Inexpensive fairly good quality home brew or kit RF power meter

" snipped-for-privacy@yahoo.com" wrote in news: snipped-for-privacy@a70g2000hsh.googlegroups.com:

: snipped-for-privacy@a70g2000hsh.googlegroups.com:

The signal is AM with a duration of .50 sec. and there is some type of digital alarm transmission which modulates the carrier

That sounds like a complex transmission , measuring the incident voltage over the 50 ohm load may be the only way , may be hire something expensive to get a calibration chart ?

G .

Graham wrote in news:329ab6b5-154c-4ee2-a6b7-77f841f27cf6 @f36g2000hsa.googlegroups.com:

One of the kits on the page I referenced could be the basis for his power meter. There are others in _The Radio Amateur's Handbook_ that would work. What he may need is probably to use a computer A/D card (possibly the audio card) to capture the waveform. Then to numerically integrate that over the time period of interest.

A simpler way would be to read the peak voltage across the load. That can be done with a simple diode detector probe. That would give the peak power with a simple calculation.

Nothing expensive is needed to get an accurate peak power reading.

A diode, a couple of small capacitors and a resistor will make a fairly accurate peak voltage probe. Elecraft has a low price kit.

A couple of 100 Ohm surface mount resistors of the appropriate power rating, soldered in parallel will give a very good, low reactance 50 ohm dummy load that should cover the frequencies of interest.

Or 20 each, 1000 ohm resistors, 10 watt resistors (non inductive) in parallel for a 200 watt 50 ohm dummy load.

P=V^2/R; V=sqrt(P*R); easy enough to make a calibration chart: v p 15.81 5 22.36 10 27.39 15 31.62 20 38.73 30 44.72 40 50.00 50 61.24 75 70.71 100 74.16 110 77.46 120

Some thoughts:

1. find a bolometer head that covers your frequency of interest on eBay and build the rest of the meter (or perhaps buy the whole thing if cheap enough).

1. look for old military RF power test sets that included a mess of attenuators, directional couplers and a bolometer head together with the meter in a steel case (used to be very cheap and readily available but perhaps times have changed).

2. build something out of the ARRL handbook.

Michael

Do you have access to a scope that has a decent response at 72 MHz? That and an accurate dummy load should be enough.

If you have a "Boonton" why arn't you using it ?

This is just the thing , analouge vswr bridge head , with conditioning amps , just need to measure the o/p voltage, with what ever , job done :)