Pre-Amps: Local powering versus Remote powering

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JMM-BDA

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I've searched for & come across a few good articles (wikis) and posts about the 2 ways of powering pre-amps: local powering & remote powering. However, I've been unable to find anything about the advantages & disadvantages of using these 2 different methods. Is one method better than the other?

Although I hate assuming anything, I would think that perhaps (logically, at least) the best way is the local method, whereby 2 separate cables are used. This way the signal feed is kept separate from the power feed, so that the power does not interfere in any way with the signal. And that by using the remote method, whereby a single cable is used, there is possibly some slight interference/degradation of the signal, but so minimal that the advantage of using a single cable outweighs any loss.

In my case, the distance between here & the airport is not very far (only 8 miles), but there's quite a bit of terrain in between. Airborne targets I can hear fine, out to about 50 miles or so. The distance ones (out to 180 miles) & communications on the ground at the airport are barely audible above the static. I have a good antenna (the LP from DPD Productions - thanks Dave) & scanner (BCT15), and I'm planning to use a filter & pre-amp to boost those weak signals. And I'm going to be using LMR400 for the feed. And before anyone asks what the he** I want to hear aircraft out to 180 miles for, I'm sitting on a little speck of land in the middle of the Atlantic, 780 miles from any other land, and the controllers here control aircraft out to 180 miles. :)

But, I digress. What I'm getting at with this post is, I'm using (IMHO) decent equipment, so I would hate to use a method of powering my pre-amp that results in any signal loss, no matter how slight it might be. Using my above assumption, if the remote powering (single cable method) indeed results in any degradation at all, no matter how minimal, then I will opt for local powering (two cable method). In other words, signal strength is more important to me than convenience.

Thanks in advance for the above, and I look forward to your thoughts on this.
 
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prcguy

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You will get the most benefit by placing the pre amp right at the antenna, so remote powering would be the better choice. If you use correct power inserter's (bias tee) there will be no degradation or problems with power on the coax.
prcguy
 

JMM-BDA

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I had planned on placing the pre-amp right at the antenna. It was just a question of which way to power it with the least amount of signal loss.

I don't mind running 2 separate cables & powering it on the 2nd cable if the single-cable method will result in some (no matter how small or neglible) signal loss.

Thanks.
 

rbm

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I use both types of power feed.

I have two Downeast Microwave 915LNAHC amplifiers with their BTL power inserters.
http://www.downeastmicrowave.com/Catalog.htm

I also have quite a few other amplifiers that receive power via a DC feed-thru.

For those that get power via a feed-thru I have several runs of RG6 & Dual RG6 cable that have a 'messenger' wire. That's just an insulated copper wire that runs along the coax. I use the messenger wire to carry the DC. The attached photo shows the Dual RG6 version.

The photo also shows the weather resistant housing I make for each amp using 2" PVC pipe, an end cap and a pressure testing cap with a hole drilled for the coax and power wires. Note that I don't show the coax adapters in the photo.

At the antenna, I use crimp connectors to attach the power wires. Then I seal the connections with silicone sealer.

For power I use a wall wart power supply and a three terminal regulator (7812 etc) built into a small box.

I prefer to use the feed-thru version only because of the reduced cost. I can't really say that I've noticed any difference in performance. If I only had one pre-amp up there it wouldn't matter that much but I currently have six pre-amps installed.

Rich
 
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JMM-BDA

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I want to thank everyone so far for their replies & comments.

Rich, I understand that you have lots of pre-amps up there, and therefore use the remote powering method to save cost. But if you only had one up there, which way would you go?

I appreciate the fact that with the remote powering method, only a single cable is used for both the radio signal and powering of the pre-amp. But wouldn't it stand to reason that there must be some interference of the radio signal by the power on the same cable? If that wasn't the case, then I would think that manufacturers would do away with the separate power feed requirement altogether, and instead have all their products powered only by a single signal/power cable.

It seems counterproductive to spend effort & money on getting the best possible signal (by buying & installing a good antenna, filters & pre-amps, etc.), only to degrade the signal ever so slightly by opting to use a single cable for both signal & power instead of separate cables.

Sorry if I keep harping on this, but I'm just trying to understand the pros & cons of both these methods. My pre-amp I'm ordering can be powerd both ways, so I'll end up experimenting with these methods. Chances are I'll be like Rich and not notice any difference in performance. I'm just trying to understand the technical side of things, and if there is any slight loss using one method over the other, which logically I think there would be.

Thanks.
 

prcguy

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There will be no degradation of the pre amp from powering via the coax if designed properly. Since the bias tee is on the output side of the pre amp, even if the design were not perfect the noise figure of the amp would not be affected because this is determined on the input side of the amp. Worst case a little output gain would be compromised and that has no bearing on the overall performance. If the amp is remoted at the antenna I say power it up the coax.
prcguy
I want to thank everyone so far for their replies & comments.

Rich, I understand that you have lots of pre-amps up there, and therefore use the remote powering method to save cost. But if you only had one up there, which way would you go?

I appreciate the fact that with the remote powering method, only a single cable is used for both the radio signal and powering of the pre-amp. But wouldn't it stand to reason that there must be some interference of the radio signal by the power on the same cable? If that wasn't the case, then I would think that manufacturers would do away with the separate power feed requirement altogether, and instead have all their products powered only by a single signal/power cable.

It seems counterproductive to spend effort & money on getting the best possible signal (by buying & installing a good antenna, filters & pre-amps, etc.), only to degrade the signal ever so slightly by opting to use a single cable for both signal & power instead of separate cables.

Sorry if I keep harping on this, but I'm just trying to understand the pros & cons of both these methods. My pre-amp I'm ordering can be powerd both ways, so I'll end up experimenting with these methods. Chances are I'll be like Rich and not notice any difference in performance. I'm just trying to understand the technical side of things, and if there is any slight loss using one method over the other, which logically I think there would be.

Thanks.
 

JMM-BDA

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PRCGUY,

Perfect, thanks for that reply. That's exactly the type of answer I was looking for, one way or the other. That's why I came to you experts on this. :)

Much appreciated for taking the time to answer this question. Have a great evening.
 

rbm

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I want to thank everyone so far for their replies & comments.

Rich, I understand that you have lots of pre-amps up there, and therefore use the remote powering method to save cost. But if you only had one up there, which way would you go?

Thanks.
prcguy speaks the truth.

If I only had one amplifier, the method of getting power to the amplifier would be the last thing I considered. If at all.

It's not really important other than a cost or convenience factor. I've used both methods for more than (too many) years and have no qualms about using either.

Rich
 
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JMM-BDA

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Great, thanks again for all the great feedback & answers.

Now I just need to Google & try to find a supplier for the filter, pre-amp, cables & adapters I want to get. I tried ScannerMaster but their system won't process my order attempts, and they haven't bothered to get back to me on an email I sent them last Thursday. I guess they're not interested in a $500 order from me, so I'm now looking for another supplier. :)
 
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