I originally posted this a month ago but I don't think it got onto the newsgroup. I will post it again because I am preparing to make a new post.
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Thankyou to everyone who has responded to my post. I appreciate that a little bit of feedback makes a task seem less daunting 8). I am going to go and buy the parts and try to construct a replacement transmitter. I will let you know how well it goes.
(Current ASCII Schematic) View in Courier font:
V+ ---+ 6VDC ** | | E * o | B * / | C * o ** | +-----+--[L1]--+------+-----+-------+ | | | | | | | [10K] [Xtal] | [30pF] [100pF] | | | /c | | [10nF] +--------+----| | +-----[L2]---Antenna | | \e | | | | | | | | | +-----+ | | | | | | [5K1] [100R] [50pF] | | | | Gnd---+-----+---------------------+-------+
L1 is possibly an inductor (RF Choke) or a combination inductor capacitor. L2 is a set of windings to decrease the size of the antenna. Xtal is set at
27.145MHz
+------+------+----+-----+-------+-+--------+ | |PD@25C|VCEO|IC |Hfe |@|IC(cont)|
+------+------+----+-----+-------+-+--------+ |ED1702|625mW |25V |500mA|132-189|@|100mA | Original
+------+------+----+-----+-------+-+--------+ |BC338 |625mW |30V |800mA|100-630|@|100mA | Proposed Replacement
+------+------+----+-----+-------+-+--------+
JK> Do you have a picture of the PCB itself somewhere?
Very difficult to get a picture that isn't blurry with my current equipment.
JK> I'd trust the scope over the meter.
I think I have been using it wrong 8). I'll make the readings again and resubmit.
JK> Wes Hayward (1994-2000) "Introduction to Radio Frequency Design" 3rd Printing, American Radio Relay League JK>
Homework
JAL> Neither link works as posted. Try these instead:
receiver:
transmitter:
My apologies for posting incorrect links.
Steven Cooke