Date   
Re: DDS spectral "purity" ?

Jaques Anthony
 

Hi all,
     Over the last week or so I have been doing quite a lot of measurements myself. They also confirm that the MMIC ruins what is otherwise quite a good spectral output, and I am thinking about various ways to fix it.
    So I would have been very interested to see Jim's video. Unfortunately though clicking on the link does not run the file.Evidently my browser does not know what to do with that extension. (I haven't come across it before either.)
     Related to this; I discovered a long time ago that the chinese modules (and possibly the AD985x itself) generates a whole forest of junk at about -60dBm (ish) while it changes frequency, and for about a second or so afterwards. In any sweep mode it does this all the time of course!
                                                                Tony (G3PTD)...

Re: DDS spectral "purity" ?

Alfredo Mendiola Loyola
 

Hello,

I advice to use the CFB Opamp THS3201.
You can use a 75 Ohm or 200 Ohm Resistor on the input instead the 50 Ohm to get more output voltage.
See the datasheet for the second and third harmonics.

I'm using these opamps with my AD9851 DDS.

Regards.
Alfredo Mendiola Loyola
OA4AJP
Lima, Peru

Re: DDS spectral "purity" ?

K5ESS
 

Jim,

Very Interesting.  Looks like the ERA3 generates lots of harmonics if the AD-9850 data sheet is to be believed.  Also found the latter part of the sweep very interesting.  I’m assuming that the responses shown marching right to left are from aliasing but they shouldn’t be showing up at output frequencies below 40 MHz with an assumed 125 MHz clock.  Maybe some funny business going on between the aliased frequencies and the harmonics generated in the ERA-3?  I’d be interested in seeing comments or just speculation on the likely source of these signals.

Mike, K5ESS

 

From: PHSNA@... [mailto:PHSNA@...]
Sent: Saturday, July 09, 2016 5:04 PM
To: PHSNA@...
Subject: [PHSNA] DDS spectral "purity" ?

 

 

Steve and other have discussed the spectral purity, or lack thereof, from our inexpensive DDS modules and accessories. Playing around a bit today with a spectrum analyzer, I made a "home movie" of a sweep from one my my very early builds of a Type-2 PHSNA

PHSNA Type-2 (push-pull transformer output)
Type-2 AD-9850 module with on board filter removed
Standard 30 Mz version LPF on the PHSNA
The ERA-3+ running with a bit too much bias, at ~ 40 mA
Using the WinPHSNA app with 9600 baud Bluetooth communications
Sweep from 1 MHz to 40 MHz, with 100 kHz steps
Rigol DSA-815TG analyzer

SA vertical divisions 10 dB (top = +10 dBm)

SA horizontal divisions 10 MHz (0 to 100 MHz scan)

 

It's too big (12 MB) for Yahoo to allow into the Files or Photos areas, so here's the URL for it on my web page

http://www.n5ib.net/DDS_Spectrum.wmv

 

The cinematography will not earn me any Red Carpet time, but it's interesting to watch the wheat field march across the screen. Gives a good feel for the limitations of inexpensive test gear. Make popcorn, call the kids. It's rated "G" and is just over minute long.


Jim, N5IB

 

DDS spectral "purity" ?

N5IB
 

Steve and other have discussed the spectral purity, or lack thereof, from our inexpensive DDS modules and accessories. Playing around a bit today with a spectrum analyzer, I made a "home movie" of a sweep from one my my very early builds of a Type-2 PHSNA

PHSNA Type-2 (push-pull transformer output)
Type-2 AD-9850 module with on board filter removed
Standard 30 Mz version LPF on the PHSNA
The ERA-3+ running with a bit too much bias, at ~ 40 mA
Using the WinPHSNA app with 9600 baud Bluetooth communications
Sweep from 1 MHz to 40 MHz, with 100 kHz steps
Rigol DSA-815TG analyzer

SA vertical divisions 10 dB (top = +10 dBm)

SA horizontal divisions 10 MHz (0 to 100 MHz scan)


It's too big (12 MB) for Yahoo to allow into the Files or Photos areas, so here's the URL for it on my web page

http://www.n5ib.net/DDS_Spectrum.wmv


The cinematography will not earn me any Red Carpet time, but it's interesting to watch the wheat field march across the screen. Gives a good feel for the limitations of inexpensive test gear. Make popcorn, call the kids. It's rated "G" and is just over minute long.


Jim, N5IB


Re: More features for experimenter's board software

vasilyivanenko@...
 

Thanks

More features for experimenter's board software

Nick Kennedy
 

I've uploaded new versions of the sketch and manual for my Experimenter's Board program.


I've made quite a few changes to make configuring the software (for chip type, etc.) easier for the user.


I also added or revised these features:


Voltage measurement. This is useful if you use battery power. The voltage can be read out on demand via a menu command. Also, voltage is checked continuously every second and a "low battery" alarm can be given if it falls below a specified level.


I added a function to save the current configuration: frequency / band and step size to EEPROM so the board will start up with the same parameters in the future.


I added a function to send a short test message in RTTY (60 WPM / 45 baud) repetitively. This is getting a little esoteric, but I wanted to try it, plus the Elecraft XG3 does it, so why not.


Separate WPM specifications can be given for the Morse messages in audio and the test message sent out via the RF output.


I did a few other things to make the user interface more friendly.


To re-iterate, this implementation uses three pushbuttons for control and a mini speaker for output via Morse.


One switch causes the frequency to be announced and the other two provide step UP and step DOWN frequency changing.  A long press of the frequency ID button causes a cycle through single-letter menu options that are now up to nine.  I won't repeat them all in this email.


73-


Nick, WA5BDU

Re: ADE-1+

lsasmazel
 

Hi Mark,

Thanks a lot.

73
Levent WW2L

Re: Bandpass filter measurement anomalies - problem identified

Steven Dick
 

I updated the file to rev2: "Bandpass filter measurement anomalies R2.pdf" in the K1RF folder in the files section showing improvement of LC bandpass filter responses on the left edge using the PHSNA Type II with and without the ERA-3+ output amplifier. I included circuit mods to eliminate the ERA-3+.  Don't do the change if your PHSNA application is working fine for you.  The mod if useful if you need to do accurate measurement on relatively wideband LC bandpass filters on the left side of the filter response if you see unexplained "jaggedies".

Regards,
"Digital Steve", K1RF


New file uploaded to PHSNA

PHSNA@...
 

Hello,


This email message is a notification to let you know that
a file has been uploaded to the Files area of the PHSNA
group.


File : /K1RF/Bandpass Filter measurement anomalies R2.pdf
Uploaded by : k1rf_digital_steve <sbdick@...>
Description : Shows bandpass filter plots using type II PHSNA with and without the ERA-3+ output amplifier and how to mod circuit


You can access this file at the URL:
https://groups.yahoo.com/neo/groups/PHSNA/files/K1RF/Bandpass%20Filter%20measurement%20anomalies%20R2.pdf


To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398


Regards,


k1rf_digital_steve <sbdick@...>

Re: ADE-1+

Mark Dunning
 

Minikits still sell them. In my experience a reliable supplier.


http://www.minikits.com.au/components/mini-circuits/mini-circuits-mixers

73


Mark Vk6WV

ADE-1+

lsasmazel
 

I cannot see ADE-1 on Kits and Parts anymore. Is there a new source for this mixer? 


Happy 4th

73 de WW2L 

Sketch uploaded for Experimenter's board

Nick Kennedy
 

I've uploaded my sketch for the N5IB Experimenter's board for the Nano and cheap DDS module.  It's in a new folder called Experimenter's Sketch WA5BDU, I think.


I chose to go with a minimal configuration using three pushbutton switches for input and a tiny speaker for output via Morse to the user.


In its simplest mode, one switch causes the frequency to be annunciated and the other two give a Step Up and Step Down frequency change function.


By holding down the annunciator button, a list of menu options will be played. This is similar to the approach used in Steve Weber's ATS-3 and Dan Tayloe's Stinger Singer frequency counter. You release the button on hearing the desired option.


I store band (actually, just ten frequencies) data and step size in EEPROM.


Functions available now are-


Change step size

Change bands

Send repetitive message in Morse via RF output

Turn RF output Off and back On

Store current frequency to 'scratch pad" EEPROM memory, and recall same

Annunciate current frequency

Step frequency up or down


My notion is to put this thing in a fairly tight box with a battery so I can use it as a signal source with minimal leakage - hence no display and no cables except RF out.


A little tweaking of the source code is required. First, there's a flag for AD9850 or AD9851 versions. Also, there are routines that do a "one time" write to EEPROM to establish band data and so on. You'll typically let them run on first loading and then comment them out so they don't run every time you start the program.


Details are in the PDF in the same folder.


73-


Nick, WA5BDU

Getting my Experimenter board going

Nick Kennedy
 

I've finally gotten into assembling my N5IB Nano / DDS experimenter board the past day or so. I initially fired it up with just the two modules plus the regulator components installed to see if they'd work.  They did, although I've worked through a few issues.  I have both an AD9850 and an AD9851 version of the Type II eBay boards and they both worked.


At first I started with the PHSNA terminal version software, but to simply things I've gone to the example sketch from a DDS library I've written, for now. Very bare bones.


I'd like to see what I can do with no interface and no display.  Maybe make it tell me stuff in Morse and I'll talk to it with two or three pushbuttons. The Elecraft XG3 is sort of a good example, in ways both good an bad. I'd like to put it into a tight box with internal battery so it can be a signal source with minimal leakage. My PHSNA leaks out too much signal to try to attenuate it down to 1 uV or so for receiver testing.


I'm using the AD9851 version, so I've changed the filter to pass 70 MHz.


73-


Nick, WA5BDU

Re: Bandpass filter measurement anomalies - problem identified

Steven Dick
 

I updated file "Bandpass filter measurement anomalies R1.pdf" in the K1RF filter showing improvement of LC bandpass filter responses on the left edge using the PHSNA Type II with and without the ERA-3+ output amplifier.

Regards,
"Digital Steve", K1RF

New file uploaded to PHSNA

PHSNA@...
 

Hello,


This email message is a notification to let you know that
a file has been uploaded to the Files area of the PHSNA
group.


File : /K1RF/Bandpass Filter measurement anomalies R1.pdf
Uploaded by : k1rf_digital_steve <sbdick@...>
Description : Shows bandpass filter plots using type II PHSNA with and without the ERA-3+ output amplifier


You can access this file at the URL:
https://groups.yahoo.com/neo/groups/PHSNA/files/K1RF/Bandpass%20Filter%20measurement%20anomalies%20R1.pdf


To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398


Regards,


k1rf_digital_steve <sbdick@...>

Re: Bandpass filter measurement anomalies - problem identified

Steven Dick
 

Problem has been isolated on my Type II PHSNA. The ERA-3+ is causing the harmonic distortion. I first tried reducing the amplitude of the input signal to ther ERA-3+ by crude tests - jumpering the output of the first attenuator at R3 with various resistors. I realize it was mismatched, but ok for this crude test. The amplitude of harmonics went down a bit but they were still there.  Then, I eliminated the ERA-3+ in  the signal path by the following crude method: I soldered a jumper across R2 to increase the amplitude, removed the jumper at pins 2-3 on P102 just after the anti-alias low pass filter, and took the output directly from pins 1 and 3 to a coax to BNC jumper to drive my filters.  This gave me about -7dbM of output power, albeit mismatched all over the place. The response was beautiful!! - no more jiggles due to harmonics on the left slop of the bandpass filter responses. 

The harmonics don't show up if you are testing lowpass filters.  The harmonics don't show up if you are testing narrowband crystal filters. The harmonics are quite obvious when you are testing LC bandpass filters on their left edge.

For the Type II PHSNA, if you remove the first attenuator and drive the antialias filter directly from the push-pull transformer, you have 6dB more power output than the Type 1 as it is no longer doubly terminate.  This is permissible per the AD9851 data sheet.  My recommended fix is to eliminate the first attenuator, take the output from the antialias filter, and use it to drive the final 6dB output attenuator from the output of the antialias filter after removing the components in and out of the ERA-3+.  I'll do a write-up on this AFTER field day.

Regards,
"Digital Steve", K1RF

 

Re: Bandpass filter measurement anomalies

Steven Dick
 

Yup, the file "BRARC BPF Sweeps 17 Dec 2013.pdf" in the Files area shows the same effect I was posting about - the weird duplicated filter shape on the left side of the bandpass filter plots.

"Digital Steve" K1RF

Re: Bandpass filter measurement anomalies

N5IB
 

A recent check with a spectrum analyzer on a Type-2 DDS module, whose on-board LPF had been removed, mounted on an Experimenter Board with the "push-pull" output transformer and a 50 ohm termination, showed the 2nd harmonic (of 10 MHz) down about 30 dB from the fundamental. This board does not include the wide band amp.

I'll see about pulling out another Type-2 DDS on a Type-2 PHSNA board with the MMIC amp and see what contribution the amp makes.

I saw the same effect when testing a bunch of our club's BPFs a couple of years ago with a Type-1 PHSNA. See the file "BRARC BPF Sweeps 17 Dec 2013.pdf" in the Files area. On those plots it looks like the 2nd harmonic was 28 dB or so down.

This is one of the few places where the interchangeable LPFs on the Type-2 PHSNA could be a useful feature. You can have a selection of them to use when testing filters at frequencies well below their pass band, where harmonics will give ghost responses. You can usually get another 20 dB or so of harmonic suppression.

Jim, N5IB



---In PHSNA@..., <sbdick@...> wrote :
Hi all. Have any of you observed any strange wiggles on the left edge of bandpass filter measurements?  This had been bugging me for awhile and I had attributed it to bad cabling, non-linearities in toroids, etc but I think I found the cause.  See writeup in the K1RF folder, file "bandpass Filter Measurementr Anomalies".  I think harmonics generated in the ERA-3+ output stane are causing wiggles and jiggles I see on the left side of a bandpass filter response. Has anyone else seen a similar problem?
Regards,
"Digital Steve", K1RF


Re: Bandpass filter measurement anomalies

Steven Dick
 

Thanks Rudolf. Good info.

Regards,
"Digital Steve", K1RF

Re: Bandpass filter measurement anomalies

Rudolf Reuter
 

Hello Steve,

Thank you for the very interesting post.

Because I did not like a wide band amplifier because of the
lack of qualified measuring equipment, I designed a passive
output filter for the DDS generator. Please look at:
http://www.rudiswiki.de/wiki9/AmateurRadioDDSgenerator#Filter_AD9850_from_DL5FA

With a symmetric transformer I reach about -3 dBm output level.
If I increase the DDS DAC output current within a allowed range,
0 dBm output level is achievable.
http://www.rudiswiki.de/wiki9/AmateurRadioDDSgenerator#Output_level_0_dBm

73, Rudolf DL5FA