Multiplier Bias Homepage

Multipliers by RPG Physics (Zimmermann), Germany

Note that all the are EXTREMELY sensitive to static discharges. These are delicate, expensive and hard to repair items. Please be very careful - wear a grounding strap, keep in contact with a chassis, do not power cycle anything unnecessarily. Also, be very careful when biasing the multipliers. Make sure you have the correct supply, that the current on the multiplier doesn't get too high (less than 2 mA for all), and that you do not ram the various tuners into their stops .

Also, please note that we now have just one kind of (Please note: NO attenuator has been implemented in the The Attenuator is a gold colored unit from Custom Microwave, and the attenuator is fully closed with the knob all the way out(anti-clockwise).

Multiplier Tuning instructions

Make sure the 230-690 GHz attenuators are fully attenuated (knob all the way out).

Tuning Procedure: Set the doubler and tripler voltage to Zero, then put the to normal, so that the multiplier can be biased as follows

180-220 GHz, Multiplier, RPG-Physics, X2: No Tuners, Self Biased

220-270 GHz, Multiplier, Millitech, X3: No Tuners, Self Biased
280-330 GHz, Millitech, X4: 2 Tuners, Bias at 2-3V
320-380 GHz, Millitech, X4: 2 Tuners, (1990 model, Both 4th, 5th harmonic), Bias at 2-3V
320-380 GHz, Millitech, X4: 2 Tuners, (1999 model, no 5th => more RF Power for 4th harmonic), Bias at 2-3V
380-440 GHz RPG Multiplier(X5): 3 Tuners, Bias at 2-3V
440-510 GHz RPG Multiplier(X6): 4 Tuners, Doubler at 3-5V, Tripler at 2V.
600-660 GHz RPG Mulitplier(X6): 4 Tuners, Doubler at 3-5V, Tripler at 2V.
660-720 GHz RPG Mulitplier(X6): 4 Tuners, Self Biased
780-840 GHz RPG Mulitplier(X6): 4 Tuners, Self Biased
840-920 GHz RPG Mulitplier(X12): 4 Tuners, Self Biased

Switch in the line with the UIP command and try to the

Set the Gunn frequency Tuner and Backshort. Instructions are laminated on the sidecab wall near the door.

General multiplier settings:

Set the 650 and 850 Multiplier tuners (4) to the position suggested on their respective specification sheets. The rebuild tuners specification sheets are quite accurate!
The 492 multiplier has not been rebuild yet, tuning is still almost arbitrary! In fact the tripler stage draws a lot of current, which is indicative of the fact the multiplier is on it's very last harmonic leg. As of 3/2001 I was still able to get 10uA of current at 492 GHz however.
The 345 Quadrupler has two tuners only. Tune the input tuner to maximize the varactor current and tune the output tuner to drop the peak varactor current by about half (couples power to the 4th harmonic). Be aware that the older Millitech X4 Multiplier puts out as much power at the 4th as 5th harmonic. Though it makes to convienient to tune the 345 GHz Rx in the 400 GHz Range, it also adds in noise from the other harmonic frequency!)

Once slowly open the attenuator and carefully monitor the current drawn by the multiplier. Note: that the 650 and 850 multiplier now have an internal 100KOhm protection. This means that w/o LO applied the will indicate a 10uA/volt bias positive current. Once LO power is applied and coupled into the multiplier, the current will go negative, though on some multipliers very little effect on the bias (with increasing LO) is noticed.

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Do NOT exceed 3mA on the doubler and 2mA on the tripler.

Tuning up the

T1 is the doubler input tuner. Tune to maximize the negative current. If there is no current, lower the varacter bias voltage until rectified current starts to show. Be careful to Moniter the at this stage. Since the 850 Multiplier chain has no attenuator, adjusting T1 is very likely to pull the frequency of the Gunn beyond the lock range of the PLL.
Be aware of this!! You can still tune with the PLL unlocked because the Gunn frequency is only off by a few hundred MHz at most. Just lock the PLL when you are done tuning the receiver.
T2 tunes is the doubler output power. Tune T2 to drop the doubler current by about 20-40%. This should increase the current on the tripler stage.
T3 is the input tuner of the tripler, tune to maximize the current on the tripler. Note that T2 & T3 interplay. the current!
T4 is the tripler output tuner. Tune T4 to drop the tripler current by 20-40%. This means that power is coupled out of the multiplier. However completely dropping the current to a local minima is most often NOT the best operation position.

Now tune the to get some SIS current reading. From now on the process is iterative. That is, optize the SIS current by adusting the:

Multiplier tuners

Gunn backshort tuners

Variable attenuator on the 230-690 Rx's

Receiver tuners

Bias of the multiplier

The 850 has one extra adjustment, the focus of the multiplier. This micrometer moves the 850 LO chain normal to the dewar, and maximizes the coupling to the SIS mixer.