Re: IK3OIL fll board.

Mark <huitmarmottes@...>

Hi George and all,

This is a great link, that illustrates what Arv said in his reply and has a very good explanation of the math used:

Have a great night!

Mark - N7EKU

From: Arv Evans <arvid.evans@...>
To: BITX20@...
Sent: Tuesday, September 27, 2011 6:50 PM
Subject: Re: [BITX20] Re: IK3OIL fll board.

George G0JKZ

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
significant problems.


On 09/27/2011 05:46 PM, G0JKZ wrote:

Looked there, all he has is the info for 5mhz and up, not for the 4mhz
needed for sunils bitxv3.

It annoys me as I did find the info somewhere, it may even have been
an old
post in this group but searching so far has come up with nothing.

I did print it/save it/ bookmark it but I'm frantically searching for the
stuff on 3 computers and a stack of paper in the 'Useful information' box.


From: cartronics@... <>
[mailto:cartronics@... <>]
Sent: 27 September 2011 22:09
To: BITX20@... <>
Subject: [BITX20] Re: IK3OIL fll board.

Hi George,

Heres a link to his website:

Regards .....Peter GW4ZUA

--- In BITX20@... <>
<> , "G0JKZ"
<g0jkz@...> wrote:

Hi guys... Almost finished my bitx20 and I am putting together the
fll board. I did find details for L1/C5/C9 somewhere a while ago and now
that I need them I can't find either the hard copy I made or the
post that detailed the coil and cap values for the 4mhz vfo.

Has anyone got the info to hand please.

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