HFU HF Underground
Technical Topics => Equipment => Topic started by: Antennae on July 17, 2014, 0356 UTC
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I just got a cheap receiving preamplifier. Its a Palomar Engineers and goes from 1.8 - 50mhz.
Does anybody have experience with a preamplifier? It seems like it wouldn't do much on my skyloop because the noise would be amplified too.
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Personally, I am not a huge fan of pre-amps for HF. They can be very useful on VHF and above where background noise levels are low, especially relatively narrow band pre-amps with good noise figures.
Virtually all decent HF receivers are already more than sensitive enough. As you said, you're most likely just going to amplify the existing noise, plus add additional noise from the pre-amp. I could possibly see some use on say 10 meters, but I'm doubtful there's any benefit on say 43 meters.
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When I bought a bunch of radio stuff about a year ago one of the things I bought was a preamp/tuner thing from MFJ & it is fairly worthless. Exactly as Chris says. It sort of looks cool if you are into having knobs & stuff to fiddle with but as a practical matter......it sucks.
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(http://www.animateit.net/data/media/august2009/th_agree.gif) Has been my experience in the past also
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I suppose if it has a sensitivity control, you could try it with it set low and see if it amplifies signals to a useful level, especially if you hear a weak one with problems due to fading, etc.
While it's true it could amplify noise, it will also amplify target signals as well.
I know there are high level DX HF rigs and ham rigs with built in pre-amplifiers, so there must be a reason for their use.
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My controls are:
gain
delay
band
tune
I don't know what delay does.
I read that smallish receiving loops need a preamplifier. Is this the same kind of preamplifier that the loops use?
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The only loops I use are for MW, and they're un-amplified, which seems fairly standard.
But I have heard of guys using amplified MW loops, and I've heard of amplified SW loops before -- usually indoor ones.
The "tune" and "band" controls imply that what you have is a sort of preselector, which is (to put it loosely, as I'm not a ham or radio expert) sort of like an amplified antenna tuner.
No idea what a 'delay' control would be for.
I'd try it at low gain, mainly on ultra weak signals you may want to ID (like on a ham band, perhaps) and see if it helps.
Most of the time, you probably won't need it. Your antenna may be more than enough for reception with a DX-398.
DX-398's have plenty of gain through the external antenna jack; and being a digital portable, they can be susceptible to overload (I have a 398 and have not experienced this, but I've read some comments on other forums where guys have said they had overload issues with a 398, and if memory serves, I think Chanter on this forum mentioned she had some overload issues on MW with her 398).
Good luck with experimenting.
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Delayed is for using with a transmitter, or transceiver
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I can't see any use for a preamp on the HF bands - the band noise alone would exceed the noise generated by the receiver's front end by quite a margin so no benefit would be realised. all you'll probably end up doing is creating intermodulation products. It may have a use if you are restricted to something like a telescopic antenna a couple of feet long, where received signals are extremely weak.
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After 40 years at this hobby, I prefer [and use] Preselectors vs straight amplifiers... I have an old Grove TUN4 I use occasionally on MW BCB [goes down to 400KHz] & Mizuho SX3 & SX59 Preselectors [Hard to find]...
They can help reception if used sparingly & with receiver RF gain... I never run them wide open, just crack them open to enhance S/N a bit...
However, now that I have gone fully into SDRs, I don't use them whatsoever. They are plenty sensitive & their noise reduction eliminates the need for them!
Rafman