8DHC


Heath Cantenna Model HN-31 (schematic sent via direct Email):

For "DC output voltage", I presume you are talking about the RCA output
jack on the small input box on the lid, opposite the 50-ohm RF input:

this jack outputs a small DC voltage that is a reduced, rectified and
filtered sample of the RF input;  however, I don't believe Heath ever
printed any table of input power to output voltage, as this DC output
was intended to be fed to any DC voltmeter to provide "only a relative
power indication" (according to the manual) - that is, you can watch a
DC meter go up and down as input power varies, but it's uncalibrated
and will also vary with different meters and SWR on the RF input line.

One can make ball-park estimates of what the DC output voltages might
be, but they may be way off - you would have to make multiple input
and output measurements with your own test equipment to find actual
readings for your stuff:

the voltage divider values suggest that with 1000 watts RF input to
the 50-ohm dummy load and no SWR, the AC input voltage to the 1/2 wave
germanium rectifier would be around 2.24 V RMS, or 6.33 V peak-to-peak,
or 3.17 V peak;  the DC output voltage buildup on the .01 ufd cap would
then depend on the loss across the diode and what kind of a load the
external DC voltmeter presents, so meters with different impedances
would show different voltages at any given input power level. With no
meter load at all the cap might charge up to near the peak value
minus the voltage drop across the diode, maybe around 2.7 to 3.17 VDC
at 1000 watts, but only an imaginary scope or meter with infinite
input impedance could show that.  Real-world measuring equipment
would show less: a VTVM would drag it down, and a straight DC meter
movement would drag it down considerably more.

More calculations suggest 500 watts might present about 1.8 to 2.23
VDC peak to the filter cap, and 100 watts might present about 0.6 to
1 VDC peak, but, as I mentioned, meter loading would then drag those
values down. As you can see, the DC outputs would not have a linear
relationship to the input power levels.

An of course, I may have made some arithmetic mistakes.

73

John   KE5ZB

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