My experience with Minicircuits is that they have EXTREME sensitivity to
the AFC line. I'd use a resistor divider from the same battery and a
bypass cap.

Something like a pair of 100K resistors and a 10 uF cap. Naturallly,
ground the cap at the oscillator ground pin.

----------

Also, the Vcc has to be well bypassed AT THE OSCILLATOR.

These things are very sensitive to any change in the VCC voltage. A
battery is often not all that low of an impedance and so some good bypassing
will help.

Finally, how are you taking the signal off to your analyzer?

I haven't used the POS-900 but in general, these critters want a paasive
50 ohm attenuator right on their output to avoid signals sneaking back and
screwing up the oscillator.


Jim Pennell
N6BIU

I've also observed................it you are not using the auto mode on your
spectrum analyzer, meaning if you have too fast of a sweep rate for your
I.F. bandwidth, you will see the results that you are running into. I use an
HP 8558B, and if I set the SA improperly, I will see the same results. Try
slowing down the sweep rate if you haven't done so.

Pete

"Jim Pennell" wrote in message
ink.net...
My experience with Minicircuits is that they have EXTREME sensitivity to
the AFC line. I'd use a resistor divider from the same battery and a
bypass cap.

Something like a pair of 100K resistors and a 10 uF cap. Naturallly,
ground the cap at the oscillator ground pin.

----------

Also, the Vcc has to be well bypassed AT THE OSCILLATOR.

These things are very sensitive to any change in the VCC voltage. A
battery is often not all that low of an impedance and so some good
bypassing
will help.

Finally, how are you taking the signal off to your analyzer?

I haven't used the POS-900 but in general, these critters want a paasive
50 ohm attenuator right on their output to avoid signals sneaking back and
screwing up the oscillator.


Jim Pennell
N6BIU

I've also observed................it you are not using the auto mode on your
spectrum analyzer, meaning if you have too fast of a sweep rate for your
I.F. bandwidth, you will see the results that you are running into. I use an
HP 8558B, and if I set the SA improperly, I will see the same results. Try
slowing down the sweep rate if you haven't done so.

Pete

"Jim Pennell" wrote in message
ink.net...
My experience with Minicircuits is that they have EXTREME sensitivity to
the AFC line. I'd use a resistor divider from the same battery and a
bypass cap.

Something like a pair of 100K resistors and a 10 uF cap. Naturallly,
ground the cap at the oscillator ground pin.

----------

Also, the Vcc has to be well bypassed AT THE OSCILLATOR.

These things are very sensitive to any change in the VCC voltage. A
battery is often not all that low of an impedance and so some good
bypassing
will help.

Finally, how are you taking the signal off to your analyzer?

I haven't used the POS-900 but in general, these critters want a paasive
50 ohm attenuator right on their output to avoid signals sneaking back and
screwing up the oscillator.


Jim Pennell
N6BIU

Thanks for all the help.

Yes, you are right in the assumption that I've had it as 'clean' as is
realistically possible.

Yes, it's random noise.

To explain, when the output of my board showed a 'triangle' as an output on
the Spectrum Analyser, I first suspected by PLL, so I took the VCO module
off the board and 'benched it up'. I used separate batteries for Vtune and
Vcc supply, with very short (2cm) connections. I even put 1UF, 1N and 100N
caps across the Vcc ** and Vtune ** pins and took the RF out on RG316
directly to the Analyzer sheilded an grounded with extreme care. When I
still observed hideous phase noise, I even tried decoupling the batteries
with a resistors/caps in each supply line. I also tried all sorts of pads
using SMD resistors cleverly soldered to the output pin and case... So I'm
convinced I've given the VCO a better environment than anyone could possibly
achieve in reality (ie. even on the best PCB layout).

The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

Perhaps if one of you guys would mind me sending you a screenshot, direct
(23kB), that may shed some light on it?

Al.
----
mail[underscore]me[at]freenet[dot]co[dot]uk

Thanks for all the help.

Yes, you are right in the assumption that I've had it as 'clean' as is
realistically possible.

Yes, it's random noise.

To explain, when the output of my board showed a 'triangle' as an output on
the Spectrum Analyser, I first suspected by PLL, so I took the VCO module
off the board and 'benched it up'. I used separate batteries for Vtune and
Vcc supply, with very short (2cm) connections. I even put 1UF, 1N and 100N
caps across the Vcc ** and Vtune ** pins and took the RF out on RG316
directly to the Analyzer sheilded an grounded with extreme care. When I
still observed hideous phase noise, I even tried decoupling the batteries
with a resistors/caps in each supply line. I also tried all sorts of pads
using SMD resistors cleverly soldered to the output pin and case... So I'm
convinced I've given the VCO a better environment than anyone could possibly
achieve in reality (ie. even on the best PCB layout).

The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

Perhaps if one of you guys would mind me sending you a screenshot, direct
(23kB), that may shed some light on it?

Al.
----
mail[underscore]me[at]freenet[dot]co[dot]uk

Alex Collins wrote:

Thanks for all the help.

Yes, you are right in the assumption that I've had it as 'clean' as is
realistically possible.

Yes, it's random noise.

To explain, when the output of my board showed a 'triangle' as an output on
the Spectrum Analyser, I first suspected by PLL, so I took the VCO module
off the board and 'benched it up'. I used separate batteries for Vtune and
Vcc supply, with very short (2cm) connections. I even put 1UF, 1N and 100N
caps across the Vcc ** and Vtune ** pins and took the RF out on RG316
directly to the Analyzer sheilded an grounded with extreme care. When I
still observed hideous phase noise, I even tried decoupling the batteries
with a resistors/caps in each supply line. I also tried all sorts of pads
using SMD resistors cleverly soldered to the output pin and case... So I'm
convinced I've given the VCO a better environment than anyone could possibly
achieve in reality (ie. even on the best PCB layout).

The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

Perhaps if one of you guys would mind me sending you a screenshot, direct
(23kB), that may shed some light on it?

Al.
----
mail[underscore]me[at]freenet[dot]co[dot]uk


Perhaps that's -75dBc at a bandwidth of 0.001Hz?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Alex Collins wrote:

Thanks for all the help.

Yes, you are right in the assumption that I've had it as 'clean' as is
realistically possible.

Yes, it's random noise.

To explain, when the output of my board showed a 'triangle' as an output on
the Spectrum Analyser, I first suspected by PLL, so I took the VCO module
off the board and 'benched it up'. I used separate batteries for Vtune and
Vcc supply, with very short (2cm) connections. I even put 1UF, 1N and 100N
caps across the Vcc ** and Vtune ** pins and took the RF out on RG316
directly to the Analyzer sheilded an grounded with extreme care. When I
still observed hideous phase noise, I even tried decoupling the batteries
with a resistors/caps in each supply line. I also tried all sorts of pads
using SMD resistors cleverly soldered to the output pin and case... So I'm
convinced I've given the VCO a better environment than anyone could possibly
achieve in reality (ie. even on the best PCB layout).

The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

Perhaps if one of you guys would mind me sending you a screenshot, direct
(23kB), that may shed some light on it?

Al.
----
mail[underscore]me[at]freenet[dot]co[dot]uk


Perhaps that's -75dBc at a bandwidth of 0.001Hz?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

In article ,
says...
Thanks for all the help.
The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

You're subtracting 30 dB (i.e., 10*log10(RBW)) to account for the 1-khz
RBW, right?

Also, to look at noise at a 1 kHz offset, you need a much narrower RBW
filter. Looking at 1 kHz from the carrier through a 1 kHz filter, you
will be only -6 dB down (or -3, depending on how your analyzer specifies
its RBW) with a perfect signal! Take a look at the parameters in the
graphs at http://www.qsl.net/ke5fx/synth.html -- I use a 100 Hz RBW
filter to make measurements at 1 kHz from the carrier.

Also, what other VCOs are you comparing to? A rule of thumb is that
equivalent-quality VCOs tend to get about 6 dB noisier per octave of
frequency. A very good 900-MHz VCO will have about the same noise
profile as a crappy 90-MHz VCO.... and that's without even getting into
the tuning-sensitivity question that others have raised.

Finally, simple temperature-related drift (both short term and long
term) will make it tough to measure anything 1 kHz from the carrier of a
900 MHz VCO. You're expecting almost one part per million stability
from an unlocked VCO, and that isn't reasonable. To characterize phase
noise at 1 kHz from the carrier, you should:

1) Lock the VCO with a PLL whose loop bandwidth is at least an order of
magnitude lower (100 Hz or less)

2) Use an analyzer RBW at least an order of magnitude lower (100 Hz or
less)

3) Perform this test only with a stabilized analyzer (otherwise, its
internal LO's noise performance may be even worse than the VCO under
test... something that's especially likely with lower-frequency VCOs)

4) Don't forget the 10*log10(RBW) adjustment factor.

Those four steps will get you close, but to do the job right, you need
two mo

5) Distinguish between AM and PM noise by using the VCO under test to
drive a mixer's LO port to saturation, with a significantly-cleaner
reference driving the other port of the mixer

6) Compensate for the noise-equivalent bandwidth of your analyzer's RBW
filters. Typically this will make the true noise values 2-3 dB worse
than the observed values.

All 6 of these steps may be necessary to reproduce Mini-Circuits'
catalog specification for the VCO.

-- john

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------

In article ,
says...
Thanks for all the help.
The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

You're subtracting 30 dB (i.e., 10*log10(RBW)) to account for the 1-khz
RBW, right?

Also, to look at noise at a 1 kHz offset, you need a much narrower RBW
filter. Looking at 1 kHz from the carrier through a 1 kHz filter, you
will be only -6 dB down (or -3, depending on how your analyzer specifies
its RBW) with a perfect signal! Take a look at the parameters in the
graphs at http://www.qsl.net/ke5fx/synth.html -- I use a 100 Hz RBW
filter to make measurements at 1 kHz from the carrier.

Also, what other VCOs are you comparing to? A rule of thumb is that
equivalent-quality VCOs tend to get about 6 dB noisier per octave of
frequency. A very good 900-MHz VCO will have about the same noise
profile as a crappy 90-MHz VCO.... and that's without even getting into
the tuning-sensitivity question that others have raised.

Finally, simple temperature-related drift (both short term and long
term) will make it tough to measure anything 1 kHz from the carrier of a
900 MHz VCO. You're expecting almost one part per million stability
from an unlocked VCO, and that isn't reasonable. To characterize phase
noise at 1 kHz from the carrier, you should:

1) Lock the VCO with a PLL whose loop bandwidth is at least an order of
magnitude lower (100 Hz or less)

2) Use an analyzer RBW at least an order of magnitude lower (100 Hz or
less)

3) Perform this test only with a stabilized analyzer (otherwise, its
internal LO's noise performance may be even worse than the VCO under
test... something that's especially likely with lower-frequency VCOs)

4) Don't forget the 10*log10(RBW) adjustment factor.

Those four steps will get you close, but to do the job right, you need
two mo

5) Distinguish between AM and PM noise by using the VCO under test to
drive a mixer's LO port to saturation, with a significantly-cleaner
reference driving the other port of the mixer

6) Compensate for the noise-equivalent bandwidth of your analyzer's RBW
filters. Typically this will make the true noise values 2-3 dB worse
than the observed values.

All 6 of these steps may be necessary to reproduce Mini-Circuits'
catalog specification for the VCO.

-- john

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------