Web-888 with the Collins R-388/URR
PTO Precision, SSB Capability, and Thirty-Band SWL Coverage — Architecture, Integration, and Eight Operating Procedures
The Collins R-388/URR brings three capabilities to the Web-888 pairing that the Hammarlund SP-600 cannot match: a Collins PTO that eliminates preselector peaking entirely, a product detector that brings SSB and CW demodulation to SWL monitoring, and thirty one-megahertz band segments covering 540 kHz through 30.5 MHz with dial accuracy that the community has measured in hundreds of hertz. Like the SP-600, the R-388 is receive-only. Unlike the SP-600, it was built to a military communications specification — and it shows.
The R-388/URR (Collins 51J-3) and the Web-888 form a more tightly integrated SWL station than the SP-600 + Web-888 combination in one specific respect: there is no preselector to peak. The R-388’s Collins PTO and crystal band-selection system automatically maintains the correct front-end tuning as the operator rotates the frequency dial. The panadapter, via the 455 kHz second IF tap, centres itself on the R-388’s current frequency with no additional operator action. Turn the dial; the panadapter follows. This is the behaviour of the R-390A and R-390 IF tap systems that the vk6ada.com.au CASCADE-390 guide describes — identical architecture, identical integration, identical operating discipline.
The R-388’s SSB and CW capability, delivered through its product detector, opens a completely different set of SWL monitoring applications from the SP-600’s primarily AM-focused design. Amateur band DX monitoring with full USB/LSB demodulation, CW traffic net listening, RTTY and digital mode decoding, utility station monitoring — these are natural R-388 use cases that the Web-888 panadapter enhances specifically. The Web-888 shows what is on the band around the R-388’s frequency; the R-388 extracts the audio from whatever the operator tunes to; together they cover the SWL spectrum in a complementary way that neither instrument achieves alone.
Section 1 — R-388/URR Architecture: PTO, Dual Conversion, and the 455 kHz Second IF
The Collins PTO — No Preselector Peaking Required
The defining characteristic of the Collins R-388 for Web-888 integration is the PTO (Permeability Tuned Oscillator). Unlike the Hammarlund SP-600, which requires the operator to manually peak a separate preselector variable capacitor at each new frequency, the R-388’s front-end bandpass filtering automatically tracks the main tuning. The operator selects a band with the bandswitch and tunes the PTO dial; the receiver’s entire front-end — preselector, RF amplifier input, and mixing circuit — is aligned to the tuned frequency by the same mechanical coupling that drives the PTO. No separate peaking procedure is required or available.
This difference has a direct consequence for the Web-888 IF tap integration: the panadapter display centred at the R-388’s tuned frequency is always maximally sensitive for the signals around that frequency, because the front-end is always optimally peaked. The SP-600 SWL guide’s BP-01 (peak the preselector before reading the panadapter) simply does not exist as a concern for the R-388 operator.
Dual Conversion and the 455 kHz Second IF
The R-388 uses a dual-conversion superheterodyne architecture. The incoming RF signal is first converted to an intermediate frequency in the low-MHz range by mixing with the crystal-controlled band oscillator frequency. This first conversion provides image rejection and establishes the initial frequency selectivity for the chosen band. The first IF is then converted to the standard 455 kHz second IF, where the primary selectivity (AM, CW, and SSB bandwidths) is applied by the crystal or LC filter complement.
The 455 kHz second IF is the tap point for the Web-888 integration. This is the same second IF frequency used by the Hammarlund SP-600, the FT-101E, and the related Collins 51J series, making the IF tap design principles identical across all of these instruments. The Web-888 receives the R-388’s 455 kHz second IF output and, with the appropriate IF offset applied in OpenWebRX, displays the correct HF frequency on the panadapter.
Coverage: Thirty 1 MHz Segments from 540 kHz to 30.5 MHz
The R-388 covers 540 kHz to 30.5 MHz in thirty successive 1 MHz segments, selected by the bandswitch. Each segment uses a different crystal for the band oscillator, with the PTO providing the 0–1 MHz variable element within each segment. The PTO’s 10-turn vernier dial provides continuous coverage within each segment to an accuracy typically within ±500 Hz of the indicated frequency after calibration — comparable to the R-390A’s PTO accuracy and far better than the SP-600’s variable capacitor tuning for precise frequency identification.
Modes: AM, SSB, CW, and FSK
The R-388 provides four operating modes through its detector and BFO circuit:
- AM (Amplitude Modulation): standard envelope detection for shortwave broadcasts, AM utility stations, and amplitude-modulated signals of all types.
- CW (Continuous Wave): BFO engaged, narrow filter selected, for Morse code reception. The R-388’s CW filter provides the selectivity needed to separate adjacent CW signals on a crowded band.
- SSB (Single Sideband): via the product detector with BFO offset set for upper or lower sideband. This is the capability the SP-600 lacks in its standard configuration and that makes the R-388 an amateur band and utility station monitor of a different class.
- FSK (Frequency Shift Keying): the R-388 was designed for military FSK/RTTY reception, and the BFO circuit supports this mode. In the Web-888 integration, the R-388’s audio output can be routed to RTTY decoding software for digital mode monitoring.
Section 2 — R-388 vs SP-600: Two Different SWL Partners for the Web-888
The vk6ada.com.au Web-888 SP-600 SWL guide provides the foundation for understanding how the Web-888 integrates with a vintage HF receiver in a receive-only station. The R-388 guide builds on that foundation, addressing the specific differences in architecture, capability, and operating procedure that distinguish the Collins military receiver from the Hammarlund professional receiver.
Front-end tuning: PTO-coupled automatic tracking; no preselector peaking; front-end always optimal at tuned frequency
Frequency architecture: dual conversion; 455 kHz second IF; 30 segments of 1 MHz each
Frequency precision: Collins PTO; 10-turn vernier; ±500 Hz accuracy after calibration; stable from warm-up
Mode coverage: AM, SSB (USB/LSB), CW, FSK — full communications receiver capability
Primary SWL applications: amateur band DX, utility monitoring, CW/RTTY traffic, military net monitoring
Web-888 panadapter view: follows PTO automatically; dual-conversion front-end filtered; no operator intervention needed on frequency change
Build specification: military (US Signal Corps); higher baseline sensitivity and stability than civilian designs
Front-end tuning: separate preselector variable capacitor requiring manual peaking at each new frequency
Frequency architecture: superheterodyne; 455 kHz IF; 6 broad frequency bands
Frequency precision: analogue variable capacitor; good for general SWL; less precise than Collins PTO for frequency identification
Mode coverage: AM primarily; CW with BFO; SSB reception with external BFO accessory on most variants
Primary SWL applications: SW broadcast monitoring, AM utility reception, general HF listening
Web-888 panadapter view: filtered by preselector; preselector must be peaked before panadapter shows maximum signal; operator must peak after each frequency change
Build specification: professional/commercial; excellent sensitivity; wide frequency coverage down to 540 kHz
Section 3 — Three Integration Approaches
Like the SP-600, the R-388 is receive-only. There is no transmit power concern at the antenna connector, no T/R switching required, and no PA-related protection needed. All three approaches are safe at all times.
Section 4 — Approach 1: Second IF Tap Installation in the R-388
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1
Discharge and verify before chassis access Power off; unplug from mains; wait for bleeder network to discharge. Verify all supply points below 30 V with DVM. The R-388’s top cover provides access to the IF strip; remove the cover screws and identify the second IF amplifier section from the service manual chassis layout.
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2
Identify the 455 kHz second IF tap point from the service manual The R-388 (Collins 51J-3) service manual identifies the second IF section on the chassis layout. The tap point is at the output of the second IF transformer or at the input to the second IF amplifier tube, providing the 455 kHz signal at a suitable level for the buffer tap. Confirm the component designator from the service manual before soldering. Contact vk6ada.com.au for the R-388-specific buffer kit documentation identifying the recommended tap location for each R-388 variant.
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3
Install the buffer PCB and RG-174 tap lead Mount the buffer PCB at a suitable chassis location inside the R-388 cabinet (near the IF section for a short RG-174 run). Route the RG-174 from the tap component lead to the PCB input. Connect the PCB output (50 Ω BNC) to a rear-panel BNC connector (15 mm drilled aperture at the position specified in the kit documentation). Power the buffer from the R-388’s regulated low-voltage supply as specified in the kit; no additional power supply is needed.
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4
Verify R-388 sensitivity unchanged; test Web-888 IF tap signal Power on via Variac. Confirm normal R-388 sensitivity on all band positions. Connect the rear-panel BNC to the Web-888 HF input. Open OpenWebRX, set centre to
455 kHz. Apply the IF offset for a busy amateur band (e.g., 20m:14.150 MHz − 455 kHz = 13.695 MHz). Tune the R-388 to 14.150 MHz on the 20m band position. Verify SSB signals appear on the panadapter. Slowly rotate the R-388 PTO dial; signals should shift across the panadapter, confirming the IF tap is working and tracking the PTO.
IF offset (Hz) = R-388 dial reading (Hz) − 455,000 HzKey frequency offsets by band:
1.900 MHz (160m) → offset =
1,445,000 Hz (1.445 MHz)3.750 MHz (80m) → offset =
3,295,000 Hz (3.295 MHz)7.100 MHz (40m) → offset =
6,645,000 Hz (6.645 MHz)10.130 MHz (30m) → offset =
9,675,000 Hz (9.675 MHz)14.150 MHz (20m) → offset =
13,695,000 Hz (13.695 MHz)18.100 MHz (17m) → offset =
17,645,000 Hz (17.645 MHz)21.150 MHz (15m) → offset =
20,695,000 Hz (20.695 MHz)24.900 MHz (12m) → offset =
24,445,000 Hz (24.445 MHz)28.500 MHz (10m) → offset =
28,045,000 Hz (28.045 MHz)Update the offset when changing band positions (bandswitch changes). Within a single 1 MHz PTO segment, the offset is constant. The R-388’s PTO stability means the displayed frequency remains accurate across the full session without recalibration, unlike the FT-101E’s VFO which drifts and requires periodic offset correction.
Section 5 — OpenWebRX Profile Configuration for the R-388 Station
The R-388’s thirty 1 MHz band segments cover frequency ranges that span SW broadcast bands, amateur bands, utility bands, and military/government frequencies. Unlike the SP-600 guide which organised profiles primarily by ITU broadcast band, the R-388 profile configuration is organised by operational focus: amateur bands (where the SSB/CW capability is primary), broadcast bands (AM reception), and utility frequencies (SSB and FSK monitoring).
Band / Segment |
R-388 Coverage |
Mode |
IF Tap Centre |
Span |
Primary SWL Use |
|---|---|---|---|---|---|
| 160m amateur | 1.800–2.000 MHz | LSB | 455 kHz + 1.445 MHz offset | 200 kHz | Amateur DX; nighttime regional SSB nets |
| 80m amateur | 3.500–4.000 MHz | LSB | 455 kHz + 3.295 MHz offset | 500 kHz | Amateur SSB/CW; regional traffic nets; SW broadcasts |
| 40m amateur | 7.000–7.300 MHz | LSB | 455 kHz + 6.645 MHz offset | 500 kHz | Amateur DX SSB; CW; international broadcasts 41m |
| 30m amateur | 10.100–10.150 MHz | CW/data | 455 kHz + 9.675 MHz offset | 100 kHz | Amateur CW DX; digital modes; 24-hour propagation |
| 20m amateur | 14.000–14.350 MHz | USB | 455 kHz + 13.695 MHz offset | 500 kHz | Primary DX SSB; DX pile-up monitoring; beacons |
| 17m amateur | 18.068–18.168 MHz | USB | 455 kHz + 17.645 MHz offset | 200 kHz | Solar max DX; trans-oceanic SSB paths |
| 15m amateur | 21.000–21.450 MHz | USB | 455 kHz + 20.695 MHz offset | 500 kHz | International SSB DX; SW broadcasts 22m/19m |
| 12m amateur | 24.890–24.990 MHz | USB | 455 kHz + 24.445 MHz offset | 150 kHz | Solar max SSB DX; long-path monitoring |
| 10m amateur | 28.000–29.700 MHz | USB | 455 kHz + 28.045 MHz offset | 1 MHz | F2 DX openings; sporadic-E; FM beacons at band top |
| WWV 10 MHz | 10.000 MHz | AM | 455 kHz + 9.545 MHz offset | 50 kHz | Propagation reference; PTO calibration check |
| Maritime HF | 4.125 / 8.291 MHz | USB | Respective offsets | 100 kHz | Maritime calling/distress; ship-to-shore SSB |
| VOLMET HF | Selected freqs 3.5–13.3 MHz | USB | Respective offsets | 50 kHz | Aviation weather; regular broadcast schedule |
Section 6 — Eight Best-Practice SWL Operating Procedures for the R-388 + Web-888 Station
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PTO Warm-Up: Allow 15 Minutes Before Relying on Frequency Accuracy
The R-388’s Collins PTO is significantly more stable than the FT-101E’s LC VFO, but it still benefits from a 15-minute warm-up before its frequency accuracy is within its ±500 Hz specification. During warm-up, the PTO may drift by 1–3 kHz from its calibrated frequency as the chassis reaches thermal equilibrium. This drift is visible on the Web-888 waterfall as a slow movement of known signals.
Unlike the FT-101E (where the waterfall drift monitor is a critical operating practice), the R-388’s PTO drift after warm-up is small enough that the Web-888 can be used as an occasional calibration check rather than a continuous drift monitor. At the start of a session, tune the R-388 to WWV on 10.000 MHz and verify the WWV signal appears at the correct frequency in the Web-888 panadapter. If it appears offset by more than 500 Hz, update the OpenWebRX IF offset by the measured error. After this one-time calibration check per session, the R-388’s PTO maintains its accuracy without further correction.
Session start: tune to WWV 10 MHz → verify panadapter position → update offset if needed → proceed to operating -
Bandswitch and IF Offset — Updating the OpenWebRX Profile on Each Band Change
The R-388’s thirty band positions each correspond to a different 1 MHz segment of the HF spectrum. When the operator changes bands by rotating the bandswitch, the operating frequency shifts by the width of the new band segment, and the OpenWebRX IF offset must be updated to reflect the new frequency range. The offset change is significant on each band change (typically several MHz), making this the primary OpenWebRX configuration action during an active monitoring session.
Procedure: rotate the R-388 bandswitch to the desired position. Read the PTO dial position and calculate the IF offset:
current frequency − 455 kHz. Update the OpenWebRX IF offset field with the new value. Verify by tuning the R-388 to a known signal in the new band and confirming it appears at the correct frequency in the panadapter.For frequent band changers: create pre-configured OpenWebRX profiles for each frequently used band position with the mid-band offset pre-calculated (as in the profile table above). Select the appropriate profile from the OpenWebRX profile selector after each band change; then fine-tune the offset if needed for the specific frequency within the band. This is faster than recalculating from scratch on each band change.
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SSB Monitoring: Web-888 for Signal Identification, R-388 for Audio Quality
The R-388’s SSB capability via the product detector is the defining operational advantage over the SP-600 for amateur band SWL monitoring. The workflow for SSB signal identification is: observe the Web-888 panadapter for SSB signal peaks (visible as asymmetric spectral shapes centred on the carrier frequency); identify the approximate frequency of interest; tune the R-388 PTO to that frequency; engage the R-388’s BFO at the correct offset for USB or LSB; listen to the product detector audio.
The Web-888’s OpenWebRX also demodulates SSB independently: in the panadapter, click on a signal peak to tune the OpenWebRX software demodulator to that frequency, select USB or LSB as appropriate, and listen to the Web-888’s audio. Compare this to the R-388’s audio for the same signal. On a busy amateur band, the R-388’s analogue IF chain with its crystal filter will typically provide better adjacent-signal rejection than the Web-888’s software filter; the Web-888 is the signal identification tool, the R-388 is the quality demodulator.
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CW Monitoring: Narrow Filter and Panadapter for Pile-Up Navigation
The R-388’s CW filter provides the selectivity needed for CW traffic monitoring on crowded bands. The Web-888 panadapter, when set to show 50–100 kHz around the R-388’s tuned frequency, displays the CW signal cluster on a net or in a pile-up as individual peaks. Each peak is a separate CW station; their spacing is visible, and the DX station’s position relative to the listening crowd is identifiable.
CW monitoring procedure: set the R-388 to CW mode with the narrowest available filter. Tune to a CW frequency of interest. In OpenWebRX, zoom the panadapter to a 100 kHz window (±50 kHz) around the R-388’s frequency. Individual CW signals appear as short vertical lines during key-down, with the signal frequency identifiable from their panadapter position. This is particularly valuable for CW contest monitoring, where dozens of stations transmit on adjacent frequencies: the panadapter shows who is where at a glance, while the R-388 filters out all but the one the operator is listening to.
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RTTY and Digital Mode Reception via R-388 Audio or Web-888 Pipeline
The R-388 was designed with FSK/RTTY capability for military communications monitoring. The R-388’s audio output, when tuned to an RTTY signal with the BFO correctly set, provides the mark-space audio tones that RTTY decoding software (Fldigi, MultiPSK, MMTTY) can decode. Connect the R-388 audio output to the computer’s sound card line input and configure Fldigi to use that input. Tune the R-388 to a known RTTY frequency (various utility and weather FAX services broadcast on predictable frequencies) and verify decoding.
The Web-888 pipeline provides an alternative: configure OpenWebRX to output USB audio and route it via a virtual audio cable to Fldigi. The Web-888 may be tuned to the RTTY frequency independently of the R-388, allowing the R-388 to monitor one frequency while the Web-888 decodes digital modes on another. For FT8 reception (the dominant digital mode on amateur bands in 2026), route the Web-888 OpenWebRX USB audio to WSJT-X via the virtual audio cable — this requires no modification to the R-388 at all.
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Amateur Band DX Monitoring: Panadapter-First, R-388-Audio-Second Workflow
The most effective SWL workflow for amateur band DX with the R-388 + Web-888 station places the Web-888 panadapter as the primary band awareness tool and the R-388 as the precision audio instrument. The workflow: open the Web-888 to the current operating band (e.g., 20m USB profile); scan the panadapter visually for signal activity; identify signal clusters, DX pile-ups, or individual strong signals of interest; note the frequencies; tune the R-388 PTO to each frequency of interest for audio monitoring.
During Solar Cycle 25 maximum conditions (2025–2026), the 17m and 12m bands are frequently open for trans-oceanic DX. Create Web-888 profiles for these bands (offsets calculated from the 455 kHz IF as shown in the profile table), and monitor the panadapter when 20m or 15m show signs of high activity — often the WARC bands have less congestion and equally good propagation at the same time. The R-388’s coverage includes both 17m (18 MHz range) and 12m (24 MHz range), making it an ideal companion for the Web-888 panadapter on these bands.
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Utility Station Monitoring: The R-388’s Military Heritage in SWL Practice
The R-388/URR was designed to receive the types of signals that utility station monitors listen to: SSB voice on diplomatic and government frequencies, CW traffic from military and commercial stations, FSK teletype from weather services and news agencies. This heritage makes the R-388 an exceptionally capable utility station monitor, and the Web-888 panadapter provides the visual context that makes utility monitoring more productive.
Key utility monitoring use cases for the R-388 + Web-888: maritime SSB voice on 4.125 MHz, 6.215 MHz, and 8.291 MHz (international distress and calling); aeronautical VOLMET broadcasts at 5.450, 6.679, 10.051, and 13.282 MHz (aviation weather, USB voice); NAVTEX and weather fax on dedicated HF frequencies; numbers stations (still active on various HF frequencies — the Web-888 panadapter helps identify these by their characteristic regular transmission patterns); and diplomatic/government nets using USB voice on frequencies published in SWL club bulletins.
For each utility frequency of interest, create a dedicated OpenWebRX profile with the correct IF offset and USB mode. The R-388’s PTO precision is particularly valuable for utility monitoring where frequency accuracy matters for station identification: a frequency readable to ±500 Hz is sufficient to distinguish adjacent utility stations that may be only a few kHz apart.
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Side-by-Side Comparison: R-388 vs Web-888 Audio on the Same Signal
One of the most instructive uses of the R-388 + Web-888 combination is the direct comparison of both instruments’ audio on the same signal. The R-388 provides its analogue output through its IF filter, product detector, and audio chain; the Web-888 provides a digital DSP-processed audio output from OpenWebRX on the same signal received via the IF tap or antenna splitter. The difference in audio character — the R-388’s analogue warmth versus the Web-888’s clean digital DSP output — is audible and informative.
More practically, the comparison reveals the R-388’s selectivity advantage: on a crowded band, tune both the R-388 and the Web-888 to the same SSB signal. The R-388’s crystal filter will typically produce cleaner audio by more effectively rejecting adjacent signals than the Web-888’s software filter, especially at close frequency separations. The Web-888 may produce “bleed-through” from an adjacent strong station that the R-388 rejects cleanly. This is the analogue filter advantage that justifies maintaining the R-388 as the primary receive instrument rather than using the Web-888 as the sole receiver.
Section 7 — Complete R-388 + Web-888 SWL Station Architecture
┌──────────────────────────────────────────────────────────────────────────┐
│ COLLINS R-388/URR + WEB-888 — COMPLETE SWL STATION ARCHITECTURE │
│ Receive-only — no T/R switching; safe at all times │
└──────────────────────────────────────────────────────────────────────────┘
R-388/URR INTERNAL ARCHITECTURE (relevant to integration):
┌──────────────────────────────────────────────────────────────────────────┐
│ │
│ Collins PTO (0–1 MHz) ─────────────────────► Automatic front-end track │
│ + Band oscillator crystal (bandswitch) No separate preselector │
│ peaking required │
│ Signal path: │
│ Antenna → RF amplifier → First mixer → First IF → Second mixer │
│ → 455 kHz second IF → Crystal/LC filter → Detector → Audio │
│ │
│ 455 kHz second IF: TAP POINT for Web-888 cascade integration │
│ IF active in receive mode only (no transmit chain) │
│ Modes: AM, SSB (USB/LSB), CW, FSK — full communications receiver │
└──────────────────────────────────────────────────────────────────────────┘
─────────────────────────────────────────────────────────────────────────
APPROACH 1: 455 kHz SECOND IF TAP (recommended)
─────────────────────────────────────────────────────────────────────────
ANTENNA (HF receive) → R-388 SO-239 → safe at all times; no PA
│
[R-388 RF front-end — automatic tracking with PTO/bandswitch]
[R-388 first conversion — crystal-controlled band selection]
│
[R-388 455 kHz second IF strip] ─────── tap point ────────────────────┐
│ (Crystal/LC filter on │
│ downstream side) │
[R-388 detector — AM/SSB/CW/FSK] │
[R-388 audio → speaker] [IF tap buffer PCB]
Primary SWL audio; crystal filter selectivity 50 Ω BNC → rear panel
│
[Web-888 HF input]
USB 3.0 → computer
[OpenWebRX — IF profiles]
Centre: 455 kHz
Offset: R-388 freq − 455 kHz
→ PTO-tracking panadapter
→ NO preselector peaking step
─────────────────────────────────────────────────────────────────────────
R-388 vs SP-600 AS WEB-888 SWL COMPANIONS — KEY COMPARISON
─────────────────────────────────────────────────────────────────────────
┌──────────────────────────────────────────┬─────────────────────────────┐
│ Collins R-388/URR │ Hammarlund SP-600 │
│ ────────────────────────────────────── │ ───────────────────────── │
│ PTO — automatic front-end tracking │ Preselector — manual peak │
│ No preselector peaking step required │ Peak before reading display │
│ SSB via product detector (USB/LSB) │ AM primarily; CW with BFO │
│ CW narrow filter; FSK capability │ No built-in SSB product det│
│ 30 bands × 1 MHz; excellent precision │ 6 bands; wide coverage │
│ Military specification sensitivity │ Professional specification │
│ Amateur band SSB/CW SWL; utility │ SW broadcast monitoring │
│ ±500 Hz frequency accuracy (PTO) │ Analogue tuning; less prec │
│ Dual conversion before IF tap │ Single conversion to 455 kHz│
└──────────────────────────────────────────┴─────────────────────────────┘
─────────────────────────────────────────────────────────────────────────
SOLAR CYCLE 25 PANADAPTER OPPORTUNITY — R-388 SPECIFIC
─────────────────────────────────────────────────────────────────────────
The R-388 covers 10m, 12m, 15m, 17m, and 20m with full SSB/CW capability.
Solar Cycle 25 maximum (2025–2026) produces excellent conditions on all
these bands. Web-888 profiles for 17m and 12m are particularly valuable:
these WARC bands are less congested than 20m and 15m, and the Web-888
panadapter shows propagation openings visually — a cluster of signals
appearing on the 17m panadapter is a direct indicator that the band is
open, allowing the R-388 to be tuned for audio monitoring of the DX.
IF offsets for WARC bands (use pre-configured OpenWebRX profiles):
17m: 455 kHz + 17.645 MHz offset → shows 18.068–18.168 MHz allocation
12m: 455 kHz + 24.445 MHz offset → shows 24.890–24.990 MHz allocation
30m: 455 kHz + 9.675 MHz offset → shows 10.100–10.150 MHz (CW/data only)
Collins R-388/URR + Web-888 SWL station. The IF tap approach requires no preselector peaking because the R-388’s PTO automatically aligns the front-end with the tuned frequency. The IF offset must be updated when the bandswitch changes the operating band, but remains constant within a 1 MHz PTO segment. The R-388’s dual-conversion architecture provides two stages of filtering before the IF tap, giving a cleaner panadapter view on crowded amateur bands than the antenna-sharing approach. All configurations are safe at all times because the R-388 has no transmitter.
References and Notes
- Collins Radio Company / US Army, Technical Manual TM 11-5820-255-12, Radio Receiver R-388/URR and associated service documentation. Primary reference for the R-388 architecture, including the dual-conversion IF chain, the 455 kHz second IF circuit, the PTO design and calibration, the crystal band oscillator complement, and the product detector SSB/CW circuit. The service manual’s circuit board layout identifies the second IF section and the component designators used to locate the IF tap point. Available through the vk6ada.com.au Collins reference archive and through the Collins Collectors Association technical resources.
- Mike Peace VK6ADA, Collins R-388/URR Failure Prevention Kit, vk6ada.com.au. The comprehensive R-388 failure mode reference, covering the 6AK5 front-end tube gassing sensitivity (noted in the chassis access warning in Section 3 of this guide), the bandswitch contact cleaning priorities, and the PTO wear modes relevant to frequency accuracy. The R-388’s 6AK5 front-end tube is more sensitive to damage from nearby RF field exposure than the 6DC6 used in the R-390A; maintaining the 6AK5 in ungassy condition is important for any station that also operates transmit equipment nearby, even though the R-388 itself is receive-only.
- Mike Peace VK6ADA, Web-888 SDR with the Hammarlund SP-600 SWL Station, vk6ada.com.au (March 2026). The companion SWL guide for the SP-600, which provides the foundation for comparing the two receivers’ Web-888 integration characteristics as described in Section 2 of this guide. Readers operating both an R-388 and an SP-600 should read both guides; the SP-600’s broadcast band coverage and the R-388’s SSB/CW amateur band capability are complementary rather than competing, and a station with both receivers and one Web-888 is a genuinely comprehensive SWL station.
- Mike Peace VK6ADA, RX-888 Mk II with the Collins R-390A — Practical Cascade Integration via the CASCADE-390 IF Tap Kit, vk6ada.com.au (March 2026). The foundational IF tap methodology guide. The IF offset formula, buffer amplifier design principles, and OpenWebRX IF offset configuration procedure documented in that guide apply directly to the R-388 IF tap integration described in this guide. The R-388’s 455 kHz second IF is identical to the R-390A’s IF frequency, making the integration fully consistent with the CASCADE-390 approach in all technical aspects.
- Mike Peace VK6ADA, Collins 51J-4 / R-388 Failure Prevention Kit (separate document), vk6ada.com.au. The 51J-series family FPK covering both the R-388 (51J-3) and the 51J-4, documenting the shared and distinct failure modes of the 51J line. The BFO coil slug fracture documented as an elevated priority in the 51J-1 FPK is mentioned in context; the R-388 (51J-3) has a different BFO configuration from the 51J-1 but shares some coil slug considerations. Operators who have not recently serviced the R-388’s BFO circuit should verify BFO functionality before relying on SSB and CW operation as described in this integration guide.
- IARU (International Amateur Radio Union), Region 1, Region 2, and Region 3 Band Plans, iaru.org. Reference for the amateur band frequency allocations used in the OpenWebRX profile table in Section 5, including the WARC band allocations (30m 10.100–10.150 MHz, 17m 18.068–18.168 MHz, 12m 24.890–24.990 MHz). The R-388 covers all WARC bands within its 30-segment frequency plan; the IF offset values for 17m and 12m in the circuit legend represent two of the most operationally valuable profiles for a Solar Cycle 25 DX monitoring station.