User manual RAMSEY PR-20

[. . . ] Q1 has a very low noise figure, determined by the bias established by R1 and R2. The actual circuit is about as simple as they come. Maximum gain and freedom from oscillation are accomplished by the quality of workmanship in parts installation and I/O connector wiring PR20--3 PARTS SUPPLIED WITH PR20 KIT CAPACITORS 2 2 or 2. 2pF disc capacitor (C1, 2) 1 10pF disc capacitor (C3) 1 100pF disc capacitor [marked 100 or 101] (C4) 1 . 01uF disc capacitor [may be marked . 01, 103, or 10nF] (C5) RESISTORS 1 470 ohm [yellow-violet-brown] (R1) 1 100K ohm [brown-black-yellow] (R2) OTHER COMPONENTS 1 PRX printed circuit board 1 shielded adjustable coil (L1) [marked 359-7787] 1 2SC2498 or 2570 microwave bipolar transistor (Q1) REQUIRED, NOT SUPPLIED 9 - 15 VDC power source RF input and output connectors (your choice of type) PR20--4 RAMSEY PR20 PRE-AMP PARTS LAYOUT * NOTE FOR PR-20: Disregard C6 PR20--5 PR20 PRE-AMP ASSEMBLY PROCEDURE Soldering nine parts to a PC board is not a big job, but good performance of the PR20 requires attention to keeping all leads as short and neat as possible. The order of parts installation is not critical for this and other small kits, so the purpose of the following suggested order of assembly is just to make it as easy as possible for you to get the parts placed correctly on the first try. [. . . ] It will take you less than a minute to completely recheck every single soldering connection as well as for the appropriate part installations. PC board soldering checked. . . touched up if needed. INPUT AND OUTPUT CONNECTIONS Use short pieces of miniature coax such as RG-174 to connect the PC board input and output points to the RF connectors you wish to use. For the neatest installation, it is good practice to pre-tin the coax ends before soldering to the PC board. Plan your probable applications with as much foresight as possible so that you don't spend more on cable adapters than you did on the kit! PR20--8 TESTING AND ADJUSTMENT With your preamp installed between antenna and receiver, the only adjustment needed is the obvious one: peaking L1 for maximum signal strength. This may require more patience than most of us would think, because the adjustment should be made on a weak signal transmitting long enough to permit the adjustment. Since this is a low noise preamp, don't look for an imaginary increase in noise level or waste time trying to make a strong repeater signal seem stronger!CAUTION Under no circumstances should transmitter RF ever be applied to the input or output of this preamplifier. Even though this sounds like unneeded advice and common-sense knowledge, we should remember that most of today's receivers are in transceiver configuration, and that all it takes is one accidental push of a button out of habit, or an inadvertent bump of a keyer, to destroy a preamplifier. PR20--9 PR20 ON-OFF SWITCHING SUGGESTION Depending on your particular application and intended frequency, you may wish to use a DPDT power switch with one pole controlling voltage and the other pole connecting the input and output of the PR20 when the DC supply voltage is in the "OFF" position. This setup is very practical when you want to switch the preamp in and out of a receiver antenna line. ALL RF connections to the switch should be as short as possible. Use good quality miniature coaxial cable. STRONG SIGNAL OVER-LOADING If you live in a situation where there are very strong nearby stations, you may experience overloading of the receiver to which the preamp is connected. This is especially true for small hand-held radios - after all, what do you think they leave out to make the size small?Front-end filtering components are large, but they serve a needed purpose in high RF environments. Unfortunately, there is little you can do except to add the missing filtering. Digi-Key (1-800-digi-key) sells the TOKO line of helical filters which are excellent. Expect to pay about twice as much as you paid for this preamp! PR20--10 A 220 MHz "ACTIVE ANTENNA" For situations where a simple indoor receiving antenna is needed, the PR20 preamp will add considerably improved performance to a whip antenna adjusted to 1/4 or 5/8 wave. And, for a very well engineered true active antenna for both HF and VHF at a break-through low price, take a look at our new model AA7 Active Antenna kit which features an on-board battery supply, adjustable gain control, heavy-duty whip, HF-VHF mode switching, and jack for using external antennas. T-R SWITCHING CONSIDERATIONS FOR TRANSCEIVER OPERATION If you wish to use the same antenna for transmit and receive, T-R switching is, of course, essential. The T-R switching may be any of the following: · manual in-line switch (NOT recommended for VHF/UHF) · relay controlled by push-to-talk line · RF sensing T-R relay (Ramsey Kit No. RFS-1) · PIN diode T-R switch PIN diode applications are discussed in amateur radio magazines and the ARRL Handbook. PR20--11 2SC2498 CHARACTERISTICS: The 2SC2498 transistor is a bipolar silicon NPN low noise UHF/VHF amplifier in a TO-92 case, suitable for service up to 5GHz, with maximum device dissipation of 600 milliwatts. Other maximum ratings: Collector -to-Base Voltage: 25 V Collector-to-Emitter Voltage: 12 V Base-to-Emitter Voltage: 3V Maximum Collector Current: 70 mA Standard replacements: ECG10 or SK9139. You may, of course, order replacement 2SC2498 transistors from the Ramsey factory in Victor, NY, but we are pleased also to give you this pipeline to your own local electronics parts dealer if 2SC2498 replacements are needed. PR20--12 TROUBLESHOOTING GUIDE The only possible causes for malfunction of the PR20 are faulty or incorrectly installed parts. Transistor replacement information is provided. [. . . ] FACTORY REPAIR OF ASSEMBLED KITS: To qualify for Ramsey Electronics factory repair, kits MUST: 1. NOT be assembled with acid core solder or flux. BE returned in fully-assembled form, not partially assembled. BE accompanied by the proper repair fee. [. . . ]