Re: IK3OIL fll board.
G0JKZ <g0jkz@...>
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 totally wrong. 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... George G0JKZ From: Arv Evans [mailto:arvid.evans@...] Sent: 28 September 2011 02:51 To: BITX20@... 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 online. I particularly like the one at: <http://toroids.info/> 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 Cvalue for 3.75 MHz we just enter 3.75 MHz and 500 ohms into the calculator and it shows 85 pf as the new Cvalue. 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 Rvalue (wire resistance) or if the Qfactor 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. Arv K7HKL _._ On 09/27/2011 05:46 PM, G0JKZ wrote: <mailto:cartronics%40yahoo.com> [mailto:cartronics@... <mailto:cartronics%40yahoo.com><mailto:cartronics%40yahoo.com>] 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"

