Questions about preamps, how power can be fed etc

[I_Am_Infinite]

I have a couple questions about all this.. All this would be being used on antennas up on about a 60ft tower.

1) When u use a pre amp like this Amazon.com, does the power through the coax have to use the same cable that I would connect to the scanner, or can I use regular coax to power it through one port and have my lmr 400 come out of it from another port to my scanner?

2) can u split power, like say have 3 pre amps powered by one coax plugged inside running up tower split into each preamp? Or would each preamp have to have its own coax feeding it to power it?

3) does return path on these pre amps have issues causing any interference with scanners?

I have amps now but at end of 60ft lmr 400s cables, but if there is noise from the long run I'm amplifying that and I'm amplifying signal that has already degraded some from the length... I figured having pre amps would be better then these amps cause I'm amplifying signal immediately before loss of anything or before any interference I might picked up down the coax. Any thoughts or experience thanks

 

[900mhz]

you would need a power inserter to send DC back up to the mast mounted preamp thru the coax. To run a split power feed, that would be a different story. You would have to first verify that the other preamps run at the same voltage as provided from the power pack. You would also need to add up the current draw of all the preamps to determine if the power pack can handle the load. Be conservative as the DC voltage will experience a drop, which would increase current draw. You would need to run a separate coax (RG-6 would work) to a splitter that does not block DC power (power passing splitter)...regular CATV type splitters do not pass voltage, then distribute the power as appropriate. Get a power passing splitter with the exact amount of ports that you need. Open ports cannot be terminated with the standard 75 ohm terminator as it will create excessive current draw. If you do decide to go with a power passing splitter with extra ports, you can use a standard 75 ohm terminator on the open port(s), but you will need to remove the resistor from the terminator and use it as a weather prevention cap.

 

[I_Am_Infinite]

you would need a power inserter to send DC back up to the mast mounted preamp thru the coax.

Ya I understand u gotta use that to send power up the coax but do I have to use that same coax for my scanner or can I have 1 regular coax go up to power pre amp thru one port and another lmr 400 coax coming out another port on the pre amp to my scanner.

I don't really want to use my lmr 400 for power and signal and a jumper from power inserter to my scanner, I'd rather have power up one coax and my signal down another coax to scanner it jus seems weird to have both in one cord seem would cause interference, im not even sure lmr 400 would even be good as a power cable also. im not very good at all this. Thanks for ur reply

 

[900mhz]

If you plan on powering up multiple preamps, I would use a separate coax for power as I outlined in my initial response. DC powering thru coax generally does not cause interference issues for VHF and above. That Channel Master preamp is designed for separate DC powering independent from RF

 

[I_Am_Infinite]

If you plan on powering up multiple preamps, I would use a separate coax for power as I outlined in my initial response. DC powering thru coax generally does not cause interference issues for VHF and above. That Channel Master preamp is designed for separate DC powering independent from RF

To run a split power feed, that would be a different story. You would have to first verify that the other preamps run at the same voltage as provided from the power pack. You would also need to add up the current draw of all the preamps to determine if the power pack can handle the load. Be conservative as the DC voltage will experience a drop, which would increase current draw. You would need to run a separate coax (RG-6 would work) to a splitter that does not block DC power (power passing splitter)...regular CATV type splitters do not pass voltage, then distribute the power as appropriate. Get a power passing splitter with the exact amount of ports that you need.

Alright so if I understand properly I can split power and I don't have to use my lmr400 to power I can have an rg6 power and my lmr400 on output? Right? I was kinda confused because of that optional power option, I thought u had to use that for longer runs of cable that would power it.

In the picture it has the power on top left port and option for power on RF on bottom left port, the latter I thought I had to use because was powering w 60ft coax but if I understand right I can use rg6 to power it from the top left port and use either of the bottom ports for the coax going to the scanners?

So my idea would be to use Amazon.com or this Amazon.com for splitting power cable into multiple to power like 3 of these https://www.amazon.com/Channel-Mast...r-antenna/dp/B001RCBX56/ref=asc_df_B001RCBX56 would I still need a power inserter, I'm still kinda confused.

 

[900mhz]

yes. You can use the top left port for power input, use the top right port for RF (from the antenna) into the preamp, and use the bottom RF out only port for the output. That would work just fine. The unused port on the bottom left would require weather protection. You don't need water getting into the amplifier. Pay special attention to be sure to weather proof all connections to the amplifier to prevent water infiltration.
And yes, either of those power pass splitters will work for splitting the power feed to other amplifiers.

 

[I_Am_Infinite]

yes. You can use the top left port for power input, use the top right port for RF (from the antenna) into the preamp, and use the bottom RF out only port for the output. Thay would work just fine. The unused port on the bottom left would require weather protection. You don't need water getting into the amplifier.
And yes, either of those power pass splitters will work.

Thanks so much. Would I still need this https://www.amazon.com/Channel-Master-Adapter-Amplifiers-Preamplifiers/dp/B084VVRDN7 on the rg6 in the house to plug it in and then run to the splitter, then to each pre amp? Or just the power adapter that came w it hooked to 60ft rg6 to splitters, to preamps? Or do i need the above , i Jus wouldn't have to hook up the tv port one like previous thought, I would just have to plug it in and hook up rg6 to the one that goes to power splitters (the, to amp labeled one) then jumpers to each preamp? Then each pre amp with a feed to the scanner?

Hopefully I wouldn't need this a just use the power things that came with the pre amps.

 

[900mhz]

You can use the power supply that comes with the preamp. Run the power from that power supply to the RG-6 and feed it out and up to power passing splitter to power your preamps.

 

[I_Am_Infinite]

You can use the power supply that comes with the preamp. Run the power from that power supply to the RG-6 and feed it out and up to power passing splitter to power your preamps.

Thanks again, I appreciate the help. Is there any limits on how long the rg6 can be before that plug would not power them right?

 

[900mhz]

I think you will be fine with what you have for distance. You did mention around 60 feet, give or take...that should work just fine.

 

[I_Am_Infinite]

I think you will be fine with what you have for distance. You did mention around 60 feet, give or take...that should work just fine.

Ya, its 60ft or so, I was just curious because of splitting to 3 pre amps and just in case I needed a longer run or went higher or something.

 

[900mhz]

Ya, its 60ft or so, I was just curious because of splitting to 3 pre amps and just in case I needed a longer run or went higher or something.

even if you doubled that length, you should be okay.

 

[I_Am_Infinite]

even if you doubled that length, you should be okay.

Thanks for the help, I appreciate you.

 

[Ubbe]

Each ChannelMaster amp takes 500mA and that power adapter can only supply 500mA to one amp.
There's no issue powering amps thru your LMR400. It's done to weak signal sat dishes amps and cellular receiving antennas and a lot of other applications.

You will have to use that all ports power pass thru splitter to get power out from it to 3 amplifiers to 3 antennas, but I suggest using much better amps that also only needs 100mA each that has a 0,5dB noise figure instead of the CM's 2dB. You will need to put amps and splitter in a weather proof box and seal the coaxes going in and out of it.

Both the CM and most other amps have too much gain and you'll need to attenuate maybe 10dB down at the other end of the coax. Best is to use a variable attenuator to set the perfect attenuation without overloading any receiver.

This $28 amplifier, and there are probably similar ones with low noise and high IP3, run on 6v-24v power from the coax, so that CM power adaptor are perfect. PGA103+ amplifier

Those CM amps are used for cable TV and have a return path for 40MHz so they cannot be used for signals below 50MHz.

/Ubbe

 

[merlin]

I am a bit confused here as to why you would need more than one preamp and antenna for a system.
Weather powered from its dedicated power port or through the drop coax, once in the shack, you can split to [n] receivers. As mentioned if you power through the drop, you need that power inserter in the drop before any splitting.
Otherwise, a separate power cable for the amp. Anything will do, even zip cord if mated to the 'F' connector properly.
My amp being similar (Scientific Atlanta) my system follows this heirarchy:
A discone antenna, good from 120 Mhz to 1500 Mhz.
In the antenna mounted box, the first thing Lightning arrester then an FM broadcast trap. This helps prevent overload of the preamp. (helps, doesn't prevent)
Then into a SA 750515C drop amp. The power in just capped off with an open 'F' connector.
The feed is 65 foot LMR600DS, connects to the antenna box, into the amp out+power
all weather sealed.
In the shack, the first thing is the grounded interface panel then the power inserter, then directly into a 4 port standard full band cable splitter. I use quality RG6 ds from the panel.
One port goes to the TV, each of the other 3 go into decade attenuators. 2 of those go to SDR dongles, the last to a bearcat scanner.
As for performance, the TV, I really need a 5 Db attenuator, the signal is very hot there.
Both SDR dongles must have a good 10 Db attenuation or they overload. I switch in bandpass filtering, that helps a lot.
As for the bearcat, that takes 15 Db attenuation (the gain of the drop amp) or the signal is just too hot especially with close by stations. It still works fine if I switch the power off to the drop amp.
Now, if you want to listen to frequencies below 120 Mhz, you would need a different antenna/amp/cable for that.
There is a way to combine a lower frequency/antenna/amp onto the one drop cable. It means more splitting and combining at both ends of the cable. (the cable is a cheaper deal)
Hope you get the gist here,
73s

 

[merlin]

Each ChannelMaster amp takes 500mA and that power adapter can only supply 500mA to one amp.
There's no issue powering amps thru your LMR400. It's done to weak signal sat dishes amps and cellular receiving antennas and a lot of other applications.

You will have to use that all ports power pass thru splitter to get power out from it to 3 amplifiers to 3 antennas, but I suggest using much better amps that also only needs 100mA each that has a 0,5dB noise figure instead of the CM's 2dB. You will need to put amps and splitter in a weather proof box and seal the coaxes going in and out of it.

Both the CM and most other amps have too much gain and you'll need to attenuate maybe 10dB down at the other end of the coax. Best is to use a variable attenuator to set the perfect attenuation without overloading any receiver.

This $28 amplifier, and there are probably similar ones with low noise and high IP3, run on 6v-24v power from the coax, so that CM power adaptor are perfect. PGA103+ amplifier

Those CM amps are used for cable TV and have a return path for 40MHz so they cannot be used for signals below 50MHz.

/Ubbe

I scarf up on the Scientific Atlanta surge drop amps I usually find on ebay for $5 to $10.
They run very nicely on 12 to 18 volts. Current is 140 Ma measured 150 ma rated.
They are rated 15 Db gain and NF < .3Db.
Bench tested they come to life at 100 Mhz, Flat +15 Db up to 1000 Mhz. Noise too low for me to measure
excellent IP3 Although rated down to 54 Mhz, I observe a reduced gain and lots of ripple below 100 Mhz.
Like the CM, they have a return 5 to 42 Mhz. I haven't tested the return.
Made for the cable industry, the best amp I have found.

 

[merlin]

Thanks again, I appreciate the help. Is there any limits on how long the rg6 can be before that plug would not power them right?

I would guess 1000 foot or more. these amps fire at 9 volts at the amp and usually max at 18 volts.
Current is like 150 ma so that length can be calculated based on the source supply.

 

[I_Am_Infinite]

I am a bit confused here as to why you would need more than one preamp and antenna for a system.
Weather powered from its dedicated power port or through the drop coax, once in the shack, you can split to [n] receivers. As mentioned if you power through the drop, you need that power inserter in the drop before any splitting.
Otherwise, a separate power cable for the amp. Anything will do, even zip cord if mated to the 'F' connector properly.
My amp being similar (Scientific Atlanta) my system follows this heirarchy:
A discone antenna, good from 120 Mhz to 1500 Mhz.
In the antenna mounted box, the first thing Lightning arrester then an FM broadcast trap. This helps prevent overload of the preamp. (helps, doesn't prevent)
Then into a SA 750515C drop amp. The power in just capped off with an open 'F' connector.
The feed is 65 foot LMR600DS, connects to the antenna box, into the amp out+power
all weather sealed.
In the shack, the first thing is the grounded interface panel then the power inserter, then directly into a 4 port standard full band cable splitter. I use quality RG6 ds from the panel.
One port goes to the TV, each of the other 3 go into decade attenuators. 2 of those go to SDR dongles, the last to a bearcat scanner.
As for performance, the TV, I really need a 5 Db attenuator, the signal is very hot there.
Both SDR dongles must have a good 10 Db attenuation or they overload. I switch in bandpass filtering, that helps a lot.
As for the bearcat, that takes 15 Db attenuation (the gain of the drop amp) or the signal is just too hot especially with close by stations. It still works fine if I switch the power off to the drop amp.
Now, if you want to listen to frequencies below 120 Mhz, you would need a different antenna/amp/cable for that.
There is a way to combine a lower frequency/antenna/amp onto the one drop cable. It means more splitting and combining at both ends of the cable. (the cable is a cheaper deal)
Hope you get the gist here,
73s

I scarf up on the Scientific Atlanta surge drop amps I usually find on ebay for $5 to $10.
They run very nicely on 12 to 18 volts. Current is 140 Ma measured 150 ma rated.
They are rated 15 Db gain and NF < .3Db.
Bench tested they come to life at 100 Mhz, Flat +15 Db up to 1000 Mhz. Noise too low for me to measure
excellent IP3 Although rated down to 54 Mhz, I observe a reduced gain and lots of ripple below 100 Mhz.
Like the CM, they have a return 5 to 42 Mhz. I haven't tested the return.
Made for the cable industry, the best amp I have found.

I would guess 1000 foot or more. these amps fire at 9 volts at the amp and usually max at 18 volts.
Current is like 150 ma so that length can be calculated based on the source supply.

Thanks for all the information. To keep it simple I got 3 yagis pointed in 3 different directions, I have another regular antenna multiband hooked up to but these were more for the yagis. I pretty much without getting into everything 3 yagis, 3 LMR 400 coaxes, 60 ft x2 and 55ft, these are in use. These come down go into house and connect to amplifiers, theres 2 RCA 12db amps and 1 RCA 10db 4 output amp. I got 3 scanners. I leave it at that but u cam get the jist of it.

I get pretty good signal really, I just want perfect, which might not really be power in my situation. Thanks for you info I appreciate it.

 

[prcguy]

The noise figure on the SA amps cannot be anywhere near .3dB, an LNA that covers those frequencies with that low of a NF simply did not exist when SA was in business. The noise figure would be well north of 3dB somewhere and probably closer to 4 or 5dB.

I scarf up on the Scientific Atlanta surge drop amps I usually find on ebay for $5 to $10.
They run very nicely on 12 to 18 volts. Current is 140 Ma measured 150 ma rated.
They are rated 15 Db gain and NF < .3Db.
Bench tested they come to life at 100 Mhz, Flat +15 Db up to 1000 Mhz. Noise too low for me to measure
excellent IP3 Although rated down to 54 Mhz, I observe a reduced gain and lots of ripple below 100 Mhz.
Like the CM, they have a return 5 to 42 Mhz. I haven't tested the return.
Made for the cable industry, the best amp I have found.

 

[Ubbe]

I scarf up on the Scientific Atlanta surge drop amps I usually find on ebay for $5 to $10.
They run very nicely on 12 to 18 volts. Current is 140 Ma measured 150 ma rated.
They are rated 15 Db gain and NF < .3Db.

Interesting. I looked at a couple but all seem to have a 3.5dB NF. What's the model number for the good ones?

/Ubbe