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TUNING VCO : error (254) for VCO1 > 2200MHz !?!
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TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by vincentvije on Thu Apr 18, 2013 10:55 pm

Please, I need some help...

I've made two RC1a WB, and all is working fine, well it seems...
With VCO2 (ROS1700), no matter min and max values, it's ok : tune and works fine

With VCO1 (ROS2500+), when asking higher frequencies, the tuning fail and send values for a wrong signal to VCO input.
For example, if I ask for 2300-2400 MHz, instead of generating the correct sawtooth in the VCO1 input, tuning choose values that generate a BIG triangle that jam for exemple 2100-2600MHz...
For values < 2200MHZ, it seems ok.

So I suppose that VCO1 limited input voltage (0-14V) is not compatible with the tuning voltage range generated from sawtooth + offset...
For the amplifier, I put R13=R15=100k and R14=R16=10k. So I've a X11 amplifier.

I think that changing VCO1 to X6 should correct the problem ?
But I could change the program too so that tuning cover just the range of VCO1.
Could someone help me with this ?

Or does someone had the same kind of problem ?

Thanks for any help, experience, recommendation !
Regards,

Vincent
vincentvije
 
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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by lightningserpent on Fri Apr 19, 2013 12:47 am

According to the datasheet the ROS-2500+ max tuning voltage is 14v. Assuming IC8/IC9 are 3.3v and using the formula "Vin*((Rf/Ri)+1)=Vout" your current resistor choice is feeding approx 36.3v into the VTune pin. A 32k(13.86v) or at most a 32.4k(13.99v) should be used instead of the 100k.

The ROS-1700(guessing "W") has a max VTune of 24v. You are also feeding approx 36.3v into that pin. You should consider changing it to a 62k(23.7v) to better match the data sheet specs.

Link to my build notes of the RC1a with a section devoted to VCOs and Tuning:
http://forums.adafruit.com/viewtopic.php?f=16&t=30621

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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by vincentvije on Fri Apr 19, 2013 2:40 am

Thanks a lot, lightningserpent,

So you confirm to me that the problem of the tuning I got is from my bad choice of resistors ?
So the tuning problem is that the most of the time, the tuning is trying out of VCO range voltage ?

Thanks, then if you confirm, I will change resistors this way !
Thanks so much !

Vincent
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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by lightningserpent on Sat Apr 20, 2013 12:19 am

My suggestion would be to change the VTune resistors to a value closer to what I suggested and see if that helps. I am sure overdriving the VCO to that degree is playing a role in your problems. You can use the formula "Vin*((Rf/Ri)+1)=Vout" to play around with different resistor values to come up with one you like. The resistor values I came up with have the Vout voltage next to them.

example: 3.3v*((64k/10k)+1)=23.7v

If the problem still exists after changing the resistors post again and we can do some more troubleshooting.

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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by vincentvije on Sat Apr 20, 2013 12:33 am

Thanks a lot, lighningserpent !
All my WBs are working well !

But I saw that with the same antenna each WB is sending a different dB level in my spectrum analyzer (with same VCO and same frequency band tuned).
So I changed the GALI, and each time I change the GALI, the dB level is different. I get an 10dB difference from -60 to -50 (with reference at -80bB).
I don't know what to think... It's a big difference.

I got one GALI with nothing in its output, do I changed it too.

Could the gain be so sensible to components placements ?
Could the difference be so high between two GALIs ?

Apart from theses differences, my 3 WBs are working perfectly with a radius of 3m with good antennas, and 1.5m or less with PCD antennas.
I made two other ABs <ith other ROS, yet I need to try them. I followed what you say to fix their resistances.
I don't think to have problems, well apart from GALIs and components exact placement differences.

Thanks again.
I will report here much more information when I finish tests...
But I really worry with dB level differences...

Best regards,

Vincent
vincentvije
 
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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by lightningserpent on Sat Apr 20, 2013 9:02 am

The only thing I can suggest to try is to check the waveform with an oscilloscope after the amplifier. If the wave is distorted try removing C60 and see how that works out for you. I had a problem with C60 distorting the waveform very badly; even after replacing it with a new one.

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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by vincentvije on Sun Apr 21, 2013 1:04 pm

Hello lightningserpent,

C60 ?
Thanks a lot, I already saw in your post that you had to remove C60, but looking in RC1a, I saw it couldn't be it's C60, because it is on VCO2 antenna output after SXA or GALI.
So I suppose it is the C60 form micronics design, between 2.5V IC14 putput (after R35), and GND, so it' for stable LMX2433 supply.

Could you confirm it was this one of 1uF ?
But in RC1a, the design is slightly different, and C60 is C77 and 4.7uF value, not sure it will change things...
I checked my sawtooth in oscilloscope, and it seems stable, sightly irregular but stable.

SXA or GALI, and dB level difference ?
Another preoccupation I have is that from one WB to another (I soldered 5), the output level after the GALI is not the same. I have a maximum of 20 to 30% difference en dB (I've a signalhound, great and cheap stuff).
It seems a lot to me.
And when I change the GALI, I get a change in output level.
I was wondering if SXA could be better. I bought some too, but didn't used them for the moment, I don't want to kill all my amps before solving this !

Thanks again, your experience and advises help me great.
I'm not specialist in RF...

Best regards,

Vincent
vincentvije
 
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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by lightningserpent on Sun Apr 21, 2013 5:11 pm

I built the RC1a and C60 is located just after Q2(which ever amp you went with: GALI, SXA, or BGA). C60 is a stabilizer for the gain stage and should be 3.9pF.

It is important to know that the silkscreen on the boards may not be correct; the silkscreen was not correct for my boards and I had to use design files for component placement.

Unfortunately I do not have a spectrum analyzer so I can not give any information about dB changes between amps.

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Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by vincentvije on Wed Apr 24, 2013 1:42 pm

Hello lighningserpent,

I've a good stability and no problem with C60, well, for the moment.

I made 5 RC1a.
Three with with ROS2500 and ROS1700, from them two with external antennas (different models), and one with PCB antenna.
Two with ROS2600 and ROS1300 (with 5V supply), from them one with external antennas (different models), and one with PCB antenna.

About PCB, when I mount all the stuff with aluminium standoff, the capacities of 68pF and 100pF leading to PCB antennas goes sometime wrong (a lot of nF), then the GALIs or SXAs warm and then burn...
So I changed for slimmer standoff and tried to avoid being so near to ground plane with external part of standoff...
It seems it's better, but it's not perfect.
I always check the capacities of 68pF and 100pF leading to antennas after putting the standoff ! When I see some 10 or 100nF, then I remove and put back standoff...
If not, amplifiers burn in less than 10s (depend of hopw much nF) ! It's good to have a RLC meter !

About GALIs and SXAs, in GSM lower band, with SXAs, it seems a lot better in my spectrum analyzer (signalhound, less than US$1000).
In higher frequencies, not much difference, but I need to make more tests...

About program, I think it's possible to jam more (better radius), changing how the program works and drive VCOs, I will check that... one day I hope.

Thanks you again for your help.
I hope to publish some more news, with time.

Best regards,

Vincent
vincentvije
 
Posts: 5
Joined: Thu Apr 18, 2013 10:39 pm

Re: TUNING VCO : error (254) for VCO1 > 2200MHz !?!

by lightningserpent on Wed Apr 24, 2013 11:53 pm

I am glad all is working well and that I was able to help to some degree. I had some concerns with the stand offs and went with slim standoffs and nylon screws to hold the boards together. I was just not comfortable with conductive screws with voltage passing through them. Good luck with future projects. The WaveBubble was the most complicated project I had ever done, but gave me a lot of confidence in building my own circuits; that and how important datasheets are.

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Please be positive and constructive with your questions and comments.