McKay Dymek company manufactured a number of products aimed at quality (HI-FI) listening of AM radio, both in the conventional AM broadcast band and the short wave broadcast bands.
The DR33C receiver is specified for coverage from 50 kHz to 29.7 MHz in AM, CW, LSB, USB and RTTY modes.
The very left control on the front panel is the filter selection switch. The next 4 knobs to the right (one small and three large) are the frequency selection switches one each for 10 MHz, 1 MHz, 100 kHz and 10 kHz. These switches control a frequency synthesizer. The LED digits directly above these switches display the corresponding frequency and on the DR 55 McKay Dymec receiver the switch has the frequency numbers around the knob and has no LED display. The next large knob to the right is the "fine" frequency control and it controls an analog VFO with a range of +/- 5 kHz. The LED display for 1 kHz and 0.1 kHz is driven from a frequency counter. The next switch to the right is the Band switch which controls the preamp and 2.5 MHz filter selection. The next control is the Mode switch with positions for: AM, SSB, CW, RTTY and it selects the BFO frequency. The front part of the next control is the standard OFF-volume and the back knob is the IF gain. Finally on the right is a noise limiter switch.
This receiver shows the carrier frequency rather than the band center frequency. For example if you are tuned to an AM station in AM mode you will hear the normal AM signal. If you now select USB you will hear only the upper sideband without retuning. This is great if there is interference just below the carrier frequency. In a like manner you can select USB.
Because the center frequency is selected by using a number of switches it is possible to track chirp sounder trtansmissions by switching up 100 kHz waiting for the chirp and switching up another 100 kHz. This works with manual switching because the chirp sweep speed is typically 100 kHz per second and you can keep up manually.
The mode switch selects the BFO frequency which is derived by dividing a crystal oscillator by 10.
By replacing the switch with one with more positions two new features were added.
The new Mode switch positions are:
- two new positions for BFO frequencies of 1000 Hz and 2550 Hz
- a position for adding an FM demodulator using the Meco kit based on the LM1358. This did not work probably because the IF AGC was not set to max gain.
- AM - BFO off
- SSB - BFO at 455 kHz for a 0 Hz audio tone
- CW - BFO at 455.8 kHz for an 800 Hz tone
- RTTY0 - BFO at 457 kHz for a 2000 Hz tone
- RTTY1 - BFO at 456 kHz for a 1000 Hz tone
- RTTY2 - BFO at 457.55 kHz for a 2550 Hz tone
Bottom Inside -
Top Inside - although the DR33 shipped with wood side panels (see brochure photo at top of page) there are threaded holes is exactly the place to add rack ears, although rack ears were not an option, so I made some.
Block Diagram -
Top Level Schematic -
|The DA-5 broadcast band loop is
on the left.
To the right is the DA-100 indoor power supply.
|GPS Timing antenna at top of
DA-100 active whip comes in a single module size outdoor electrical box.
Note whip is horizontal to lower noise pickup.
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page created 8 March. 2002.