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
Raduino question.
|
The Raduino uses the si5351 clock generator, outputs from si5351 have just a series cap where they leave the raduino.
toggle quoted message
Show quoted text
Datasheet here: ? says outputs are 3.3v CMOS with a 50 ohm output impedance. You can adjust the output drive level through i2c registers. Farhan is successfully driving schottky diode ring mixers on the ubitx: ? He shows both the ubitx and raduino schematics at the bottom of that webpage. So raduino should be fine with any of the level 3 diode ring mixers. An update on the ubitx is in this thread: ?/g/BITX20/message/33255 On Sat, Oct 21, 2017 at 01:53 pm, Ian Gerard wrote:
I was wondering what the output of the Raduino is?? In particular is the output enough to drive an SBL-1 or an ADE-1 between 7 and 28Mhz? |
|
Gordon Gibby
开云体育?think you're off a decimal point there.... 2 mA into 50 ohms is 1/5 of a milliwatt so it wold not be 3dBm....
From: [email protected] <[email protected]> on behalf of Kelly Jack <kellyjack1968@...>
Sent: Monday, October 23, 2017 5:30 AM To: [email protected] Subject: Re: [BITX20] Raduino question. ?
this page indicates that setting the drive at 2ma equates to 3dbm into a 50ohms load.
|
|
Probably could drive a level 7 mixer from the si5351 cmos outputs.
toggle quoted message
Show quoted text
Though I'm not entirely sure. Assume the si5351 truly does have a 50 ohm output impedance as per the datasheet, and is driving into that 50 ohms from rails between 3v and ground. ?(3.3v, but with some losses) The rms voltage is half of that (this is a square wave, not a sine wave). With a 50 ohm load resistor, the load sees half of that rms voltage. Farhan's ubitx 150/36/150 pi attenuator reduces it by 6db, which means the voltage swing gets halved again. Power is volts squared over ohms, ?so power to the diode ring is ? ((3v/8)**2)/50 = 0.0028 watts = 2.8mw? In dbm, that's 10*log10(2.8mw) = 4.47 dbm. So should be adequate for a level 3 mixer ?(wants 3dbm into the local oscillator port). And could drive a level 7 mixer if you hack that attenuator back to 3 db. If any of you RF guys see errors in this, do let me know. Jerry On Sat, Oct 21, 2017 at 05:54 pm, Jerry Gaffke wrote:
|
|
Gordon Gibby
开云体育Hi, I didn't follow all of that, but RMS for a sine wave is .707 times peak
Thanks for all that information about the signal levels!
Sent from my iPhone
|
|
Yes, but the si5351 gives a square wave.
toggle quoted message
Show quoted text
And the root-mean-square voltage of a square wave is half of the peak-to-peak voltage. From ? ?? "RMS is equal to the value of the??that would produce the same average power dissipation in a? Another thought: asking the si5351 to drive a 50 ohm load is asking a lot. There is only one pin going in for the 3.3v rail, so this would certainly aggravate any crosstalk between the three output buffers. The diode ring mixer wants to see a 50 ohm source impedance at the local oscllator input to avoid reflections there. Might be better off with an asymmetric resistor network there. Or an mmic buffer amp. And/or use multiple si5351 chips. Jerry On Mon, Oct 23, 2017 at 09:47 am, Gordon Gibby wrote:
|
|
Gordon Gibby
开云体育?I see where you are coming from........
but the DESIRED frequency is a sine wave.? ??
All that "other stuff" that makes it into a square wave?? ?Those are UNDESIRED freuencies.? ? (Fourier analysis).? ?
so......if you're interested in the power level of the 5 or 19 MHz signal itself, it would still be the sine wave component that you're interested in, not the square wave.? ?
But the difference, when squared is only a factor of 0.5 or 2.
Mind you, I know precious little about mixers.....but a lot about fourier.? ?
From: [email protected] <[email protected]> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Monday, October 23, 2017 1:01 PM To: [email protected] Subject: Re: [BITX20] Raduino question. ?
Yes, but the si5351 gives a square wave.
And the root-mean-square voltage of a square wave is half of the peak-to-peak voltage. From ? ?? "RMS is equal to the value of the??that would produce the same average power dissipation in a? Another thought: asking the si5351 to drive a 50 ohm load is asking a lot. There is only one pin going in for the 3.3v rail, so this would certainly aggravate any crosstalk between the three output buffers. The diode ring mixer wants to see a 50 ohm source impedance at the local oscllator input to avoid reflections there. Might be better off with an asymmetric resistor network there. Or an mmic buffer amp. And/or use multiple si5351 chips. Jerry On Mon, Oct 23, 2017 at 09:47 am, Gordon Gibby wrote:
|
|
Vince Vielhaber
The output level is also frequency dependent. I already knew this but
toggle quoted message
Show quoted text
needed some more concrete numbers so I did some testing last nite. At 7.5 MHz I was getting approx 2VRMS with the current set at 2ma (I was using your library, Jerry). At 35.5 MHz that level dropped to less than 0.25VRMS. In at attempt to minimize this, at various points added some code to increase the output at certain frequencies. The best I was able to get at 35.5 MHz was a little over 0.5VRMS with 8ma selected. Vince. Yes, but the si5351 gives a square wave. --
Michigan VHF Corp. |
|
Gordon Gibby
measured where, across what impedance?
thanks for the information!!! ________________________________________ From: [email protected] <[email protected]> on behalf of Vince Vielhaber <vev@...> Sent: Monday, October 23, 2017 1:10 PM To: [email protected] Subject: Re: [BITX20] Raduino question. The output level is also frequency dependent. I already knew this but needed some more concrete numbers so I did some testing last nite. At 7.5 MHz I was getting approx 2VRMS with the current set at 2ma (I was using your library, Jerry). At 35.5 MHz that level dropped to less than 0.25VRMS. In at attempt to minimize this, at various points added some code to increase the output at certain frequencies. The best I was able to get at 35.5 MHz was a little over 0.5VRMS with 8ma selected. Vince. Yes, but the si5351 gives a square wave. -- Michigan VHF Corp. |
|
Vince Vielhaber
measured where, across what impedance?Typically my RF measurements are all at 50 ohms, but right now I can't say for certain that last nite's were. I'll have to double check when I get home. Also I need to correct something, my initial output was 4ma, not 2ma. Vince. -- Michigan VHF Corp. |
|
No. ?The desired drive into a balanced ring mixer is a square wave.
toggle quoted message
Show quoted text
You are driving diodes, the current through the diodes is an exponential function of the voltage across them. So they are effectively either on or off, with very little transition between the two. Which is not necessarily a bad thing. The diode ring is best thought of as a commutating mixer. ? Which means it is best analyzed as switches. Something like a Gilbert cell can be used to truly do an analog multiply of the incoming signal with the local oscillator. But even these mixers are typically driven hard to where the Gilbert cell acts as switches. If you really want a sine wave into your diode ring mixer, you will have to choose between a sine wave in voltage presented or a sine wave in current through the diodes. You can't have both, as them diodes are far from linear. Some in this forum have experimented with adding filters between the si5351 and the diode ring mixer. Some do report fewer birdies, though there are lots of possible reasons for that. I doubt it has anything to do with presenting a square wave to the mixer. If using more than one of the si5351 outputs, a filter might help reduce crosstalk. It would also help prevent vfo harmonics from radiating into off the open cabling into other parts of the radio. Jerry On Mon, Oct 23, 2017 at 10:08 am, Gordon Gibby wrote:
|
|
Rather surprising you only saw a fraction of a volt from the si5351 at 35mhz..
toggle quoted message
Show quoted text
If so, hard to imagine Farhan would get the ubitx to work at all, as his first local oscillator is at 45mhz + signal Apparently works up to a 30mhz signal frequency, so 75mhz from the si5351. And it has to drive something like 0.6v into two series schottky diodes for them to start conducting. The si5351 outputs should work up to something like 200mhz. (Though my library is only good to a bit over 100mhz, as it does not mess with varying the vco frequency). Jerry On Mon, Oct 23, 2017 at 10:21 am, Vince Vielhaber wrote: At 35.5 MHz that level dropped to less than 0.25VRMS. |
|
Oh, and the si5351 is driving those series schottky diodes through a 6db attenuator, which cuts the voltage in half.
toggle quoted message
Show quoted text
Maybe you had your scope on some low bandwidth setting or something. On Mon, Oct 23, 2017 at 10:44 am, Jerry Gaffke wrote: If so, hard to imagine Farhan would get the ubitx to work at all, as his first local oscillator is at 45mhz + signal |
|
Gordon Gibby
开云体育fascinating.? ?
I'm not an expert at all on mixers, so you know a lot more about them than I do!? ?But the desired frequency is still only a sine wave.? ?The rest of the squre wave....is not at the desired frquency.? ?? If all those other harmonics etc help you out in some
interesting way, that's fine, but my pea brain thought you mixed one frequency with another and through the miracle of non-linearity, you get their sum and difference.? ? I don't quite understand how any other frquency enters into the equation.? ? but then
again, I don't claim to understand them.? ?Maybe I'll better understand them some day!!!!
cheers!
gordon
From: [email protected] <[email protected]> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Monday, October 23, 2017 1:34 PM To: [email protected] Subject: Re: [BITX20] Raduino question. ?
No. ?The desired drive into a balanced ring mixer is a square wave.
You are driving diodes, the current through the diodes is an exponential function of the voltage across them. So they are effectively either on or off, with very little transition between the two. Which is not necessarily a bad thing. The diode ring is best thought of as a commutating mixer. ? Which means it is best analyzed as switches. Something like a Gilbert cell can be used to truly do an analog multiply of the incoming signal with the local oscillator. But even these mixers are typically driven hard to where the Gilbert cell acts as switches. If you really want a sine wave into your diode ring mixer, you will have to choose between a sine wave in voltage presented or a sine wave in current through the diodes. You can't have both, as them diodes are far from linear. Some in this forum have experimented with adding filters between the si5351 and the diode ring mixer. Some do report fewer birdies, though there are lots of possible reasons for that. I doubt it has anything to do with presenting a square wave to the mixer. If using more than one of the si5351 outputs, a filter might help reduce crosstalk. It would also help prevent vfo harmonics from radiating into off the open cabling into other parts of the radio. Jerry On Mon, Oct 23, 2017 at 10:08 am, Gordon Gibby wrote:
|
|
Gordon Gibby
thanks. I assume you measured right at the output of the radiuno and not after the 6db attenuator.
I'm hoping to use this thing as a replacement VFO for some old heathkits once I learn what THEIR vfo output voltage was.....I'm pretty sure they were at 2K ohms so I may be able to use a ferrite transformer and step up voltage through simple impedance matching. It would be really cool to have the advantages of the digital VFO on my old (and EMP proof) SB-102!!!! Gordon ________________________________________ From: [email protected] <[email protected]> on behalf of Vince Vielhaber <vev@...> Sent: Monday, October 23, 2017 1:20 PM To: [email protected] Subject: Re: [BITX20] Raduino question. measured where, across what impedance?Typically my RF measurements are all at 50 ohms, but right now I can't say for certain that last nite's were. I'll have to double check when I get home. Also I need to correct something, my initial output was 4ma, not 2ma. Vince. -- Michigan VHF Corp. |
|
Vince Vielhaber
Nope, I don't bandwidth limit that scope (Tek 2430A). I'll do another
toggle quoted message
Show quoted text
measurement tonite with the Tek 11402 and see what it says. Vince. Oh, and the si5351 is driving those series schottky diodes through a 6db --
Michigan VHF Corp. |
|
Hi Gordon,
...With a diode mixer, yes you get the sum and difference, but you also get all the harmonic mixing products, too; reduced in amplitude, of course---it's the "nature of the beast," so to speak. 73, David KB4FXC On Mon, 23 Oct 2017, Gordon Gibby wrote: fascinating.than I do! But the desired frequency is still only a sine wave. The rest of the squre wave....is not at the desired frquency. If all those other harmonics etc help you out in some interesting way, that's fine, but my pea brain thought you mixed one frequency with another and through the miracle of non-linearity, you get their sum and difference. I don't quite understand how any other frquency enters into the equation. but then again, I don't claim to understand them. Maybe I'll better understand them some day!!!!
|
|
Vince Vielhaber
Not coming off the Raduino, I'm using one of these:
toggle quoted message
Show quoted text
Much simpler but does the same thing. My own Nano connects to it without the need for a display. Vince. thanks. I assume you measured right at the output of the radiuno and not --
Michigan VHF Corp. |
开云体育I have made my own version of these.? They work fine on a Nano, but since there is NO Address selection it probably collides if you put it on Raduino with its SI5351. The 20 Pin version of the SI5351A has ONE address selection pin, so the next ones I make with be with the 20 QFN part. It is over 2 the price and in the QFN package. Mike, WA6ISP On 10/23/2017 10:59 AM, Vince Vielhaber
wrote:
Not coming off the Raduino, I'm using one of these: Much simpler but does the same thing. My own Nano connects to it without the need for a display. Vince.thanks. I assume you measured right at the output of the radiuno and not after the 6db attenuator. I'm hoping to use this thing as a replacement VFO for some old heathkits once I learn what THEIR vfo output voltage was.....I'm pretty sure they were at 2K ohms so I may be able to use a ferrite transformer and step up voltage through simple impedance matching. It would be really cool to have the advantages of the digital VFO on my old (and EMP proof) SB-102!!!! Gordon ________________________________________ From: [email protected] <[email protected]> on behalf of Vince Vielhaber <vev@...> Sent: Monday, October 23, 2017 1:20 PM To: [email protected] Subject: Re: [BITX20] Raduino question.measured where, across what impedance? thanks for the information!!! -- Mike Hagen, WA6ISP 10917 Bryant Street Yucaipa, Ca. 92399 (909) 918-0058 PayPal ID "MotDog@..." Mike@... |
to navigate to use esc to dismiss