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RACAL 6790 Front end




 
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December 12, 2018, 09:24:44 PM *
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Author Topic: RACAL 6790 Front end  (Read 369 times)
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KL7OF
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« on: November 19, 2018, 01:12:11 PM »

I have acquired another Racal 6790.  This rx has a gary wingerd board with the SD50001 quad mosfet in the front end....I need to replace that mosfet..Do I have to use a SD50001 or can I use a SD5000  ?  I can't see any difference in the specs but I'm not familiar with these devices so I'm sure I'm missing something..  The SD50001 is in the $30 range and the SD5000 sells for under $2.  Any insight appreciated....Steve
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #1 on: November 19, 2018, 02:00:44 PM »

Link to the spec sheets?

Likely (guessing) one may be "hardened" or may be selected for lowest noise.
The other possibilities include gain and bias...

W3JN seems to know a bunch about these Racal boxes...

Edit:

Nominally it is a zener protected switch.
Devices like this have been known to be used as linear devices...

Looking at the pdf, seems like the 5000 handles more volts.
Also there are two packages, the plastic and the ceramic.

Looks interchangeable to me.

https://www.universalsemiconductor.com/SD5000-5002.pdf


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_-_- bear WB2GCR                   http://www.bearlabs.com
KL7OF
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« Reply #2 on: November 19, 2018, 03:35:57 PM »

https://uk.rs-online.com/webdocs/0026/0900766b80026c92.pdf
The chip that is in the radio is a SD5000I  (letter I) 20 V .......  same rating as SD 5000 (no letter) 20V  I will see if I can find a place that will sell me a SD5000I...
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WBear2GCR
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« Reply #3 on: November 19, 2018, 03:54:51 PM »

The "I" version is the expensive ceramic "side brazed" package.

I'd opt for the cheap plastic version myself.
If it shows it is susceptible to local RF, then go for the $20 package?
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KL7OF
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« Reply #4 on: December 04, 2018, 06:14:27 PM »

I got the receiver working.  I installed the s d5000 i chip. I had to send to China seems that chip is obsolete. I ordered two of the non hardened versions but haven't tried them.
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KL7OF
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« Reply #5 on: December 08, 2018, 11:34:47 AM »

I see that there is an overvoltage protection module for the A1 board in the 6790 available from  sales@a6a2.co.uk  I can see the website but my emails get rejected for some reason.  Has anyone used this module that can report on it?  Does anyone have a working email address for a6a2??  Thanks 73 Steve...
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