Re: IK3OIL fll board.
Many thanks for that Arv, I guess I was just being a bit lazy and not being
bothered to work it out properly.
Half the problem will be the fact that I'm using a core that was salvaged
from a computer psu so it isn't a fully known entity. I have a rough idea
what it should be like going by size and colour so I will have to do the
basics and then try it in circuit to see if it behaves as expected As you
say, only if the core is completely different will it make the calculations
Mark. yes, I knew I had the vfo board from Sunil, I knew I would have to
wind the coil so when I saw the figures for the inductors and capacitors I
just knew I had to save them. Now do like my wife does. 'Put in a safe place
for later', and it turns out so safe nobody can ever find it again!
Thanks for the other link as well. I think I'm going to have to relearn
stuff that I forgot again...
From: Arv Evans [mailto:arvid.evans@...]
Sent: 28 September 2011 02:51
Subject: Re: [BITX20] Re: IK3OIL fll board.
Maybe I can help relieve some of the frustration you have expressed?
It is rather easy to scale resonant circuit components up or down in
frequency. The trick is in maintaining the same LC ratio so that RF
impedances will be the same in the new layout as they were in the
original. This is the process that was used with the original BITX20A
to make a BITX17A, BITX30A, BITX40A, BITX80A, BITX160A, and even
a BITX1750A for the US LF experimenter's band.
To make this work you will need to calculate the impedance of each
frequency dependent inductance and capacitance in the original circuit.
Once you have that information documented, you can then calculate
new inductances and capacitances based on the new frequency.
There are many useful L, C, F, and Z calculators available on-line.
I particularly like the one at:
but that is just a personal preference because it also tells me how
many turns I need on a particular toroid core to build the new
inductors. It also simultaneously tells me both L and C values for
a specific impedance at a particular frequency.
For example, lets say we have a tuned circuit that works at 5.0 MHz
in it's original configuration, but we want to make that work at 3.75
MHz in a new configuration. If the original network used 64 pf and
16 uh to resonate at 5.0 MHz, the L and C would each have an
impedance of 500 ohms at that frequency. We can prove that by
entering 16 uh and 64 pf into the calculator to get the 500 ohms
impedance for L and C at resonance.
If we want to find the equivalent impedance C-value for 3.75 MHz
we just enter 3.75 MHz and 500 ohms into the calculator and it
shows 85 pf as the new C-value. At the same time it shows the
matching 500 ohm impedance L value to be 21.2 uh.
There are some possible traps to take into account. If the new
inductor is quite different in R-value (wire resistance) or if the
Q-factor of the new inductor core is significantly different, the
bandwidth may be different between old and new configurations.
But in most cases these are not different enough to cause any
On 09/27/2011 05:46 PM, G0JKZ wrote:
Sent: 27 September 2011 22:09<mailto:BITX20%40yahoogroups.com>
Subject: [BITX20] Re: IK3OIL fll board.<mailto:BITX20%40yahoogroups.com>
<mailto:BITX20%40yahoogroups.com> , "G0JKZ"