User manual RAMSEY RFS1

[. . . ] 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. 4. Orient the circuit board as shown in the parts layout diagram. [. . . ] If you wish to send DC power up the transmission line to power the RFS1, install JMP1 using a scrap piece of clipped-off component lead; if not then leave this jumper out. Now is a good time to check solder joints and part orientations for proper installation. Check for cold solder joints or solder bridges. RFS1 --6 To Connect an Amplifier : 12-14 VDC RF IN RF OUT RFS1 Radio A B C Ant Y Z AMP To Connect a Preamplifier : 12-14 VDC RF OUT RF IN RFS1 Radio A B Ant Q1 C Y Z Pre Amp Follow these simple diagrams to connect your RFS1 to a preamp or amplifier. Use coax only and make sure the shield conductor on the coax and center conductor are as short as possible when soldered together. RFS1 --7 FREQUENCY CONCERNS OF L1 If you are planning on powering your RFS1 through the transmission line instead of the power leads, notice that the value of L1 is going to be frequency dependent. Its purpose is to channel DC from the transmission line into the circuit, but block the RF from coming into the power. A coil has a certain resistance to RF called reactance. The larger the value of the coil, the more reactance it has at a particular frequency. The less frequency there is, the less reactance there is. So if you are working with HF, the coil provided will not be large enough in value. What we are looking for is a coil with a reactance value larger than 1K ohms. To solve for this part value the formula is a relatively simple plug and chug. Put the value for your coil in "L" and frequency in "F". Remember to take the numerical values of your extensions into account such as Mega = 1 million and micro = . 000001. The formula is as follows: X = 2 * 3. 14 * L * F For example, to find the reactance of the supplied coil in the two meter band, plug in the numbers as follows: 2 * 3. 14 * . 0000022 * 146520000 = 2025 ohms RFS1 --8 So we find the coil has a reactance of about 2K ohms in the two meter band. Rearranging the formula so we can find the value of a coil that has a reactance of 1K ohms at any frequency: L = 1000 / (2 * 3. 14 * F) where F is the frequency you will be operating on. Use this value of coil for both at the power source and as L1 in the RFS1. Note the diagram for jumper setting and parts placement for feeding the power up the transmission line. The coil near the radio end of the coax should be mounted as close as possible to the connections on the coax to prevent unwanted radiation. Block diagram : 12 - 15VDC Choke Value >= L1 . 01uF Center conductor Coax shield JMP1 R RFS-1 Radio RFS1 --9 Hook up of coil near radio : F r o m r a d io . 0 1 u F T o R F S -1 H e a t s h r in k o r in s u la te d w ir e C o il To pow er s u p p ly g r o u n d To pow er s u p p ly + V OPERATING NOTES: 1. If the relay chatters, it is a sign of high SWR, which you will wish to resolve anyway by antenna system or amplifier output adjustments. If the relay action is "sloppy", there is insufficient RF to drive the RFS1 circuit. This may occur when using a "low power" HT setting. The RFS1 will handle a range of powers depending on frequency. [. . . ] Don't be afraid of telling us that you 'blew-it', we're all human and in most cases, replacement parts are very reasonably priced. MISSING PARTS: Before assuming a part value is incorrect, check the parts listing carefully to see if it is a critical value such as a specific coil or IC, or whether a RANGE of values is suitable (such as "100 to 500 uF"). Often times, common sense will solve a mysterious missing part problem. If you're missing five 10K ohm resistors and received five extra 1K resistors, you can pretty much be assured that the '1K ohm' resistors are actually the 'missing' 10 K parts. [. . . ]