[hpsdr] Front End protection

[Larry Taft]

Which explains why in the TR-7 the MPN3404 PIN diode is the first thing 
to go.  Hmmmm.........and it always shorts out providing protection for 
the mixer.

RF Space is telling me the max input to the SDR-IQ board is +7dBm but 
there is preamp/attenuator/band filter stuff in front of the A/D.  +7 
dBm isn't much, what with cheap coax from Radio Shack carrying +65 dBm 
mixed in the spaghetti pile of cables around the operating position.

What diodes are in the RA 6830?  Rail volts?  Time for a little 
protector board?  Cerberus?  And Gian just suggested LEDs across the input.

73, Larry  K2LT

FRANCIS CARCIA wrote:
> Larry,
> Those gas tubes don't conduct until 70 or so volts. I would think the 
> A/D toast at that voltage. I have a TR7 and never leave it connected 
> to the antenna when not in use.
> My RA 6830 is rated 20 watts input. It also has a gas tube ahead of 
> the the active limiter made up from two voltage regulators and some 
> high speed diodes. The Cubic R3030 has a sensor on the front ent that 
> opens a relay if the input gets too high. That is too slow for a 
> lightning transient.
>
> */Larry Taft <ltaft at charter.net>/* wrote:
>
>     FRANCIS CARCIA wrote:
>     > ***** High Performance Software Defined Radio Discussion List *****
>     >
>     >
>     >
>     ------------------------------------------------------------------------
>     >
>     > I don't know which Greek God guarded the gate but how are we
>     going to
>     > protect this fast A/D from static and lightning transients?
>     Racal used
>     > an interesting active limiter ahead of the RA6830 because the older
>     > RA6790 had real bad burnout problems with the FETs in the first
>     mixer.
>     > I would think we need more than a NE2 across the input. Frank WA1GFZ
>     >
>     ------------------------------------------------------------------------
>     Drake used a small gas tube across the TR-7 input along with a RF
>     choke. The weak link in the TR-7 is the PIN diode that switches the
>     calibrator signal into the receiver front end. The first mixer
>     seems to
>     hold up quite well. Of course the schematic doesn't show the parts or
>     the values but I can find them. They were a field fix.
>
>     73, Larry K2LT
>
>
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