Bob

Splitting the signal before the pre-amp is a bad idea.  It costs you at least 3.5 dB of s/n on all signals.

I am using an RP-14 for 8 bands of FT8 skimming.

As per your instructions I set 6 meters to Antenna "2" and the other 7 bands to "1" in "sdr_receiver_hpsdr/start.sh" "1 1 1 1 1 1 1 2 &"

All bands except 6 meters have spotted FT8 stations.  There has been activity on 6.

After not receiving any 6 meter spots I took another very careful look at the setup info at https://sm7iun.ekelund.nu/red-pitaya/ft8-skimmer

"You may also want to modify the band selection for the three daylight periods. This is done by commenting/uncommenting the corresponding lines. If you do this, make sure you activate exactly eight bands and also keep an eye on the commas for correct syntax. The number after "chan ="  is the input used for that frequency. The receiver thus supports the use of two different antennas."

My understanding from this is that you can select which antennas you want, either "1" or "2" for each band for each time period.  I am using an RP-14 with 8 bands selected.  I have now selected "chan = "2" for only 6 meters for all 3 time periods.  The other bands all use antenna = "1".  Unfortunately 6 is dead right now.  Tomorrow I will hopefully see whether this works for 6.

There is no mention of using "sdr_receiver_hpsdr/start.sh" for antenna selection in the write up. 

Lee

----- Original Message -----
From: Bob Wilson, N6TV <n6tv@arrl.net>
To: SkimmerTalk Reflector <skimmertalk@contesting.com>
Sent: Wed, 17 Jul 2019 11:08:42 -0600 (MDT)
Subject: Re: [Skimmertalk] Difference of RP10 14 16

On Tue, Jul 16, 2019 at 4:07 PM Lee Sawkins <ve7cc@shaw.ca> wrote:

> It's a trade off for me. Sensitivity on high bands with a 20 dB pre-amp or
> a few busted calls on lower bands.
>

Well, since the RP has two antenna inputs, one can assign the low band
slices to antenna input 1 (no preamp), and the high band slices to input 2
(with preamp).  If using one common antenna, use a splitter:

                                                   +------------> Input1
(Low Bands)
Antenna -> Front End Protector -> Passive Splitter +
                                                   +-> Pre-amp -> Input2
(High Bands)

A passive attenuator in the low band input could also achieve the same
result.

Antenna assignments for all 16 receiver slices are defined in
*sdr_receiver_hpsdr/start.sh*, and are independent, but not dynamic, so
this works best with no .ini file rotation in Aggregator.

73,
Bob, N6TV