[Hallicrafters] Measurement of Low Resistance

[Roger D Johnson]

Al Parker wrote:
> Hi David,
>     It sounds like you're a candidaate for an ESR meter (Equivalent Series
> Resistance).  They're great for measuring electrolytic filtering
> effectiveness.  Garey Barrell put me onto them about 4 yrs ago and showed
> me his.  They measure in 100ths of an ohm.  I use mine regularly.  Here's
> what I've written abt them b4:

> ----- Original Message ----- 
> From: "David C. Hallam" <dhallam at rapidsys.com>
> To: "Hallicrafters List" <hallicrafters at mailman.qth.net>
> Sent: Monday, August 22, 2005 2:16 PM
> Subject: [Hallicrafters] Measurement of Low Resistance
> 
> 
> 
>>Several months ago someone posted a link to an article in an old
> 
> electronics
> 
>>magazine (on this list I think) on a practical method to measure low
>>resistances.  I thought I saved the article, but I can't find it on my
> 
> HD.
> 
>>Does anyone remember this article or a similar one?
>>
>>I have an old transmitter I am restoring and want to check some ground
>>connections to see if they are really at ground.
>>
>>David C. Hallam
>>KC2JD

The problem with ESR meters is that there is no way to compensate for
the resistance of the meter probes in the circuit to be measured.
Without knowing that you have good zero resistance contacts, the meter
reading is suspect.

One way to check the resistance between antenna elements is to hook up
a power supply and pass a known current through the junction. Measure
the voltage drop between the tubing sections and compute the resistance.
In this case the resistance of the power supply connections is not
relevant as long as they allow sufficient current to flow. Using a
high Z meter to measure the voltage insures that contact resistance
of the probes is not significant. This is usually referred to as the
4 terminal method.

I'm sure you could come up with some variation that would allow the
measurement of small resistances on a chassis.

73, Roger

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