Many thanks Jerry and Sarma. yeah, I was figuring that out by looking
at the previous stage, but I always see the 7805 with decoupling caps
in both input and output from the datasheet so I kept it there. now I
get it. Decoupling caps for everyone then.
Thanks again.
73!
Dan
HK4DEI

On Thu, Jun 22, 2017 at 11:48 PM, Jerry Gaffke via Groups.Io
<jgaffke@...> wrote:

Here's some thread from 2016:
/g/BITX20/topic/4105252

Farhan says it is a decoupling resistor for a driver stage.
So R144 and C142 do the same job for T6 as R135 and C133 are doing for T5 in
the previous stage,
keep power supply noise from getting into that amplifier (and vise versa).

Note that R144 is 2.2 ohms, not 2.2k. The 2n2219a sees quite a bit of
collector current.

U3 pin 3 just has a connection to the TX 12v rail, there is no cap local to
U3 shown in the schematic.
Though not a bad idea to put one there.

You might consider building the newer uBitx PA instead:

Farhan is still working on a minimal set of uBitx LPF's that meet FCC specs
for undesired emissions.
LIkewise, the Bitx PA should probably have Don Cantrell's second harmonic
fix:




Jerry, KE7ER


On Thu, Jun 22, 2017 at 09:16 pm, Daniel Isaza wrote:

R144 in parallel with a short?

Here's some thread from 2016:
? ?/g/BITX20/topic/4105252

Farhan says it is a decoupling resistor for a driver stage.
So R144 and C142 do the same job for T6 as R135 and C133 are doing for T5 in the previous stage,
keep power supply noise from getting into that amplifier (and vise versa).

Note that R144 is 2.2 ohms, not 2.2k. ?The 2n2219a sees quite a bit of collector current.

U3 pin 3 just has a connection to the TX 12v rail, there is no cap local to U3 shown in the schematic.
Though not a bad idea to put one there.

You might consider building the newer uBitx PA instead:
? ??
Farhan is still working on a minimal set of uBitx LPF's that meet FCC specs for undesired emissions.
LIkewise, the Bitx PA should probably have Don Cantrell's second harmonic fix: ?
? ??


Jerry, KE7ER

--

Hello everyone, I'm in the process of scratch building the BitX40 PA for a DSB rig, but I don't really understand the driver stage/7805 regulator from the schematic. R144 in parallel with a short?
I edited that portion of the schematic to what would make sense to me, but I wanted to ask anyway so I don't mess up my new PA. I'm I right or am I missing something?
I found some thead from 2016 refering to that topic but still isn't clear to me.
Thanks, 73!
Dan

Pavel,

I looked over you Si5351 library. ?I like that it is kept simple and easy to understand.
I think it could be a good starting point for a stripped down library specific to the Bitx40.
It operates the VCO at the highest acceptable frequency (near 900 mhz max) that is an even multiple of the desired output frequency,
The even multiple of two allows the output multisynth divider to always operate in integer mode, which reduces phase noise
and simplifies programming those output multisynth registers.
Given the vco frequency fvco and the 25mhz crystal oscillator frequency int_xtal, all that remains is to find non-negative integers
a, b and c with b less than c such that ? fvco/int_xtal == (a + b/c)?

Your code to do this has one floating point number f which is used in the computations of a, b, c.
I believe that is the only place in the entire sketch where floating point is used.
The amount of flash consumed would be reduced considerably if we could do without floating point.

I suggest you replace this:
######################################
    #define c 1048574;
    uint8_t a;
    unsigned long b, fvco, int_xtal;
    float f;
    ....
    a = fvco / int_xtal;
    f = fvco - a * int_xtal;
    f = f * c;
    f = f / int_xtal;
    b = f;
######################################


with something like this:
######################################
    uint8_t a;
    unsigned long b, c, fvco, int_xtal;
    unsigned long f; 		// temp variable, no longer a float
    ...
    a = fvco / int_xtal;	// find the quotient of the divide
    b = fvco % int_xtal;	// find the remainder of the divide
    c = int_xtal;
    while (c & 0xfff00000) {
        b = b>>1;		// divide by two till fits in 20 bits
        c = c>>1;
    }
######################################

(Note, I have not tried either your code or my integer only code on Si5351 hardware,
I don't have access to my Bitx40.)

The integer only code above should give accurate frequency synthesis better than 100ppb,
similar to your original code. ?It is possible to gain another factor of 5 or so in the accuracy
of the computations for (a+b/c) by going to 64 bit arithmetic, but we have already exceeded
the short term stability of our 25mhz crystal oscillator using 32 bit arithmetic, so not much point.?

The above code for finding a, b and c could be applied to the output multisynth dividers without any change.
In this case we are looking at the ratio of the vco to the output clock, instead of vco to 25mhz crystal oscillator.
On the bitx40, I'd tend to make CLK2 the VFO (as it is now), and CLK0 the BFO, each operating from a separate VCO.
The third output CLK1 could operate from the same VCO as the BFO (since the BFO rarely changes in frequency)
and could be set to well within a Hz of the desired frequency using the output multisynth divider.?




Perhaps I don't understand what you are doing on the S meter, but looks like the two diodes are drawn backwards.
Does your circuit improve on what Don Cantrell posted here??
? ??
Don shows a 1n32, a part I am not familiar with. ?Perhaps he meant 1n34a, that germanium diode would
be considerably more sensitive than a 1n4148. ? A schottky diode such as the Bat54s would also work.
As Don notes, his S meter is not very accurate.
Also, be aware that one S unit is a difference of 6 dB in signal strength, an S meter ideally has a logarithmic response.
A really good (but relatively expensive) way to implement this would be to use an AD8307 or AD8310.


Best Regards,
Jerry Gaffke, KE7ER

开云体育

开云体育

?

----- Original Message -----

From: Ashhar Farhan

To: [email protected]

Sent: Thursday, June 22, 2017 5:50 PM

Subject: Re: [BITX20] uBITX - A reboot of the old BITX

We have to first characterize the crystal. that's measure their motional inductance and capacitance. i do this using the G3URR's method. it is a very simple two transistor oscillator. after that, i use the same oscillator to measure the frequency of each crystal and sort them into bins.

thanks to the bitx40 production, at least for 12 mhz crystals, i don't have to match them. they are kept prematched in separate pouches. i just dip into one!

- f

?

Virus-free.

OK John,
never mind, good to hear you got it all working now!

73 Allard PE1NWL

On Thu, Jun 22, 2017 at 01:18 pm, Allard PE1NWL wrote:

Yes that's correct and as designed. So why is this an issue?
Why would you want to press PTT and close the key at the same time?
Sorry I don't understand.

I was pressing the PTT in place of having the RX-TX transistor connected.

But anyway, I just finished reconnecting the transistor and everything works as it should now!!! Don't know what I did wrong before (and don't really care)!

Thank you so much for your help, Allard. It's nice to know that there are still people in this world that will take a few minutes out of their busy schedules to try to help an idiot like me out!!!
?
--
John - WA2FZW

On Thu, June 22, 2017 21:19, John P wrote:

That's what I thought, so back to the original issue, with the whole TX-RX
modification (i.e. the transistor) completely removed, when the key is
closed and I press the PTT, it reverts to LSB TX mode, instead of
transmitting in CW mode.

Yes that's correct and as designed. So why is this an issue?
Why would you want to press PTT and close the key at the same time?
Sorry I don't understand.

73 Allard PE1NWL

Where is agc_software.png ?

My display is now just? bars. I lost? the computer? chip on bitx40. Where can i get another board?
Francesca W7LTG NV
Sent from Hotmail Email App for Android

Thursday, 22 June 2017, 00:07PM -07:00 from Ashhar Farhan farhanbox@...:

--
I have ?bitx40 ?and completely wired up. get nice hiss when the volume up. display lights up only showing Raduino V1.01. ?frequency never shown, anyone have that problem? ?i think the software is not in the chip.
Francesca W7LTG ? NV?

Thursday, 22 June 2017, 00:07PM -07:00 from Ashhar Farhan farhanbox@...:

--
I have ?bitx40 ?and completely wired up. get nice hiss when the volume up. display lights up only showing Raduino V1.01. ?frequency never shown, anyone have that problem? ?i think the software is not in the chip.
Francesca W7LTG ? NV?

"Here is a screenshot of my simulation. i run it under ubuntu, hence the weird window style."

Doesn't look weird to me... I use Ubuntu, too. :)
--
Darren, W9ZIM

On Thu, Jun 22, 2017 at 10:42 am, Allard PE1NWL wrote:

Yes John, you got that right!
The transistor just bypasses the switch (as it's in parallel to the switch).
So the result is the same whether you close the switch or whether you
cause the transistor to conduct. In either case the TX relay will become
activated.

That's what I thought, so back to the original issue, with the whole TX-RX modification (i.e. the transistor) completely removed, when the key is closed and I press the PTT, it reverts to LSB TX mode, instead of transmitting in CW mode.
?
--
John - WA2FZW

On Thu, Jun 22, 2017 at 12:14 pm, Ashhar Farhan wrote: