EMRFD Message Archive 12753
Message Date From Subject 12753 2016-04-29 12:20:42 peter_dl8ov UHF Power Meter Detector Diodes I want to build a simple power meter to measure the output of a 70cm amplifier. Can someone suggest a suitable detector diode?
Power is 100W but this is sampled down to a more manageable level.
12754 2016-04-29 14:02:34 K5ESS Re: UHF Power Meter Detector Diodes
12755 2016-04-29 14:20:32 Phil Sittner Re: UHF Power Meter Detector Diodes Peter-
I have found that several Chinese sources sell the AD8307 log amp for around $1.00 each. If you build a simple resistor divider and add an inexpensive voltmeter you'll have a very accurate and simple power meter. I have purchased the AD8307 from several of the Chinese sources and found them all to work fine.
12756 2016-04-29 14:23:58 kerrypwr Re: UHF Power Meter Detector Diodes I spent some time one-finger-typing a reply but Yahoo seems to have devoured it. :(
The essence was, as Mike said, a Schottky diode; I've found that the ordinary leaded 1N5711 works fine in measuring 5 watts at 477MHz. That's the highest frequency at which I can generate "real" power and it probably works at higher frequencies.
In that "lost" post I suggested a coupler to "tap" from your 100 watts but I've since realised that a ferrite coupler won't go that high in frequency; there are other ways to reduce the voltage to below the 1N5711's maximum rating.
12757 2016-04-29 14:36:58 kerrypwr Re: UHF Power Meter Detector Diodes My little power meter, seen here on the left;
uses a 1N5711;
It's accurate up to at least 477MHz, which is as high as I've tested it, and SWR looks like this;
This seems to indicate that the 1N5711 will do your job provided, as you propose, the voltage is kept below the maximum rating of the diode.
I use home-made couplers like this 30dB one;
but there are other methods.
12759 2016-04-29 15:14:35 DuWayne Schmidlko... Re: UHF Power Meter Detector Diodes There are a couple VHF UHF power meter projects at
12764 2016-04-29 21:31:49 Bill Carver Re: UHF Power Meter Detector Diodes Or get the Analog Devices "RF Detector Surf Board Kit" from
RichardsonRFPD. The populated board has an ADLS5902 .05-9 GHz true RMS
detector, an ADL5512 .001-4 GHz 80 dB range logaithmic detector, and an
ADL5511 DC-6 GHz 47 dB range Envelope/RMS detector. RIchardsonRFPD was
selling the board ("ADL5XDETECTRKIT") for $5 plus shipping.
12765 2016-04-30 01:01:25 peter_dl8ov Re: UHF Power Meter Detector Diodes Thank you for all of the replies, I just purchased some 1N5711 devices and they work quite well at 70cm.
12772 2016-04-30 15:44:25 K5ESS Re: UHF Power Meter Detector Diodes
It appears the price has gone up to $10 now.
12773 2016-05-01 01:30:33 LEON HELLER Re: UHF Power Meter Detector Diodes I got two of them for $20. Shipping to the UK was a lot more.73, LeonG1HSM 12774 2016-05-01 06:36:10 Bill Carver Re: UHF Power Meter Detector Diodes Re the Analog Devices RF Detector board, I got two for $10, plus $15
shipping inside the USA. Kept one, gave one to W7OUU who's a
moonbouncer/meteor scatter guy and breathes rarified GHz air regularly.
12778 2016-05-02 06:04:14 Nick Kennedy Re: UHF Power Meter Detector Diodes I wonder if the OP was after something so exotic. I was visualizing a simple peak detector that could be calibrated in watts.I don't think I've ever seen the square law compliance of a diode used in a ham power / SWR meter.73-Nick, WA5BDU 12783 2016-05-03 14:39:41 peter_dl8ov Re: UHF Power Meter Detector Diodes Your guess was correct, all I was seeking was a relative indication of 70cm output power using a cheap edge meter. a 10 USD board would have been a massive overspend.
12787 2016-05-04 00:03:19 kerrypwr Re: UHF Power Meter Detector Diodes For interest, Peter, how did you "tap" the 100 watts?
12838 2016-05-17 12:39:00 peter_dl8ov Re: UHF Power Meter Detector Diodes Correct, see the W7ZOI RF power meter for details.