Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Bitx40 BFO
¿ªÔÆÌåÓýGet dds and lcd setup
Sent from my iPhone
|
|
I want to try without using the DDS for BFO. 73 Ken On Fri, Dec 30, 2016 at 3:44 PM, ron van doremalen ronvandoremalen@... [BITX20] <BITX20@...> wrote:
|
|
Ken Maybe a better answer is to talk a bit about crystal pulling and how it is done. As you may already know it is possible to use a variable capacitor in series with a crystal to make slight alterations to its oscillation frequency.? While this has some effect and is frequently used to bring a crystal to its exact stated operating frequency it does have some limitation in pulling range. An alternative to using just a variable capacitor to change crystal frequency is to make a series LC network for the crystal frequency and then add the crystal in series with that.? When the L or C value is changed slightly the LC network tends to pull the crystal up or down in frequency by a larger amount than can be done with just a capacitor. The series LC-Xtal network can be applied to many types of oscillator circuit.? Arv? K7HKL _._ On Fri, Dec 30, 2016 at 1:44 PM, ron van doremalen ronvandoremalen@... [BITX20] <BITX20@...> wrote:
|
|
Thanks Arv Lots of reading to do this weekend. Also will be pulling out the bible(EMRFD). 73 Ken On Fri, Dec 30, 2016 at 3:56 PM, Arv Evans arvid.evans@... [BITX20] <BITX20@...> wrote:
|
|
Hey, Ken--
toggle quoted message
Show quoted text
Lots of reading indeed. Arv is right. That is where to start. But what you really want to know is: What do I do to hack my BITX40 board? There is provision on the board for an LC pulling circuit via L5, C102, and C103. See the files and look at the various schematics to see what others have done. Especially that of the BITXv.3, the BITX20A and BITX17A, the mode variation circuit of PY2OHH, and the multiband circuit of G6LBQ (and the MKARS80). And don't forget F8VOA. What is it that has to be done exactly? There are several approaches but the usual one is to change the IF to allow or send the USB rather than the LSB through the filter. Which way does one move the frequency? Probably lower, since one is looking at getting the USB into the passband. But it really depends upon your particular rig and what it actually is doing. And how does one get both USB and LSB? Either by shifting the LC circuit in and out to change the BFO frequency, or putting in another crystal and setting that up to respond to a different LC constant, and using diodes (or transistors) to "ground" which one wants to run at any given time. How much shift is needed? Remember that AM radio stations are 10 KHz apart. They have a carrier and two sidebands of about 5 KHz each. You probably will have to shift the IF less than 5 KHz to get either sideband through the filter. The files section has plenty of examples. Hope this helps. john AD5YE ---In BITX20@..., <chase8043@...> wrote : Thanks Arv Lots of reading to do this weekend. Also will be pulling out the bible(EMRFD). 73 Ken
|
|
Doesn't need to move that far. ?Typically it only needs to be shifted approx 6 kHz to the other side of the crystal filter's bandpass.?
Eg LSB (as it is now) requires the filter's bandpass to be below the carrier crystal frequency. ? USB requires the filter's bandpass to be above the carrier crystal frequency.? Since it's easier to change the frequency of a single carrier crystal rather than the centre frequency of a ladder crystal filter that's what we do.? So to get USB we need to move the carrier crystal DOWN by approx 6kHz. ?Fortunately shifting a 12 MHz crystal down this amount is fairly easy and you won't necessarily need a crystal of another frequency. ?You just put inductance in series with it to provide a VXO. ?Adding a second crystal in parallel makes shifting down easier but is probably not required. ? 73, Peter VK3YE |
to navigate to use esc to dismiss