Ramsey RFS1 User Manual
• Instant TR switching with 1 to 100
watts RF
• Compact and easy to install
• Operates on 12 - 14 VDC
• Matches Ramsey RF Amps and
Preamps
• Convenient size for mounting
within 1 1/2” PVC pipe - ideal for
mast mounted preamps
If you need a convenient way of bypassing or enabling an RF preamp or amplifier when
you key your rig, then this is the way to go! The RFS-1 can be configured to switch in or out
either a receive preamp or transmit power amp. Also has the ability to feed DC power
directly up the transmission line, making it great for mast mounted preamps and amps. A
very versatile transmit/receive switch for almost all RF switching purposes.
RFS1 —1
Kit No. RFS1
INTRODUCTION TO THE RFS1
The RFS1 has been designed to work in conjunction with external RF preamps or RF power amplifiers to detect when the connected radio has been keyed, thereby bypassing a delicate preamp or
enabling a booster amplifier. It can be used in a range of RF powers ranging from 1 to 100 watts.
An inverter is supplied so that the relay can be opened when the radio is keyed to bypass a preamp without sending power to it. Without the inverter the relay is closed upon keying to allow a
booster amplifier to be in circuit.
RFS1 PARTS LIST
❒ 1 10ρF ceramic capacitor (marked 10 or 10K) (C3)
❒ 4 .01µF ceramic capacitors (marked .01, 10nF, or 103) (C1,C4,C5,C6)
❒ 1 100µF to 220µF electrolytic capacitor (C2)
❒ 4 10K Ω resistors [brown-black-orange] (R1,R2*,R3,R4)
❒ 1 1K Ω resistor [brown-black-red] (R2*)
❒ 1 100 Ω resistor [brown-black-brown] (R2*)
❒ 3 1N4148 diodes (D1,D2,D3)
❒ 3 2N3904 NPN transistors (Q1,Q2,Q3)
❒ 1 12 Volt DPDT relay (K1)
❒ 1 RFS circuit board
❒ 1 2.2mH coil, green body [red-red-gold-black] (L1)
*NOTE: To determine the value of R2 for your application, see Assembly step 4.
RFS1 —2
RFS1 PC BOARD ASSEMBLY
As you can see there isn’t very much to do in this project, but be careful! Don’t rush and
improperly mount a part or leave long lead lengths on components. As all good RF technicians
and experimenters know, parts must be mounted flush to the PC board - not only for mechanical
strength and looks, but also to prevent radiation problems by long lead lengths acting as small
antennas. Just follow the assembly instructions carefully and take your time. Before you know it
you will be satisfied and have a working project!
RFS1 —3
ASSEMBLY OF THE RFS1
❒ 1. Orient the circuit board as shown in the parts layout diagram.
❒ 2. Install C3, the 10ρF ceramic capacitor (marked 10 or 10K).
❒ 3. Install R3, a 10K resistor [brown-black-orange].
❒ 4. Installing R2: First, determine the power output of your RF transceiver. This is, of
course, the power input to the RFS1. Then choose the appropriate value of R2 from
the table below (all three resistors have been supplied in this kit).
TABLE FOR R2
Power to RFS1 Value of R2
less than 10W
100Ω
10 to 30W
1KΩ
30 to 100W
❒ 5. Install D3, one of the 1N4148 type diodes. Be sure to note the cathode (banded)
10KΩ
end of the diode and its orientation on the layout diagram.
❒ 6. Install D2, another 1N4148 type diode. Again, observe correct orientation of the
banded end.
❒ 7. Install R4, a 10K resistor [brown-black-orange].
RFS1 —4
❒ 8. Install C4, a .01µF ceramic capacitor (marked .01, 10nF, or 103).
❒ 9. Install C1, a .01µF ceramic capacitor (marked .01, 10nF or 103).
❒ 10. Install R1, a 10K resistor [brown-black-orange].
❒ 11. Install Q2, another 2N3904 type NPN transistor. Be sure to observe correct
orientation.
❒ 12. Install D1, the last 1N4148 type diode. Be sure to observe orientation of the banded
end.
❒ 13. Install Q3, the last transistor. Note again the orientation of the flat side.
❒ 14. Install K1, the DPDT RF relay. Note that this fits in only one way. Securely solder all
connections.
❒ 15. Install C5, a .01µF ceramic capacitor (marked .01, 10nF, or 103).
❒ 16. Install C6, another .01µF ceramic capacitor (marked .01, 10nF, or 103).
❒ 17. Install the 2.2µH coil (resistor shaped body, green color) [red-red-gold-black].
❒ 18. Install C2, the 100µF to 200µF electrolytic capacitor. Make sure the positive side of
the capacitor is mounted in the correct hole. In some cases only the negative lead is indi
cated with a stripe down the body of the capacitor. Make sure to orient the capacitor cor
rectly.
RFS1 —5
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