[600MRG] Best receiver settings

Tue Mar 31 13:04:27 EDT 2020

Its been a few years since I was QRV,  Inverted-L has been on the 
ground for a year.

But back when I was  actively  listening, I used my SDR-IQ with 
Spectravue.  Noise floor of the disconnected receiver was -130 dBm 
and when antenna connected typically -115 to -110 dBm.  Sometimes 
noise ran up to -95 dBm.  I also have a K3 with filter modifications 
to receive 470-KHz but not  made any comparison with either noise or signals.

We put in a new lawn last spring where the vertical part of the 
antenna is located so all my ground radials were removed.  Have to 
lay new radials once ground thaws (mid-May).  I run a 100w NDB 
modified to be driven by 1mw from the K3.  EIRP est. at 4w but that 
may change with new radial system.

73, Ed - KL7UW

At 07:26 AM 3/31/2020, Eric NO3M wrote:
>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
>
>
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
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