I am very noob to RF area so o got few questions. First, which components are critical? I mean i should use 1% precison or less? On the noise modulated pulse generator he used some old transistors with Hfe of 50. Any recomedation about this specific transistor? Any cheap partnumeber that would do the job? On the transmitter i was not able to find the 2N5109. I think it is a very old power RF transistor. Any good substitute that would work on this project? I am getting all parts from Farnell Spain, so if in stock i would apreciate :) .
I was looking for a substitute for 2N2369 becouse its very expensive. I could find BSV52 , but the power dissipation and max curretn is lower. Is it a good choice? Any good SMD sugestion?
Thank you!
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It looks to me as if the passive parts really do not require precision, or matching. Standard 5% resistors and 10% capacitors should be fine.
2N3904 comes to mind - it's a small-signal general-purpose "jellybean" NPN, with sufficient gain and voltage and bandwidth to handle the needs of the pulse generator. They're very widely available; even Radio Shack sells them.
If you have some 2N2222 or PN2222 or any similar parts in your junk box, those would do just as nicely.
Correct (for some values of "very old" which would probably raise bitter objections from some posters here :-)
The 2N5179 is similar, but in a smaller package, with lower power ratings.
Finding new-stock "through-hole" RF transistors in that sort of package is very difficult these days. I don't think they're being made, except as specialty parts.
Dan's Small Parts and Kits
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does have some 2N5109 transistors available... I assume that these are "new old stock".
NEC's "CEL" division makes a whole range of microwave transistors with plenty of bandwidth, and many are available in SOT-89 surface-mount packages.
Some of the BFR parts, in X-lead surface mount packages, could probably be substituted.
At first glance it looks to me as if the lower maximum dissipation and currnet limits would not be an issue in this circuit. The current drawn through this transistor looks like it would be about half a millipamp through the pullup resistor (10k) plus pulses drawn through the 68-ohm resistor between the two sampling diodes. Since Vref is only 2.5 volts, you're looking at pulses of under 40 mA, which is well within the transistor's limits... the pulses may be somewhat higher due to the need to discharge the junctions in the diodes but I doubt it'd be a problem. Power dissipation should be a non-issue as well... since the transistor spends most of its time switched off (essentially no dissipation) or driven into saturation (low forward voltage drop), the total dissipation should be negligible.
I do have a bunch of 2N2369s (unused, with trimmed leads) in my supplies at home... I lucked into finding a bag or two of them at a surplus dealer a few years ago. If you really want a few, drop me a message privately.
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Dave Platt AE6EO
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On Nov 2, 10:52=A0am, "Sink0" wrote: On the transmitter i was not able to find the 2N5109. I
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I remember the 2N5109 for no good reason. Found data sheets on the internet. And 2n5109 transistors available on Ebay. There are probably a number of transistors that could be substituted.
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