I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

" wrote in
:

I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

http://www.elecraft.com/mini_module_...ni_modules.htm



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

On Apr 18, 11:26*pm, bz wrote:
" wrote :

I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, *a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

http://www.elecraft.com/mini_module_...ni_modules.htm

--
bz * * *73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

* remove ch100-5 to avoid spam trap

..

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:

On Apr 18, 11:26*pm, bz wrote:
" wrote innews
:

I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, *a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

http://www.elecraft.com/mini_module_...ni_modules.htm

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 ?


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





--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

wrote:
I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

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).

2. 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).

3. build something out of the ARRL handbook.

Michael

On Apr 18, 9:29*pm, msg wrote:
wrote:
I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, *a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

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).

2. 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).

3. 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.

wrote:
I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.



http://www.ramseyelectronics.com/cgi...ction&key=PM50

wrote:

I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

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

--
Best Regards:
Baron.

On Apr 19, 3:48*pm, Baron
wrote:
wrote:
I have a need for a power meter for general low band and VHF work. I
would like it to have at least two scales. One, *a 0 - 10 W or so
scale and if possible another which would enable it to measure up to
around 125 W as well. The immediate need to satisfy the requirements
of a job we're doing is for an instrument that can measure 1.0 W at
72.0 MHZ. The signal is AM with a duration of .50 sec. and there is
some type of digital alarm transmission which modulates the carrier.
The only way I think that I can do this now is to measure the RMS
voltage accross a 52 ohm dummy load with my Boonton, and then
calculate the power. I feel though that this is clumsy and may be
potentially inaccurate. I'd love to have a Bird with all the bells and
whistles but I really can't afford one. Does anyone know of a home
brew project for doing this or even an inexpensive accurate kit?
Thanks, Lenny.

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

--
Best Regards:
* * * * * * * * * * *Baron.


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

http://business.listings.ebay.co.uk/...istingItemList