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What is hilarious is that you are saying this and then 'promoting' changes that won't make any significant difference! If you wanted more gain from TR14 then bias it slightly harder and the gain will go up. All it will cost is a 2 cent resistor. :laugh:

The schottky diode mod on the noise blanker diodes won't help with hiss noise. I don't 'need' to test that because I know how the circuit works. It might help with very weak ignition noise from a car but that isn't the same thing as hiss noise from the receiver. As for using the schottky...

Just so you understand where I'm coming from on this, I have a lot of test gear here for RF design etc. But no way, NO WAY could I walk into a room, switch on a CB and tell the receiver sensitivity by simply plugging it into an aerial and tuning across the band and listening to other signals...

So basically you have nothing. This thread is several years old and there are no credible tests done to prove this 2SC2999 mod works. Just a lot of very bad science trying to justify that it DOES work and that any failures are due to fakes. Also a lot of crap about the importance of Hfe...

But you are happy to quote specs for Hfe to justify your purchase of 2SC2999E devices? Despite the fact that even elementary analysis of the circuit shows that typical Hfe values will have miniscule impact on the gain of TR14? Much less impact than the effect of bias resistor tolerance and...

Hi Robb I'd expect that there wouldn't be any significant difference (<1dB gain) if you (or the CB manufacturer) bought a bucketful of 2SC1674L devices and tried each one in turn assuming none of the devices were faulty. This is because of the nature of a common base amplifier like TR14. The...

The other thing is I just downloaded the datasheets for the 2SC2999 and the 2SC1674L and the test conditions for determining noise figure are very different. In the case of the 2SC1674L the device test fixture is driven directly from a 50 ohm source into the transistor base and uses a 22k...

Look, I'm not the one spewing out false info like: TR14 is NOT the AM detector. Not even close! I've certainly looked at the front end circuit design of similar CBs and examined what causes the most noise. A better tip would be to tell people how to adjust the transformer ahead of...

I guess you now know not to listen to techno 'kids' on forums that don't have any RF design experience. The best bits for me are their ridiculous technical explanations as to why these mods work. :laugh::laugh::laugh:

People keep rating transistors based on the NF on a spec sheet when really each amplifier design should be looked at from the perspective of the components and impedance driving it and the device operating point. The front end common base amps in old Uniden CBs are not ideal designs but if...

I would suggest that Uniden bias their common base RF amplifiers to provide a compromise between gain and signal handling and stability and (maybe) noise figure. The collector current affects noise figure and so there's a tradeoff with NF and gain and signal handling. You can get more RF gain...

As you may need a hint: Work out the voltage drop in those bias resistors for the change in required base current for 1.5mA collector current according to Hfe across 80-220. This will give you the change in emitter voltage. Then you can work out the change in collector current. The result...

The collector current in a typical amplifier is always is set such that the operating point is dominated by the biasing resistors and not HFe. A correct design will make this operating point stable wrt changes in HFe. Hfe is really only relevant when designing the transistor to operate as a...

Also, if anyone thinks excess gain is a good thing then they should spare a thought for the mixer that follows the RF amplifier. If this mod did provide 6dB more gain then that will degrade the dynamic range of the radio. If you don't know what this means then just imagine a world where...

Judging the (CB amplifier) performance of the 2SC2999 based on Hfe is daft. The operating point of the transistor when in a typical CB RF amplifier will be set by the resistor networks around it. By operating point I mean the collector current obtained from the biasing nework around the...