Thread: Mcl Sbl-1
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Old September 12th 10, 03:30 AM
vk3akc vk3akc is offline
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First recorded activity by RadioBanter: Sep 2010
Location: Australia
Posts: 2
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Quote:
Originally Posted by Sven Lundbech View Post

This seems to indicate to me that the mixer input is not 50 ohm but a
lot lower. I tried terminating all other ports with 50 ohms with no
noticeable difference. What am I missing?

Why can't I see the correct level in to the device. I have plenty of
drive before the pad but it reduces when connected to the SBL-1.

I am missing something. Can anyone prompt me?




--
vk3akc


You are on the right track: The SBL-1 LO port input impedance is not 50 ohms
as you have correctly measured. On top of that, it is rather unlinear, i.e.
drive level dependent.

Reason: LO drive has to turn mixer quad diodes in and out of conduction. The
RF current needed for that depends on the instantaneous voltage/current
point on the diode characteristic.

Conclusion: Important thing is that the three ports of the SBL-1 are
terminated in 50 ohms, i.e. 'see' a low swr/return loss from the mixer's
viewpoint. Your 3 dB pad adds nicely to that. You have done just the right
thing.

Ease back and enjoy the result!

vy 73
OZ7S Sven
Thank you very much Sven for going to the trouble of answering my query.

I will continue on with the next phase of the project with confidence.

Kind Regards
Kevin