Re: 1000 Miles/watt awards


From: Jim W7LS (
Date: Mon Aug 04 1997 - 17:02:37 EDT

Oopsie, Ed...... Check your formula again for power. :-)

Comments below in the text...

At 01:18 PM 8/4/97 -0700, you wrote:
>Hi Homebrew and QRP-L folks, I'm done determining
>the ouptut power of my Pixie2. Many thanks to all
>who sent excellent suggestions via email. I thank
>each and every one for the comments. I have no o-scope
>so am stuck with the voltage measurement. Now that I've
>researched the internal design of the 8471A Detector, I
>realize the measurements were BOGUS. However, the output
>power of the pixie2 was still low. Read on.....
>The detector is the HP8471A (Correct Part Number), which
>incorporates a 'Point Contact diode'.
>Here's what I found out last night.
>1. The 8471A has an internal 50 ohm load. So I didn't
>need to load the pixie2.
>2. I had used a 100 pF cap on the collector of Q2 instead
>of the .1uF originally designed. Big mistake -- That's where
>the power loss was!!!!!!!!
>So Here's What I got:
>Original transmission was at 69.7 mW (100 pF coupling cap)
>Measured 1.32 Volts out of Pixie2 with xtal detector.
>Peak Power=(1.32/.707)^2/50=69.7 mW
>So 637 Miles/.0697=9139.17 Miles/Watt (I really Believe this)
>PIXIE Coupling Cap changed BACK To ORIGINAL .1 uF:
>(Broadcast noise Bad again)
>Measured 2.52 Volts out of Pixie2 with xtal detector.
>Peak Power=(2.52/.707)^2/50=254 mW

Power formula should be as follows:

Peak power is Peak TIMES .707, then squared, then divided by 50 ohms.

So, (2.52*.707)^2/50=63.5 mW (again, by shear luck!!)

Now, the miles per watt should be 637/.064=9,953 miles per watt...

Hey, knock the cap down a bit more and let's go the the 10K award!!!!

>This all on 7.04 MHz Xtal.
>On 3.579 and 3.6864 I got 2.85 V or 324 mW.
>Thanks one and all.
>-Ed Loranger
>72/73 de we6w qrp es cw ONLY (From non-ham to extra in one day!)
>HW-8;OHR-100, Pixie2, Johnson Viking II w/VFO.
>QRP-L#1068/Norcal#2227/ARS#275/ARCI#9397 grid CM88ok

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