Because they want to be able to switch parts or even vendors at the drop of a hat. People tend to forget that Mini-Circuits doesn't actually make chips.
-- john, KE5FX (yes, this has hosed me before)
We got burned once when their parts (ERA-5?) changed radically.
At least with ordinary MAR-x MMICs, the frequency is quite high and hence the parameters are quite non-ideal, so you may have to consult the Smith chart to make it work reliably.
All those s-params are basically useless when you want to use an RF part in time domain, namely large-signal nonlinear. Even DC behavior is usually poorly defined. Some RF data sheets show a bias trimpot and say "turn the pot until it works."
One has to breadboard and measure to understand the DC and nonlinear behavior of things like MMICs. You are lucky to get any DC curves on an RF fet data sheet. The SAV series is a welcome exception, and I measured more.
A Spice model would be far better than tables of S-params. S-params can be derived from a Spice model, but not the reverse. I think a lot of RF design was created for the pre-computer days.
The max voltage ratings of RF parts seem to (sometimes) assume that peak voltage will be some multiple of supply voltage, and the spec is actually max supply voltage. Sometimes. We've used 7-volt rated parts at 25 volts peak and they were fine.
Cryteck (not right spelling but close) makes some in that range at ~$25 apiece. I have one currently that outputs 1 to 2 ghz. Power supply is 10 volts @ 25 ma and the frequency selection is 1v to 20v. It's recieved some tough handling and some excessive soldering & it's still working like a trooper... It's built on a 1/32 alumina board. Both Digikey & Mouser carry them.
Hul
John Lark> What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I
hat are you trying to do ?
Are you trying to transfer a very broad band DC based _analog_ signal (say DC .. 500 MHz) over an AC link (say 2 GHz).
Why not simply frequency module a VCO ? Why PWM ?
fredag den 30. april 2021 kl. 07.07.16 UTC+2 skrev snipped-for-privacy@downunder.com:
easy demodulation?
That, or just ship a single-bit logic level over a telecom type link. It's just a shower musing, not serious yet.
FM is more work on both ends. Commercial VCOs have pitiful modulation bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast.
For the logic level case, we'd want it to be fast with low jitter. Whatever modulation scheme is used, the time jitter should be a fraction of the "carrier" period.
This problem is similar to the Shannon sampling theorem. A bandlimited signal can be sampled at some rate and reproduced perfectly from the sampled values. The trick is to have the modulation scheme be continuous and bandlimited such as to eliminate the jitter of the modulation/demod scheme.
Wideband FM gets mathematically messy too. Ugly sidebands.
PWM would be fairly easy to generate and detect. I've tested some 10 GBPS tosa/rosa optical links and they do transmit PWM, to various extents. Of course they go bonkers at extreme duty cycles.
What is the problem with a simple FM-demulator ? At the transmitter site just insert some sync pulses that goes to 0 V into the analog input of the VCO. At the receiver site, after the FM demodulator, a simple capacitor/diode circuit s used to restore the 0 V DC level, thus compensating for VCO drift.
Think about analog composite video processing.
What about phase shifting keying (PSK) ?
Just invert the output from the oscillator at input signal change. Of course, you have to establish the initial state somehow to be able to decode current state from only phase changes.
To always know the state, you could use return to zero coding, i.e. a carrier at 0 degrees, a 0->1 transition as +90 degree phase change and
1->0 input change as -90 degrees phase shift (QPSK).Also take look at Manchester coding.
How can you DC couple PSK?
Manchester is phase ambiguous! A long string of 1's looks just like a long string of 0's. And the decode is clock synchronous, so has massive jitter when shipping an arbitrary signal.
PSK ditto. I want to modulate, not encode.
AM/OOK won't work when the receiver has AGC.
fredag den 30. april 2021 kl. 19.04.03 UTC+2 skrev John Larkin:
wouldn't your pwm be OOK?
In analog TV (with negative video modulation) uses maximum power to transmit the synch pulses.
As soon as the TV-receiver has achieved line sync, only the maximum amplitude synch pulse is gated into the AGC circuit. The variable intensity video doesn't affect the AGC. You could use the same principle.
No. It would be a fixed frequency continuous square wave of modulated duty cycle. That does DC coupled transmission of an asynchronous analog or logic-level baseband signal.
The duty cycle can't get extreme or the optical receivers get unhappy.
40/60 % seems conservative for a typical telecom rosa. I might look into duty cycle modulation over an ethernet type path, twisted pairs with magnetics.The Shannon-type math is beyond me here, so I'll just Spice it.
fredag den 30. april 2021 kl. 19.51.58 UTC+2 skrev John Larkin:
so the ~2GHz it self have varying duty cycle? not ~2GHz on/off ?
I guess with two pairs you could send the carrier on one pair to demodulate the other pair at the far end
How about a very fast logic gate (or string of gates) moderated by a delay line. Make one a NOR or NAND and that gets the PWM input?
piglet
BPSK is: Ring mixer like MCL IE-500
RF port: input LO port: output IF port: modulation in
Demodulation / bit sclicing happens in Squaring or Costas loop.
Gerhard
Right. It shouldn't be difficult.
OOK has the long-term receive threshold problem.
AM with synchronous demodulation? PWM only needs one channel and a lowpass filter to demodulate.
Video, like encoded digital data, has continuous activity and known levels (black and white, for instance) to feed back on for AGC. A DC signal might be 0 for six weeks. Can't AGC on zero.
Even digital data needs algorithms, like 8b10b or something, to ensure lots of activity for AGC and phase locking.
I don't want to send clocked digital data, I want to send an analog level.
Suppose the input to the transmitter (IF port here) is +0.5 volts. That makes a carrier of some amplitude and phase.
The receiver gets that carrier. The channel has attenuation. How does the receiver know it's supposed to output +0.5 volts?
It could guess the phase wrong and output -0.5 volts. Or not know the channel attenuation and output +7 volts.
If it sees an invariant sine wave for six weeks, or at powerup, is the signal positive or negative?
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