User manual RAMSEY PR10

[. . . ] PR10 PR10--1 INTRODUCTION TO THE PR10 LOW NOISE PREAMPLIFIER A "preamplifier" gives an initial boost, measured in decibels, to the level of a signal before it is further processed by tuned circuits, filters, amplifiers, mixers, detectors, or other circuit stages. Preamps may be designed for either RF or audio use and may be either tuned or broadbanded. The Ramsey Low Noise PR10, 20, and 40 Preamplifiers for 144, 220, and 440 MHz, respectively, differ from our popular SA7 and PR2 broadband preamplifiers in that these models include high-Q tuned input circuits to pre-select the desired frequency range, restricting the strength of other out-of-band signals. Also, the microwave transistor is biased for best low noise performance. PR10--2 CIRCUIT DESCRIPTION L1 and C2 form a tuned input filter for the preamp to reject out-of-band signals. [. . . ] It will take you less than a minute to completely recheck every single soldering connection as well as the correctness of parts installation. 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! PR10--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 inadvertant bump of a keyer, to destroy a preamplifier. PR10--9 PR10 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 PR10 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. 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! PR10--10 A 2 METER "ACTIVE ANTENNA" For situations where a simple indoor receiving antenna is needed, the PR10 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 low price, take a look at our 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. RFS1) · PIN diode T-R switch PIN diode applications are discussed in amateur radio magazines and the ARRL Handbook. PR10--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. PR10--12 TROUBLESHOOTING GUIDE The only possible causes for malfunction of the PR10 are faulty or incorrectly installed parts. [. . . ] If you believe we packed an incorrect part or omitted a part, please write or call us with information on the part you need and proof of kit purchase 3. FACTORY REPAIR OF ASSEMBLED KITS: To qualify for Ramsey Electronics factory repair, kits MUST: 1. No repair will be undertaken until we have received the MINIMUM repair fee (1/2 hour labor) of $25. 00, or authorization to charge it to your credit card account. DO NOT send a separate letter; include all correspondence with the unit. [. . . ]