I kinda like the ideas presented. This maybe the more precise one though
more difficult. The measurements can be taken and insrted into a program.
Jim:
You mention a "... RS232 DVM, an RS232 controlled transceiver ... "
. Now, I not being very up on the latest technology would like some more
data. The RS232 DVM, would the Radio Shack (RS) 2200805 24range digital
multimeter be what you are suggesting. I need to buy some equipment for the
shack but how do I do it so that I can use it for many other things??
Starting back into haming my IC735 bit the dust (second
hand). Unforunately, fortunately, my mother died and my wife did not want
any of the money from the sale of my mother's house. So I bought a new,
yes, new rig, the first that I have ever had, and probably the
last. However, just starting back again, I forgot about that the second
most important part of the shack is the antenna. So I am trying to
re-learn about the antenna system. With help of some of the more
knowlegable hams I am so doing. I am now casting about on how to build
some of the antenna garden without too much expense. I though that growing
my own would be the better way to go. So I am asking many questions.
Thank you for your input.
Chris opr VE7HCB
At 01:00 PM 2002-05-04 -0700, Jim Lux wrote:
>One can make quite accurate impedance measurements using the "three meter"
>approach at very low cost. Essentially, you hook a capacitor (chosen to
>have an impedance around 50-100 ohms at the frequency of interest), a
>resistor (50 ohms), and your unknown all in series and drive it from an RF
>source at the desired frequency (low power... a couple of volts is good).
>You then measure the AC voltage across each component, and, with a bit of
>math, can turn that into R, X, etc... (this is essentially what the
>analyzers are doing).
>
>Ideally, one would like a good detector diode(s) for all this, but, one can
>use 1n914 diodes, especially if you have some more drive voltage available.
>You also will need some calibration standards (nonreactive resistive load, a
>short, and some reactive standards, which can be made from transmission line
>of known properties)
>
>This has been written up in the antenna compendia in several of the
>volumes.. Modern computers make it MUCH easier...
>
>A RS232 DVM, an RS232 controlled transceiver, and some relays controlled by
>the printer port could make the whole thing automated.
>
>If you have a LOT of motivation, you could also make very precise
>measurements by using the sixport technique, but calibration is tedious and
>the math a bit complex, however, six port networks are the standard by which
>other techniques are compared. The NIST web site has a fair amount of
>information on this.
>
>----- Original Message -----
>From: "Chris BONDE" <ve7hcb@rac.ca>
>To: <towertalk@contesting.com>
>Sent: Saturday, May 04, 2002 10:43 AM
>Subject: Re: [Towertalk] Antenna Analyzer Suggestions?
>
>
> >
> > >The MFJ-269 has a 12bit A/D converter whereas the 259B only used
> > >8 bits to digitize the detector voltages. From what I have heard this
>gives
> > >the 269 more accuracy at high and low values of impedance when
> > >compared to the 259 (the 269 over-ranges at a much higher impedance
> > >level than the 259).
> > Is the MFJ the only analyzer or is it just superior?
> > What other measuring devices can be used if the budget does not support
>the
> > MFJ269 plus stuff. (Close to CA$800 landed) (Or close to 3/4 gross
>monthly
> > pension)
> >
> > Chris opr VE7HCB
> >
> >
> > _______________________________________________
> > Towertalk mailing list
> > Towertalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
|