[SPAM] [Elecraft] K2 - signal loss in band-pass filter

[Geoffrey Mackenzie-Kennedy]

Dave,

If you "jack up" the the type of 8V regulator used in the K2 by adding a 
diode in series with the regulators ground lead, have you found any sign of 
oscillation at the regulator's 8V output terminal?  Also, if my memory is 
working properly, the regulator's ground lead is connected to its heatsink 
tab which would require that an insulated thermal pad be added and 
non-conductive (DC) hardware used for mounting the regulator.

In my opinion the reverse connected diode which you mention as a protective 
device should always be used with these three terminal voltage regulators.

FWIW the regulators made by Motorola or ST which I have purchased from 
Farnell in the past have always produced the correct output voltage be it 
5V, 8V, 10V or 15V, both positive and negative.

73,
Geoff
GM4ESD

David Lankshear G3TJP wrote on Tuesday, June 03, 2008 at 10:00 PM



>From postings on the reflector, it would seem that more than a few of K2 8v 
>regulators are on the low side, including mine.

I've just ordered a couple from a local supplier to see if they are any 
better, but if they are not, I will "jack up" the ground lead of the 8v 
regulator by connecting a diode in series with it - i.e. interposed between 
the regulator's ground lead and the ground it was connected to.  A silicon 
diode like a 4148 (or 4001 to 4007) will effect about a 0v6 increase in 
output voltage and a schottky or germanium diode will give about 0v2 to 0v3 
increase.

Of course, this "jacking up" compromises the regulator's inbuilt short 
circuit protection but in a stable environment like the K2 it can either be 
accepted that it is unlikely to ever be called to work into a short circuit, 
or a reverse connected diode can be introduced between output and ground as 
protection.

73   DaveL  G3TJP