Strange thing on Vero 1W

[Fleming]

Hi all

What do you think of this signal at the exit of a Vero 1w.
In red marked the strange thing ... will be the Modulator or the Stereo Encoder.?

[s2000]

What are you using for your stereo coder and exciter? I take it by the use of the word "vero" you have built some kind of prototype?

The stereo pilot looks very high, how did you set it?

[MC Spanner]

The audio level could be low
What are you saying is strange? Everything in your trace could be quite legit depending on the programme content and levels. How does it sound?

[Fleming]

What are you using for your stereo coder and exciter? I take it by the use of the word "vero" you have built some kind of prototype?

The stereo pilot looks very high, how did you set it?

Thank you for answering s2000

It is a Veronica VCO 5W like that of the image (+ external PLL) but with (driver) 2N2219 + 2N3866 (out), it does not reach 1W ....
The Stereo Encoder is prototype .. (8X) the pilot level can be ajusted.... But together they produce the output of the image. It seems to have spurs on both sides of the carrier ...
Any ideas...?


"We are all very ignorant, what happens is that we do not all ignore the same things" Albert Einstein

[Fleming]

The audio level could be low
What are you saying is strange? Everything in your trace could be quite legit depending on the programme content and levels. How does it sound?

Hi .... MC Spanner

The audio level is not low ... but if you raise it, it overmodulates and the spurs grow.
It sounds good, with good separation but the output is dirty around the carrier ...
This image shows it clearly ...without modulation

"We are all very ignorant, what happens is that we do not all ignore the same things" Albert Einstein

[Fleming]

This image shows only the carrier (without encoder) clearly ... something dirty on the sides ..
Any ideas?

"We are all very ignorant, what happens is that we do not all ignore the same things" Albert Einstein

[s2000]

What type of IC's are you using in the stereo encoder? Is it the type of chip used in ipod transmitters? Or logic discretes?

[Fleming]

It is CMOS logic ...clock +( 2) 4051..to form Mux and Pilot.., audio in flat...to mux ....and all mix passive at end..

[sinus trouble]

Hello Mr Fleming

The uniform spikes closest to your carrier are produced by the stereo pilot! You should see them raise or lower as you adjust the pilot output! Perfectly normal!

It seems clear that you are using some kind of SDR and these are notorious for showing spurs that don't really exist!
The problem worsens with coupling to the SDR via an antenna, Allsorts of noise can be mixed in!
As you may know that spectrum analysis is generally coupled direct to test equipment via attenuators etc..

Also have you checked the signal purity of you pilot tone?

[MC Spanner]

I'm vaguely with Sinus on this one, but there's still a bunch of stuff which doesn't make sense to me and since you're using an SDR, there are all sorts of other artefacts which may be in play due to sampling rates and birdies from the receiver hardware. So all bets are off for proper analysis really. As Sinus says, first make sure you're not overloading the SDR front end.
The pilot-only trace is wide. Your pilot could be so high that it's overdeviating and even causing something to distort in the modulator. How did you set up the pilot level? One method without test equipment is to ramp the pilot up from nothing until the stereo indicator shows on a decent receiver, then bump the level up just a tiny bit more (to compensate for over/under sensitive receivers). That should get you in the ballpark, and hopefully give you an improvement on your observations on the top trace.
Interesting is the second trace with nothing connected to the modulator. You said you're using an external PLL. For this observation, that would be the next place I'd look. Do you know the PLL reference frequency? Try it with the PLL disconnected from the VCO.

[sinus trouble]

Totally agree Mr Spanner!

Its like a jigsaw puzzle with half the pieces missing and trying to make logical sense of the image?

I have to dismiss any SDR test results because of the many variable factors involved! The only observation as you mentioned is the pilot looks way too high!

[Fleming]

Hello Mr Fleming

The uniform spikes closest to your carrier are produced by the stereo pilot! You should see them raise or lower as you adjust the pilot output! Perfectly normal!

Thanks Sinus
I agree ... if you exceed the level of the pilot and also the encoder has multiples of the pilot we have a problem.
But even without the Encoder there are spurs around the carrier and the visible frequencies ... they are not all 19K multiples ... that led me to consider the suggestion of MCSpanner (thank you too) to revise VCO + PLL ... and look what I found ... the image also of a humble SDR ... says it all ...
All that comes to the Modulator from the PLL! Add those in the Encoder and you have a fatal mix.

PD. Do not despise the option of using an SDR as an analyzer ... it is clear that it is not accurate or perfect ... but it is a wonderful alternative, which does not cost hundreds of dollars and allows .. an analysis of the invisible to many followers. ..of this great forum.

[Fleming]

Now I start a new year working to correct the problems ... in the PLL + VCO..and improve the Encoder ... I will keep you informed ...
Thank you and Happy 2019

[radium98]

post pictures and happy new year ,remmber could be some harmonics due to trimmer vc65 vishay etc....

[Fleming]

Hi all
Finally I was able to correct the problems of the transmitter and the encoder. They are attached images. I had an error in the encoder!
Although they do not believe it works very well ... in protoboard ...
Now I go for the development of the PCBs for the PLL and the Encoder

[Fleming]

...

[nrgkits.nz]

...

This will have a lot of half frequency breaking through to the output because the oscillator coils are not matched - they look all over the place.

[radium98]

Oops ,what is this ,how strange that work .

[Fleming]

...

This will have a lot of half frequency breaking through to the output because the oscillator coils are not matched - they look all over the place.

It is not like this.
The output of the modulator is clean at half the frequency and at 2f and above
Look the images taken at 4m from the antenna.
It is necessary to correct the relation between L / C of the varactors ... but it works and the PLL is lock without problems ..

[Fleming]

Oops ,what is this ,how strange that work .

It's not that hard, because you doubt it works?
Only the PLL (different from the Original VERO) and the Stereo Encoder are in development, it is the same idea with other elements .. Look at the diagram ..
It does not look cute on the Protoboard ... but lets see what works.
It will always be easier to copy a PCB ...