Hi Scott,
On the 400MR system the TTL line is low or 0V for selecting channel 1 (high
band) and 5V to select channel 2 (low band). If you have a problem passing
the high band (1H) you may want to check the TTL line to make sure that the
line drops to 0V, if it does not then the switch cannot pass the high band.
I just ran the TTL control to a scope and tuned on the manual tune, selected
either channel 1 or channel 2 to see the change in the output voltage. Please
note that the voltage on the TTL line stays at whatever the last setting was.
If that works fine, I would guess that the Mini Circuit switch is bad.
If you have a frequency synthesizer you could bench test the switch is a
similar manner.
Shawn
________________________________
> From: main_at_ammrl.groups.io on behalf of Smith, Scott K
> Sent: Wednesday, March 27, 2024 10:40 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] MR400 LO switching
I am sure nearly everyone has had to track down a missing signal.
In this case the root cause in somewhere in the MR400’s LO switching device.
The MR has a single receiver box for both channels. The LO used in detection
is pre-selected by an external module (Mini Circuits RF switch ZASWA-2-50DRA+).
In short, this switch is no longer passing through high band LO to the receiver
making it appear that there is no signal. It looks like the LO for low band
channel is passively allowed through, so one gets the curious result that a
carbon spectrum with full proton decoupling can be acquired while nothing not
even tuning works on the high band channel. All the transmitter pathways checkout
as do the LO’s themselves. Proton work if I manually swap the LO input cable
directly to the receiver.
Are these mini circuit devices known to just quit working? Or might there
be a problem with the power-supply and TTL control lines feeding the switch?
I now have two MR’s with this error.
I would appreciate any suggestions or help I can get at this point.
Cheers,
Scott
Scott K. Smith, Director of NMR Spectroscopy
The University of Texas at Austin | Chemistry | 832-294-1928 |
https://www.utexas.edu/
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Received on Wed Mar 27 2024 - 14:31:01 MST