A Home Brew 224 MHz Repeater Project. May 2009 Part 2 The Receiver First Post May 2, 2009, this post May 6, 2009
This text is part 2 of a description of a recently completed 224 MHz Repeater Project. One could easily apply the same techniques toward a repeater project in different frequency ranges. Pictures of the completed repeater project reside in the group photos section. http://groups.yahoo.com/group/Repeater-Builder/photos/album/1157128983/pic/list I selected a Hamtronics R302-6 Receiver for the project for a few of the following reasons. The receiver is frequency synthesized, relatively low in cost (about $229 each at the time of this post), respectable in performance and fairly straight forward to interface. Hamtronics normally requests the frequency of operation at the time of purchase so the receiver arrives "pre- tuned" and ready to interface after mounting. Having an original Hamtronics Equipment box from a previous project I drilled the proper locations for threaded standoffs at the receiver PC-Board corners. The volume and squelch controls extend through the front panel and are normally accessible with the repeater in operation. There are pro and con reasons for leaving controls accessible to magic fingers. New old stock ("NOS") Com Spec TS-32 CTCSS (PL) tone boards are very nice "Ebay sleeper deals". Using one of the available sub audible CTCSS tones validates the TS-32 unit for use in this type of repeater performing 3 different functions. If you need a CTCSS tone not available with a TS-32, try looking for a TS-64 or similar easy to use Tone Board. Repeat Receiver audio is routed through the TS-32 on-board CTCSS tone filter to provide fairly clean filter flat audio output to your external controller. The repeater audio source connection point from the receiver provides De-Emphasized "flat audio" with CTCSS present. The output of the TS-32 tone filter section (to your external repeater controller) is De-Emphasized (relatively) flat audio without CTCSS. Connect the Hamtronics R302-6 repeater audio output direct to the TS-32 tone filter input. Don't panic, the TS-32 also provides a separate tone generation "encoder" section for your transmitter CTCSS requirement. A shielded audio quality wire is routed out of the receiver box to the transmitter board at the proper CTCSS connection point. After levels are properly set, you need not worry about transmit CTCSS. Of course a third section of the TS-32 board provides CTCSS (sub audible tone, aka "PL") detection. The Hamtronics R302-6 Receiver provides a connection point from the discriminator to the TS-32 decoder input. The first transistor switch "Out-1" is active low and JU1 & JU2 or normally removed (opened). Don't forget to ground the TS-32's Mic Hangup lead to enable the decoder function. Diagrams for the TS-32 with instructions are easily found on the web using Google. The Hamtronics Receiver COR/COS output is active high, which I don't like one bit. So I simply routed the receivers COS/COR Output logic line through a 120 ohm resistor to the gate of a 2N7000 FET (also known as a VN10K and similar device). The FET source lead is grounded and the drain output lead becomes the main active low logic output source routed to your external repeater controller. DB-9 Connectors are very popular with repeater builder types. I for personal preference and experience tend to move away from using them in for this type of repeater chassis through hole connections. I have returned to using through hold feed-through capacitors and while the value is not ultra critical, you don't want the capacitance value large enough to impact the information passing through. I found and used surplus 100pf (pico farad) feed-through capacitors although I'm sure higher values will work. In my opinion the 100pf value is enough to bypass troublesome stray RF, but not greatly impact or modify the audio information passing through to the external controller. A square pattern of 3 X3 feed through capacitor holes was drilled in the back panel. I also included solder lug ground connections on some of the mounted capacitor bodies, both inside and out. Through any choice of the 9 available feed-through capacitors: 1. Repeater Audio, gated on/off with squelch, De-Emphasized and CTCSS filtered. Level is fixed at "what you get", which is not a problem with external repeater controllers with adjustable input controls. This "tone filtered audio" is taken direct from the TS-32 tone filter output pin. The input to the TS-32 tone filter circuit on the TS-32 board. 2. Carrier Squelch COS/COR active low logic (connection is grounded with the receiver squelch open/on. I wired a 2N7000 fet drain lead directly onto the feed-through capacitor lead (chassis inside) and adjacent ground lug receives the fet source. The receiver COR/COS logic output wire arrives at the fet gate through a series 120 ohm resistor. The function of the fet is to invert and isolated the receivers active high COR/COR logic to a more standard (and what I consider safer) active low (grounded when on) logic operation. 3. CTCSS output from the TS-32 tone encoder section, which is routed directly to the transmitter sub audible (CTCSS) tone input connection. The transmit CTCSS level is set using the available output level control on the TS-32 circuit board. The TS-32 CTCSS audio output level is quite a bit more than required by the transmitter. If you "knock down the level" with a series 100K resistor, do it inside the transmitter box, not the receiver. I only used the TS-32 level control in this application (no resistor required). 4. Valid CTCSS tone detect active low logic direct from the TS-32 "Out-1", transistor logic, which works very well with controllers able to detect and operate both carrier squelch and CTCSS Operation. If your repeater controller doesn't have a CTCSS input logic line, you can and might use the CTCSS logic as your Controller's COR input if your repeater will be operated in constant CTCSS mode. 5. Local carrier squelch speaker audio, level set by the front panel volume control (pot). I actually removed one of the feed through capacitors and mounted a 1/8 inch (aka 3/32 inch) phone jack for an external speaker. I also wired in a small internal speaker easily seen silicone glued down onto the receiver chassis. Normally I don't wire and use local speaker audio but even a cheap speaker can be handy for casual local listening. 6. Power input to the receiver and TS-32 boards. Paranoid types (like myself) can and probably should consider connecting a 16 Volt, 5 watt Zener diode at the chassis feed-through capacitor mounting point. If the receiver is properly power lead fused, the Zener will open the fuse in both reverse and over voltage conditions. Power, both AC and DC ground connections are wired to each repeater box item and connected through lugs to the chassis metal base plate (described in part one) . Everything Receiver and TS-32 checked out... I mounted the receiver box down to the metal plate using serious screws. The flying wire leads from the feed-through capacitors and ground lugs were routed toward the base plate rear chassis center section and later (not shown in the pictures) secured to the plate with black plastic cable clamps. Next we move on to the the Hamtronics T301-6 transmitter in Part 3. Cheers, skipp skipp025 at yahoo.com
