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Author Topic: What Does A 'Pre-Amp' Do?  (Read 9371 times)

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Johnn

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What Does A 'Pre-Amp' Do?
« on: April 09, 2009, 08:38:23 PM »
Thanks
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Blackthorn

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Re: What Does A 'Pre-Amp' Do?
« Reply #1 on: April 09, 2009, 09:07:26 PM »
Amplifies the signal from the antenna to the receiver and in most cases the noise as well.

Johnn

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Re: What Does A 'Pre-Amp' Do?
« Reply #2 on: April 09, 2009, 09:09:58 PM »
More Range?, or am I at the wrong end of the stick!
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CoastGuardJon

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Re: What Does A 'Pre-Amp' Do?
« Reply #3 on: April 09, 2009, 10:04:17 PM »
Hi John, if mast-head type used or very close to antenna, it will boost signal (and noise) which will counteract losses in a long run of co-ax.   There is a certain amount of insertion loss, as with connectors and adapters, and the pre-amp will also generate a small amount of electrical noise itself.    I wouldn't waste my hard earned money, fitting one at the back of the box (a load of bo***x IMO!!).
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Johnn

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Re: What Does A 'Pre-Amp' Do?
« Reply #4 on: April 09, 2009, 11:39:57 PM »
Okay, Thanks For That!
Johnn
Johnn -

jetset

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Re: What Does A 'Pre-Amp' Do?
« Reply #5 on: April 09, 2009, 11:47:31 PM »
I'm after the answer to this question as well.

CoastGaurdJon.
Is there a layman's guide anywhere.? I don't even know what a 'mast-head' is, let alone what you mean by 'counteract losses in a long run of co-ax' and 'insertion loss'

Just starting out here


Steve

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Re: What Does A 'Pre-Amp' Do?
« Reply #6 on: April 10, 2009, 06:03:57 AM »
I'm after the answer to this question as well.

CoastGaurdJon.
Is there a layman's guide anywhere.? I don't even know what a 'mast-head' is, let alone what you mean by 'counteract losses in a long run of co-ax' and 'insertion loss'

Just starting out here




Mast Head (amplifier) - the signal amplifier is mounted as close to the antenna as possible i.e. on the antenna mast.  This means that ALL the signal is being amplified, rather than what is left of the signal after it has travelled down the cable to your receiver (RadarBox).  This should in part make up for the signal loss caused by the cable.  All co-ax cable reduces the signal as it travels along it - more efficient cable is thicker and is more expensive.  Use a cheap "lossy" co-ax and you might gain nothing from an external antenna - you might get a better signal using the standard antenna!

A mast head antenna needs powering, often through the co-ax itself, so more complicated and more expensive!

Insertion loss - put anything between the receiver and the antenna and it is going to cause signal loss.  This could be a long run of co-ax cable, a cheap plug adaptor, or even the pre-amp itself.

Put the pre-amp at the receiver end and it's easy to fit and power, but the signal is already degraded by the co-ax, so the amp is trying to boost a degraded signal.

Unfortunately, there aren't any certainties here, as loads of things can affect the signal that the receiver sees.  The standard RB antenna and short cable is exceptionally good if you get it out in the clear.  Try running RB on a laptop with the standard antenna on the roof of a car out in the open - and save yourselg a few hundred GBP :-)

Blackthorn

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Re: What Does A 'Pre-Amp' Do?
« Reply #7 on: April 10, 2009, 07:57:21 AM »
I agree with Allocater the standard antenna is very good, the downside is the very short cable, the other option is the MyDell 1105 whip with the longer cable.

I spent many years in Radio Electronics and other than testing never used a pre-amp.

CoastGuardJon

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Re: What Does A 'Pre-Amp' Do?
« Reply #8 on: April 10, 2009, 12:33:38 PM »
I'm after the answer to this question as well.

CoastGaurdJon.
Is there a layman's guide anywhere.? I don't even know what a 'mast-head' is, let alone what you mean by 'counteract losses in a long run of co-ax' and 'insertion loss'

Just starting out here




Mast Head (amplifier) - the signal amplifier is mounted as close to the antenna as possible i.e. on the antenna mast.  This means that ALL the signal is being amplified, rather than what is left of the signal after it has travelled down the cable to your receiver (RadarBox).  This should in part make up for the signal loss caused by the cable.  All co-ax cable reduces the signal as it travels along it - more efficient cable is thicker and is more expensive.  Use a cheap "lossy" co-ax and you might gain nothing from an external antenna - you might get a better signal using the standard antenna!

A mast head antenna needs powering, often through the co-ax itself, so more complicated and more expensive!

Insertion loss - put anything between the receiver and the antenna and it is going to cause signal loss.  This could be a long run of co-ax cable, a cheap plug adaptor, or even the pre-amp itself.

Put the pre-amp at the receiver end and it's easy to fit and power, but the signal is already degraded by the co-ax, so the amp is trying to boost a degraded signal.

Unfortunately, there aren't any certainties here, as loads of things can affect the signal that the receiver sees.  The standard RB antenna and short cable is exceptionally good if you get it out in the clear.  Try running RB on a laptop with the standard antenna on the roof of a car out in the open - and save yourselg a few hundred GBP :-)

Thanks for that reply Allocator, saves me an hour's typing! - couldn't have clarified any of it better!    Sorry Johnn and Jetset, for not being a bit more clear in my initial reply.   If a pre-amp is to be used, it needs to be as close to the antenna as possible.
ANRB :  AOR AR8000 : Icom R-7000 : Icom IC-R9000 : JRC NRD-545 : OptoElectronics Digital Scout and OptoLinx Interface; Realistic Pro-2005 : UBC 800XLT - listed in alphabetical order, not cost, preference, performance or entertainment value!

jetset

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Re: What Does A 'Pre-Amp' Do?
« Reply #9 on: April 10, 2009, 05:12:48 PM »
Great, thanks for the info
Steve

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Re: What Does A 'Pre-Amp' Do?
« Reply #10 on: April 10, 2009, 06:14:07 PM »
What does a 'pre-amp' do?? usually nothing other than cost a lot of well earned money, because people can't use the basic property of antenna location / construction. I'm not an expert, but if you can't get the antenna into open, un-interupted airspace, then the signal is going to be reduced, no matter what the finicial outlay, a poor location = a poor return for the money paid out!
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AirNav Support

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Re: What Does A 'Pre-Amp' Do?
« Reply #11 on: April 10, 2009, 06:53:11 PM »
Obviously if your location is poor nothing is going help whether a better antenna or preamp.

But where a preamp comes into play is when you have long cable (explained by Allocator above) from your antenna to the RadarBox or your trying to squeeze the last amount of signal you can from your antenna.

We have found from tests in finding the best antenna setup that having a masthead amp on a 10 metre cable we managed to get a 25% boost than without. The shorter the cable the less the increase was but even with a short 2 metre cable the boost was about 15%.
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OKC-Steve

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Re: What Does A 'Pre-Amp' Do?
« Reply #12 on: April 11, 2009, 10:05:33 AM »
As you go up in frequency, the type of coax you use becomes more important. If you scrimp on coax, then often you need a pre-amp to offset the attenuation.  At a certain point, coax doesn't work very well anymore, and you have to go to waveguide.

Just before you get to waveguide, there's a class of coax called heliax.  This is a very stiff coax that comes in various sizes (1/2", 7/8").  The 1090 MHz band has traditionally used heliax (even in commercial radar/IFF systems).  Some use heliax with nitrogen in it to handle higher power.

So, my recommendation would be to skip the pre-amp, unless it had a noise-figure of less than 1 dB (the higher the noise-figure, the more noise it amplifies), use 1/2" heliax down from the antenna to the radio room, and then a short piece of flexible coax to the radio.  No pre-amp.

This high-lights how these radios are actually poor designs.  There is no reason you need to transport microwave signals long distances.  If the 1090 MHz receiver was at the antenna, you could then just send a video signal down to the radio room.  Video doesn't require fancy coax.  If I was to design a new radio for base-station use, I would design the digital side of the radio to sit on a 1X PCI-E circuit card, and have a remote analog side at the antenna.  This then gets rid of the ethernet and USB interface.  Plugging things into the computer buss has always been better than the I/O interface.

I own a first version of the SBS-1. This circuit board was designed so you could cut-off the analog side of the board, move it to the antenna, and use cheap coax.  That's how I've run mine.  Rather than run power up the coax to power-up the remote receiver, I used a solar panel that has a built-in battery.  This provides 5 volts DC to the receiver, and the battery can run for days without sun.  It's very green!  They sell these solar panels at the home and garden center for use with lawn lights that have LED's in them.  Very cheap.

Pre-amps are to radio, what cardboard box homes are to humans.
« Last Edit: April 11, 2009, 10:13:41 AM by OKC-Steve »