Globe Logo
Recent changes to the WebSDR server system (April, 2020)

The version 3 upgrade consists of a complete replacement of server hardware and HF radio receiving equipment as well as the implementation of several new features in the user interface.
Please email Craig with questions and comments.

===================================

RF system improvements

Techical Background:The 8 Fifi SDR receivers used in the former system have been replaced by eight RSP1A receivers from SDRplay in England. These are a fairly recent addition to the suite of "high performance" receivers. They have the advantage of having an available AGC to better-accommodate both weak and strong-signal conditions. The work of several volunteers at the Northern Utah WebSDR has produced drivers that allow these to be used with the 16 bit audio interface up to 768 kHz. Additional modificiations to some drivers/programs in the Linux operating system has permitted these same devices to operate at 384 and 768 kHz which means that most HF bands can be covered with a single receiver with the 16 bit interface. This permits the KFS WebSDR that had used eight 192 kHz wide Fifi receivers to cover some of the bands (e.g. 160, 80, 40, 20) to, instead, use a single receiver per band.

*** Increased performance: The RSP1A receivers are more sensitive and have better signal handling compared to the Fifis. They also offer much improved AGC capability.

***Wider frequency coverage: The Fifi receivers were limited to 192 kHz bandwidth, requiring up to 3 recevers to cover the wider amateur bands. The RSP1A receivers have up to 768 kHz bandwidth on the WebSDR, enabling just one receiver to cover 75 and 80 meters, for instance.

***More amateur bands: Due to the wider bandwidthe, the 8 receiver slots are now used to add several amateur bands to the KFS WebSDR, namely 60, 30, 17, 15, and 10 meters. Aditionally some interesting frequencies outside the amateur bands are now covered, for instance CHU at 3330 kHz and WWV/WWVH at both 5 and 10 Mhz - and some interesting utilty and sw broadcast bands.

*** New front end filters: A set of custom bandpass filters, designed and built by KA7OEI, proceeds the RSP1A receivers to decrease interference from from out of band signals.

===================================

User interface enhancements

It's nearly the same! Don't worry, the new presentation on your web browser looks and operates very much the same as the former KFS WebSDR. In most case, everyting listed below is an enhancement - we have tried to maintain the original look and feel.

*** Two VFOs (A/B): Dual VFOs, with A/B (swap) and B=A buttons. They handle both frequency and mode.

*** Additional audio buffering selections: includes 31.25 and 62.5 msec settings. These may be somewhat useful, but (especially the 31.25) only if the Internet is behaving itself on both ends of the connection.

*** Alternate AGC for AM: The original AGC tends to badly over/undershoot, causing loud clicks and pops when signal strength is changing rapidly - mostly due to QSB, or when someone keys/unkeys. The "Alt AGC" attempts to overcome these deficiencies as much as possible. The nature of this AGC is that the audio recovery will likely be a bit lower (e.g. quieter) than with the normal "RF AGC". The "Alt AGC" works with SSB to a degree, but it is not optimized for such.

*** S-meter squelch: Used to squelch signals based on signal strength - faster than the normal squelch. Set slider fully to the left to disable. Best for very strong AM signals that are significantly higher than the noise floor - less useful for SSB and for conditions where QSB or strong noise pulses (static) is present. 'SET' button presets just above the current S-meter reading, but use ONLY when no signal is present: It is much faster to respond than the existing (and slow) noise-based squelch.

*** Apparent SNR indication: This is displayed under the S-meter and is based on the audio peaks/valleys over the past two seconds.

*** Context-sensitive frequency step buttons: The buttons now show the step size, appropriate to the mode.

*** Higher tuning resolution: The tuning resolution has been increased from the original 31.25 Hz to 1 Hz - which is a number beyond the temperature stability of the receivers!

*** Vari-Notch: This is a manually-tunable notch filter that may be used in addition to the "Notch1" and "Notch2" filters. Like Notch2, this is an audio-only notch and will notprevent desense from very strong carriers - use "Notch1" for that!

*** CW Peak filter: This is a manually-tunable audio-only filter that may be handy for CW reception under busy conditions. The "Ref. Tone" button enables a tone of the same frequency as the filter to aid in tuning.

*** "SAM-U" and "SAM-L" demodulation: This is synchronous AM for the upper and lower sidebands, respectively. Due to the architecture of the WebSDR double-sideband synchronous AM demodulation is not practical. Note that the carrier of the AM receiver must between 80 and 1000 Hz on the "filter" side of receiver - in other words, when using SAM-U, the carrier must be 80-1000 Hz above the "zero" frequency of the receiver and when using SAM-L, the carrier must be below the "zero" frequency. If you are listening to an AM net where stations may not be vary close to the desired frequency you may have to retune and/or switch between SAM-U and SAM-L.

Prior to the recent upgrade, recorded audio did not include the effects of any DSP or filtering by Notch2 - now it does!

*** Security improvements:
--- New code can detect and block abusers. Please be sure to put your call sign, only, in the Your name or callsign box.
--- Additional layers of firewall have been implemented.

*** Embedded commands in startup URL:
Now, a number of different things can be specified when you access the WebSDR with your browser:
--- Set frequency and mode: Start your browser session pretuned to a frequency & mode. Parameter = ?tune= example http://kfsdr.com/?tune=7293am to listen to 7293 kHz in AM (40M AM window).
--- Set zoom level: Zooms in "n" times on startup. Parameter = ?zoom=n example http://kfsdr.com/zoom=3. Best used when a frequency is specified using "?tune=". Zooms will be centered on the tuned frequency. The number of available zooms depends on the band.
--- Set Squelch: Enable squelch by default. Parameter = ?squelch=n example http://kfsdr.com/squelch=1 turns on squelch. This is not the S-meter squelch, but the squelch check-box (noise operated).
--- Set S-meter Squelch: Enable S-meter squelch by default. Parameter = ?smsquelch=x example http://kfsdr.com/smsquelch=1 sets on the S-meter squelch. The "X" parameter is the signal level, in dBM (as displayed on the S-meter) of the squelch threshold. Set slider fully to the left to disable.
--- No labels: Suppress "DX Labels" Parameter = ?nolabels=n example http://kfsdr.com/nolabels=1 n=1 to suppress the "DX Labels" (stationinfo) below the waterfall.
--- Alternate AGC: Startup using altrnate AGC. Parameter = ?altagc=n example http://kfsdr.com/?altagc=1 uses Alt AGC.

*** Display of frequency: The frequency is now displayed after the user name in the graph-like portions below the screen. Please be sure to enter your call sign (only) in the Name name or callsign box so that this feature works properly.

*** Annunciators for Mute and Squelch: Red text "Audio muted" appears after the mode display in the Frequency box. Red text "Squelch Enabled" appears if the squelch is on.

*** Additional Bandwidth Buttons: There are now three buttons per mode to select wide, medium, and narrow passband bandwidths.

*** Frequency entry now allows frequency in MegaHertz: You may now enter the receive frequency in MHz by typing it in the "Frequency" box. That is, if you wanted to tune to 3579.55 kHz, you could enter either "3579.55" or "3.57955". If you enter the frequency in MHz, the system will convert it to kHz and tune there after 3 seconds. If you attempt to enter a frequency not covered by any receiver on the WebSDR us are currently using, it's likely that nothing will happen at all.

***Frequency-centering zoom: The code for zooming in has been tweaked so that the frequency to which the receiver is tuned stays within the spectrum display.