LF Stuff

Frank Gentges fgentges at mindspring.com
Wed Oct 1 21:39:47 CDT 2003


I checked out your web page a bit.  You sure look like a member of  
AMRAD with all your interests and activities.  I  note you still have 
your  Ford Cobra.  I almost bought a 289 version in 1966 but in the end 
I did not go over to the dealer to look at it.  My boss was trying to 
get me to get it as it was the last one of the 289s and it was priced 
really right.

I see you have some really good impedance test equipment and use some 
nice techiques to expand the useage.

I have an old 4815A here and its design inspired the work you saw.  I 
would like anyone with a few hunded dollars to be able to measure 
impedance magnitude and phase up through the HF band.  This could really 
help in dealing with LF designs and help to kick up the quality of work 
a notch.

Larry Kayser's program is a serial port program for the PIC.

We discovered that some silicon rectifier diodes create sharp current 
pulses at the point the voltage goes through zero and conduction turns 
off very abruptly.  This in turn can generate some hash at least in the 
LF range.  A 0.01 or a 0.1 ufd disk capacitor across the power 
transformer secondary or better yet at the diodes can suppress this 
hash.  It was supposed to be added to the design but the change got lost 
and then did not prove out to be a problem on all diodes.  Higher PIV 
diodes seem to be worse.   I did not push the change but in retrospect, 
I should have.

There is a good low pass filter we put into our LF converter covered in 
the April 2002 QST.  The PC is seperate so you can order the PC alone 
without the converter board.  I have measured pretty good ultimate 
rejection with the massive ground plane used on the PC.  This filter can 
keep some pesky AM BC signals out of your LF receiving gear.

Since LF was denied by the FCC we have been concentrating on 
understanding the impact of Broadband on Powerline transmission of high 
speed internet and the interference of ham radio on it.  It  looks like 
hams and this technology may have some problems living together.

Frank K0BRA

Brooke Clarke wrote:

> Hi:
> I had a look at you web page for LF and have some comments.
> LF Impedance "AMRAD Presentation on LF Impedance Measurement"
> _______________________________________________________
> The method in the paper is very similar to the one in HP patents 
> 5,345,182 and 5,463,323. I think these were for the 4191A Impedance 
> Analyzer. A classical bridge has the measuring instrument connected 
> with both ends above ground and that's not so good for RF 
> measurements, so a balun can be used. . . .
> I have been making some measurements on how the characteristic 
> impedance of a transmission line varies with frequency when the 
> frequency is below the line corner frequency. To make these 
> measurements in the 10 Hz to 500 kHz range I have been using the 
> HP/Agilent 4395A Network Analyzer and the Z Transformation method. See:
> http://www.pacificsites.com/~brooke/Zo.shtml
> http://www.pacificsites.com/~brooke/4395A.shtml#ZT
> The Z transformation method measures the DUT connected in series 
> between the center conductors of a normal network analyzer test setup 
> , like an S21 measurement. Then the analyzer does the math to convert 
> the result into impedance and can be displayed as Lin Mag, Log Mag, 
> phase, real or imaginary. The beauty of this method is that it can be 
> used over the full 10 Hz to 500 MHz range of the 4395A. Note that the 
> 43961A Impedance test kit only works above 100 kHz. The 43961A uses 
> the technology of the above patents. It may be possible to home brew a 
> version of the 43961A that would work lower in frequency.
> The Z Transformation method is what's used in the HP/Agilent E5100 
> series High Speed Network Analyzers that are specifically designed for 
> crystal characterization.
> PS the spiral graphic in this paper takes a very long time to 
> download. A plain white background pdf version would make net viewing 
> a lot less painful.
> Larry Kayser’s,, PIC Program .ASM file
> ________________________________
> What does this program do?
> Low Pass Filter?
> _____________
> The reason I Was on this page was to find details of a low pass filter 
> to use with your active LF antenna which I now have.
> Have their been any updates on the power supply to reduce the line 
> conducted noise that I found with the original design?
> 73,
> Brooke Clarke, N6GCE
> http://www.PRC68.com

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