On Thu, 27 Jan 2005 16:12:27 -0800, Richard Clark
wrote:

On Fri, 28 Jan 2005 12:13:51 +1300, MikeN
wrote:

That's an interesting dissertation Richard, but I'm not sure that it
readily suits my needs.


Hi Mike,

Well, you are going to have to make up your mind. In one post you
want a simple instrument, in another post you are fishing for answers
with an antenna analyzer (but you don't have a FSM?). That seems to
me to be at least a 10dB variation in $$$. Now if the spec is that
loose, I can up the ante another 10dB to give you a direct reading
answer.

How much are you willing to spend?

73's
Richard Clark, KB7QHC

Hi Richard

Well that calorimeter is a simple instrument, but how can I apply my
simple knowledge to give a meaningful result.

Would it go something like this?

1. Take a polystyrene cup packed in a piece of polystyrene foam,
and with a polystyrene lid.

2. Pass a piece of thin - say RG174 - coax through the lid.
Run the centre conductor through the bead and wrap back around bead
and solder to to braid.

3. Immerse the bead in say 150 cc of H20 - initially at freezing.
Use an in-glass thermometer to measure temperature. Apply some 70 cm
rf from my handheld (on low power).

4. Measure the rf voltage across to the coax at the ferrite bead
using a simple diode detector - calibrated to give RMS applied
voltage E.

5. Measure the temperature rise with time until a steady state
above ambient temperature is reached.

6. Replace the ferrite bead with a resistor, and apply DC voltage
same as E to get the same temperature rise in the same time period.
Change the resistance value as necessary to get the same temperature
rise over same time.

7. Dummy load is now dissipating the same power as the ferrite
core did.

8. Calculate the impedance from Z=E^2 / W.

9. Repeat to see if results are reproducable.

10. Substantial inaccuracy will result from differing thermal mass
of bead and resistor. Bead is 29mm long, with 16mm OD, and 8mm ID.

11. So what should I do to refine this procedure?. What am I
missing here?

I'd like your comments.

Thanks

MikeN, ZL1BNB