[Skimmertalk] RP-16 front end tenderness

[N4ZR]

Thanks, Ted.  Very interesting, and timely, with IARU coming up.  
Looking forward to your design - it would be even better if it 
incorporated the first-stage limiting - one fewer box hi.

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 7/11/2019 10:06 AM, Ted Gisske wrote:
> Front-end protection for your new Red Pitaya is a worthwhile investment. RP
> specs the maximum input voltage at 1V P-P. This is probably so low due to
> the 1:14 input transformers. My guess is that older RP-14 and RP-10 boards
> have a similar maximum voltage rating, if you are using the external
> transformers.
>
> I am using a DX Engineering receiver protector, which I recommend, as it has
> lightning protection, as well gross overload protection, built-in. It's not
> enough, though. I hooked up a scope to my skimmer antenna and ran some
> high-power transmitting test. My skimmer antenna is a couple of hundred feet
> from my 40M Delta-Loop and, when running full power, it puts 15V P-P across
> my 50 Ohm scope input. The DXE protector does a great job of limiting this
> voltage to 2V P-P. That, however, is twice the rated max voltage of the RP.
> Not good enuf...
>
> The easiest solution is to disconnect, or short, the antenna with a T/R
> relay activated by your PTT line. That will work, but isn't ideal. I'm a
> pretty hard-core contester and likely am transmitting at over a 50% duty
> cycle in a contest, which would result in a lot of chopped-up decodes. My
> skimmer is in a pole-shed quite a ways from the shack, so running a PTT line
> is inconvenient, in any case.
>
> I'm working on a more elegant design to work in conjunction with the DXE
> protector, which will do the heavy lifting. It is an adaptive PIN-Diode
> attenuator that will reduce the 2V P-P out of the DXE protector to below the
> 1V P-P max RP spec. the trick is to do the limiting in a "soft" way that
> does not generate a lot of harmonics that result in false decodes on higher
> bands.
>
> I'm modeling the design at the moment. It's a few discrete parts driving a
> PIN-Diode bridge. I'll publish the design to this list when I get it up and
> debugged.
>
> 73,
> Ted
> K9IMM
>
>
>
>
>
>
>
>
> _______________________________________________
> Skimmertalk mailing list
> Skimmertalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/skimmertalk
>