vk6ada.com.au • SDR Integration Series • Hammarlund SP-600 SWL Station

Web-888 with the Hammarlund SP-600
The Simplest and Cleanest Web-888 Integration in the Series — A Complete SWL Station Guide

The Hammarlund SP-600 is a receiver. It has no transmitter, no PA, no ALC feedback loop, no T/R relay, no high-voltage output at the antenna connector. Every concern that dominates the KWM-2A, FT-101E, and S-Line Web-888 guides — protecting the SDR from transmit power, managing T/R switching timing, monitoring PA tube health — simply does not apply here. What applies instead is an integration of remarkable elegance: the SP-600’s extraordinary shortwave receive capability paired with the Web-888’s real-time spectrum display, producing a complete SWL station of a capability the SP-600’s designers could not have imagined.

✍ Mike Peace VK6ADA / r-390a.net Administrator 📅 March 2026 ⚙ Web-888 • Hammarlund SP-600 • 455 kHz IF tap • SWL • SW broadcast bands 🌏 Receive-only integration • Broadcast band profiles • Propagation monitoring • SWL logging

This is the simplest Web-888 integration in the vk6ada.com.au SDR series — and potentially the most rewarding. Every previous guide in this series has been dominated by the transmitter problem: how to connect the Web-888 to a transceiver’s antenna system without exposing the SDR to high-power transmit energy. The SP-600 has no transmitter. The antenna connector carries only received signals, always. The Web-888 can be connected to the SP-600’s antenna system in any of three ways without a single safety concern about transmit power, relay timing, or PA protection. The only considerations are receive performance, preselector interaction, and SWL operating practice.

The SP-600’s coverage from 540 kHz through 54 MHz is broader than any other receiver in the vk6ada.com.au series: it reaches below the international shortwave bands into the medium-wave AM broadcast band, and it extends above the HF spectrum into the lower VHF region. Paired with the Web-888’s equally broad direct-sampling coverage, the combined station provides a visual-and-audio panorama of the medium-wave through lower-VHF spectrum that no other instrument combination in this series matches. This guide documents the three integration approaches, the complete set of OpenWebRX SWL band profiles for all fourteen ITU shortwave broadcast bands, and eight best-practice operating procedures specifically for the SWL context.

Section 1 — SP-600 Architecture: Frequency Coverage, IF, and Preselector

Coverage and IF

The Hammarlund SP-600 covers 540 kHz to 54 MHz in six switched bands, using a superheterodyne design with a 455 kHz intermediate frequency. The 455 kHz IF is the same standard used by the R-390A, Collins S-Line, and all other receivers in this series, making the IF tap approach directly applicable using the same principles as the CASCADE-390 and similar kits.

The SP-600’s selectivity is provided by a set of interchangeable crystal filters at 455 kHz, offering bandwidths from approximately 16 kHz (for AM reception) to 0.5 kHz (for CW) depending on the variant and configuration. These filters determine what the IF strip carries; the Web-888 IF tap receives the signal as shaped by whichever SP-600 filter is in use at the time.

The Preselector: The SP-600’s Front-End Variable Capacitor

The SP-600’s preselector is a variable capacitor that tunes the receiver’s front-end bandpass filter to maximise sensitivity at the desired frequency. It must be adjusted (peaked) by the operator at each new frequency for best performance; unlike a synthesised receiver that automatically tracks the front-end filter, the SP-600 requires the operator to manually tune the preselector.

For the Web-888 IF tap integration, the preselector has an important implication: the signal that reaches the 455 kHz IF strip — and therefore the signal that the Web-888 receives via the IF tap — has already been filtered by the preselector. Only signals within the preselector’s passband (typically several hundred kilohertz wide, centred on the preselector’s current tuning) reach the IF and appear on the Web-888 panadapter. This is actually an advantage for SWL panadapter use: the preselector acts as a front-end bandpass filter that protects the Web-888’s ADC from out-of-band strong signals (AM broadcast stations, amateur transmitters, utility stations) that are not in the currently monitored frequency range.

✎  The Preselector as ADC Protection — Why the IF Tap Outperforms Antenna Sharing on Crowded Bands In the antenna-sharing approach, the Web-888 receives the full antenna signal including every signal across the entire HF spectrum. On a typical HF antenna during evening hours, this includes dozens of strong AM broadcast stations, amateur transmitters, utility stations, and atmospheric noise — all simultaneously on the ADC. If the Web-888 RF gain is set high enough to show weak signals, strong out-of-band signals may cause ADC overload (visible as spurious mirror images). If the gain is reduced to prevent overload, weak signals disappear from the panadapter. The SP-600’s preselector, by filtering the incoming signal before it reaches the IF strip and therefore the Web-888, eliminates the out-of-band content that causes this problem. The IF tap approach with the SP-600’s preselector in circuit provides a pre-filtered panadapter view that is cleaner on crowded bands than the antenna-sharing approach, even though it covers a narrower frequency window around the preselector’s tuned frequency.
Preselector rotor bearing contact — handle gently. The SP-600’s most mechanically fragile component is the preselector variable capacitor’s rotor bearing contact, as documented in the vk6ada.com.au SP-600 Failure Prevention Kit. When tuning the preselector during Web-888-assisted monitoring sessions, rotate the preselector control smoothly and deliberately. Do not rapidly rotate the preselector to optimise the panadapter view — frequent rapid rotation accelerates the rotor bearing contact wear that the FPK identifies as the SP-600’s primary mechanical failure mode. Peak the preselector carefully, confirm the Web-888 panadapter shows the expected improvement, and leave it set.

The Crystal Calibrator

The SP-600J and some other SP-600 variants include an internal crystal calibrator that produces marker signals at 100 kHz intervals across the tuning range. These calibration markers are visible on the Web-888 panadapter as a series of evenly spaced peaks, providing a built-in frequency calibration reference for the entire panadapter display. The crystal calibrator also calibrates the Web-888’s own reference oscillator indirectly: if the calibrator signals appear at the correct 100 kHz intervals on the Web-888 panadapter, the IF offset is correctly applied and the display frequencies are accurate. If they appear at irregular intervals or at incorrect positions, either the IF offset needs adjustment or the SP-600’s calibrator crystal needs attention.

Section 2 — Three Integration Approaches: No Safety Tradeoffs Required

Because the SP-600 is a receiver-only instrument, all three integration approaches are safe at all times. There is no transmit power to protect against, no relay timing to calibrate, no attenuation calculation required. The selection between approaches is based purely on operational preference and the level of integration desired.

◆  Approach 1 — 455 kHz IF Tap (Recommended)

A high-impedance buffered tap from the SP-600’s 455 kHz IF strip feeds the Web-888 HF input. Web-888 is set to 455 kHz centre with OpenWebRX IF offset displaying the correct HF frequency.

Key advantage for SWL: the panadapter display automatically centres on the SP-600’s tuned frequency and shows what the preselector is passing. When the preselector is peaked at the desired frequency, the panadapter shows signals in the preselector passband. This pre-filtered view is especially valuable on crowded broadcast bands (49m, 31m, 25m) where the antenna-sharing approach would show too many signals for useful identification.

SWL advantage: the SP-600’s crystal calibrator marks are visible on the Web-888 panadapter as frequency references when the calibrator is engaged.

Requires: internal chassis work to install the IF tap buffer PCB. The SP-600 chassis is accessible and well-documented; this is a straightforward installation.

◆  Approach 2 — Passive Antenna Splitter

A passive RF power splitter (Mini-Circuits ZFRSC-42 or equivalent) connects the antenna to both the SP-600 and the Web-888. Both receivers see the full antenna signal simultaneously.

Key advantage: no chassis work required. The Web-888 provides an independent wideband view of the spectrum while the SP-600 handles precision narrowband demodulation. The operator can see signals across several MHz simultaneously on the Web-888 regardless of where the SP-600 is tuned.

Disadvantage: 3.5 dB insertion loss on the SP-600’s receive path. On crowded bands, the Web-888 may show ADC overload from strong adjacent broadcast stations without the SP-600’s preselector filtering. The Web-888 RF gain must be managed carefully on busy bands.

Best for: operators who prefer no chassis work and want the Web-888 to operate independently of the SP-600’s tuning.

◆  Approach 3 — Dedicated Web-888 Antenna

A separate small antenna (1–3 m random wire, small active loop, or secondary receive antenna) connects exclusively to the Web-888. The SP-600 retains its primary antenna without sharing.

Key advantage: simplest possible configuration. No splitter, no chassis work, no insertion loss on the SP-600’s primary antenna. Both the SP-600 and the Web-888 operate independently on their own antennas.

Disadvantage: the Web-888’s dedicated antenna will typically have less sensitivity than the SP-600’s primary antenna. On the lower HF bands (40m and below), a short indoor wire may be adequate; on the upper bands (15m and above), it may miss weaker signals that the SP-600’s primary antenna receives.

Best for: operators who want instant Web-888 capability with zero impact on the SP-600’s primary antenna performance.

The recommendation for SWL operators who want the most useful panadapter: use the IF tap approach (Approach 1). The preselector-filtered view is significantly cleaner on the broadcast bands than the antenna-sharing approach, and the IF tap requires only modest internal chassis work on an SP-600 whose chassis is straightforward to access. For operators who prefer zero chassis work and accept the splitter’s insertion loss and potential ADC management overhead, Approach 2 (passive splitter) provides a functional panadapter without any internal modifications. Approach 3 (dedicated antenna) is recommended for operators who travel with their Web-888 setup or who want to maintain strict antenna separation between instruments.

Section 3 — Approach 1: IF Tap Installation for the SP-600

Internal chassis voltage safety. The SP-600 is a mains-powered tube receiver with plate voltages up to approximately 250 V DC on the IF amplifier stages. Although this is far lower than the PA plate voltages in the KWM-2A and FT-101E, it is still sufficient to cause harm. Power off and unplug the SP-600 from the mains before opening the chassis for IF tap installation. Verify with a DVM that the supply voltage has discharged below 30 V before touching any internal component. The SP-600’s filter capacitors discharge relatively quickly through the normal bleeder resistor network; verify by measurement rather than assumption.
  • 1
    Access the SP-600 IF strip — top cover removal The SP-600’s IF strip runs along the chassis longitudinally. Remove the top cover (typically four screws). The IF transformers are clearly visible as shielded cans in the IF section of the chassis. The 455 kHz IF tap point is at the input to the second or third IF amplifier stage, where the signal level is sufficient for the buffer amplifier input without excessive loading of the preceding stage.
  • 2
    Identify the tap point from the service manual Consult the SP-600 service manual (available through the vk6ada.com.au Hammarlund resource archive) for the specific IF stage component designator at which the tap is made. The buffer PCB (available from vk6ada.com.au) includes application notes identifying the recommended tap point for each SP-600 variant (the L/JL/VJ/JX and other model suffixes have slight IF stage differences that affect the optimal tap location).
  • 3
    Install the buffer PCB and route the RG-174 tap lead Mount the buffer PCB to a suitable chassis standoff inside the SP-600 cabinet. Route a short RG-174 coax from the tap point to the PCB input. The buffer amplifier output (50 Ω BNC) routes to a rear-panel BNC connector (single 15 mm aperture, drilled from the outside at a position that does not conflict with existing SP-600 rear-panel connectors). Power the buffer from the SP-600’s regulated heater supply or a suitable B+ tap point via a dropping resistor as specified in the kit documentation.
  • 4
    Verify SP-600 sensitivity unchanged; verify Web-888 IF tap signal Power on. Confirm the SP-600 receives normally on all bands. Connect a BNC cable from the rear-panel tap output to the Web-888 HF input. Open OpenWebRX, set centre to 455 kHz. Tune the SP-600 to a busy shortwave broadcast band (7.100–7.350 MHz, 49m band, is usually active during evening hours in all regions). Apply the IF offset (7.200 MHz − 455 kHz = 6.745 MHz as an example) and verify multiple signals appear on the panadapter. Tune the SP-600 across the band and confirm that signals shift on the panadapter, confirming the IF tap is correctly installed and tracking the SP-600’s tuning.
IF offset formula for any SP-600 frequency:
IF offset (Hz) = SP-600 dial reading (Hz) − 455,000 Hz

Example offsets for major SWL frequencies:
 7.200 MHz (41m broadcast) → 6,745,000 Hz (6.745 MHz)
 9.600 MHz (31m broadcast) → 9,145,000 Hz (9.145 MHz)
15.000 MHz (WWV)           → 14,545,000 Hz (14.545 MHz)
 1.000 MHz (MW)             →    545,000 Hz (0.545 MHz)
 6.000 MHz (60m broadcast) → 5,545,000 Hz (5.545 MHz)

The preselector relationship: the panadapter window shown by the Web-888 via the IF tap is centred on the SP-600’s tuned frequency and limited in width by the SP-600’s preselector passband. On a well-peaked preselector, the visible bandwidth is typically ±300 kHz to ±500 kHz. Set the Web-888 sample rate at 1 MSPS to show ±500 kHz and capture most of the preselector passband comfortably.

Section 4 — OpenWebRX SWL Band Profile Configuration

The shortwave broadcast band allocation is defined by the ITU and consists of fourteen internationally recognised bands from 120 m through 11 m. The Web-888’s OpenWebRX should have a profile for each of these bands, plus profiles for the medium-wave broadcast band, the primary utility/VOLMET frequencies, and the amateur HF bands that the SP-600 also covers. The following profiles represent a complete SWL configuration for the SP-600 + Web-888 station.

ITU International Shortwave Broadcast Bands

120m Band 2.300–2.498 MHz | Centre: 2.400 MHz | AM
90m Band 3.200–3.400 MHz | Centre: 3.300 MHz | AM
75m Band 3.900–4.000 MHz | Centre: 3.950 MHz | AM
60m Band 4.750–5.060 MHz | Centre: 4.900 MHz | AM
49m Band 5.900–6.200 MHz | Centre: 6.050 MHz | AM
41m Band 7.100–7.350 MHz | Centre: 7.225 MHz | AM
31m Band 9.400–9.900 MHz | Centre: 9.650 MHz | AM
25m Band 11.600–12.100 MHz | Centre: 11.850 MHz | AM
22m Band 13.570–13.870 MHz | Centre: 13.720 MHz | AM
19m Band 15.100–15.800 MHz | Centre: 15.450 MHz | AM
16m Band 17.480–17.900 MHz | Centre: 17.690 MHz | AM
13m Band 21.450–21.850 MHz | Centre: 21.650 MHz | AM
11m Band 25.600–26.100 MHz | Centre: 25.850 MHz | AM
MW Broadcast 0.530–1.700 MHz | Centre: 1.100 MHz | AM

Utility and Reference Frequency Profiles

Profile Name
Centre Frequency
Span
Mode
Use
WWV 5 MHz 5.000 MHz 50 kHz AM Time/freq standard, propagation reference
WWV 10 MHz 10.000 MHz 50 kHz AM Time/freq standard; propagation assessment
WWV 15 MHz 15.000 MHz 50 kHz AM Primary daytime propagation reference
VOLMET HF (sample) 10.051 MHz 30 kHz USB Aeronautical weather broadcast
Maritime (distress) 8.291 MHz 100 kHz USB International maritime calling/distress
RNZI Pacific 9.700 MHz (check) 200 kHz AM Radio New Zealand International — verify current schedule
SWL broadcast schedules change seasonally. International shortwave broadcasters change their frequencies and transmit schedules in March and September each year, aligned with seasonal propagation patterns. BBC World Service, Voice of America, Radio New Zealand International, and other broadcasters publish their current frequency schedules at their respective websites. Update the OpenWebRX band profiles in March and September to match the current season’s active frequencies on each band. The centre frequencies shown in the broadcast band grid above are nominal band centres; specific broadcasters will be found at various positions within each band.

Section 5 — Eight Best-Practice SWL Operating Procedures

  • BP
    01
    PRSL
    Peak the Preselector Before Reading the Panadapter (IF Tap Approach)

    The SP-600’s preselector must be correctly peaked at the operating frequency before the Web-888 IF tap panadapter provides a meaningful view of that frequency’s spectrum. A preselector that is off-peak attenuates not only the signal the operator wants to hear but also the signals on either side of the tuned frequency that the panadapter would otherwise show. The result is a panadapter that appears to show a quieter, less populated band than is actually the case.

    Procedure: tune the SP-600 to the desired frequency. Listen to the audio while slowly rotating the preselector control; peak for maximum audio (or maximum S-meter deflection if fitted). Then look at the Web-888 panadapter — signal peaks will have increased in amplitude as the preselector was peaked. This is the correct operating sequence: set SP-600 frequency → peak preselector → observe panadapter. Attempting to peak the preselector by watching the panadapter rather than the audio is less reliable, because the panadapter shows the aggregate signal in the preselector passband, which can peak at a different position from the optimal single-signal audio peak.

  • BP
    02
    LOG
    Use the Web-888 Waterfall for SWL Station Logging Confirmation

    SWL reception logging — the practice of maintaining a log of received stations with date, time, frequency, and signal quality — benefits significantly from the Web-888 waterfall as an evidentiary record. A screenshot of the Web-888 waterfall showing a station’s signal at a specific frequency and time provides visual confirmation of the reception that audio notes alone cannot. Some SWL awards and verifications accept waterfall screenshots as supplementary evidence of reception.

    Waterfall screenshot discipline: at the moment of log entry (when a station is identified and logged), capture a Web-888 waterfall screenshot via the OpenWebRX interface. Note the UTC time displayed in the waterfall, the frequency, and the signal strength visible in the waterfall. Store the screenshot alongside the log entry. Over time, a collection of waterfall screenshots builds a visual archive of band conditions that is both a reception record and a personal propagation database.

    For formal SWL reception reports (QSL card requests), the waterfall screenshot showing the station’s signal at the logged frequency and time is useful supporting evidence. Many international broadcasters still respond to SWL reception reports with QSL cards; attach the waterfall screenshot image to the reception report email.

  • BP
    03
    PROP
    WWV as a Propagation Monitor on the Web-888 Waterfall

    WWV (Fort Collins, Colorado, USA) and WWVH (Kauai, Hawaii, USA) broadcast continuous time signals and solar/geomagnetic data on 2.5, 5, 10, 15, and 20 MHz. These signals serve as an ideal propagation monitor on the Web-888 waterfall: because their transmission schedule is absolutely continuous, any variation in the waterfall signal strength is a direct indicator of propagation change rather than broadcast schedule.

    Procedure: open the Web-888 15 MHz WWV profile (or 10 MHz during low solar activity). The WWV carrier should appear as a consistent horizontal stripe on the waterfall when propagation is stable. Fading (the stripe varying in brightness over seconds to minutes) indicates multipath propagation. Complete disappearance indicates a propagation disruption. Rising and falling signal over periods of 30–60 minutes tracks the daily ionospheric cycle. Comparing the 10 MHz and 15 MHz WWV profiles simultaneously (in a two-receiver OpenWebRX configuration if available, or by rapid profile switching) shows which frequencies are currently supporting propagation from North America — a direct indicator of which SW broadcast bands will be active from that region.

  • BP
    04
    UTIL
    Utility Station Monitoring: VOLMET, Maritime, and Aeronautical HF

    Beyond the international broadcast bands, the HF spectrum contains a rich population of utility stations — those operated by aviation services (VOLMET weather broadcasts), maritime services (ship-to-shore communications, distress calling), and government/military services. The Web-888 panadapter is an excellent tool for identifying utility station activity because utility stations typically transmit on fixed, predictable schedules on known frequencies.

    VOLMET monitoring: set the Web-888 to the VOLMET profile (10.051 MHz is a commonly active frequency in the Pacific/Atlantic regions; verify current active VOLMET frequencies from national aviation authority publications). The VOLMET broadcast appears as a regular, consistently strong SSB signal on the panadapter during its scheduled broadcast periods. Tune the SP-600 to the VOLMET frequency with BFO engaged for SSB demodulation of the weather broadcast.

    Maritime monitoring: the international maritime calling and distress frequencies (4.125, 8.291, and 12.290 MHz) show intermittent SSB voice traffic from commercial shipping. The Web-888 panadapter at these frequencies shows traffic as brief signal bursts; the SP-600 with appropriate SP-600J SSB filter demodulates the SSB voice. For detailed VOLMET and maritime frequency tables, see the vk6ada.com.au Collins CP-1 Crystal Pack guide which documents these frequencies comprehensively.

  • BP
    05
    DIGI
    Digital Mode Reception via Web-888 Audio Output to Fldigi or WSJT-X

    The Web-888’s OpenWebRX interface can stream audio from the demodulated SDR signal to the operator’s computer’s audio system. This audio can be routed to Fldigi (for RTTY, Olivia, PSK, and other HF digital modes) or to WSJT-X (for FT8, WSPR, JS8Call) via a virtual audio cable (VAC) application. The SP-600’s audio output can also be routed similarly, but the Web-888’s digital frequency display and easy frequency adjustment make it more convenient for digital mode monitoring without requiring the SP-600 to be retuned to every active digital frequency.

    Setup: install a virtual audio cable application (VB-Cable on Windows, PulseAudio on Linux, BlackHole on macOS). Configure OpenWebRX to output audio to the virtual cable device. Configure Fldigi or WSJT-X to use the virtual cable as its audio input. Select the appropriate demodulation mode in OpenWebRX (USB for FT8 and most data modes; AM bandwidth modes for RTTY). The Web-888 then acts as an SDR frontend for digital mode decoding, with the SP-600 available alongside for conventional AM/SSB monitoring of the same or different frequencies.

  • BP
    06
    SKED
    Broadcast Schedule Correlation with Web-888 Band Profiles

    International shortwave broadcasts follow published schedules with specific frequencies, times (UTC), and target regions. Matching the Web-888 band profiles to the current broadcast schedule allows systematic SWL monitoring: before an operating session, consult the current schedule (available from broadcasters’ websites, ADDX, DSWCI, or similar SWL club publications) and note which frequencies will be active during the session. Pre-configure OpenWebRX profiles for those frequencies before the session begins.

    A useful operating practice: open the Web-888 profiles for the two or three most active broadcast bands for the current time of day and season, and let the waterfall run while listening to the SP-600 on a selected station. When the waterfall shows a new strong signal appearing on an adjacent band, note the frequency and time, then tune the SP-600 to investigate. This parallel monitoring (SP-600 for detailed listening; Web-888 for peripheral band awareness) is the SWL equivalent of the amateur DX operator’s panadapter workflow.

  • BP
    07
    LONG
    Long-Duration Monitoring: Web-888 as an Unattended Recording Station

    The Web-888 running OpenWebRX can be left operating unattended for hours, with the waterfall continuously recording to screen or to a waterfall logging file. This is particularly valuable for SWL on bands where interesting activity (DX openings, rare station broadcasts, propagation events) may occur at times when the operator is not present. The SP-600 can also be left running unattended receiving on a specific frequency, with the audio recorded via the computer to capture broadcast content.

    Long-duration monitoring configuration: ensure the Web-888 computer is connected to a reliable power supply and has sufficient storage for waterfall logging if enabled. Disable screensavers and sleep modes that would interrupt the display. Set the OpenWebRX band profile to the band most likely to show interesting activity during the unattended period (the 49m and 31m bands, for example, are active throughout most of the night in temperate regions). On return, review the waterfall for signals that appeared and disappeared during the session, noting times and frequencies for potential follow-up identification.

  • BP
    08
    REM
    Remote SWL: Accessing the SP-600 Antenna from Anywhere

    The Web-888’s network-accessible interface, configured following the procedures in the vk6ada.com.au Web-888 Remote Access Setup guide (R-390A companion), allows remote access to the SP-600’s antenna system from any internet-connected browser. For SWL operators, this enables monitoring of a fixed shack antenna system while travelling, listening to shortwave broadcasts from the home antenna during working hours, or sharing the SP-600’s antenna system with other SWL operators as a public or semi-public receiver.

    The remote SWL application is simpler to configure than the remote amateur radio applications in the series because there is no transmit capability to secure or manage: the only exposure is the Web-888’s web interface. Use the security hardening procedures from the Web-888 R-390A guide (WireGuard VPN for private access, or OpenWebRX authentication for semi-public access) to protect the interface. Consider listing the SP-600 antenna system on the sdr.hu public SDR directory if the antenna is of sufficient quality to benefit other SWL operators — a well-sited antenna with an SP-600’s IF quality pre-filtering is a genuine community resource for international SWL monitoring.

Section 6 — Complete SP-600 + Web-888 SWL Station Architecture

  ┌──────────────────────────────────────────────────────────────────────────┐
  │   HAMMARLUND SP-600 + WEB-888 — COMPLETE SWL STATION ARCHITECTURE       │
  │   Receive-only: no T/R switching, no PA concerns, no relay timing        │
  └──────────────────────────────────────────────────────────────────────────┘

  ─────────────────────────────────────────────────────────────────────────
  APPROACH 1: IF TAP (recommended — preselector-filtered panadapter)
  ─────────────────────────────────────────────────────────────────────────

  ANTENNA (HF receive antenna)
          │
  [SP-600 antenna input SO-239] → no T/R switching needed; safe at all times
          │
  [SP-600 preselector] ─────── peaks at operating frequency; filters OOB signals
          │ preselector passband: ±300–500 kHz around tuned frequency
  [SP-600 first mixer and converter stages]
          │
  [SP-600 455 kHz second IF strip] ─── pre-filter tap point (see kit notes)
          │                                      │
          │                            [IF tap buffer PCB]
          │                            high-Z → 50 Ω → rear-panel BNC
          │                                      │
          ▼                                      ▼
  [SP-600 detector → audio → speaker]   [Web-888 HF input]
  Primary SWL audio                     USB 3.0 → computer
                                        [OpenWebRX — IF tap profiles]
                                        Centre: 455 kHz
                                        Offset: SP-600 freq − 455,000 Hz
                                        → Panadapter in preselector window
                                        → Crystal calibrator marks visible

  ─────────────────────────────────────────────────────────────────────────
  APPROACH 2: PASSIVE SPLITTER (no chassis work — wideband independent view)
  ─────────────────────────────────────────────────────────────────────────

  ANTENNA
          │
  [Passive RF splitter — ZFRSC-42] (3.5 dB insertion loss each port)
   ├── Port A: → SP-600 antenna input (slight sensitivity reduction — audible
   │             on weakest signals above 14 MHz; inaudible on low bands)
   └── Port B: → Web-888 HF input
               [OpenWebRX — direct HF frequency profiles, no IF offset]
               Wideband view: entire HF spectrum visible simultaneously
               Manage RF gain carefully on crowded 49m/31m broadcast bands

  ─────────────────────────────────────────────────────────────────────────
  APPROACH 3: DEDICATED WEB-888 ANTENNA (simplest — full SP-600 antenna)
  ─────────────────────────────────────────────────────────────────────────

  ANTENNA (primary) → SP-600 full sensitivity, no insertion loss
  ANTENNA (dedicated Web-888: 1–3m indoor wire) → Web-888 HF input

  ─────────────────────────────────────────────────────────────────────────
  SW BROADCAST BAND OPENWEBRX PROFILE REFERENCE (14 ITU bands)
  ─────────────────────────────────────────────────────────────────────────

  Band   │ Frequency Range         │ Approx. Centre  │ Span     │ Mode
  ────── │ ───────────────────────── │ ─────────────── │ ──────── │ ────
  120m   │ 2.300 – 2.498 MHz       │ 2.400 MHz       │ 200 kHz  │ AM
  90m    │ 3.200 – 3.400 MHz       │ 3.300 MHz       │ 200 kHz  │ AM
  75m    │ 3.900 – 4.000 MHz       │ 3.950 MHz       │ 100 kHz  │ AM
  60m    │ 4.750 – 5.060 MHz       │ 4.900 MHz       │ 300 kHz  │ AM
  49m    │ 5.900 – 6.200 MHz       │ 6.050 MHz       │ 300 kHz  │ AM
  41m    │ 7.100 – 7.350 MHz       │ 7.225 MHz       │ 250 kHz  │ AM
  31m    │ 9.400 – 9.900 MHz       │ 9.650 MHz       │ 500 kHz  │ AM
  25m    │ 11.600 – 12.100 MHz     │ 11.850 MHz      │ 500 kHz  │ AM
  22m    │ 13.570 – 13.870 MHz     │ 13.720 MHz      │ 300 kHz  │ AM
  19m    │ 15.100 – 15.800 MHz     │ 15.450 MHz      │ 700 kHz  │ AM
  16m    │ 17.480 – 17.900 MHz     │ 17.690 MHz      │ 400 kHz  │ AM
  13m    │ 21.450 – 21.850 MHz     │ 21.650 MHz      │ 400 kHz  │ AM
  11m    │ 25.600 – 26.100 MHz     │ 25.850 MHz      │ 500 kHz  │ AM
  MW     │ 0.530 – 1.700 MHz       │ 1.100 MHz       │ 1.2 MHz  │ AM

  ─────────────────────────────────────────────────────────────────────────
  WHAT SETS THIS INTEGRATION APART FROM EVERY OTHER WEB-888 GUIDE
  ─────────────────────────────────────────────────────────────────────────
  ┌────────────────────────────────────────────────────────────────────────┐
  │  ONLY SWL guide in the series — no T/R switching, no PA protection    │
  │  BROADEST coverage: SP-600 0.54–54 MHz + Web-888 direct-sampling      │
  │  PRESELECTOR acts as ADC front-end protection on crowded bands        │
  │  14 ITU SW broadcast band profiles vs 6–8 amateur bands in TX guides  │
  │  LONG-DURATION monitoring: Web-888 as unattended reception recorder   │
  │  DIGITAL MODE reception via Web-888 audio → Fldigi / WSJT-X pipeline │
  │  WATERFALL LOGGING: screenshots as SWL reception confirmations        │
  │  CRYSTAL CALIBRATOR markers from SP-600 visible as freq reference     │
  └────────────────────────────────────────────────────────────────────────┘

Hammarlund SP-600 + Web-888 SWL station. Approach 1 (IF tap, recommended) requires SP-600 chassis access for buffer PCB installation; approaches 2 and 3 require no chassis work. All three approaches are safe at all times because the SP-600 has no transmitter; there is no PA power at the antenna connector under any operating condition. SW broadcast band profiles show nominal band centres; actual broadcasters are found at specific frequencies within each band as per current seasonal schedules. Update OpenWebRX profiles in March and September when broadcasters change seasonal frequencies.

References and Notes

  1. Hammarlund Manufacturing Company, SP-600 Instruction Manual and Circuit Diagrams. Available through vintage radio archives and the vk6ada.com.au Hammarlund resource section. The service manual is the authoritative reference for the SP-600’s IF strip circuit topology, the preselector variable capacitor design, the crystal calibrator circuit (SP-600J), and the IF amplifier stage component designators used to identify the IF tap point. SP-600 variants (L, JL, VJ, JX, XL, etc.) have some circuit differences; confirm the service manual edition matches the specific variant in hand before undertaking IF tap installation.
  2. Mike Peace VK6ADA, Hammarlund SP-600 Failure Prevention Kit, vk6ada.com.au. The comprehensive SP-600 failure mode reference, covering the preselector variable capacitor rotor bearing contact failure (first-priority failure mode, documented in detail in the FPK) that is the most mechanically sensitive aspect of SP-600 operation. The caution in Section 1 of this guide about gentle preselector rotation during Web-888-assisted monitoring is consistent with the FPK’s guidance on preselector contact life extension. Operators who have not yet read the SP-600 FPK should do so before beginning any Web-888 integration work that involves preselector adjustment.
  3. International Telecommunication Union (ITU), Radio Regulations, Article 12: International Frequency Allocations, and Table of Frequency Allocations for International Broadcasting. Primary authority for the fourteen ITU shortwave broadcast band definitions used in the OpenWebRX profile table in Section 4. Band frequency ranges shown in this guide reflect the ITU allocation as of 2020; verify current allocations from the ITU frequency allocation documents for any boundary frequencies that may have been revised by subsequent WRC decisions.
  4. Mike Peace VK6ADA, Web-888 Remote Access Setup for Vintage Receivers, vk6ada.com.au (March 2026). The primary reference for Web-888 hardware configuration, OpenWebRX software installation, network setup (static IP, DDNS, WireGuard VPN security), and the security hardening procedures referenced in BP-08 (remote SWL access). The remote access procedures documented in that guide apply without modification to the SP-600 + Web-888 SWL station; the only difference from the R-390A companion scenario is that there is no transmit capability to restrict or manage in the SP-600 context.
  5. BBC World Service, BBC Frequency Guide, bbc.com/worldservice. Current schedule and frequency information for BBC World Service shortwave broadcasts, published and updated seasonally. Equivalent resources for other broadcasters: Radio New Zealand International (rnzi.com), Voice of America (voanews.com), and ADDX (the German shortwave club) maintain a comprehensive international broadcast schedule database at addx.de. The SWL club publications referenced in BP-06 (Cumbre DX, World of Radio, Hard-Core-DX) provide additional current frequency and schedule information updated weekly.
  6. Mike Peace VK6ADA, Collins Crystal Pack CP-1 — Non-Amateur Band Coverage and 2026 Use Cases, vk6ada.com.au (March 2026). Reference for the VOLMET and maritime HF frequency tables cited in BP-04. The CP-1 guide documents these frequencies as practical use cases for the Collins S-Line with CP-1 crystals; the same frequencies are relevant to the SP-600 + Web-888 SWL station for utility monitoring. The specific VOLMET frequency assignments (ICAO-published) and maritime ITU frequencies cited in the CP-1 guide are applicable to the SP-600’s full coverage range without any crystal accessories.
✍ Mike Peace VK6ADA  /  r-390a.net Administrator  •  March 2026 vk6ada.com.au — Collins Radio Technical Resource

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