[PVRCNC] [PVRC] MFJ-259B inductance measurement

[James Jordan]

Mike,
My experience is the MFJ-259b is a great tool which I have used for many years for SWR and the like but a precision bench instrument it ain't. I tried building some coax traps and had the same problem. It works best with empirical testing. Get the coil close and see how it matches. Of course that may not be easy going up and down the tower! Measuring resonance with known high precision capacitance and calculating from that like a GDO may work but lead effect is still a factor. Experiences of a tinkerer, not an engineer....
73,
Jim

Sent from my iPhone

> On Sep 13, 2014, at 7:02 PM, Mike Barts <mike at bentwire.net> wrote:
> 
> I'm building some loading coils for my 40m beam. I designed the coils using several of the online calculators as sanity checks. The final design is built using 1/4" copper tubing, 5" air coil supported by two 3/4" strips of Delrin. The design inductance is 2.64 uH. When measured by my MFJ-259B in inductance mode, it's measuring a little over 4 uH. I've got the inductor suspended by a string, hanging in the air in the garage to minimize coupling. Anything metallic (except the -259B case) is at least a foot or two away. The lead lengths to the MFJ-259B are about 6" long.
> 
> Are there any known issues with inductance measurements with the -259B? (yes, other than it being an MFJ product....) While I didn't expect an on the money inductance, 4 vs 2.6 is a big error. Don't think the lead lengths are THAT long to add almost 2 uH, and I don't think my inductor design is THAT far off.. Looking to see if I'm missing something obvious or there are issues I'm not cognizant of. All suggestions, other than trashing the -259B, welcome.
> 
> 73, Mike N4GU
> 
> 
> ______________________________________________________________
> PVRC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/pvrc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:PVRC at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html