[Elecraft] [K2] Inductivity of Toroids

[Fred Townsend]

Brain, let me amplify a little on what Don said. 
First most laboratory inductance bridges measure at a 1000 Hz. A few will option to measure at 1 MHz.
Second, the core material used here tends to act like a bandpass filter because it has an upper and a lower cut off frequency. If a measurement is made at a frequency below the cut off frequency it will vary considerably.
Third, because of parasitic capacitance, all inductors will resonate at some frequency.  Parasitic capacitance is a combination of the winding technic and test configuration.  Resonance will effect measurements tremendously. 
 
All these factors combine to create a large zone of uncertainty. The uncertainty increases with frequency increase.  A RF circuit designer will estimate circuit vales but will 'tweak' those values in once the real circuit is built. I have heard Eric speak of this experience. Many times the original estimates remain on schematics because absolute values can not be measured. This why some specifications rely on a 'brass board' as the absolute standard rather than paper standards. 

Test bridges are useful for comparing a lot of same type components but will otherwise accumulate dust in a RF lab.

73,
Fred, AE6QL
-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Brian Alsop
Sent: Tuesday, January 01, 2013 6:54 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] [K2] Inductivity of Toroids

Don,

Interesting that one never knows just how the quoted inductance is determined.

Do you have any idea just how the Elecraft quoted inductances are determined?

If measured, what frequency and test jig.
If based upon calculations, how much as built variation will there be.

Have had the same problems as Daniel.  The objective of my measurements is usually to determine the the toroid is the right one.  Color aside, there are so many bad/counterfeit parts out there, I want to detect such a beastie before installation.

73 de Brian/K3KO


On 1/1/2013 14:37, Don Wilhelm wrote:
> Daniel,
>
> The inductance of the RF Choke toroids measured at DC or low 
> frequencies may not agree with the published inductane which is 
> measured at a higher frequency.  Those RF Chokes are not critical, 
> they just need to block the RF flow and the bypass capacitor takes care of the rest.
>
> The inductors that are critical are those in the Low Pass Filter. In 
> any case, wind them as instructed in the manual and spread the turns 
> over 85% of the core and they will work.  There are over 7000 K2s out 
> there working fine with the toroids wound as instructed in the manual.
>
> 73,
> Don W3FPR
>
> On 1/1/2013 9:14 AM, Daniel Heise wrote:
>> Dear K2-Experts,
>>
>> I´m just assembling my K2, and it´s true: It really is addictive :) 
>> After winding my first toroid inductors, I measured their inductivity 
>> with an atlas LCR40 component analyser before I soldered them into 
>> the RF board.
>> Though I closely adhered to the manual, the measured inductivities 
>> are almost twice as high than the values stated in the manual (on the 
>> parts list in appendix A).
>>
>> It was good to read on the elecraft homepage, that the inductivities 
>> are not too critical for the entire function of the transceiver. But 
>> I´m still wondering if anyone else measured the inductivities of the 
>> toroid inductors and made similar experiences...