7designs
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Anyone use an amplifier?
Here is a schematic to one:
Shortwave antenna amplifier
Would it actually help?
Here is a schematic to one:
Shortwave antenna amplifier
Would it actually help?
Shortwave Antenna Amplifier
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I have done considerable experimenting with amplifiers on HF. They definitely have their uses, but misuse can be costly, in terms of performance.
I'm not that familiar with that circuit, but there's a design by Doug DeMaw published by the ARRL years ago that used an MPF102 JFET that worked quite well as an active antenna preamp. So, the choice of front-end device is a good one.
In general, if you have a decent size wire antenna, you won't need a preamp, unless your receiver becomes numb at the higher frequencies. If you want to experiment with active antennas, that circuit would probably work just fine. It would be useful with a loop antenna, as well.
I'm not that familiar with that circuit, but there's a design by Doug DeMaw published by the ARRL years ago that used an MPF102 JFET that worked quite well as an active antenna preamp. So, the choice of front-end device is a good one.
In general, if you have a decent size wire antenna, you won't need a preamp, unless your receiver becomes numb at the higher frequencies. If you want to experiment with active antennas, that circuit would probably work just fine. It would be useful with a loop antenna, as well.
No
Rule of thumb for shortwave: if you can hear additional noise when you plug the antenna in to your radio, a pre-amp would make things worse, not better.
The circuit you show seems to be for a very short MW or perhaps a LW active antenna design. Note that this is a cheap high impedance JFET amplifier (WHY do we keep building amplifiers with the MPF 102 JFET?) with an emitter follower, and then a Darlington pair for real gain. The bandwidth of this amplifier can't be all that good, and frankly the IMD from this thing is likely to be a limiting factor.
Frankly, there are less expensive, and far better designs out there. Build this thing if you're interested in having a learning experience.
73,
Rule of thumb for shortwave: if you can hear additional noise when you plug the antenna in to your radio, a pre-amp would make things worse, not better.
The circuit you show seems to be for a very short MW or perhaps a LW active antenna design. Note that this is a cheap high impedance JFET amplifier (WHY do we keep building amplifiers with the MPF 102 JFET?) with an emitter follower, and then a Darlington pair for real gain. The bandwidth of this amplifier can't be all that good, and frankly the IMD from this thing is likely to be a limiting factor.
Frankly, there are less expensive, and far better designs out there. Build this thing if you're interested in having a learning experience.
73,
I have had some remarkable successes with a HF preamp. Take a look at this YouTube video that demonstrates exactly the same design preamp, which has been fitted internally to a TenTec 1254. For an untuned, high impedance antenna, it generally works well.
It has its problems though: image problems from FM broadcasting become worse, and no doubt it would cause overloading on HF with strong signals; lucky I'm not in a high signal area.
3680kHz TenTec 1254 preamp demo2.mp4 - YouTube
(the preamp design is explained a little more in detail here: Active antenna to pull in those hard to get signals, 1-30 MHz )
It has its problems though: image problems from FM broadcasting become worse, and no doubt it would cause overloading on HF with strong signals; lucky I'm not in a high signal area.
3680kHz TenTec 1254 preamp demo2.mp4 - YouTube
(the preamp design is explained a little more in detail here: Active antenna to pull in those hard to get signals, 1-30 MHz )
Reducing Image Response
Consider placing some ferrite beads on the Gate, Source, and Drain of that first stage of the pre-amp to help reduce FM Image Response.
For what it is, the 1254 is not a bad receiver. You should not need this pre-amp ahead of it, unless your antenna options are very poor.
Consider placing some ferrite beads on the Gate, Source, and Drain of that first stage of the pre-amp to help reduce FM Image Response.
For what it is, the 1254 is not a bad receiver. You should not need this pre-amp ahead of it, unless your antenna options are very poor.
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