[TenTec] Eagle -- power measurement

[Jeramy Ross]

Here's a simple and cheape solution that is easily homebrewed:

http://k4eaa.com/dummy.html

73,
Jeramy W5XTL

On Sat, Apr 2, 2011 at 11:54 AM, Dr. Gerald N. Johnson
<geraldj at weather.net> wrote:
> While a 6AL5 and transformer could be cheap, the venerable HP 410B and
> 410C used a smaller diode in the AC probe and they also made a 10:1
> voltage divider and a coax tap adapter for this very purpose. So it can
> be had ready made.
>
> One other technique is to use a water proof dummy load submerged in an
> insulate water bath. Then monitor the temperature rise of the water. Its
> best if the water is circulated and you know the amount of water and the
> thermal mass of the dummy load. It can be calibrated by heating the
> dummy load with AC or DC that's more easily measured than RF power and
> setting the applied AC or DC power to achieve the same rate of
> temperature rise of the water. Then there's no math, the test power
> equals the applied Rf power. Called calorimetry and there are commercial
> products for that too though probably neither readily available or
> suited for 100 watts.
>
> Then there directional couplers with RF out that can go to an RF power
> meter and head like the HP 432 and 436 families. Where the head can only
> stand 10 milliwatts. And they can be used with a power attenuator. The
> 432 and previous work with thermistors biased to get their resistance to
> 50 ohms and the meter works by showing the reduced bias power required
> to keep the thermistor resistance to 50 ohms. The later 436 family uses
> thermocouples and load resistors sensing the temperature rise of the
> load resistors and are much revered in the microwave industry, but a new
> one with power head can cost the price an Eagle.
>
> 73, Jerry, K0CQ
>
> On 4/2/2011 9:46 AM, Roy wrote:
>> Don't dismay...there's a way.
>>
>> A 52-ohm dummy load with a rectifier and filter cap yields an accurate dc
>> voltage in proportion to the power being dissipated. Today's vom's and dvm's
>> are pretty accurate (average the readings of all your meters). The rectifier
>> can be a 6AL5 with its plates connected in parallel, and its heater
>> connected to its cathode, so the output voltage rating is high enough for a
>> kw. The plates are connected to the hot side of the dummy, and a 0.01 disc
>> in parallel with say a 1-uF connect to the cathode for a positive dc voltage
>> out with a hold time for peak readings. It's inherently self accurate and
>> requires no calibration.
>>
>> 73,   Roy     K6XK
>>
>>
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