RLBagley
06-09-2010, 06:31 PM
A few months back, Dave answered a query from a customer on our website (http://marshallradio.com/en/am-falconry-support/customer-forum/26-ask-dave/24-qantenna-power-boosterq) about "signal boosters" for yagi antennas. I thought his answer might also be of interest to some here as well:
Solving a problem that doesn't exist
A power booster on your antenna? It sounds good... A "boost" of the signal, more power, more range... What's not to like about all that. Couldn't hurt. But before assuming, let's really consider. Does "boosting" the signal at your antenna really translate into more range? If so, why doesn't everyone already use them? Some people might portray this as a new idea, but such things were around in your grandfather's time...
These things are more often called "preamplifiers" or preamps, or "active antennas". But do they work? The answer is yes and no. More often no.
You see, the only thing one of these boosters does is to amplify the signal at the antenna. But it doesn't just amplify the signal -- it also amplifies the noise that your antenna is picking up. So it hands over both the signal and the noise to your receiver in the same ratio as before, both stronger.
So what's wrong with that, you say?...
Nothing's wrong with that, but follow along with me here and I'll do my best to explain what little I know about this... You realize from experience that the frustration in tracking a weak signal from your transmitter is simply this -- you can't hear the darn thing for the noise. So you turn up the volume, but that just makes the both noise and the signal louder (just like a booster does.) But hang on, this noise is not just an annoyance -- it's the thing that prevents you from getting unlimited range. This might not be obvious, but the one and only fundamental problem in tracking over long ranges is distinguishing the signal from the noise, and the booster doesn't help at all with that. (You actually have to boost the signal or decrease the noise...now we're talking...)
So the result of adding an antenna booster is usually nothing at all. No change. Same range as before. Except you might have a louder signal than before, so you don't have to turn up the volume on your receiver as much... and I guess maybe that's kind of nice, not having to turn the volume knob (or control) as much... (attempt at humor...)
The fact is that your receiver already has plenty of amplification built in, and adding more doesn't help at all. Look at it this way: the booster is actually something that is already built into your receiver. Or at least should be. Maybe some receivers exist which are poorly designed, without enough amplification. Well, then a booster might add the missing amplification so you don't have to put your ear right up to the speaker. But it still won't change the ratio of the signal to the noise, and won't increase your range. Sorry, there's no getting around the physics of this situation... I know I've tried. I've got a drawer full of power boosters...
So it doesn't help and it doesn't hurt. The only downside that I can think of (besides spending money for nothing)... is that a booster might just boost the signal too much and overload your receiver. That's probably not good...
If you're still following my speil here and want to know more, I'll go on some more... Although the above is probably true for most situations, it's also true that there are certain other cases where a booster can really help to increase your range:
Case I: If your receiver, by design, already has a poor "front-end signal-to-noise ratio" and if the antenna booster's signal-to-noise-ratio is better than that, then the booster will genuinely increase your range. In this case, the booster is simply remedying a defect in the receiver. Good receivers have expensive parts in their front-ends and don't need boosters. Cheaper receivers whose designers have skimped on parts might benefit. But beware... a booster that actually has a great signal-to-noise ratio is also going to be quite expensive, and there are a lot of cheap boosters out there...
Case II: If you have a long piece of cable (say, more than 2 meters) between your receiver and your antenna, or if you are using poor, cheap coaxial cable, or the cable is defective --- then a power booster at the antenna might be just the thing... but in most cases, not likely enough to notice.
If you have one of these two situations, I say go for it...
Good hunting,
Dave Marshall
Solving a problem that doesn't exist
A power booster on your antenna? It sounds good... A "boost" of the signal, more power, more range... What's not to like about all that. Couldn't hurt. But before assuming, let's really consider. Does "boosting" the signal at your antenna really translate into more range? If so, why doesn't everyone already use them? Some people might portray this as a new idea, but such things were around in your grandfather's time...
These things are more often called "preamplifiers" or preamps, or "active antennas". But do they work? The answer is yes and no. More often no.
You see, the only thing one of these boosters does is to amplify the signal at the antenna. But it doesn't just amplify the signal -- it also amplifies the noise that your antenna is picking up. So it hands over both the signal and the noise to your receiver in the same ratio as before, both stronger.
So what's wrong with that, you say?...
Nothing's wrong with that, but follow along with me here and I'll do my best to explain what little I know about this... You realize from experience that the frustration in tracking a weak signal from your transmitter is simply this -- you can't hear the darn thing for the noise. So you turn up the volume, but that just makes the both noise and the signal louder (just like a booster does.) But hang on, this noise is not just an annoyance -- it's the thing that prevents you from getting unlimited range. This might not be obvious, but the one and only fundamental problem in tracking over long ranges is distinguishing the signal from the noise, and the booster doesn't help at all with that. (You actually have to boost the signal or decrease the noise...now we're talking...)
So the result of adding an antenna booster is usually nothing at all. No change. Same range as before. Except you might have a louder signal than before, so you don't have to turn up the volume on your receiver as much... and I guess maybe that's kind of nice, not having to turn the volume knob (or control) as much... (attempt at humor...)
The fact is that your receiver already has plenty of amplification built in, and adding more doesn't help at all. Look at it this way: the booster is actually something that is already built into your receiver. Or at least should be. Maybe some receivers exist which are poorly designed, without enough amplification. Well, then a booster might add the missing amplification so you don't have to put your ear right up to the speaker. But it still won't change the ratio of the signal to the noise, and won't increase your range. Sorry, there's no getting around the physics of this situation... I know I've tried. I've got a drawer full of power boosters...
So it doesn't help and it doesn't hurt. The only downside that I can think of (besides spending money for nothing)... is that a booster might just boost the signal too much and overload your receiver. That's probably not good...
If you're still following my speil here and want to know more, I'll go on some more... Although the above is probably true for most situations, it's also true that there are certain other cases where a booster can really help to increase your range:
Case I: If your receiver, by design, already has a poor "front-end signal-to-noise ratio" and if the antenna booster's signal-to-noise-ratio is better than that, then the booster will genuinely increase your range. In this case, the booster is simply remedying a defect in the receiver. Good receivers have expensive parts in their front-ends and don't need boosters. Cheaper receivers whose designers have skimped on parts might benefit. But beware... a booster that actually has a great signal-to-noise ratio is also going to be quite expensive, and there are a lot of cheap boosters out there...
Case II: If you have a long piece of cable (say, more than 2 meters) between your receiver and your antenna, or if you are using poor, cheap coaxial cable, or the cable is defective --- then a power booster at the antenna might be just the thing... but in most cases, not likely enough to notice.
If you have one of these two situations, I say go for it...
Good hunting,
Dave Marshall