This preselector is an outgrowth of the Type-6 and the original RFP. It has been streamlined into a 2RU (3.5" rack panel. It also incorporates a 'hi' and 'lo' "Q-Factor" in the
peaking circuitry and covers a greater range than any previous design; 20KHz through 50MHz. Additionally, I've added a 100KHz Marker Oscillator for calibration purposes
and a 10MHz up-converter for receivers that can't tune the LF and VLF bands, will now be able to tune from 20KHz to 500KHz. The RFP-1 also includes a 4-radio
Multicoupler, a 4 antenna selector switch, individual RF Gain controls for each receiver, and comprehensive static, bleed, impulse and transient protection, along with
antenna-line shunting for when the radios are not in use.
All of these layouts and designs are subject to some change. The schematic circuitry is
tried and proven and probably won't change.
The panel layout is subject to parts sizes and logistics, but seems to be pretty well finalized.
The Multicoupler is totally passive, with noise factor being a leading prerequisite. If the
radios have at least one input stage before the mixer (most every receiver today does),
then the reflected impedances diminish to an insignificant figure. Example: I currently have
a Racal, Watkins-Johnson, MacKay, and JRC connected to the prototype. Disconnecting
any one, two or three radios does not change the signal level on the remaining receiver.
Likewise, by placing a dead short across one of the ports, the active radio drops less than
1/4 of an S-Unit. I guess it's about 1 to 1.5dB. The benefits of the passive coupling are very
apparent in total noise floor measurements.
The filtering circuitry is very sharp for passive bandpass filters. This is due to two factors:
1. Very high Q inductors; about 200-230 Q-Factor and,
2. A very high "L" to "C" ratio. This gives off-center frequency reactances in the area of
5,000 ohms, or about 40dB (100:1).
The criteria for the selectivity is the 5 or 10 KHz channel spacing of International
broadcasters. This kind of selectivity really excels in the MF or AM broadcast band for AM
Above: Left side; Below: Right side
To read schematic, <right click> and select <copy> to save it to your files, or just click <print>.