Topband: PREAMP/PRESELECTOR

[Tom W8JI]

> Now, IF you need a bit of a boost, consider killing two stones with one
> bird.  If you have a need to eliminate some noise, the MFJ 1025/1026 noise
> reducers have a bit of a preamp built in.  It is just a few db but it 
> might
> suffice.

That is a mediocre TOI amplifier for a "line driver" or broadband "booster" 
application. It is a simple single J310 JFET source follower, and only makes 
about 5 -15 dBm TOI. That device also has pretty high noise floor because of 
gain distribution. It has a good bit of loss ahead of the 2N5109 output 
transistor. It also has a back-to-back diode clamp inside.

It does the job it was intended to do pretty well, which is to mix a "noise 
signal" into a transmitting antenna's receive path, but I would not 
recommend it for amplification.

By the way, if you match the emitter follower on the output to the receiver 
a bit better the gain and TOI will get a few dB better. It's pretty hard to 
quantify the TOI, because control settings and receiver impedance affects 
it, but someone is far better off using a "real" amplifier if needed.

73 Tom