[600MRG] Best receiver settings

[Eric NO3M]

Realistically, you're shooting blind without a second "reference" 
receiver sharing the same antenna with the rig under evaluation. There's 
no way to know what changes actually made a difference in realtime.  
Data collection over a reasonable time period may expose whether AGC off 
vs. fast vs. slow or if any other setting made a difference, but there 
will still be a margin of error (perhaps large) because the data would 
be collected under varying conditions.  Who has time for that!  Seems 
every night brings it's own quirks.

The whole subject of optimizing the RX environment is long and complex.  
But in a nutshell:

1. Find the most well suited antenna for the local installation (ie. one 
that fits!) that will provide the best SNR in the desired direction(s)

2. Chokes, chokes and more chokes.... is the noise floor we are hearing 
really being set by the antenna, common mode ingress, receiver internal 
noise?!?  An anecdotal experience here was placing a CM choke right at 
the RX input of a TS590SG.... the difference on 2200m was phenomenal 
despite having extensive and proper bonding, single point cable entry, 
etc.  The practice here is to place chokes on both ends of any 
feedlines, along the length if relatively long, and at each rig's RX 
input.  Either a pass-thru type choke or a 1:1 isolation xfmr can be 
suitable.  The latter is generally regarded as a differential choke 
(also provides DC isolation), but can provide useful CM choking if the 
interwinding capacitance is kept low..... how?.... using small tubular 
sleeves (teflon, or slightly shrunk heatshrink tubing) in a binocular 
core (#73) to keep the two windings separated (no twisted pairs!!!!).

3. adjusting gain.... optimal weak signal gain is such that the change 
in noise from no antenna connected to antenna connected is about 
10-18dB.  Use the dB meter in WSJTX to verify.  If the difference is not 
at least the previously stated range or more than 20 dB, the system gain 
needs adjusted.......

I prefer not to use the RF gain control on any modern rig, including the 
K3.  It's really an IF gain control (not the first RF amp like in old 
radios) and in the K3 in particular, based on what I have read from 
other sources, may start to suffer degradation in the IF amp stage 
(J309?) when not at max gain.....

better is to adjust the front-end gain.... add a preamp if needed. I 
need preamps on just about everything here, despite the common idea that 
"the noise temperature at LF is too high".... using low gain RX antennas 
in a rural quiet location demands the use of a preamp on nearly every 
receiver I've used to get in that ideal range mentioned above.  However, 
preamps are definitely abused and overused by many, not understanding 
what the optimal gain is.  Also with any preamp, unless it's a proven 
stout design, put an LPF in front of it to reduce/eliminate IMD from BCI 
and other sources.

Add attenuation (fixed, switched step att, etc.) if needed to get in the 
optimal range, that's including in conjunction with a preamp to really 
dial in to the optimal gain range or be able to adjust with condx......

4. now we can start monkeying with rig settings......

I've been testing several rigs over the last few months by sharing a 
single RX antenna (proper splitting of course) and I find that while the 
K3 (native or thru a xvtr) is fine, it is far from the best performer 
over a wide range of conditions.  Under quiet condx, all receivers 
basically are even.  When it starts getting noisy, the ranking is:

Softrock Ensemble LF or QRP Labs QSD RX
TS-590SG
K3

The SDRs generally do the best over a wide range of condx.  Software is 
sdr-core (Dttsp) w/ SDR-shell (my own highly modified version) in Linux 
w/ noise blanker ON and AGC-fast.  The TS-590SG is often best w/ 
AGC-off, no other mitigation settings (NB, NR, etc.) enabled. The K3 is 
almost hopeless under high noise... no combination of settings (AGC 
off/on/fast/slow and adjustments to threshold, slope, etc), NB, NR, etc. 
etc. are able to keep up with the SDRs.

So, the point is, every rig is different.... AGC characteristics vary 
and are implemented in some platforms better than others.  Same goes for 
noise blankers, noise reduction, etc.

That's why I recommend having a second RX as a reference.  Every change 
and adjustment on the main RX becomes evident in realtime (well.... 
within a couple or few WSPR periods!).



73 Eric NO3M