Amateur Radio Products

1268 South Ogden Street Denver, Colorado 80210 USA
email Phone: 303-722-2257 FAX: 303-744-8876
9 a.m. - 5 p.m. MST Monday - Friday

Receiver Test Data
First-IF Crystal Roofing Filters	Electronic Kits	Owners Manual
Band Crystals	Custom Front-Panel Switch	Filter Brackets
Crystal Cover	Mode Switch Cover	Cleaner & Lubricant
PRE-4 Preamp	FS-4 Interface Kit	Receiver Modification Service
Sherwood Engineering Inc. Home Page	Short Wave Listener Catalogue	SE-3 Synchronous AM Detector

Sherwood / Drake R-4C
Still the Finest Competition-Grade Receiver

Receiver performance tests were taken on current, popular receivers and transceivers. Dynamic-range measurements were made using two equal-strength test signals 2 kHz apart to approximate a "real-life" pile up, plus then more normal 20 kHz spacing. A few radios had to be tested at 50 or 100 kHz because of synthesizer noise. (See below for additional details). Some units, due to limitations in the i-f filters or board layouts, had excessive test-signal leakage, requiring close-in measurements be made at 3- or 4-kHz spacing. AGC threshold, the point below which audios falls off rather linearly with signal, is listed in microvolts across the antenna input (assumed to be 50 ohms). Also listed is the drop in audio-output level at the AGC threshold, as compared to a 5 mV (typically S9 + 40 dB) signal. Tests were made using a 500- or 600-Hz CW filter, when available.

Receiver noise floor can be degraded by the reciprocal mixing of an adjacent strong signal with phase noise from local oscillators, LO amplifier stages, phase-locked loops, or synthesizers. Noise from the receiver LO chain is listed for a normalized bandwidth of 1 Hz at a given kHz offset in dB below the LO carrier (dBc). To calculate actual noise from the table for a given filter: Integrated Noise = Table Value N minus 10 log (filter bandwidth in Hz). Thus an LO with noise 100 dBc and a filter 500 Hz wide would degrade the noise floor at least 3 dB (at the listed signal spacing or less) whenever a signal was 73 dB above the reciever noise floor (about S9 + 15 dB). 120 dBc or greater is desirable.

Drake R-4C

Testimonial on SEI Modifications
to the R-4C

A rating of front-end selectivity is provided, with broad delineations of A through F, rating the ability to reject out-of-band signals. A tracking pre-selector is graded as A+, while no input selectivity would be F.

Receiver ultimate rejection rating is not standard. It is NOT what the rejection is 10, 20 or 50 kHz off frequency. This shows whether signals two to four filter bandwidths off frequency will be heard as undesired leakage. Ultimate rejection of 120 dB will not show leakage until approximately S9 + 60 dB.

Also on this web site is information on our complete line of products, plus certain circuits to improve specific subsystemns in the R-4C. Most of our modifications have been published in Ham Radio magazine. We offer assembled PC board update kits, along with in-house installation services.

For further explanation of our receiver testing procedure, see: "Present-Day Receivers - Some Problems and Cures". ham radio, December 1977, page 10. PDF copies of our ham radio articles are available for download from the web site front page.

R-4C SSB 8-Pole First-IF Crystal Roofing Filters

Improve the early-stage selectivity of your Drake R-4C by adding eight additional poles with an internally-mounted, switchable set of first-IF roofing filters. This provides 16-pole total receiver cascaded filter selectivity. The filters will reduce QRM leakage, overload, and eliminate blanker false-triggering from adjacent stations. Ideal for DX and contest work. The overall shape factor is better than 1.5. Maximum skirt selectivity with maximum intelligibility. Variable bandwidth can be obtained by offsetting first and second-IF filters with passband tuning control. Total bandwidth with CF-2K/8 and FL2400 is 1900 Hz at -6dB and 2900 Hz at 60 dB. The ultimate rejection is better than 120dB.

Other Available Filters

Two-filter switching with PC board, relays & sockets: No longer available*
Three-filter switching with 2 PC boards, relays & sockets: No longer avaialble*
Four-filter switching with 2 PC boards, relays & sockets: No longer available*
LSB & USB CF-2K/8 filter pair: No longer available

* Increased prices of switch kit parts have made these products uneconomical to sell.