Hi...
At my shop, we currently use a Rohde&Schwarz ZVH4 Antenna/cable/spectrum analyzer.
We've been using this portable unit for almost 10 years... but...
Two weeks ago, the ZVH4 shown an issue: Noisy s11 / Smith curves and mediocre isolation limits.
I analysed the case to find a 50 dB weak tracking generator.
On spectrum analyser, the ZVH shows excellent behavior (i can easily measure a -140 dBm signal on a 1 kHz span (30 Hz RBW)), so the "receive" side is no issue.
However, in both "Antenna & Cable test" and "Network Analyzer" modes the tracking generator is about 50 dB down, greatly handicapping s11 / Smith measurments (noisy curves) and making isolation tests totally unuseable above a mere 40 dB.
On "Antenna & Cable test", the tracking output is the same 50 dB down on both Port 1 and Port 2.
Also, TG level (from 0 dBm down to -40 dBm) is linear (from -50 dBm down to -90 dBm).
I opened the unit to take pictures to try to spot something revelant w/o success.
Our ZVH4 being still useable, i did not go any further (no probing / signal level measurment) with the unit open.
Notes:
1 - That ZVH4 RF board has SEVERAL SPDT RF switches, mainly 42551 (Peregrine Semi PE42551 9k - 6 GHz SPDT) and S50 / S60 (the nearest device i found on DK is SKY13298-360LF).
2 - Several S50 / S60's switches are used in cascade. I suspect that R&S used this arrangment for maximum port-to-port isolation.
3 - The "75" devices are probably also RF switches but i didn't want to remove the stickers for reliability purposes.
Does anyone have worked with ZVH-4
Do you have a service manual or, at least, "Thery of Operation" / block diagram
Thank you.
Normand Martel VE2UM
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