[Premium-Rx] Mini-Circuits SRA-3MH+

[Ahmet Gundes]

I used a couple different types of mixers. One had a lower LO drive of +7
dBm ( made by Synergy ) and I had to put a pad between the mixer and the
LO drive.  Another one was an RF Prime ( no longer in business ) +17dBm
mixer. Results are the same without getting into usual IMD performance,
etc... of mixers under normal usage conditions. But I still think that
using a Pad between mixer and LO Drive helps clean up the signal and get
a bit lower Noise ( in my opnion ! ). But then again lower LO power
mixers have lower IPs.

Original mixer used by WJ, M9D, has a more limited range on the lower
frequency side according to catalog info. It is rated at RF 2 - 400MHz.  
Also the LO Drive power is rated at +20dBm and an Intercept point of
+30dBm.  I checked a few 8718's and their LO drive power levels vary from
unit to unit.

I am wondering if the 8718's that have a front plate with a 15kHz - 30MHz
range indication are using the M9D also or a different mixer for better
lower frequency coverage.

I believe Mini Circuits also might have a mixer which will exactly match
the M9D's PinOut configuration so this way you do not have to cut any
trace on the PCB.

A funny design "flaw" in my opinion is that this First mixer is not
"properly" grounded and the input side uses the connector's contact with
the case for grounding as opposed to also using the PCB trace like the
other pins that are grounded via the pcb traces.  When installing the new
Mixer, I would ground the Case as well and connect all grounded pins to
one spot on the PCB. 

Not to mention an ineffective Surge/Lightning protection used in the Low
Pass Filter module.  I wonder why they even installed it.

Regards,

Ahmet


[IMAGE]

Has anyone had experience using the SRA-3MH+ mixer in place of the
standard WJ M9D mixer?  It appears that Mini-Circuits has improved both
the mid-band conversion loss and lower cutoff frequency from the older
SRA-3H commonly used to replace the WJ M9D in the 87xx series radios. I
have one with a blown M9D and need to replace it soon.

“Old”   Mini-Circuits SRA-3H, RF 0.05-200 MHz, IF DC-200 MHz, P_LO=17dBm,
Loss=5.18dB, Model features SP, IMT

“New” Mini-Circuits SRA-3MH, RF 0.025-200 MHz, IF DC-200 MHz, P_LO=13dBm,
Loss=4.77dB, Model features SP, IMT

How much trace cutting is needed?

W9CLA

Craig L. Anderson, Ed.S.

Vice President - Administration

Saint Paul College

Minnesota State Colleges & Universities System

Voice:  651.846.1365

Fax:     651.846.1675

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