Teardown of 2 hp samplers - Page 1
Forum section: electronics / testgear

author: RoV
author_rank: Regular Contributor
timestamp: October 20, 2021, 09:15:20 pm
content: I bought them for curiosity and at a low price, so the first thing I did was to open them: they are small jewels. I would say practically identical (one seems a little damaged, but maybe it still works) even if the models are different: the 7806 should go on the YTO of analyzer hp8595e, while the 7964 should go on the hp8594e.The only tuned part is the SRD matching network; the rest seems usable at frequencies much higher than the 3-6.8 GHz that I see in the block diagram of the analyzer(s). Of course the diodes may set some limit.I try an explanation, on the basis of my understanding.From right (RF input) to left:the block on the right (which is also mounted a bit rotated on one) could be an attenuator pad. Or simply a piece of absorber material;then I would say there is a coupling capacitor (single layer ceramic);across the track feeding the capacitor there are two resistive traces towards ground, connected in the center to the RF feed line. I suppose these realize the right side termination of the slotline that is furthest to the left, to reduce the residual pulse after driving the diodes;a double beam-leaded schottky diode (two diodes in series) takes the RF signal in the center; the sample pulse comes from the left through the slotline and puts the diodes into conduction; the sampled RF signal appears then on both opposite diode sides (top and bottom) and is low pass filtered by two small ceramic capacitors to ground. Follow two series termination resistors towards the outputs, which due to the way the circuit is made will be in phase with each other;further to the left of the diodes is the slotline that carries the sample pulse. The slotline is terminated on the left by a broadband dummy load (the brown triangle where the slotline opens);in the middle of the slotline there is a jumper that brings the pump signal to the SRD diode, which is located on the bottom, with one side grounded. It's hard to say that's it's a diode, it looks like a pad... But with the meter from the outside I could see the junction with the cathode to ground, 0.7 V typical of a silicon diode. On the upper side of the jumper there is a large ceramic capacitor towards ground, which resonates with the jumper and completes the matching network;the jumper, in addition to acting as a driving inductor for the SRD, feeds the slotiline whith the pulses produced by the diode, which then propagate in two directions: on the left they are absorbed, on the right they reach the schottky diodes. After the diodes, further to the right, the slotline widens increasing its impedance, but is immediately terminated (see above);the series of bridges on the upper left is the rest of the matching network of the SRD, so probably the sampling signal to be multiplied cannot be too different from the 279-298 MHz indicated in the block diagram of the spectrum analyzers.

author: jeremy
author_rank: Super Contributor
timestamp: October 21, 2021, 12:29:35 am
content: Very cool! Any idea what the discolouration on the substrate is from?