Re: Follow-up Antuino question
On Sat, Nov 14, 2020 at 05:33 PM, Tom, wb6b wrote:
using the ATTiny481 chip
That was a typo. The chip is the ATTiny841. Tom, wb6b
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Re: Follow-up Antuino question
I was expecting Arv to write in about H&P schemes. Between him and Hans, there is all we know about how this scheme works. The challenge of Huff and Puff is that it needs a very stable oscillator to begin with. It should have very minimal wobble (short term drift). The drift between two correction pulses should be less than its step size. That is not difficult to obtain. The inherent drawback of H&P is that the oscillator is always being pushed up or down from the central frequency between two cycles. This can have a disastrous effect on digital modes. There is probably another way to fix this. It is to use two flip flops as parallel mixers, each is fed the clock pulse that is 90 degrees out of phase from the other (imagine it to be a phasing receiver). Noe, the combined DC output of the two will indicate if we have drifted above, below or stayed on the frequency. I haven't tried this, but I am guessing that this will work. In the professional literature it is called a phase frequency detector. - f
This H&P jitter may not matter much if it isn't very frequent.
If it's a second or two between updates and the frequency slews
at a reasonable rate after an update, the "jitter" should be
no more objectionable than when manually making slight adjustments.
Jerry, KE7ER
On Sat, Nov 14, 2020 at 01:56 PM, Arv Evans wrote:
H&P stabilization is interesting because by default it sets the tuning?
step size as well as holding frequency drift to around 1 Hz, sometimes?
less.? However it does introduce its own type of slow jitter.?
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Re: Follow-up Antuino question
On Sat, Nov 14, 2020 at 01:33 PM, Gareth Evans wrote:
To do this, up to what frequency will the counters of an Arduino work!
The Arduino (ATMega328) can count external clocks up to 1/2 the clock used to run the chip. With a 16mhz clock for the ATMega328 that would be external frequencies up to just shy of 8mhz can be counted. You could use an external pre-scalar if desired. There are a few AVR chips that have PLL clock multipliers for the I/O circuits clock. One of those chips is the ATTiny85, another the ATTiny861. Those may be able to count external frequencies to 32mhz, as the PLL pushes the internal I/O clock to 64mhz. I'm sure there are other possible chips. My MFJ auto antenna tuner uses a PIC processor, and if I recall the PIC chip is counting the transmit frequency from my radio without a pre-scalar needed. Here is a library to support the above chips and a number of other ATTiny chips for the Arduino IDE. At the moment I'm using this board library to program a project using the ATTiny481 chip and it is working great at programming bare chips (no boot loader needed) using an inexpensive eBay USBAsp programmer. I bought one (USBasp) that included a 10pin to 6pin adaptor board and I wired a 6pin ISP programming header on my project's circuit board that works like the 6pin ISP header on the Arduino Nano board.? The library will let you burn boot loaders if you wish. Interestingly, on many chips the library included a bit banged USB boot loader that allows a direct USB connection to the chips, even though the chips do not normally support USB. I have an Atmel ICE and development IDE, but now that I found this board library, I'm using the Arduino IDE with USBasp for my project.? Tom, wb6b
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Can you hear static or at least an increase in background noise
as you plug the antenna in?
Perhaps bring a wire from the antenna connector over near the 25mhz
crystal of the Si5351 on the Raduino, see if you can tune that in.
Could be as simple as a bad BNC antenna connector.? In the distant past,
some of the supplied BNC connectors were machined incorrectly, and did not
reliably make contact.? Use an ohmmeter to verify that the antenna wire is connected
all the way into the main board of the uBitx.? And while you are at it, make sure the
antenna wire is not shorted to ground.
Here's an old Video of Farhan using one or two meters of wire (connected to nothing)
as an antenna to inject local QRM into the various stages of a Bitx40,
this same trick should work on the uBitx as well.
If your issue is an issue with menu settings or needing a to go through some?
calibration sequence, I defer to others here more familiar with current firmware.
Jerry, KE7ER?
If there's a nearby AM broadcast station down around 1mhz,
try tuning that in.? Or whatever else might be especially loud in your area.
Can you hear a nearby AM broadcast station when you tune down around 1MHZ
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On Sat, Nov 14, 2020 at 02:58 PM, Patrick Peter Rosney wrote:
Hello to? One & All...
?
Put together this uBitx . I have double checked all the wiring and all is correct .
But when I power it up all I can hear is?? hiss? from the speaker . I uploaded V5 Firmware but this has made no difference . I have the radio connected to?
50 feet of wire which is outside the Shack & up about 12 feet in the air.?
Not great?@ TROUBLESHOOTING? but have a feeling it is the settings that are not correct ?? Have seen a few posts from people with similar problems?
but I dont?know where to start and dont?really understand digital radio & SDR in general .?
Anybody got any? ?simple things I could check or try? ....and assume I know nothing ( which I dont ! )?
Thanks for reading?
Kind Regards?
Patrick? Ei2if?
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My son did not have time to go into great detail. I'll find out and report it later.
My son lives about 3000 miles away (KY to CA) so while swapping radios to see if the problem follows the radio is a good idea, it is not practical.
I'll find out more later and report it here.
Bob ¡ª KK5R
On Saturday, November 14, 2020, 7:16:26 PM EST, Jerry Gaffke via groups.io <jgaffke@...> wrote:
Maybe try swapping uBitx's with your son.
See if the problem follows the rig or stays with the QTH.
Out of curiosity, do all these extra carriers move at the same speed
as normal signals as he tunes through them, or at some faster rate?
Jerry, KE7ER
On Sat, Nov 14, 2020 at 04:06 PM, Bob Lunsford wrote:
As many of you know, I gave my V6 to my son in Sacramento, CA. He's an avid QRPer and would rather make a contact with low power/QRP than with a kilowatt.
?
His first impression is that the radio is great. I ordered two AGC boards (will arrive on Tuesday) and plan to send one of them to him for his V6
?
However, I got a message from him today and he said:
?
The uBITX radio was acting funny yesterday after work. The receiver was full of am carriers. Even on 80 way early in the afternoon long before the band ever opened. Hope it¡¯s not acting up. May go to HRO next week and buy a little manual antenna tuner to dedicate to the qrp radios.
?
Since he lives in Sacramento and there are some industry and hospitals not far from where he lives, I suspect there is some RF generated and he's hearing some harmonics. Since radios shine best (for him) on some mountaintop away from the city, I hope this will be the answer. I know the V6 is not a $1000 radio with technology that reduces/eliminates most interference, some design idiosyncrasies have to be endured and this is one area where the price of the radio has been kept low compared to radios designed for country club elites. Otherwise, I'd not be able to afford one. Ha
?
Does anyone have other ideas regarding the signals he heard? I told him to try it again later to see if the signals are still there ... or what!
?
I have heard others comment re the radio being bothered, sometimes, with strong signals but to be flooded with what seems to be harmonics is a new one on me ... BUT I do not have vast experience with the V6 and the uBITX radios in general as some in this forum do.
?
Bob ¡ª KK5R
?
?
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I put a home made broadcast band filter in the rf Path of my one bitx and a kit one in the rf path of my v6. They kill broadcast AM interference from KDKA which is a 50kw blowtorch not? 10 miles from my home.? You can see it pointed out in the pic I attached. It goes in the same line as the kit projects agc board.
As many of you know, I gave my V6 to my son in Sacramento, CA. He's an avid QRPer and would rather make a contact with low power/QRP than with a kilowatt.
His first impression is that the radio is great. I ordered two AGC boards (will arrive on Tuesday) and plan to send one of them to him for his V6
However, I got a message from him today and he said:
The uBITX radio was acting funny yesterday after work. The receiver was
full of am carriers. Even on 80 way early in the afternoon long before
the band ever opened. Hope it¡¯s not acting up. May go to HRO next week
and buy a little manual antenna tuner to dedicate to the qrp radios.
Since he lives in Sacramento and there are some industry and hospitals not far from where he lives, I suspect there is some RF generated and he's hearing some harmonics. Since radios shine best (for him) on some mountaintop away from the city, I hope this will be the answer. I know the V6 is not a $1000 radio with technology that reduces/eliminates most interference, some design idiosyncrasies have to be endured and this is one area where the price of the radio has been kept low compared to radios designed for country club elites. Otherwise, I'd not be able to afford one. Ha
Does anyone have other ideas regarding the signals he heard? I told him to try it again later to see if the signals are still there ... or what!
I have heard others comment re the radio being bothered, sometimes, with strong signals but to be flooded with what seems to be harmonics is a new one on me ... BUT I do not have vast experience with the V6 and the uBITX radios in general as some in this forum do.
Bob ¡ª KK5R
|
Maybe try swapping uBitx's with your son.
See if the problem follows the rig or stays with the QTH.
Out of curiosity, do all these extra carriers move at the same speed
as normal signals as he tunes through them, or at some faster rate?
Jerry, KE7ER
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On Sat, Nov 14, 2020 at 04:06 PM, Bob Lunsford wrote:
As many of you know, I gave my V6 to my son in Sacramento, CA. He's an avid QRPer and would rather make a contact with low power/QRP than with a kilowatt.
?
His first impression is that the radio is great. I ordered two AGC boards (will arrive on Tuesday) and plan to send one of them to him for his V6
?
However, I got a message from him today and he said:
?
The uBITX radio was acting funny yesterday after work. The receiver was full of am carriers. Even on 80 way early in the afternoon long before the band ever opened. Hope it¡¯s not acting up. May go to HRO next week and buy a little manual antenna tuner to dedicate to the qrp radios.
?
Since he lives in Sacramento and there are some industry and hospitals not far from where he lives, I suspect there is some RF generated and he's hearing some harmonics. Since radios shine best (for him) on some mountaintop away from the city, I hope this will be the answer. I know the V6 is not a $1000 radio with technology that reduces/eliminates most interference, some design idiosyncrasies have to be endured and this is one area where the price of the radio has been kept low compared to radios designed for country club elites. Otherwise, I'd not be able to afford one. Ha
?
Does anyone have other ideas regarding the signals he heard? I told him to try it again later to see if the signals are still there ... or what!
?
I have heard others comment re the radio being bothered, sometimes, with strong signals but to be flooded with what seems to be harmonics is a new one on me ... BUT I do not have vast experience with the V6 and the uBITX radios in general as some in this forum do.
?
Bob ¡ª KK5R
?
?
|
As many of you know, I gave my V6 to my son in Sacramento, CA. He's an avid QRPer and would rather make a contact with low power/QRP than with a kilowatt.
His first impression is that the radio is great. I ordered two AGC boards (will arrive on Tuesday) and plan to send one of them to him for his V6
However, I got a message from him today and he said:
The uBITX radio was acting funny yesterday after work. The receiver was
full of am carriers. Even on 80 way early in the afternoon long before
the band ever opened. Hope it¡¯s not acting up. May go to HRO next week
and buy a little manual antenna tuner to dedicate to the qrp radios.
Since he lives in Sacramento and there are some industry and hospitals not far from where he lives, I suspect there is some RF generated and he's hearing some harmonics. Since radios shine best (for him) on some mountaintop away from the city, I hope this will be the answer. I know the V6 is not a $1000 radio with technology that reduces/eliminates most interference, some design idiosyncrasies have to be endured and this is one area where the price of the radio has been kept low compared to radios designed for country club elites. Otherwise, I'd not be able to afford one. Ha
Does anyone have other ideas regarding the signals he heard? I told him to try it again later to see if the signals are still there ... or what!
I have heard others comment re the radio being bothered, sometimes, with strong signals but to be flooded with what seems to be harmonics is a new one on me ... BUT I do not have vast experience with the V6 and the uBITX radios in general as some in this forum do.
Bob ¡ª KK5R
|
Re: Follow-up Antuino question
This H&P jitter may not matter much if it isn't very frequent.
If it's a second or two between updates and the frequency slews
at a reasonable rate after an update, the "jitter" should be
no more objectionable than when manually making slight adjustments.
Jerry, KE7ER
toggle quoted message
Show quoted text
On Sat, Nov 14, 2020 at 01:56 PM, Arv Evans wrote:
H&P stabilization is interesting because by default it sets the tuning?
step size as well as holding frequency drift to around 1 Hz, sometimes?
less.? However it does introduce its own type of slow jitter.?
|
Hello to? One & All...
Put together this uBitx . I have double checked all the wiring and all is correct . But when I power it up all I can hear is?? hiss? from the speaker . I uploaded V5 Firmware but this has made no difference . I have the radio connected to? 50 feet of wire which is outside the Shack & up about 12 feet in the air.? Not great?@ TROUBLESHOOTING? but have a feeling it is the settings that are not correct ?? Have seen a few posts from people with similar problems? but I dont?know where to start and dont?really understand digital radio & SDR in general .? Anybody got any? ?simple things I could check or try? ....and assume I know nothing ( which I dont ! )? Thanks for reading? Kind Regards? Patrick? Ei2if?
|
Re: Follow-up Antuino question
Gareth Evans
We have the same last name...are we related?? ?8-)
H&P stabilization is interesting because by default it sets the tuning? step size as well as holding frequency drift to around 1 Hz, sometimes? less.? However it does introduce its own type of slow jitter.? H&P? stabilization is based on alignment?of edge of an LF clock with an edge? of a VFO cycle.? If the VFO edge is before the LF clock edge it pushes? the VFO slightly higher.? If the VFO edge is after the LF clock edge it? pushes the VFO slightly lower.? Design of H&P stabilization is for it to? be only slightly more aggressive than the VFO drift as referenced to? the VFO drift during one period of the LF clock.??
? ? ?
The LF clock probably needs to be in the 10 Hz to 30 Hz range and can? be derived from dividers on the output of an HF crystal oscillator.? Some? GPS receivers also can be programmed to give stable clock output in the? 10 Hz to 32 Hz range.??
Arv _._
On Sat, Nov 14, 2020 at 2:33 PM Gareth Evans via <headstone255= [email protected]> wrote: Perhaps the Huff-and-Puff stabiliser needs revisiting, where an occasional
frequency correction is applied to correct drift?
To do this, up to what frequency will the counters of an Arduino work!
A much more complex form of that stabilisation was used in the Eddystone
1837 RXs.
73 de Gareth G4SDW
On Sat, Nov 14, 2020 at 07:01 PM, Ashhar Farhan wrote:
> Contrary to a popular opinion, a free running LC oscillator can be the
> quietest there is. Any attempt that holding it to a frequency (phase locked
> loop) starts adding to the phase or amplitude noise. Consider the phase
> correction being applied like a modulation (which it is), hence it will
> spread the signal from being a single solid carrier. That's the phase noise!
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Re: Follow-up Antuino question
Perhaps the Huff-and-Puff stabiliser needs revisiting, where an occasional
frequency correction is applied to correct drift?
To do this, up to what frequency will the counters of an Arduino work!
A much more complex form of that stabilisation was used in the Eddystone
1837 RXs.
73 de Gareth G4SDW
toggle quoted message
Show quoted text
On Sat, Nov 14, 2020 at 07:01 PM, Ashhar Farhan wrote: Contrary to a popular opinion, a free running LC oscillator can be the
quietest there is. Any attempt that holding it to a frequency (phase locked
loop) starts adding to the phase or amplitude noise. Consider the phase
correction being applied like a modulation (which it is), hence it will
spread the signal from being a single solid carrier. That's the phase noise!
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Did some digging into the KD8CEC code.? In that version, there is not a globally defined value for the first IF.? There is in this segment hardcoded if values:  Note that there is a different value for the v4 vs v5 boards (all v4 and prior use the same code, as all v5 and later use that code). I would think that by changing the USB and LSB values as well as the hardcoded 1st IF frequency you should be good.? NOTE: the settings in the Si5351 code have a max of 109.000MHz.? Above that, you will need to redo the Si5351 setup.? The code in that section is well commented on and includes an explanation of how the values were picked. Had some spare time as was curious myself, so I dug into the other code. 73 Evan AC9TU
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Re: Follow-up Antuino question
Farhan, and others...
Designing a free-running VFO is challenging.? Good variable capacitors? are becoming difficult to obtain.? Older Colpitts?and Hartley?layouts are not? as stable as we have become used to with digital synthesizer chips.?? Square-wave outputs have been blamed for spurious signals.? And so on.
Well designed Vackar oscillators are a partial solution to stability issues. Additional stability can be had by using Huff-and-Puff stabilization.? The? Vackar oscillators also have low impedance sine-wave output.? Some? PLL based oscillator systems can be very stable and do have sine-wave? outputs.
For slow-motion frequency change we will probably have to design our? own variable capacitance units (threaded rod drive system seems likely).
Most important, we probably have to keep an open mind in order to reject? some of the myth, hype, and mystique that exists relative to oscillator? selection and design.
Arv? K7HKL _._
On Sat, Nov 14, 2020 at 9:31 AM Ashhar Farhan < farhanbox@...> wrote: Barry, I too built a direct conversion transceiver a few months ago. I chose a fully analog design without any ICs. A carefully designed free running vfo is used. It is so stable that I can continuously monitor the FT8 spot! On the other hand, when I substitute it with an Si5351, the difference is immediately obvious. The CW is noiser and the SSB audio has less fidelity. I can no longer copy the signals that were barely above the noise floor. Given a choice, I would use a free running VFO any day. Except that it is very expensive to build them with a good slow motion and implementing multiband design is always a?challenge. - f
On Sat 14 Nov, 2020, 9:55 PM barry halterman, < kthreebo@...> wrote: Hi fellow DC rx fans. Back in 1992, Rick Campbell had a design in QST for a direct conversion receiver he called the R1. Later he upgraded this to the R2. I have the R1 that I have used the si5351 to drive the SBL-1 mixer with excellent results. I use a 6 db pad on the LO port, per a recommendation from Ashar. Later I changed the LO to a PLL oscillator with a sine wave output. I did not notice any difference at all between the two oscillators. The recovered audio is fantastic from this R1 board. Rick had a few different LC designs for filters, SSB narrow and wide and a cw filter.? For those who want a serious DC receiver, I highly recommend looking at his design. It is a little more complicated then just a mixer and LM386, but very well worth the effort. K3BO
Would be interesting to try sine wave vs square wave.
But I doubt you will notice much difference,
Assuming you have a low pass (or band pass) filter on the RF input,
the harmonics in a square wave should not cause any first order products in the resultant audio.
Also, your mixer is likely to have a non-linear voltage vs current relationship
at the local oscillator port anyway.
However, the clean audio one can get from a DC receiver make it?
an excellent testbed for trying this sort of thing.
And I have heard that a sine wave is somewhat preferred for driving
even a diode ring mixer, which has an extremely non-linear LO port.
Note that the Antuino has a very nice ADE-1 mixer.
Might be possible to include that in your DC receiver.
Jerry, KE7ER
On Fri, Nov 13, 2020 at 08:35 PM, Bob Lunsford wrote:
There was some comment in the webpage about the signal being a square wave. If this shows up in the signal, causing harmonics, then included in the amp should be a "smoothing" circuit or some way to make it show up as a sine wave. This is theoretically simple since an inductor's flywheel effect would actually convert it to a sine wave. How well it does this is another question and it would/could cause some refinement of the signal. A simple resistor-capacitor circuit followed by an amp may be better.
?
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Re: Follow-up Antuino question
Farhan,
What you say sounds right.
There's a reason why people have moved away from analog VFO's, they are finicky.
The Si5351 is not necessarily the best choice, just the cheapest and easiest,
so it gets used everywhere in homebrew radio these days.
Not unlike how most designs go with the LM386 as an audio amp.
Depending on the goals, both of these are often the best choice.
It's difficult to get simple, cheap, and excellent to all fit in one box.
There are plenty of Si5351 libraries out there that use integer output divides.
Would be interesting to try that as a VFO on your DC radio,
compare it to the si5351bx routines with fractional output divides,
and with your analog VFO.
Would be worth trying multiple Si5351 boards.? Some of this jitter
may?be in board layout, nearby digital devices, or a noisy power supply.
G0UPL's QCX gets good reviews as a receiver, it uses an Si5351,
and is basically a DC receiver, uses audio phase shift networks to get
single signal reception.? The Si5351 on it uses integer output divides.?
Many in this forum have one, that might be another point of comparison.
Jerry, KE7ER
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On Sat, Nov 14, 2020 at 11:01 AM, Ashhar Farhan wrote:
Jerry,
Contrary to a popular opinion, a free running LC oscillator can be the quietest there is. Any attempt that holding it to a frequency (phase locked loop) starts adding to the phase?or amplitude noise. Consider the phase correction being applied like a modulation (which it is), hence it will spread the signal from being a single solid carrier. That's the phase noise!
The circuit that I used is pretty simple. Similar to the one at? (except that I used a tap on the inductor instead of a secondary?winding).? The section on VFOs in the EMRFD book is a thorough?text on building VFOs. To put it in a nutshell, VFO design is not as important as the building of it is. You must use polystyrene?capacitors if possible, or at least NP0 capacitors. Both of these are freely available?from Mouser. I have ordered a bad full of 100 pfs and I just keep paralleling them until I hit the values I need. I built it over a ground plane, I kept the regulator away to prevent its heat from heating up the rest of the components. Most importantly, there are no hanging wires at all. All components are directly soldered to each other and the entire VFO is mounted on the back of the tuning capacitor.?
When the time permits, I will write up about the transceiver. It is a full-break in CW transceiver for 40 meters with two selectable filters for SSB and CW. It has 7 watts of CW power from an IRF510. It is very similar to the W7EL's transceiver. That article is one of those that pack so many things in that each time you read those few pages, you learn something new. It is available on?
?
- f
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Re: Follow-up Antuino question
Jerry, Contrary to a popular opinion, a free running LC oscillator can be the quietest there is. Any attempt that holding it to a frequency (phase locked loop) starts adding to the phase?or amplitude noise. Consider the phase correction being applied like a modulation (which it is), hence it will spread the signal from being a single solid carrier. That's the phase noise! The circuit that I used is pretty simple. Similar to the one at? (except that I used a tap on the inductor instead of a secondary?winding).? The section on VFOs in the EMRFD book is a thorough?text on building VFOs. To put it in a nutshell, VFO design is not as important as the building of it is. You must use polystyrene?capacitors if possible, or at least NP0 capacitors. Both of these are freely available?from Mouser. I have ordered a bad full of 100 pfs and I just keep paralleling them until I hit the values I need. I built it over a ground plane, I kept the regulator away to prevent its heat from heating up the rest of the components. Most importantly, there are no hanging wires at all. All components are directly soldered to each other and the entire VFO is mounted on the back of the tuning capacitor.? When the time permits, I will write up about the transceiver. It is a full-break in CW transceiver for 40 meters with two selectable filters for SSB and CW. It has 7 watts of CW power from an IRF510. It is very similar to the W7EL's transceiver. That article is one of those that pack so many things in that each time you read those few pages, you learn something new. It is available on?
- f
Farhan,
What do you think is the major factor in the relatively poor performance of the Si5351?
I suspect it is jitter, not the fact that it is a square wave.
The Si5351 is their cheapest part at $1, there are other Silicon Labs parts
with far better jitter performance at around $10 to $15.
Would be interesting to compare results using one of those.
Make sure the other Si5351 outputs are shut down to avoid crosstalk.
I've heard it reported in this forum that the Si5351 has less phase noise (one way of
thinking about jitter) than most analog VFO's.? So I could be wrong.? Or they could
be wrong.? Or there might be good kinds of jitter and bad kinds of jitter.
This might be a case where you want to run the Si5351 with integer divide
on the output multsynth dividers, setting the frequency by adjusting the PLL multisynth.
That will give significantly less jitter than using fractional divides on the outputs.
It's is with all the stuff from QRP Labs does, but since the Si5351 has only two
PLL's/VCO's, this approach gives only two outputs.
On the uBitx, we use a fixed PLL VCO frequency of 875mhz, and divide it down
to each output using fractional output divides so we can get three independent outputs
from one chip.? Perhaps the uBitx should use?VCOa for the VFO at CLK1, VCOb for
the the mostly fixed LO into the second mixer at CLK2, and a fractional output divide
of VCOb for the relatively low frequency (and thus low jitter) CLK0 that is used for the BFO.? ?
That would burn more Nano flash for the firmware, but might be worth exploring.
Jerry, KE7ER
On Sat, Nov 14, 2020 at 08:31 AM, Ashhar Farhan wrote:
Barry,
I too built a direct conversion transceiver a few months ago. I chose a fully analog design without any ICs.
A carefully designed free running vfo is used. It is so stable that I can continuously monitor the FT8 spot!
On the other hand, when I substitute it with an Si5351, the difference is immediately obvious. The CW is noiser and the SSB audio has less fidelity. I can no longer copy the signals that were barely above the noise floor.
Given a choice, I would use a free running VFO any day. Except that it is very expensive to build them with a good slow motion and implementing multiband design is always a?challenge.
- f
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Gordon,
Any assembly can be cut into pieces. Advantage, one can change/ improve a module at its convenience.
The best system (in my opinion) is a board with main functions and a bus with several connectors (Like a pc)
Then you will be free to modify (for example, there was a lot of discussion on the AGC) --> It's will be and addon near the audio module.
Provide in this case an interconnexion by jumper on the mother board.
There¡¯s a lot to think about interconnexions...and others, ex:1 or 2 free slots also for personal fabrications, etc.
In short, this is no small matter.
But if you want to cut out a Ubitx, is that allowed??Only the author can tell you.
cdt
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Re: Follow-up Antuino question
Farhan,
What do you think is the major factor in the relatively poor performance of the Si5351?
I suspect it is jitter, not the fact that it is a square wave.
The Si5351 is their cheapest part at $1, there are other Silicon Labs parts
with far better jitter performance at around $10 to $15.
Would be interesting to compare results using one of those.
Make sure the other Si5351 outputs are shut down to avoid crosstalk.
I've heard it reported in this forum that the Si5351 has less phase noise (one way of
thinking about jitter) than most analog VFO's.? So I could be wrong.? Or they could
be wrong.? Or there might be good kinds of jitter and bad kinds of jitter.
This might be a case where you want to run the Si5351 with integer divide
on the output multsynth dividers, setting the frequency by adjusting the PLL multisynth.
That will give significantly less jitter than using fractional divides on the outputs.
It's is with all the stuff from QRP Labs does, but since the Si5351 has only two
PLL's/VCO's, this approach gives only two outputs.
On the uBitx, we use a fixed PLL VCO frequency of 875mhz, and divide it down
to each output using fractional output divides so we can get three independent outputs
from one chip.? Perhaps the uBitx should use?VCOa for the VFO at CLK1, VCOb for
the the mostly fixed LO into the second mixer at CLK2, and a fractional output divide
of VCOb for the relatively low frequency (and thus low jitter) CLK0 that is used for the BFO.? ?
That would burn more Nano flash for the firmware, but might be worth exploring.
Jerry, KE7ER
toggle quoted message
Show quoted text
On Sat, Nov 14, 2020 at 08:31 AM, Ashhar Farhan wrote:
Barry,
I too built a direct conversion transceiver a few months ago. I chose a fully analog design without any ICs.
A carefully designed free running vfo is used. It is so stable that I can continuously monitor the FT8 spot!
On the other hand, when I substitute it with an Si5351, the difference is immediately obvious. The CW is noiser and the SSB audio has less fidelity. I can no longer copy the signals that were barely above the noise floor.
Given a choice, I would use a free running VFO any day. Except that it is very expensive to build them with a good slow motion and implementing multiband design is always a?challenge.
- f
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Re: Follow-up Antuino question
Ashar, I agree that a analog vfo would be superior but I have not had much luck building one that was stable enough. That was the reason I chose to use the 5351 or my PLL. Any chance you would share your vfo design with us? Barry
On Sat, Nov 14, 2020, 11:31 AM Ashhar Farhan < farhanbox@...> wrote: Barry, I too built a direct conversion transceiver a few months ago. I chose a fully analog design without any ICs. A carefully designed free running vfo is used. It is so stable that I can continuously monitor the FT8 spot! On the other hand, when I substitute it with an Si5351, the difference is immediately obvious. The CW is noiser and the SSB audio has less fidelity. I can no longer copy the signals that were barely above the noise floor. Given a choice, I would use a free running VFO any day. Except that it is very expensive to build them with a good slow motion and implementing multiband design is always a?challenge. - f
On Sat 14 Nov, 2020, 9:55 PM barry halterman, < kthreebo@...> wrote: Hi fellow DC rx fans. Back in 1992, Rick Campbell had a design in QST for a direct conversion receiver he called the R1. Later he upgraded this to the R2. I have the R1 that I have used the si5351 to drive the SBL-1 mixer with excellent results. I use a 6 db pad on the LO port, per a recommendation from Ashar. Later I changed the LO to a PLL oscillator with a sine wave output. I did not notice any difference at all between the two oscillators. The recovered audio is fantastic from this R1 board. Rick had a few different LC designs for filters, SSB narrow and wide and a cw filter.? For those who want a serious DC receiver, I highly recommend looking at his design. It is a little more complicated then just a mixer and LM386, but very well worth the effort. K3BO
Would be interesting to try sine wave vs square wave.
But I doubt you will notice much difference,
Assuming you have a low pass (or band pass) filter on the RF input,
the harmonics in a square wave should not cause any first order products in the resultant audio.
Also, your mixer is likely to have a non-linear voltage vs current relationship
at the local oscillator port anyway.
However, the clean audio one can get from a DC receiver make it?
an excellent testbed for trying this sort of thing.
And I have heard that a sine wave is somewhat preferred for driving
even a diode ring mixer, which has an extremely non-linear LO port.
Note that the Antuino has a very nice ADE-1 mixer.
Might be possible to include that in your DC receiver.
Jerry, KE7ER
On Fri, Nov 13, 2020 at 08:35 PM, Bob Lunsford wrote:
There was some comment in the webpage about the signal being a square wave. If this shows up in the signal, causing harmonics, then included in the amp should be a "smoothing" circuit or some way to make it show up as a sine wave. This is theoretically simple since an inductor's flywheel effect would actually convert it to a sine wave. How well it does this is another question and it would/could cause some refinement of the signal. A simple resistor-capacitor circuit followed by an amp may be better.
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Bob Lunsford
Patrick Peter Rosney
Gerard