[Skimmertalk] Red Pitaya STEMlab SDR 122-16 now online at N6TV

[Lee Sawkins]

Hi Bob.

I had the same problem with my old Red Pitaya.  FM stations causing big problems on 10 meters.

My solution was to put in a pair of 1/4 stubs cut for 100 Mhz made out of low loss coax.  These completely eliminated the FM station interference.  I have these stubs about 3 ft apart on the RG58 feedline after my rx saver/pre-amp inside the house.  

I am sure the new on board transformers must have a better high frequency response than the external ones, contributing to your increased level of FM stations.

Lee

----- Original Message -----
From: Bob Wilson, N6TV <n6tv at arrl.net>
To: SkimmerTalk Reflector <skimmertalk at contesting.com>
Sent: Tue, 04 Jun 2019 22:04:35 -0600 (MDT)
Subject: [Skimmertalk] Red Pitaya STEMlab SDR 122-16 now online at N6TV

. 
. 

The only problem I'm seeing is very broad and loud AM or FM broadcast band
(?) inter-mod at the top and bottom ends of the two 10m segments, as shown
here:

https://www.kkn.net/~n6tv/STEMlab_SDR_122-16_Intermod_N6TV.png

The screen shots are from HDSDR via Extio_CWSL.dll and Extio_CWSL2.dll.

There are FM broadcast stations very close to me, but the closest AM
broadcast station is a few miles away.

The antenna is a VE3DO loop
<http://www.ok1rr.com/index.php/antennas/8-the-ve3do-receiving-loop> (passive
antenna) which isn't particularly sensitive on 10m, but I saw some of the
same inter-mod issues on my Pixel loop (active preamp).

Switching back to the STEMlab SDR 125-14 with the same VE3DO loop antenna
and preamp, but with the 14:1 transformer inline, I see only a little bit
of the same interference (it is much weaker).  It disappears completely
when I disconnect the antenna.

I tried bypassing the preamp, but it made little difference.  Maybe I need
a high-pass or low-pass filter on the SDR input, or both, or a broadcast
band filter.  I haven't identified the station yet.

 

73,
Bob, N6TV
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