Inexpensive fairly good quality home brew or kit RF power meter
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. |
Inexpensive fairly good quality home brew or kit RF power meter
" 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 |
Inexpensive fairly good quality home brew or kit RF power meter
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 . |
Inexpensive fairly good quality home brew or kit RF power meter
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 |
Inexpensive fairly good quality home brew or kit RF power meter
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Inexpensive fairly good quality home brew or kit RF power meter
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. |
Inexpensive fairly good quality home brew or kit RF power meter
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Inexpensive fairly good quality home brew or kit RF power meter
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 |
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