Topband: PREAMP/PRESELECTOR
Most Beverages don't require a preamp of any type, in my estimation. The shorter ones may need a bit of a boost but those over 500 ft seem to do quite nicely on their own most of the time. If you do believe that some amplification is necessary then 6-10 db is about all that you should consider using lest you overwhelm your front end and introduce more noise and garbage. 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. When I need just a bit of amplification I use the preamp built into my radios (PRO2 and K3). The preamps in both these radios appear to do a good job in my application (though I have no real idea what the REAL noise figure is). For loops and other RX antennas whose gain is -12db and beyond, an external 10-20db amplifier is desireable and there are a lot of choices out there, from the simple but effective W7IUV and KD9SV designs ( both of which I have built and use) to the more exotic designs by the likes of W8JI. I am referring only to amplification above. If you require selectivity in front of the RX antenna for any reason then that is a completely different situation and one of the commercially manufactured preamps with tuned input is desireable. IMHO anyhow. Bill VE3CSK - No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2197 / Virus Database: 2437/5223 - Release Date: 08/25/12 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: PREAMP/PRESELECTOR
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 ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
