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Raduino question.

Pavel Milanes Costa
 

El 23/10/17 a las 13:34, Jerry Gaffke via Groups.Io escribió:
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.
Hi, My two cents on this.

I used a Si5351 for VFO and BFO in another project for a generic radio controller, like the raduino but more broad in capabilities (see ) and I can tell that lower the freq you generate greater the harmonic content (aka. general noise and birdies).

Two samples, and comments.

-> Old marine radio (really oooold... Spilbury... if not wrong), BFO freq is 1.6 Mhz, direct square wave to DBM as a detector yields to a noisy but usable receiver... after placing a back to back red toko If cans (broadcast radio oscillator IF can, via a 47pf cap) and tune to 1.6 Mhz you got a very decent receiver noise, not measured by lab instruments but by ear I say about one or two S unit of band noise was cut after filter placement.

-> Homebrew monoband (40m) 500Khz heterodyne radio based on a old Russian filter/xtal from a KARAT transceiver... Rx was useless without the filter... with the lesson learned from the above example, two back to back 455 khz toko IF cans re-tuned via a 100 pf cap solved the issue and reception is very good now.

So, the lower the freq you generate the dirtier it get's and it make sense as the harmonics are quite close in range and the mumbo-jumbo of strong freqs mixing each other it's a nightmare...

Then you have the Square vs Sine in a DBM...

I doubt it has anything to do with presenting a square wave to the mixer.
I'm not agree, in my experiments I found that driving it with Square Waves is more efficient, but a lot dirtier. ARRL and RSGB Handbooks agree on that, several academic papers on the internet are agree.

Back in the beginning of the year I spent a few days with a borrowed Tektronix oscope and this was one of the issues I studied with it... (Santa take note: I like a Textronix this year for Xmas, hi hi hi)

I'm not a electronic engineer (actually industrial engineer in the ISO certification and IT consulting field)? but I dare to speculate about the root cause: zerocrossing.

In a square wave via a DBM the harmonics (dirt) are created in the zerocrossing of the square wave from one cycle to another.

Think about it: a sine wave has a region that results on both diodes to be off in a certain time (amount) before cycle inversion and that's allows the inductors to collapse it's fields and reset for the next cycle.

Square wave have virtual no zero off time between cycle inversion and...

With light filtering (top square smooth on the scope but not good like a sine wave, just a low pass filtering) you don't have chance to see it as it's almost square at the bottom of the signal near zero, it still a square wave.

To actually see a improvement you have to place a real band pass filter that get the signal as much as a sine wave and the important part is the lower one near the zero, to let a little gap of both branches of the DBM in the off state by the 0.2 or 0.6 volts of conduction of the diodes.

I'don't have the chance to test the back to back IF cans with the oscope, but in practice they make A LOT of difference, some simulations with ELSIE software shows that with that kind of filtering the signal get a pretty sine wave... (also confirms that a simple LPF don't change the skirt of the Square wave)

Bitx40 uses 12MHz IF so dirt is 12 Mhz away (not taking into account reciprocal mixing and other inter heterodyne products) so you may expect a few birdies and low noise, but beware if you use a low IF frequency...

BTW I saw a youtube video this weekend of a SDR forum presentation in germany on this year (don't have the URL, a friend pass it to me via a fash stick) of the CEO of Flex talking about SDR tech, the reciprocal mixing of phase noise in the VFO make me proud of my decision of make my Si5351 lib with only two outputs at a time and use integer division to avoid jitter and phase noise.

Google it, it's a must see one.

--
73 CO7WT, Pavel.
 

Hmm. ?I guess opinions vary.

In my 2015 edition of the ARRL Handbook, page 10.19, section 10.5.2 for "Switching Mixers",
the discussion about diode ring mixers assumes a square wave for the local oscillator.
The only reference to a sine wave local oscillator in that section is this:
"Normally, the harmonic outputs are so widely removed from the desired output frequency
that they are easily filtered out, so a reversing-switch mixer is just as good as a sine wave
driven analog multiplier for most practical purposes, and usually better for radio purposes,
in terms of dynamic range and noise."

The si5351 is not very well spec'd, but the si5338 of the same famiily is, and those docs suggest?
the phase noise when using fractional values in the output msynth dividers is well under
a factor of two worse than running the part with integer divides on both pll and output msynths. ?
Many in this forum are very happy with their analog vfo, once they've tamed it's tendency to wander.?
That analog vfo would have much worse phase noise than the si5351.

I suspect many of the issues with mixers and birdies and such revolve around poorly terminated mixers,
especially at the if port, and poorly shielded rigs allowing vfo harmonics to crawl into places they should not. ?
On the si5351, I'd be more concerned about crosstalk when using mulltiple outputs than with phase noise. ?

This post from last February: ?/g/BITX20/message/22530
plus a few of the neighboring posts in that thread describe how a diode ring mixer works,
and how a square wave switching an incoming signal can be considered a multiplier. ?

Jerry


On Mon, Oct 23, 2017 at 11:52 am, Pavel Milanes Costa wrote:
I'm not agree, in my experiments I found that driving it with Square Waves is more efficient, but a lot dirtier. ARRL and RSGB Handbooks agree on that, several academic papers on the internet are agree.
Gordon Gibby
 

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?Again I'm not an expert, but even tho this isn't a linear system, for small signals one might be able to make an approximation of it using the superposition principle.


In other words,? ?that square wave has WITHIN IT the sine wave of the desired frequency, and the diode mixer probably responds (to a first order appxoimation) as:


sine wave LO? x modulation frequency --->? ?sum & difference


2nd harmonic of LO? x moduclation frequency? ---> sume and difference


......


nth harmonic of LO x modulation ferequency --->? sum & difference.....


and then the filter next throws out everything except the desired one......hence the book's observation that it doesnt make a huge amount of difference.? ??


In the long run, it is the tiny tiny changes as a result of interaction between the two frequencies on a non-linear transfer function that accomplishes the mixing.? ?The diode isn't a binary device (1 and 0 only) but instead is a non-linear device with a transfer function that has infinite steps between? ?0 volts and 1 volt.? ?


(my 2 cents worth)


I think looking at it in the frequency domain may be more instructive than looking at it in the time domain.? ??


gordon



From: [email protected] <[email protected]> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Monday, October 23, 2017 3:54 PM
To: [email protected]
Subject: Re: [BITX20] Raduino question.
?
Hmm. ?I guess opinions vary.

In my 2015 edition of the ARRL Handbook, page 10.19, section 10.5.2 for "Switching Mixers",
the discussion about diode ring mixers assumes a square wave for the local oscillator.
The only reference to a sine wave local oscillator in that section is this:
"Normally, the harmonic outputs are so widely removed from the desired output frequency
that they are easily filtered out, so a reversing-switch mixer is just as good as a sine wave
driven analog multiplier for most practical purposes, and usually better for radio purposes,
in terms of dynamic range and noise."

The si5351 is not very well spec'd, but the si5338 of the same famiily is, and those docs suggest?
the phase noise when using fractional values in the output msynth dividers is well under
a factor of two worse than running the part with integer divides on both pll and output msynths. ?
Many in this forum are very happy with their analog vfo, once they've tamed it's tendency to wander.?
That analog vfo would have much worse phase noise than the si5351.

I suspect many of the issues with mixers and birdies and such revolve around poorly terminated mixers,
especially at the if port, and poorly shielded rigs allowing vfo harmonics to crawl into places they should not. ?
On the si5351, I'd be more concerned about crosstalk when using mulltiple outputs than with phase noise. ?

This post from last February: ?
plus a few of the neighboring posts in that thread describe how a diode ring mixer works,
and how a square wave switching an incoming signal can be considered a multiplier. ?

Jerry


On Mon, Oct 23, 2017 at 11:52 am, Pavel Milanes Costa wrote:
I'm not agree, in my experiments I found that driving it with Square Waves is more efficient, but a lot dirtier. ARRL and RSGB Handbooks agree on that, several academic papers on the internet are agree.
Vince Vielhaber
 

As I pointed out, I'm using my own Nano. No Raduino is used in this.

Vince.

On 10/23/2017 02:25 PM, Michael Hagen wrote:
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!!!
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.












--
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID "MotDog@..."
Mike@...

--
Michigan VHF Corp.

 

The ARRL Handbook says square waves are better,
though does not say anything about how huge the difference is.

My understanding is that the more a diode ring mixer departs from being a perfect switch
driven by a square wave, the greater the intermodulation distortion.
Slowing down the switching edges by driving with a sine wave does not help
in most measures of performance.

The action of an ideal switching mixer is that of doing an analog multiply of the incoming signal
with a square wave, as described in post 22538 (one beyond the post previously cited).
You could break that square wave down into odd harmonics of specific amplitude through
its Fourier expansion ? and multiply those by
the incoming signal to calculate?hard numbers for what comes out of the IF port. ?
No need for any small-signal handwaving.

Jerry


On Mon, Oct 23, 2017 at 01:15 pm, Gordon Gibby wrote:

hence the book's observation that it doesnt make a huge amount of difference.? ??

?
 

Take a look at this video for an explanation why square signals are better for mixers:?https://youtu.be/WwJKxvz7qbs
Vince Vielhaber
 

I'm going to have a look at the 2430A.

Current setup:
Tek 11402 Scope w/ 11A32 400MHz plugin
Tek P6121 10x probe - 1 meg termination in the scope
No bandwidth limiting

Adafruit si5351 board CLK2 terminated into 51 ohms.
Standalone Nano controlling it.
NOTE: CLK2 is also used for the following measurements.

There is a difference in output between 7.5MHz and 35.5MHz, but only about 15mv rms.

There's a bit of ringing on the square wave but that's probably in my setup.

Ok, with the above setup, at 11.020 MHz:

2ma setting: 190 mv rms.
4ma setting: 380 mv rms.
6ma setting: 560 mv rms.
8ma setting: 735 mv rms.

Vince.

On 10/23/2017 01:50 PM, Vince Vielhaber wrote:

Nope, I don't bandwidth limit that scope (Tek 2430A). I'll do another
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
attenuator, which cuts the voltage in half.
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
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.
--
Michigan VHF Corp.

Gordon Gibby
 

开云体育

Thanks, all, very cool, learned a lot!!


Sent from my iPhone

On Oct 23, 2017, at 5:07 PM, Karl Heinz Kremer, K5KHK <khk@...> wrote:

Take a look at this video for an explanation why square signals are better for mixers:?

Pavel Milanes Costa
 

El 23/10/17 a las 16:53, Jerry Gaffke via Groups.Io escribió:
The ARRL Handbook says square waves are better,
though does not say anything about how huge the difference is.
We are talking the same language, we are agree on the point that square is better, but not always... I'm just making a little note to the side of the page about a special case as per my experience...

Grab your digital copy of the ARRL handbook and keep looking at chapter 10... search for figure 10.22 on page 10.21 just in the next page of your note. Look at the graphic at the bottom of figure 10.22 compare the output from using a sine wave vs square wave, square wave has ALL the harmonics (solid line), the sine one has none (dashed line)

Also the output from a sine VFO is 3dB lower than the square one. ;-)

I was only saying that if you use the Si5351 as BFO to mix with the IF and grab the audio, and you use a low freq on it (below ~2 Mhz as per my experience, worst on the 500 Khz range) you may get a very noisy audio as those solid lines (harmonics) are very close? each other and will mix again and again inside the mixer/amplifiers and you will get a very noisy reception, full of carriers here and there...

On tx there is no problem as the SSB filter wipe them away...

In deed if you use a high enough IF (as the bitx40 do, in 12 Mhz) all the unwanted mixing are cleaned by simple filtering, but beware if you use a low freq as 455Khz or 500 Khz... those unwanted mixing products will haunt you...

Been there, done that, must filter it if you use a Si5351 for BFO below ~2Mhz.

--
73 CO7WT, Pavel.
 

Trouble with a 455khz IF makes sense.?
There is a reason Farhan went to a 45mhz IF on the ubitx.

Plenty of weird things going on around mixers,?
many of which I am sure will surprise me if I ever get beyond armchair pontificating
and try getting designs of my own working.

I really don't have the tools to look for phase noise or minor mixer products.
But did order an sdrplay after hearing Pavel recommend it a few weeks ago for
inspecting crystal filter shapes. ?Is there software appropriate for measuring phase noise
using the sdrplay? ?Does the sdrplay have a local oscillator with significantlly
less phase noise than?the si5351? ?Also hope to use it as a spectrum analyzer,
hooking it up to a Rasberry Pi 3..

Phase noise may matter at some point, perhaps with narrow band digital modes like JT65?
I assume phase noise would present itself as more random noise when tuning in a weak signal,
though there are other possible causes for that symptom. ?
Many say the bitx40 sounds good, even compared to commercial gear that costs 10 or 20
times as much. ?And the Raduino has always had si5351 code that used a fractional output divider,
first with the Etherkit library and now with the si5351bx routines.




On Mon, Oct 23, 2017 at 03:12 pm, Pavel Milanes Costa wrote:
In deed if you use a high enough IF (as the bitx40 do, in 12 Mhz) all the unwanted mixing are cleaned by simple filtering, but beware if you use a low freq as 455Khz or 500 Khz... those unwanted mixing products will haunt you...
 

I believe that phase noise from the si5351 will scale up proportional to the output frequency.
So while phase noise from a 5mhz vco could be fine, it might become more of an issue
with the 45mhz IF of the ubitx. ?Receiving a 30mhz signal would put the vfo at 45+30=75mhz.
So phase noise on 10m with the ubitx that's 15 times worse than the Bitx40 on 40m.
However, several ubitx have been built, and apparently work well.
Jerry


On Mon, Oct 23, 2017 at 04:29 pm, Jerry Gaffke wrote:
Trouble with a 455khz IF makes sense.?
There is a reason Farhan went to a 45mhz IF on the ubitx.
?.....
Phase noise may matter at some point, perhaps with narrow band digital modes like JT65?
 

And what would happen using Si5351 with analog switcher mixer (Tayloe detector). The square wave only close and open the switch.-
LU5DNM

-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Pavel Milanes Costa
Enviado el: lunes, 23 de octubre de 2017 07:13 p.m.
Para: [email protected]
Asunto: Re: [BITX20] Raduino question.


El 23/10/17 a las 16:53, Jerry Gaffke via Groups.Io escribió:
The ARRL Handbook says square waves are better,
though does not say anything about how huge the difference is.
We are talking the same language, we are agree on the point that square
is better, but not always... I'm just making a little note to the side
of the page about a special case as per my experience...

Grab your digital copy of the ARRL handbook and keep looking at chapter
10... search for figure 10.22 on page 10.21 just in the next page of
your note. Look at the graphic at the bottom of figure 10.22 compare the
output from using a sine wave vs square wave, square wave has ALL the
harmonics (solid line), the sine one has none (dashed line)

Also the output from a sine VFO is 3dB lower than the square one. ;-)

I was only saying that if you use the Si5351 as BFO to mix with the IF
and grab the audio, and you use a low freq on it (below ~2 Mhz as per my
experience, worst on the 500 Khz range) you may get a very noisy audio
as those solid lines (harmonics) are very close each other and will mix
again and again inside the mixer/amplifiers and you will get a very
noisy reception, full of carriers here and there...

On tx there is no problem as the SSB filter wipe them away...

In deed if you use a high enough IF (as the bitx40 do, in 12 Mhz) all
the unwanted mixing are cleaned by simple filtering, but beware if you
use a low freq as 455Khz or 500 Khz... those unwanted mixing products
will haunt you...

Been there, done that, must filter it if you use a Si5351 for BFO below
~2Mhz.

--
73 CO7WT, Pavel.
 

Hmm, my analysis in post /g/BITX20/topic/6215251
might be full of beans.

The SiLabs document an619 shows that registers 16,17,18 can set drive levels at clk0,clk1,clk2 to values of 2,4,6 or 8 ma.
With 8ma max into 50 ohms that's a 0.008*50 = 0.4v pk-pk square wave across the 50 ohm load.
Farhan's ubitx has a 6db pad between the raduino and T1, so the primary of T1 sees 0.4v/2 = 0.2v.
T1 has two windings driving the diodes, a step-up transformer, so the diodes see a 0.4v pk-to-pk.
But a single schottky diode has a forward voltage of around 0.4v at 10ma, I have no idea how this
0.4v signal source can drive two schottky diodes in series. ?

But the ubitx apparently works.
What am I missing here?
I'll have to put a 50 ohm load on a si5351 someday, see just how much drive the si5351 can give.

Might be best to include a buffer amp, if only to reduce all the crosstalk you would get between si5351 channels
when asking it to deliver maximum drive.



On Mon, Oct 23, 2017 at 02:54 am, Gordon Gibby wrote:

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:?Kelly Jack <kellyjack1968@... ? ?Sent: Monday, October 23, 2017 5:30 AM?
this page indicates that setting the drive at 2ma equates to 3dbm into a 50ohms load.
Gordon Gibby
 

开云体育

Well again, I didn't follow all of that, but if you put 8 mA into 50 ohms, you get .4 V peak; ?0.8 p-P

(Proof: ?use a halfway rectifier on your home outlet 120 V RMS, and you'll discover that you get somewhere around 160 V DC or more out of it. ? it's not 120 V peak to peak, it is 240 peak to peak!!)



Someone on this forum recently measured the voltages, out of some board or something. ?

I looked at the schematic of the micro bit X that was linked to here, and the RF signal seems to be in series with the transformer winding providing the Heterodyne signal, so the sum of the two could reach much higher levels than either alone at times.

Furthermore, I went and looked at the data sheet of a small signal Schottky diode here:

And there is significant conduction even at 200 mV. ? ?Sure, if you want 10 mA you'll need a little higher voltage, but you can get some signal out of those things at a lot lower voltage than that.

And of course, you already know the punchline, the thing does work!!



Sent from my iPhone

On Oct 24, 2017, at 2:14 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Hmm, my analysis in post
might be full of beans.

The SiLabs document an619 shows that registers 16,17,18 can set drive levels at clk0,clk1,clk2 to values of 2,4,6 or 8 ma.
With 8ma max into 50 ohms that's a 0.008*50 = 0.4v pk-pk square wave across the 50 ohm load.
Farhan's ubitx has a 6db pad between the raduino and T1, so the primary of T1 sees 0.4v/2 = 0.2v.
T1 has two windings driving the diodes, a step-up transformer, so the diodes see a 0.4v pk-to-pk.
But a single schottky diode has a forward voltage of around 0.4v at 10ma, I have no idea how this
0.4v signal source can drive two schottky diodes in series. ?

But the ubitx apparently works.
What am I missing here?
I'll have to put a 50 ohm load on a si5351 someday, see just how much drive the si5351 can give.

Might be best to include a buffer amp, if only to reduce all the crosstalk you would get between si5351 channels
when asking it to deliver maximum drive.



On Mon, Oct 23, 2017 at 02:54 am, Gordon Gibby wrote:

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:?Kelly Jack <kellyjack1968@... ? ?Sent: Monday, October 23, 2017 5:30 AM?
this page indicates that setting the drive at 2ma equates to 3dbm into a 50ohms load.
Gordon Gibby
 

开云体育

Oh and I forgot to say, I think if either of those two Schottky diode's conducts, you get an output. I don't think you have to make both of them conduct simultaneously. ? So I think the barrier to get some output is more like 200 mV ; and I think your signals easily provide that as you have proven.

Sent from my iPhone

On Oct 24, 2017, at 3:34 PM, Gordon Gibby <ggibby@...> wrote:

Well again, I didn't follow all of that, but if you put 8 mA into 50 ohms, you get .4 V peak; ?0.8 p-P

(Proof: ?use a halfway rectifier on your home outlet 120 V RMS, and you'll discover that you get somewhere around 160 V DC or more out of it. ? it's not 120 V peak to peak, it is 240 peak to peak!!)



Someone on this forum recently measured the voltages, out of some board or something. ?

I looked at the schematic of the micro bit X that was linked to here, and the RF signal seems to be in series with the transformer winding providing the Heterodyne signal, so the sum of the two could reach much higher levels than either alone at times.

Furthermore, I went and looked at the data sheet of a small signal Schottky diode here:

And there is significant conduction even at 200 mV. ? ?Sure, if you want 10 mA you'll need a little higher voltage, but you can get some signal out of those things at a lot lower voltage than that.

And of course, you already know the punchline, the thing does work!!



Sent from my iPhone

On Oct 24, 2017, at 2:14 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Hmm, my analysis in post
might be full of beans.

The SiLabs document an619 shows that registers 16,17,18 can set drive levels at clk0,clk1,clk2 to values of 2,4,6 or 8 ma.
With 8ma max into 50 ohms that's a 0.008*50 = 0.4v pk-pk square wave across the 50 ohm load.
Farhan's ubitx has a 6db pad between the raduino and T1, so the primary of T1 sees 0.4v/2 = 0.2v.
T1 has two windings driving the diodes, a step-up transformer, so the diodes see a 0.4v pk-to-pk.
But a single schottky diode has a forward voltage of around 0.4v at 10ma, I have no idea how this
0.4v signal source can drive two schottky diodes in series. ?

But the ubitx apparently works.
What am I missing here?
I'll have to put a 50 ohm load on a si5351 someday, see just how much drive the si5351 can give.

Might be best to include a buffer amp, if only to reduce all the crosstalk you would get between si5351 channels
when asking it to deliver maximum drive.



On Mon, Oct 23, 2017 at 02:54 am, Gordon Gibby wrote:

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:?Kelly Jack <kellyjack1968@... ? ?Sent: Monday, October 23, 2017 5:30 AM?
this page indicates that setting the drive at 2ma equates to 3dbm into a 50ohms load.
Vince Vielhaber
 

I posted the RMS values of all four output modes yesterday. Do you also want the P-P values?

Vince.

On 10/24/2017 02:14 PM, Jerry Gaffke via Groups.Io wrote:
Hmm, my analysis in post /g/BITX20/topic/6215251
might be full of beans.

The SiLabs document an619 shows that registers 16,17,18 can set drive
levels at clk0,clk1,clk2 to values of 2,4,6 or 8 ma.
With 8ma max into 50 ohms that's a 0.008*50 = 0.4v pk-pk square wave
across the 50 ohm load.
Farhan's ubitx has a 6db pad between the raduino and T1, so the primary
of T1 sees 0.4v/2 = 0.2v.
T1 has two windings driving the diodes, a step-up transformer, so the
diodes see a 0.4v pk-to-pk.
But a single schottky diode has a forward voltage of around 0.4v at
10ma, I have no idea how this
0.4v signal source can drive two schottky diodes in series.

But the ubitx apparently works.
What am I missing here?
I'll have to put a 50 ohm load on a si5351 someday, see just how much
drive the si5351 can give.

Might be best to include a buffer amp, if only to reduce all the
crosstalk you would get between si5351 channels
when asking it to deliver maximum drive.



On Mon, Oct 23, 2017 at 02:54 am, Gordon Gibby wrote:

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:* Kelly Jack <kellyjack1968@... *Sent:* Monday, October 23,
2017 5:30 AM
this page indicates that setting the drive at 2ma equates to 3dbm
into a 50ohms load.

<>

--
Michigan VHF Corp.

 

As I recall, you showed some alarmingly low signal levels as the frequency went up.
If the si5351 can only give 8ma at dc, your notes suggest it gets awfully small at 45mhz+SignalFreq
into the first mixer on the ubitx.

Though Gordon's right, there is some conduction through a schottky diode even at 200mv or less.
Perhaps somehow the ubitx works well enough, but could do better if the diode ring mixers were driven harder.

Jerry


On Tue, Oct 24, 2017 at 01:03 pm, Vince Vielhaber wrote:
I posted the RMS values of all four output modes yesterday. Do you also want the P-P values?
 

Ah, ok. ?I'd somehow missed this one.

With the 8ma setting, you have 735mv rms, or 14.7ma rms.
That's a more robust driver than I was expecting. ?
Especially considering that this is an rms value.



On Mon, Oct 23, 2017 at 02:08 pm, Vince Vielhaber wrote:
I'm going to have a look at the 2430A.

Current setup:
Tek 11402 Scope w/ 11A32 400MHz plugin
Tek P6121 10x probe - 1 meg termination in the scope
No bandwidth limiting

Adafruit si5351 board CLK2 terminated into 51 ohms.
Standalone Nano controlling it.
NOTE: CLK2 is also used for the following measurements.

There is a difference in output between 7.5MHz and 35.5MHz, but only about 15mv rms.

There's a bit of ringing on the square wave but that's probably in my setup.

Ok, with the above setup, at 11.020 MHz:

2ma setting: 190 mv rms.
4ma setting: 380 mv rms.
6ma setting: 560 mv rms.
8ma setting: 735 mv rms.
Vince Vielhaber
 

You either don't recall or you didn't read it. Yesterday afternoon I re-measured using a Tek 11402 scope and corrected my previous comment.

Vince.

On 10/24/2017 04:42 PM, Jerry Gaffke via Groups.Io wrote:
As I recall, you showed some alarmingly low signal levels as the
frequency went up.
If the si5351 can only give 8ma at dc, your notes suggest it gets
awfully small at 45mhz+SignalFreq
into the first mixer on the ubitx.

Though Gordon's right, there is some conduction through a schottky diode
even at 200mv or less.
Perhaps somehow the ubitx works well enough, but could do better if the
diode ring mixers were driven harder.

Jerry

On Tue, Oct 24, 2017 at 01:03 pm, Vince Vielhaber wrote:

I posted the RMS values of all four output modes yesterday. Do you
also want the P-P values?

--
Michigan VHF Corp.

Gordon Gibby
 

Well, I sure am grateful for people with great test equipment!!!!

Sent from my iPhone

On Oct 24, 2017, at 6:46 PM, Vince Vielhaber <vev@...> wrote:


You either don't recall or you didn't read it. Yesterday afternoon I re-measured using a Tek 11402 scope and corrected my previous comment.

Vince.


On 10/24/2017 04:42 PM, Jerry Gaffke via Groups.Io wrote:
As I recall, you showed some alarmingly low signal levels as the
frequency went up.
If the si5351 can only give 8ma at dc, your notes suggest it gets
awfully small at 45mhz+SignalFreq
into the first mixer on the ubitx.

Though Gordon's right, there is some conduction through a schottky diode
even at 200mv or less.
Perhaps somehow the ubitx works well enough, but could do better if the
diode ring mixers were driven harder.

Jerry

On Tue, Oct 24, 2017 at 01:03 pm, Vince Vielhaber wrote:

I posted the RMS values of all four output modes yesterday. Do you
also want the P-P values?
--
Michigan VHF Corp.

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