Forums

200MHz VFO

Started by George Herold February 21, 2014
Hi guys,  The 200 MHz. frequency synthesizer thread got me thinking.  
I could use a 200MHz VFO (say 150 to 250 MHz or something like that)
I don't need much stability, a part per thousand for a several minutes would be enough. 
So what's the simplest way to get there?  An LC oscillator (I've got some nice tunable few pF caps)
There's also a VCO from Maxim.  (max2607) that looks easy.
http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf
Would the manually tunable cap be more stable than the VCO?  

Thanks,  
George H.  
On Fri, 21 Feb 2014 12:00:28 -0800, George Herold wrote:

> Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. > I could use a 200MHz VFO (say 150 to 250 MHz or something like that) > I don't need much stability, a part per thousand for a several minutes > would be enough. > So what's the simplest way to get there? An LC oscillator (I've got > some nice tunable few pF caps) > There's also a VCO from Maxim. (max2607) that looks easy. > http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf Would > the manually tunable cap be more stable than the VCO?
In general a manually tunable cap is more stable, yes. Maxim used to suck at delivery, I've avoided them for so long that I don't know if they still do. Basically they denied that they ever discontinued parts, but on the other hand they'd only make a run of a particular chip when they got enough orders to make up a batch. So if you're a low-volume customer and you want something that doesn't move fast, you're screwed. That was a decade ago -- people with current experience are welcome to speak up. Do you need turn-on to turn-on stability, just something that keeps on frequency once it's tuned, or what? If you want to tune it mechanically and you care at all about getting it dead nuts on then the mechanical design can get painful -- that's part of the reason why everyone uses synthesizers these days. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Fri, 21 Feb 2014 12:00:28 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >I could use a 200MHz VFO (say 150 to 250 MHz or something like that) >I don't need much stability, a part per thousand for a several minutes would be enough. >So what's the simplest way to get there? An LC oscillator (I've got some nice tunable few pF caps) >There's also a VCO from Maxim. (max2607) that looks easy. >http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf >Would the manually tunable cap be more stable than the VCO? > >Thanks, >George H.
People sell VCOs. Emhiser, Mini-Circuits, Z-Comm. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
George Herold wrote:
> Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. > I could use a 200MHz VFO (say 150 to 250 MHz or something like that) > I don't need much stability, a part per thousand for a several minutes would be enough. > So what's the simplest way to get there? An LC oscillator (I've got some nice tunable few pF caps) > There's also a VCO from Maxim. (max2607) that looks easy. > http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf > Would the manually tunable cap be more stable than the VCO? >
Nowadays the decadent method would be to use a DDS chip, a little uC and an encoder. Then you don't have much temperature drift issues which otherwise could pose a problem with your 0.1% requirement. -- Regards, Joerg http://www.analogconsultants.com/
On a sunny day (Fri, 21 Feb 2014 12:00:28 -0800 (PST)) it happened George
Herold <gherold@teachspin.com> wrote in
<853b5d06-2544-4718-a9e0-4fff49f17a86@googlegroups.com>:

>Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >I could use a 200MHz VFO (say 150 to 250 MHz or something like that) >I don't need much stability, a part per thousand for a several minutes would be enough. >So what's the simplest way to get there? An LC oscillator (I've got some nice tunable few pF caps) >There's also a VCO from Maxim. (max2607) that looks easy. >http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf >Would the manually tunable cap be more stable than the VCO? > >Thanks, >George H.
1 in 1000 makes 250 kHz drift. Any VCO will do, transistor some coil. Hand effect, use metal box. Buffer amp to prevent output loading.
On Fri, 21 Feb 2014 12:00:28 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >I could use a 200MHz VFO (say 150 to 250 MHz or something like that)
That is a quite broad range +/-25 %
>I don't need much stability, a part per thousand for a several minutes would be enough.
An FM broadcast tuner with 100 MHz +/-10 % tuning range would be a good reference. 1000 ppm would mean 100 kHz error, which is comparable to FM frequency raster (200 kHz), thus without AFC things would work and if AFC is used, it would not jump to the wrong station.
>So what's the simplest way to get there? An LC oscillator (I've got some nice tunable few pF caps)
FM broadcast receivers have achieved such stability with simple mechanical LC local oscillators for at least 60 years.
>There's also a VCO from Maxim. (max2607) that looks easy. >http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf
Check if Mini Circuits would have some usable VCO modules.
>Would the manually tunable cap be more stable than the VCO?
Definitively. However, there are issues like microphonics. There are issues with the slip ring connectors, so if you have a dual section variable capacitors, connect the sections in series, i.e. connect the stators into the resonance circuit and no connection to the rotor. Any two section BC FM variable capacitor should be ideal for 200 MHz, however the large tuning range might be an issue.
On Friday, February 21, 2014 3:27:17 PM UTC-5, Tim Wescott wrote:
> On Fri, 21 Feb 2014 12:00:28 -0800, George Herold wrote: > > > > > Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. > > > I could use a 200MHz VFO (say 150 to 250 MHz or something like that) > > > I don't need much stability, a part per thousand for a several minutes > > > would be enough. > > > So what's the simplest way to get there? An LC oscillator (I've got > > > some nice tunable few pF caps) > > > There's also a VCO from Maxim. (max2607) that looks easy. > > > http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf Would > > > the manually tunable cap be more stable than the VCO? > > > > In general a manually tunable cap is more stable, yes. > > > > Maxim used to suck at delivery, I've avoided them for so long that I > > don't know if they still do. > > > > Basically they denied that they ever discontinued parts, but on the other > > hand they'd only make a run of a particular chip when they got enough > > orders to make up a batch. So if you're a low-volume customer and you > > want something that doesn't move fast, you're screwed. > > > > That was a decade ago -- people with current experience are welcome to > > speak up. > > > > Do you need turn-on to turn-on stability, just something that keeps on > frequency once it's tuned, or what? If you want to tune it mechanically > and you care at all about getting it dead nuts on then the mechanical > design can get painful -- that's part of the reason why everyone uses > synthesizers these days.
Thanks Tim, I guess I should have mentioned this is just a one-of. So no production. (I thought I'd order a few of the maxim chips with my next digikey order. I looked at some the the synthesizer chips.. I just strikes me that it's a whole design project to get one up and running. (since I've never used on before.) George H.
> > > -- > > > > Tim Wescott > > Wescott Design Services > > http://www.wescottdesign.com
<upsidedown@downunder.com> wrote in message 
news:fiefg9td6mm9g08gvanoojd1bbeffo7ufc@4ax.com...
> On Fri, 21 Feb 2014 12:00:28 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > >>Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >>I could use a 200MHz VFO (say 150 to 250 MHz or something like that) > > That is a quite broad range +/-25 % > >>I don't need much stability, a part per thousand for a several minutes >>would be enough. > > An FM broadcast tuner with 100 MHz +/-10 % tuning range would be a > good reference. 1000 ppm would mean 100 kHz error, which is comparable > to FM frequency raster (200 kHz), thus without AFC things would work > and if AFC is used, it would not jump to the wrong station. > >>So what's the simplest way to get there? An LC oscillator (I've got some >>nice tunable few pF caps) > > FM broadcast receivers have achieved such stability with simple > mechanical LC local oscillators for at least 60 years. > >>There's also a VCO from Maxim. (max2607) that looks easy. >>http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf > > Check if Mini Circuits would have some usable VCO modules. > >>Would the manually tunable cap be more stable than the VCO? > > Definitively. > > However, there are issues like microphonics. > > There are issues with the slip ring connectors, so if you have a dual > section variable capacitors, connect the sections in series, i.e. > connect the stators into the resonance circuit and no connection to > the rotor. Any two section BC FM variable capacitor should be ideal > for 200 MHz, however the large tuning range might be an issue. >
You will need to go back a few 10's of years to find any mechanical tuned FM broadcast receivers. Most now are synthesized. tm
On Fri, 21 Feb 2014 13:32:30 -0800, George Herold wrote:

> On Friday, February 21, 2014 3:27:17 PM UTC-5, Tim Wescott wrote: >> On Fri, 21 Feb 2014 12:00:28 -0800, George Herold wrote: >> >> >> >> > Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >> >> > I could use a 200MHz VFO (say 150 to 250 MHz or something like that) >> >> > I don't need much stability, a part per thousand for a several >> > minutes >> >> > would be enough. >> >> > So what's the simplest way to get there? An LC oscillator (I've got >> >> > some nice tunable few pF caps) >> >> > There's also a VCO from Maxim. (max2607) that looks easy. >> >> > http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf Would >> >> > the manually tunable cap be more stable than the VCO? >> >> >> >> In general a manually tunable cap is more stable, yes. >> >> >> >> Maxim used to suck at delivery, I've avoided them for so long that I >> >> don't know if they still do. >> >> >> >> Basically they denied that they ever discontinued parts, but on the >> other >> >> hand they'd only make a run of a particular chip when they got enough >> >> orders to make up a batch. So if you're a low-volume customer and you >> >> want something that doesn't move fast, you're screwed. >> >> >> >> That was a decade ago -- people with current experience are welcome to >> >> speak up. >> >> >> >> Do you need turn-on to turn-on stability, just something that keeps on >> frequency once it's tuned, or what? If you want to tune it >> mechanically and you care at all about getting it dead nuts on then the >> mechanical design can get painful -- that's part of the reason why >> everyone uses synthesizers these days. > Thanks Tim, I guess I should have mentioned this is just a one-of. So > no production. (I thought I'd order a few of the maxim chips with my > next digikey order. > > I looked at some the the synthesizer chips.. I just strikes me that it's > a whole design project to get one up and running. (since I've never > used on before.)
I think you're right. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Tim Wescott wrote:
> On Fri, 21 Feb 2014 13:32:30 -0800, George Herold wrote: > >> On Friday, February 21, 2014 3:27:17 PM UTC-5, Tim Wescott wrote: >>> On Fri, 21 Feb 2014 12:00:28 -0800, George Herold wrote: >>> >>> >>> >>>> Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. >>>> I could use a 200MHz VFO (say 150 to 250 MHz or something like that) >>>> I don't need much stability, a part per thousand for a several >>>> minutes >>>> would be enough. >>>> So what's the simplest way to get there? An LC oscillator (I've got >>>> some nice tunable few pF caps) >>>> There's also a VCO from Maxim. (max2607) that looks easy. >>>> http://datasheets.maximintegrated.com/en/ds/MAX2605-MAX2609.pdf Would >>>> the manually tunable cap be more stable than the VCO? >>> >>> >>> In general a manually tunable cap is more stable, yes. >>> >>> >>> >>> Maxim used to suck at delivery, I've avoided them for so long that I >>> >>> don't know if they still do. >>> >>> >>> >>> Basically they denied that they ever discontinued parts, but on the >>> other >>> >>> hand they'd only make a run of a particular chip when they got enough >>> >>> orders to make up a batch. So if you're a low-volume customer and you >>> >>> want something that doesn't move fast, you're screwed. >>> >>> >>> >>> That was a decade ago -- people with current experience are welcome to >>> >>> speak up. >>> >>> >>> >>> Do you need turn-on to turn-on stability, just something that keeps on >>> frequency once it's tuned, or what? If you want to tune it >>> mechanically and you care at all about getting it dead nuts on then the >>> mechanical design can get painful -- that's part of the reason why >>> everyone uses synthesizers these days. >> Thanks Tim, I guess I should have mentioned this is just a one-of. So >> no production. (I thought I'd order a few of the maxim chips with my >> next digikey order. >> >> I looked at some the the synthesizer chips.. I just strikes me that it's >> a whole design project to get one up and running. (since I've never >> used on before.) > > I think you're right. >
What some of the Chinese vendors do is copy an example design from a datasheet or app note, verbatim. It seems to work. -- Regards, Joerg http://www.analogconsultants.com/