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Old 2nd Oct 2016, 3:02 pm   #1
Wendymott
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Default RF Power meter (AD8307)

Hi Peeps. While building my SSB exciter and PA... I realised I had no method of checking the RF Power output, or "Relative" power. Thus I started a search on the tinternet and came across various projects and modules using the AD8307 device. I purchased a module from the far east, and also a number of chips only, to make my own, using a circuit by FOXDELTA. Being a canny yorkshire person with lots of spare time, I made my own pcb, bought the 16F876 PIC which I programmed from the files published. The original file date was 2002, but a recent 2008 file was also downloaded.

The main thrust of my query is this.. The Power meter uses 2 X AD8307, one for RF measurement and the other for Reverse voltage in a SWR meter bridge. However both have an input resistive divider of 3 x parallel 100R in series with the input and 3 X parallel 100R to ground, thus giving an input R of 33R. Now you and I know that most circuits chose or use 50R as the terminal impedance.
I looked at the complete module and that has a 50R input impedance.
I can only assume that the software writer used an "odd" lookup table for 33R instead of 50R.
Has anyone "out there" either bought a module or tried the FoxDelta module and what conclusions were made.
I am quite impressed with the display data, and I am loathed to start again.
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Old 2nd Oct 2016, 4:44 pm   #2
ms660
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Default Re: RF Power meter (AD8307)

Ignoring the amplifiers input impedance I make it approx 66 Ohms?

Lawrence.
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Old 2nd Oct 2016, 10:03 pm   #3
Wendymott
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Default Re: RF Power meter (AD8307)

Ooops how clumsy of me..... grrrr Thanks Lawrence....
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