[Elecraft] [K2] Inductivity of Toroids

[Don Wilhelm]

Brian,

The K2 toroids are specified in the manual for a given number of turns 
on the proper core rather than their absolute inductance.  The only 
reference to the inductance is on the schematic and in some instances on 
the parts list.  What I can say for certain is that whatever the 
resulting inductance may be in your measuring jig, the manual turns 
count works just fine.  I have had repair experience with over 1000 K2s 
and in all cases, the toroids work well with the specified number of turns.

I really do not have that detailed information, and I doubt if Wayne 
remembers the "details" either.  What I do know is that the toroids with 
the specified number of turns do work and work quite well.  As I 
indicated, the inductance of the LPF toroids is the most important 
because an extra turn will cause HI CUR messages on the upper band of 
the band pair.  The RF Chokes are tolerant of an extra turn.

73,
Don W3FPR

On 1/1/2013 9:54 AM, Brian Alsop wrote:
> 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