Narda 1970's Isotropic Radiation Monitor

[joeqsmith]

Pictures are of an old 70's broadband isotropic radiation monitor.   The 300MHz 20mW/cm^2 H field probe was the only one included with the set.   

The plastic selector knob was gone but the metal insert was still on the unit.   The knob shown I believe was from an old HP scope.   The rest of the unit appears original and in near mint condition.      The battery still had a very small charge but would need to be replaced. 

[joeqsmith]

Showing the model 8631 10-300MHz H field probe.   Also shown is a page from the manual that shows the basic construction.

 

[joeqsmith]

Pictures showing the model 8616 radiation meter.   The paint cracked when I removed the cover.  I think this is the first time this unit was taken apart.

[joeqsmith]

The battery pack appears to be no longer available.     

[joeqsmith]

I doubt you would find too many wooden spacers in a modern battery pack.

[joeqsmith]

Even though the manual talks about running the unit from AC, it would not run without the battery pack as there is not enough filtering on the supply.   Picture showing the original mount for the probe. 

Short clip of the unit now running.   
https://www.youtube.com/watch?v=2iOCgbWuvwc&feature=youtu.be

[sarepairman2]

it looks like a hitachi magic wand lol.

I have seen similar things in a RF  compliance laboratory.

[joeqsmith]

it looks like a hitachi magic wand lol.

I have seen similar things in a RF  compliance laboratory.

Certainly had enough batteries.

The book refers to ANSI C95.1-1974 "Safety Level of Electromagnetic Radiation with Respect to Personnel"   
They have a lot of notes warning the user to make sure they know the field levels before just blindly walking into them.   

At 20mW/cm^2 (the probe's rating), that would be a field strength of 274 Volts/meter.   When I worked in automotive, we would test at 100 Volts/meter.   I was at a lab for some outside testing that was capable of 1000 V/m. 

[cdev]

"isotropic radiator" ?  My money is on that being a marketing ploy.. 


It looks very high tech, though. I agree it does look a lot like a vibrator..

The design of the probe is kinda interesting from a DIY point of view, though, IMO.

are the wires implemented in the form of flexible PCB or minicoax? (can you tell?) It is possible to make conductive foam of course but since its doped with carbon, that stuff is always black.

Maybe those capacitors in the diagram are supposed to indicate a sort of "moebius strip" topology? 

just guessing..

okay, I admit it, I like strange looking antennas..

[joeqsmith]

I did not try to take the antenna apart but the manual does a fair job explaining things.   There are three orthogonal thin-film thermocouples inside it.  They claim +/-0.5dB except when the handle is aligned with the field. 

The current model looks a little more high tech.
http://www.rf-safety.com/pdfs/SRM3000.pdf

[sarepairman2]

oh, so its a thermal RMS meter?

I thought the thermocouple provide compensation, kind of like in a advanced fluxgate transformer, granted a thermally compensated antenna is some next level shit

[joeqsmith]

oh, so its a thermal RMS meter?

I believe that is correct.