User manual RAMSEY FHT1

[. . . ] Sly Fox FOX-HUNT TRANSMITTER KIT Ramsey Electronics Model No. FHT-1 Get involved in the fox hunting fun!This kit combines a crystal locked true FM transmitter with a microprocessor for reliable operation. Multiple transmission "modes" assure a "sly fox" that will challenge any fox hunter. · · · · · · · · · · Selectable high (5W) or low power (800 mW) operation - unit can even be programmed to change power levels during use! [. . . ] Be sure to install with the flat side oriented correctly. See the parts diagram for correct placement. Install R18 and R19, the two large 47 ohm resistors (yellow-violetblack). These resistors function by limiting the current to the RF "final" amplifier. This in turn lowers the power output of the transmitter. Lets "pick apart" the switching network consisting of Q7, Q8 and associated components. Have a look at the schematic diagram and follow along. When voltage is applied to the base of Q7 (from the microcontroller U2) transistor Q7 is turned "on". This causes current to flow through Q7's collector and Component side of board Solder side of board Transistor can Solder can to PC creates a voltage drop across resistors R15 and R16. This "voltage divider" is tied to the base of Q8, the power PNP transistor, forward biasing Q8 and supplying 12VDC to the final transistor, Q6. This is the "high power" mode. Conversely, when there is no voltage applied to Q7, both Q7 and Q8 are turned "off", and the current must flow through resistors R18 and R19. The voltage drop across these resistors causes less potential to be applied at the collector of Q6, lowering the output power. Note to more experienced kit-builders The "low power" setting can be adjusted by changing the values of R18 and R19. Please keep both values the same (for equal power dissipation), The higher the total value - remember that these resistors are in parallel - the lower the RF output power will become. Please use at least one watt resistors for this modification. FHT-1 · 18 Also there is a provision to adjust the "high power" output. Notice that jumper J5 connects the collector of Q8 to the final transistor Q6. by removing this jumper and installing a suitable resistor (remember to calculate the power dissipation) the high power output can be lowered from its full 5 watt value. Heavy buss wire jumper (not a scrap component lead) Wire sits flat against board PC board 1/2 inch Please understand that these modifications should not be attempted unless you are experienced enough to calculate the current and power yourself and they are not recommended until after the entire unit has been fully tested. The testing instructions are intended for the existing unmodified kit. As long as we're stopped already, now would be a good time to recheck your work, focusing on parts placement and soldering. Are all the components snug to the PC board?Resolder any connections that are less than perfect, and trim all the leads to a reasonable length. Install C1, . 01 uF disc (marked . 01 or 103 or 10nF). [. . . ] Please do not include your own hardware such as These short checks in noknobs, cables, external battery problems that can rear their non-Ramsey cabinets, way detail any and all packs and the like. Ramsey Electronics, Inc. , reserves the on the way to on ANY most errors. We'd like ugly head, but should get youright to refuse repairsolvingitem in which we find excessiveto problems or damage due to construction may encounter, but the such situations, be able to foresee a problem a buildermethods. To assist customers in sheer number Ramsey Electronics, Inc. , reserves the right to solve their needs on a case-by-case basis. of parts and the permutations and combinations of installing them makes an The repair is $36. 00 per hour, regardless of the cost of the you run into a roadblock, gather list of precise, exact solutions impossible. [. . . ]