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Re: Tiny low cost home build spectrum analyzer #spectrum_analyzer

 

Hi Erik,
That is a really nice idea, thank you very much for the suggestion. I have ordered a few parts and look forward to having something to play with a in few weeks. Would you be able to provide a bit more direction as to the source of the software?? I had a quick look in Git-Hub today but did not find anything that looks close to the GUI (windows I guess?) or the associated Arduino sweep/receive code.?

Thanks again
Jim
Re: Tiny low cost home build spectrum analyzer #spectrum_analyzer

 

Very good effort and finally a? nice working instrument,? thanks and Congrats please.
Sarma vu3zmv

On Tue, 3 Dec 2019, 6:41 pm , <erik@...> wrote:
Some more real measurements.
Now with calibrated dBm scale

First to determine the IIP2 I'm using two clean sinus generators through two attenuators combined into the input to measure the IIP3
One is set to 6MHz, the other at 7MHz



At 5MHz and 8MHz you can just see the input third order intermodulation products (IIP3) at -79dB and -74dB.
Calculating the IIP3 gives +9.5dB which is surprisingly good.
This implies that when you keep your input signal below 25dB there will be no internally generated spurs.

It's good practice to check by adding 10dB attenuation if any harmonics you see are internally generated or already present in the input signal.

A good example of measuring IMD is this measurement of my Softrock Ensemble RXTX during transmission through 60dB of attenuation:



The fundamental is at 11.45MHz and second, third and fourth harmonic at -47dB, -46dB and -58dB compared to the the fundamental.
It seems the output low-pass filter of the SoftRock is doing a good job.

Re: Tiny low cost home build spectrum analyzer #spectrum_analyzer

 
Edited

Some more real measurements.
Now with calibrated dBm scale

First to determine the IIP3 I'm using two clean sinus generators through two attenuators combined into the input to measure the IIP3
One is set to 6MHz, the other at 7MHz



At 5MHz and 8MHz you can just see the input third order intermodulation products (IIP3) at -79dBm and -74dBm.
Calculating the IIP3 gives +9.5dBm which is surprisingly good.
This implies that when you keep your input signal below -25dBm there will be no internally generated spurs.

It's good practice to check by adding 10dB attenuation if any harmonics you see are internally generated or already present in the input signal.

A good example of measuring IMD is this measurement of my Softrock Ensemble RXTX during transmission through 60dB of attenuation:



The fundamental is at 11.45MHz and second, third and fourth harmonic at -47dBm, -46dBm and -58dBm compared to the the fundamental.
It seems the output low-pass filter of the SoftRock is doing a good job.

TinySA IMD.PNG

Tiny low cost home build spectrum analyzer #spectrum_analyzer

 

Building and tuning GHz cavities is not everyone's hobby but if you need a zero till a couple of hundred MHz spectrum analyzer there is a much simpler build possible.



This is all you need to measure signals between? 0 and 400MHz at levels between -80dbm and -20dBm
Top blue module is a mixer. Can be found on eBay either as complete module (ADE-1) for 10$ of you only buy the mixer (AD-25MH (much better level 13 mixer), 5pc for 4$) and put it on a small PCB
The two small identical blue modules are SI4432 modules (do NOT use SI4463 modules as these use non overlapping bands) that can be found on eBay for less than 2$
The one directly connected to the mixer acts as a tunable LO with 20dBM? output between 433MHz and 860MHz
The copper module is a 433MHz band pass filter you either buy from eBay for 25$ or build yourself from two EPCOS SAW filters and two SMD inductors for less then 10$
Datasheet
The bottom blue module is the receiver SI4432. Its set at a fixed frequency of 433MHz and does the the logarithmic signal strength measurement. The officiel range is -120dB till 0dB but the range is limited in practise between -100dBm and -20dBm as above -20dBm the SI4432 will start to produce all kind of intermodulation products.?
The module with the USB plug is an Arduino zero compatible to provide the 3.3Volt and to control the SI4432 modules (these need 3.3V MISO/MOSI/CLK)

Some real measurements
Scan from 0 to 5MHz



The phase noise of the LO SI4432 is very visible but the 3kHz RBW results in a nice sharp peak. The noise floor is not very flat but no spurs
The AD9851 clearly delivers a nice clean signal at 1MHz through 40dB of attenuators

Switching to 0-100MHz you get



RBW now set to 300kHz. Output of the same AD9851 at 46MHz
Some small spurs but contrary to cheap "spectrum analyzers" you can buy on eBay which are basically nothing more than a LO, a mixer to DC, a LF RBW filter and a log detector, this SA does not have the many spurs from the harmonic modes of the LO due to proper filtering. The second harmonic from the AD9851 at 92MHz is clearly visible

And for the full range



This is the output of a ADF4351 at 75MHz. The harmonics at 150MHz and 225MHz are visible but sensitivity quickly reduces above 200MHz as I did not yet remove the low pass filter at the output of the LO module so the mixer loses its LO at higher frequencies. The spur at 30MHz is probably an alias from the ADF4351 signal as there is no low pass filter at the input yet.

The datasheet of the SI4432 can be found
And is the module used

For SW you can go to github as there are several repositories that contain usable libraries.

Hope this inspires some creative use of the SI4432 module

tinySA.jpg

Re: Building and tuning a narrow band 2GHz cavity filter

 

This one on eBay

See picture of graph for roll off
Re: Building and tuning a narrow band 2GHz cavity filter

 

I was very lucky to find some cheap on ebay.
But here you can find how to build yourself
Re: Building and tuning a narrow band 2GHz cavity filter

 

Hello Erik, I am following your postings for some time now, as I am also building a spectrum analyzer. I am struggling with the design of an input lowpass. Could you perhaps publish the design of your 1.8GHz lowpass?

J?rg
Re: Measuring the 2GHz cavity filter #spectrum_analyzer

 

Satish

SW (both PC and Arduino)?
HW description incl schematic of the mixers?/g/HBTE/files/SimpleVNA

Will do an update as the current documentation and Arduino SW on github does not yet include the ebay ADF4351 modules, only for the SI5351 module
The principles are the same.

But it will never be a simple kit with fool proof documentation.?
Re: Measuring the 2GHz cavity filter #spectrum_analyzer

 

Hello Erik
Can you place the complete project of your home brewed Ghz VNA analyzer here on the group
That is circuit diagram, and the required boards and also the software or link for it.
Many of us do lack in such a good home brewed equipment and can not afford commercial ones
being very costly
Satish
VU2SNK


On Sat, Nov 30, 2019 at 2:08 PM <erik@...> wrote:

To complete the building I measured the S21 of the cavity filter

First the pass band



As the home build GHZ VNA does not have any shielding the dynamic range is rather limited but the -3dB bandwidth?is about 4MHz and the loss is -3dB. From other measurements its clear the suppression of the image at 21.4MHz offset is good enough.

Certain cavity filters do have harmonic modes that will allow 2nd or higher order harmonics to pass.

I can only measure S21 till 4.3GHz so here is a wide sweep.



The peak at 4.3GHz is an artifact of my SW, its not there when you zoom in. So interdigital filter instead of a comb filter does indeed suppress?the harmonics modes

The S11 measurement shows there is still some room for improvement



but for now I'm happy.

Re: Building and tuning a narrow band 2GHz cavity filter

 

Neat trick with the field sensor. And as always thanks for sharing your interesting experiments.
/Marcus
Measuring the 2GHz cavity filter #spectrum_analyzer

 

To complete the building I measured the S21 of the cavity filter

First the pass band



As the home build GHZ VNA does not have any shielding the dynamic range is rather limited but the -3dB bandwidth?is about 4MHz and the loss is -3dB. From other measurements its clear the suppression of the image at 21.4MHz offset is good enough.

Certain cavity filters do have harmonic modes that will allow 2nd or higher order harmonics to pass.

I can only measure S21 till 4.3GHz so here is a wide sweep.



The peak at 4.3GHz is an artifact of my SW, its not there when you zoom in. So interdigital filter instead of a comb filter does indeed suppress?the harmonics modes

The S11 measurement shows there is still some room for improvement



but for now I'm happy.
Building and tuning a narrow band 2GHz cavity filter

 

During my 2 GHz SA experiments it became more obvious that having three IF's (2.5GHz, 110MHz and 10.7MHz) was leading to all kind of problems so I went looking for a very narrow band cavity filter. To be able to go from above 2GHz directly to 10MHz the 20MHz offset suppression? should be more then 90dB. I could not find a filter with these specs.

According to?calculator?it should be possible to build a 5 resonator interdigital filter at 2 GHz with acceptable loss and narrow enough so I decided to build it. As I have no access to a machine shop I followed the construction proposed??on another web site?and using the square tube and the input/output antenna's from the later and I build the calculated filter from the first link.

Result is a 5 resonator interdigital filter in a square aluminium tube with solid copper resonators as can be seen in this picture

You can just see the input antenna and two copper resonators with their tuning screws

The only special tool I used was a 4mm wire tap for attaching the resonators and the tunng screws.

After building the real problem start. A filter of this order will not let anything through if not tuned correctly. I could not find how other people did this initial tuning so I created a field sensor as shown in this picture

It was small enough to be inserted from one side of the filter past all the untuned resonators till the resonator up for tuning so I could tune one resonator at a time.

The end result was a 2MHz 3db bandwith at 2.016Ghz and sufficient suppression at 20MHz offset to ommit my 110MHz IF.

This led to an updated SA with this block diagram

?

?

Short specs; 0-2GHz input, 0-30dB attenuator IP3 at +17dB with 0dB attenuator. Noise floor around -100dB with 300kHz bandwidth, 300/30kHz HW resolution filters and FFT resolution filters down to 1Hz. Almost no spurs.

You can see the full set of components in this picture

?

?

As the ADF4351 have two outputs I added a 3GHz bridge and a triple receiver so the HW doubles as a 35MHz till 3GHz VNA

The unmarked module at the left bottom is a third ADF4351 that can be used is mixed (0-2GHz) or direct (35MHz-2GHz) tracking generator

I hope this inspires more people to build their own GHz cavity filters
Home brew setup for antenna test

 

Hi all! ?Your ideas born out of actual experiences are appreciated.
1.Objective :just a simple knock out test to have an antenna system for the best bang of the buck.
2.For qrp and qth use.To use same type of antenna for both installation.
3.To include comparison of transmission line and atu's.
4.Will use hf beacons all over the world as signal sources.
5.Test site:a deserted salty beach.
6.Inclined to test unsymetrical type,EFHW ,long wire due to location of the qth to the space available and
personnal bias for ease of installing long wires in emergencies.
7.Limitations:I can only fabricate f.s. meters, simple swr bridges and attenuators. Antenna analysers with micro
? processors ?are over me and my budget. Big toroids for baluns are beyond my reach. But i can make air core
? cores as I have an LC meter.
? My receiver is a Tecsun PL365 with built in signal meter.It cover 1.7 to 29.99mhz .

Thanks in advance,

EmiConstantino. /DW3 CBO
Re: XR2206 function gen for vfo

 

Thank you all guys!
I am convinced the Xr function gen is not the answer to my need.
Your suggestions saved my time and resources.
Gary's Si5351 suggestion is great.Cheap modules are available and affordable.

Thanks again!!

73
Emi , DW3CBO







On Tue, Jul 23, 2019 at 9:44 PM, wb6ogd
<garywinblad@...> wrote:
You should do something like everyone else.

I would use an Si5351, not DDS but hi tech PLL.? Mounted on a board they
are now down to < $4 on ebay.
They are xtal locked, sub Hz resolution, <8KHz-? >200MHz (as I recall).?
There are any number of complete
projects you could copy, just google "Si5351 VFO"..? You do need a
controller (I recommend $3 Arduino) but you can get
someone's program.? Complete VFO (actually 3 output freqs) will cost <$20.
These work great for what you want.
73,
Gary
WB6OGD

On 7/22/2019 10:35 PM, John kolb wrote:
>
> Never used the XR2206 but me experience with discrete component
> function generators in the 1960's indicates the cycle to cycle jitter
> would be too poor for a VFO.
>
> Besides jitter, the XR2206 has a 20 PPM per degree C temperature
> coefficient with a 20K timing resistor, and gets very rapidly worse as
> the timing resistor changes. Saw a comment that the part heats up
> noticeably,? and the data sheet indicates that the deice current
> changes, and thus power and internal heating, with timing resistor
> change.? Sounds far too unstable for SSB.
>
> There are a number of DDS modules on ebay with frequency controlled
> with pushbuttons that are likely stable enough.
>
> John
>
> On 7/21/2019 9:36 PM, emi constantino via Groups.Io wrote:
>> Hello every one.
>>
>> May I know if anyone has the experience of using the XR2206 modules
>> available at ebay?
>> Its rated up to 1mhz sine wave.I am thinking of the idea of mixing
>> its output with a 3mhz xtal
>> oscillator to be used as a vfo for a 40m Bitx clone.
>>
>> My questions are 1)Is it stable enough for qso with modern dds rigs
>> ?2) how much is its current draw ?
>>
>> I know its old school as most of the topics at BITX group is about
>> DDS.My rational are 1)its available
>> and affordable 2) ?I understand the module 3) and most importantant.
>> ?No programming is involved.
>>
>> If there are more modern function gen available I am open to it as
>> long as no programming is required.
>>
>> Thanks in advance for ideas or bits of info.
>>
>> Emi , DW3 CBO
>>
>
>
>
Re: XR2206 function gen for vfo

 

You should do something like everyone else.

I would use an Si5351, not DDS but hi tech PLL.? Mounted on a board they are now down to < $4 on ebay.
They are xtal locked, sub Hz resolution, <8KHz-? >200MHz (as I recall).? There are any number of complete
projects you could copy, just google "Si5351 VFO"..? You do need a controller (I recommend $3 Arduino) but you can get
someone's program.? Complete VFO (actually 3 output freqs) will cost <$20.
These work great for what you want.
73,
Gary
WB6OGD

On 7/22/2019 10:35 PM, John kolb wrote:

Never used the XR2206 but me experience with discrete component function generators in the 1960's indicates the cycle to cycle jitter would be too poor for a VFO.

Besides jitter, the XR2206 has a 20 PPM per degree C temperature coefficient with a 20K timing resistor, and gets very rapidly worse as the timing resistor changes. Saw a comment that the part heats up noticeably,? and the data sheet indicates that the deice current changes, and thus power and internal heating, with timing resistor change.? Sounds far too unstable for SSB.

There are a number of DDS modules on ebay with frequency controlled with pushbuttons that are likely stable enough.

John

On 7/21/2019 9:36 PM, emi constantino via Groups.Io wrote:
Hello every one.

May I know if anyone has the experience of using the XR2206 modules available at ebay?
Its rated up to 1mhz sine wave.I am thinking of the idea of mixing its output with a 3mhz xtal
oscillator to be used as a vfo for a 40m Bitx clone.

My questions are 1)Is it stable enough for qso with modern dds rigs ?2) how much is its current draw ?

I know its old school as most of the topics at BITX group is about DDS.My rational are 1)its available
and affordable 2) ?I understand the module 3) and most importantant. ?No programming is involved.

If there are more modern function gen available I am open to it as long as no programming is required.

Thanks in advance for ideas or bits of info.

Emi , DW3 CBO
Re: XR2206 function gen for vfo

 

Never used the XR2206 but me experience with discrete component function generators in the 1960's indicates the cycle to cycle jitter would be too poor for a VFO.

Besides jitter, the XR2206 has a 20 PPM per degree C temperature coefficient with a 20K timing resistor, and gets very rapidly worse as the timing resistor changes. Saw a comment that the part heats up noticeably, and the data sheet indicates that the deice current changes, and thus power and internal heating, with timing resistor change. Sounds far too unstable for SSB.

There are a number of DDS modules on ebay with frequency controlled with pushbuttons that are likely stable enough.

John

On 7/21/2019 9:36 PM, emi constantino via Groups.Io wrote:
Hello every one.
May I know if anyone has the experience of using the XR2206 modules available at ebay?
Its rated up to 1mhz sine wave.I am thinking of the idea of mixing its output with a 3mhz xtal
oscillator to be used as a vfo for a 40m Bitx clone.
My questions are 1)Is it stable enough for qso with modern dds rigs ?2) how much is its current draw ?
I know its old school as most of the topics at BITX group is about DDS.My rational are 1)its available
and affordable 2) ?I understand the module 3) and most importantant. ?No programming is involved.
If there are more modern function gen available I am open to it as long as no programming is required.
Thanks in advance for ideas or bits of info.
Emi , DW3 CBO
Re: XR2206 function gen for vfo

 

You should reference the chip's datasheet for estimated current draw.? It's out on the 'net.

Given the ship's age, its current draw is likely higher than a complete Raspberry Pi or similar micro.? However, this is a particularly interesting idea, and since I have a few of these chips lying about, I may try it.? But my first XR2206 project is to make an infrasound driver for a Halloween project.?

And I have a story about this chip from the mid-80s when my Elmer was teaching electronics at a local trade school ...

73
Jim N6OTQ


On Mon, Jul 22, 2019 at 6:34 AM emi constantino via Groups.Io <emiconstantino=[email protected]> wrote:
Hello every one.

May I know if anyone has the experience of using the XR2206 modules available at ebay?
Its rated up to 1mhz sine wave.I am thinking of the idea of mixing its output with a 3mhz xtal
oscillator to be used as a vfo for a 40m Bitx clone.

My questions are 1)Is it stable enough for qso with modern dds rigs ?2) how much is its current draw ?

I know its old school as most of the topics at BITX group is about DDS.My rational are 1)its available
and affordable 2) ?I understand the module 3) and most importantant.? No programming is involved.

If there are more modern function gen available I am open to it as long as no programming is required.

Thanks in advance for ideas or bits of info.

Emi , DW3 CBO
XR2206 function gen for vfo

 

Hello every one.

May I know if anyone has the experience of using the XR2206 modules available at ebay?
Its rated up to 1mhz sine wave.I am thinking of the idea of mixing its output with a 3mhz xtal
oscillator to be used as a vfo for a 40m Bitx clone.

My questions are 1)Is it stable enough for qso with modern dds rigs ?2) how much is its current draw ?

I know its old school as most of the topics at BITX group is about DDS.My rational are 1)its available
and affordable 2) ?I understand the module 3) and most importantant. ?No programming is involved.

If there are more modern function gen available I am open to it as long as no programming is required.

Thanks in advance for ideas or bits of info.

Emi , DW3 CBO
When to use the low spur mode of the ADF4351 #spectrum_analyzer

 

For some time I have been fine tuning my spectrum analyzer. Did some improvements like replacing the cavity filter with a much narrower version so the 10.7MHz second IF no longer creates spurs.
And I have replace the Ceramic 30kHz resolution with a 6 pole crystal filter with 40kHz bandwidth but much better form factor.
The total looks now like this with shielding removed:




The phase noise picture overall looked ok apart from some annoying spurs between 30kHz and 100kHz and many small spurs above 200kHz:



After trying many things I switched on the low spur mode of ADF4351 first and second LO and that did make a difference:



Although the phase noise around 30kHz went up with 5dB most of the spurs there did disappear. Did not yet look into the spur at 150kHz
For the many spurs above 200kHz, these are caused by the PC and its USB peripherals as the unconnected Audio input has low noise floor but as soon as connected to the Spectrum Analyzer the noise goes up 20dB.
One small step completed, many to go, the journey is the goal.
Re: Is this a good approach to measure phase noise of a single ADF4351? #spectrum_analyzer

 

Could be as the actual performance of the SA using two of these modules is better than what I measure with the audio method
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