The only reason for having an aerial amplifier is to overcome the losses down the cable to the receiver - and that means it should be a mast-head amplifier, probably with quite low gain (6dB). Anything else is likely to amplify muck and expose the receiver's front-end to overload and intermodulation. Nothing beats a better aerial.
Actually, one thing does. A better feeder. Most aerial cable is so leaky that it picks up as much signal as the aerial. Trouble is, unlike the aerial, it's not tuned and it's not pointed in the right direction. Use a proper low loss professional cable with a foil Rheunissen screen.
Actually, one thing does. A better feeder. Most aerial cable is so leaky that it picks up as much signal as the aerial. Trouble is, unlike the aerial, it's not tuned and it's not pointed in the right direction. Use a proper low loss professional cable with a foil Rheunissen screen.
This is exactly the reason I recommend excessive antenna gain.
Feeder pickup is always a fixed, constant value (for a given installation) and always non-zero. By having excessive gain and therefore signal strength, you can attenuate at the receiver input. This brings the input signal to the correct level, whilst attenuating the fixed, unwanted, cable pickup.
Andy.
I dug out my old Heathkit switched attenuator (up to 70 db)
and plugged it into my mediocre Fisher tuner. No amount of
attenuation will drive most of the local stations into the
noise. Cheap plastic case and open wiring still leaks in
a useable amount of signal. I'll have to try to rewire the
input with proper coax; originally it was 300 ohm balanced, to
which I'd added a balun and a F connector on the back panel.
I was hoping to make a guess as to how much signal that jpole
is pulling in; wonder if my ham neighbor has a RF microvoltmeter?
My presently defunct Heathkit AJ-29 was modified for coax and
that effectively eliminated leakage.
At one time I had a FM band JFET preselector, designed by Bob Cooper, I think; it actually worked fairly well in combination
with the attenuator (which originally came with the IM-57 TV
sweep generator). There are other ham tricks I haven't tried,
such as tuned cavity traps and bandpass filters, but I haven't
been in a position to need such, yet.
I found some general comments on RF amplifiers and preselectors
with a working example of a low-noise MOSFET preamp on this page:
http://www.geocities.com/toddemslie/bf981_preamp.html
and plugged it into my mediocre Fisher tuner. No amount of
attenuation will drive most of the local stations into the
noise. Cheap plastic case and open wiring still leaks in
a useable amount of signal. I'll have to try to rewire the
input with proper coax; originally it was 300 ohm balanced, to
which I'd added a balun and a F connector on the back panel.
I was hoping to make a guess as to how much signal that jpole
is pulling in; wonder if my ham neighbor has a RF microvoltmeter?
My presently defunct Heathkit AJ-29 was modified for coax and
that effectively eliminated leakage.
At one time I had a FM band JFET preselector, designed by Bob Cooper, I think; it actually worked fairly well in combination
with the attenuator (which originally came with the IM-57 TV
sweep generator). There are other ham tricks I haven't tried,
such as tuned cavity traps and bandpass filters, but I haven't
been in a position to need such, yet.
I found some general comments on RF amplifiers and preselectors
with a working example of a low-noise MOSFET preamp on this page:
http://www.geocities.com/toddemslie/bf981_preamp.html
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