How Is Powering An LNA Best Accomplished?

Merovingian

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I was thinking to use this LNA: Mini-Circuits at an antenna. I have never used this type of an LNA before so I'm not sure what is the best way to power it. I see it has two posts on the side of it for power but I was planing to use a bias tee ( https://www.minicircuits.com/WebStore/dashboard.html?model=ZNBT-60-1W+ ) to send power up the coax to the LNA, I use N connectors for everything, so I will have to adapt that to SMA at the LNA. I see the bias tee has a BNC connector for power so I will have to figure out something there. . .

So what I am asking is: Will the LNA accept power either through the coax or the posts? Or will it "only" accept power through the posts and I will have to somehow separate the power from the coax up at the antenna to apply 5V to those two posts on the side? It would be nice if I could just send 5V through the coax and power the LNA through the coax like I do with my TV antenna.

Additionally, does anyone know of a high quality linear power supply with maybe a small voltage adjustment range (to compensate for resistance in the coax cable) to convert 120V AC to 5V DC that I can connect to the BNC connector on the bias tee?

Thanks for your time.
 

bchappuie

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Check the radio you are connecting it to, some support a Bias-T connection to send 5V out the center conductor just for that reason, and the LNA should support it also.
 

prcguy

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That amp and most amps will not take voltage up the coax and you would use a bias tee at the amp and near the radio to get voltage in and out of the coax. Search Ebay for "bias tee" and you will find thousands of them for $5 on up. Some are junk and others are great for the price.

The particular amp you are looking at might work ok in your area connected to a wide band antenna with no filtering or it might not. It also has 7dB of slope in the wrong direction losing 7dB gain as you go from 100MHz to 1GHz. There are other models with flatter gain across a wide band and better IP1/IP3 specs.


I was thinking to use this LNA: Mini-Circuits at an antenna. I have never used this type of an LNA before so I'm not sure what is the best way to power it. I see it has two posts on the side of it for power but I was planing to use a bias tee ( https://www.minicircuits.com/WebStore/dashboard.html?model=ZNBT-60-1W+ ) to send power up the coax to the LNA, I use N connectors for everything, so I will have to adapt that to SMA at the LNA. I see the bias tee has a BNC connector for power so I will have to figure out something there. . .

So what I am asking is: Will the LNA accept power either through the coax or the posts? Or will it "only" accept power through the posts and I will have to somehow separate the power from the coax up at the antenna to apply 5V to those two posts on the side? It would be nice if I could just send 5V through the coax and power the LNA through the coax like I do with my TV antenna.

Additionally, does anyone know of a high quality linear power supply with maybe a small voltage adjustment range (to compensate for resistance in the coax cable) to convert 120V AC to 5V DC that I can connect to the BNC connector on the bias tee?

Thanks for your time.
 

Merovingian

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166
Check the radio you are connecting it to, some support a Bias-T connection to send 5V out the center conductor just for that reason, and the LNA should support it also.
I hadn't thought of that. My SDRPlay RSP Duo apparently does output 4.7V @ 100mA max, my HF+ Discovery apparently does not and my Ettus B200 does not but it only goes down to 70MHz anyway. The RSP Duo might work, the LNA seems to be looking for 5V, I don't know if 4.7V will be just as good or not.
 

Merovingian

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That amp and most amps will not take voltage up the coax and you would use a bias tee at the amp and near the radio to get voltage in and out of the coax. Search Ebay for "bias tee" and you will find thousands of them for $5 on up. Some are junk and others are great for the price.
I see. So the simple method won't work, with the LNA accepting power through the coax. . . So I will need two bias tees. . . Okay, thanks.


The particular amp you are looking at might work ok in your area connected to a wide band antenna with no filtering or it might not. It also has 7dB of slope in the wrong direction losing 7dB gain as you go from 100MHz to 1GHz. There are other models with flatter gain across a wide band and better IP1/IP3 specs.
I was planing to use the LNA between 50MHz and 85MHz (mostly around 50MHz) with this antenna directional antenna VHF 2 elements yagi 50-87MHz - Antenne directionnelle 2 éléments - Antena Direccional de 2 elementos mod. ARYCK-A-25XA - ARYCK-A-25XI - ARYCKM-A-25XA - ARYCKM-A-25XI . The other LNA I had considered was Mini-Circuits it is a little cheaper but some of the specs. I know to look for didn't seem quite as good. Would you have a better suggestion for an LNA between 50MHz and 85MHz or so?

Thanks
 

prcguy

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The devices inside the 5v preamp are probably 3.3v with a regulator in front. 4.7v should be fine.

I hadn't thought of that. My SDRPlay RSP Duo apparently does output 4.7V @ 100mA max, my HF+ Discovery apparently does not and my Ettus B200 does not but it only goes down to 70MHz anyway. The RSP Duo might work, the LNA seems to be looking for 5V, I don't know if 4.7V will be just as good or not.
 

prcguy

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The antenna you are looking at seems to be a narrow band antenna that can be cut to frequency then it only covers about 4MHz of range. It doesn't cover the entire 50 to 85MHz range.

The Minicircuits ZX60-P103LN+ should be ok if you put a band pass filter in front of it or use a high pass and a low pass, especically something to keep high power FM and TV broadcast signals. It also has a lot of gain like 22-23dB in the lower frequency range. You would want to attenuate after the preamp so you don't have more than 2-4 dB after feedline loss unless your feeding a very old numb receiver.

I just used one of my spare ZX60-P103LN+ preamps as a UHF repeater master receive front end feeding several repeaters and its working really well, but its got a filter in front of it that is a good 55dB down 5Mhz either side of my operating frequency.

I see. So the simple method won't work, with the LNA accepting power through the coax. . . So I will need two bias tees. . . Okay, thanks.




I was planing to use the LNA between 50MHz and 85MHz (mostly around 50MHz) with this antenna directional antenna VHF 2 elements yagi 50-87MHz - Antenne directionnelle 2 éléments - Antena Direccional de 2 elementos mod. ARYCK-A-25XA - ARYCK-A-25XI - ARYCKM-A-25XA - ARYCKM-A-25XI . The other LNA I had considered was Mini-Circuits it is a little cheaper but some of the specs. I know to look for didn't seem quite as good. Would you have a better suggestion for an LNA between 50MHz and 85MHz or so?

Thanks
 

Merovingian

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The antenna you are looking at seems to be a narrow band antenna that can be cut to frequency then it only covers about 4MHz of range. It doesn't cover the entire 50 to 85MHz range.
Yeah, I wish it was wider 50MHz-85MHz bandwidth but that is the best I could find for what I want to do. It is very difficult to find an antenna that covers this range that is not made for amature radio bands only. I would have liked to have more versatility in receive frequency range but this should accomplish what I want to do, I think. . . I don't want high gain or directivity I just need something that will "look" in one direction not omnidirectional.

The Minicircuits ZX60-P103LN+ should be ok if you put a band pass filter in front of it or use a high pass and a low pass, especically something to keep high power FM and TV broadcast signals. It also has a lot of gain like 22-23dB in the lower frequency range. You would want to attenuate after the preamp so you don't have more than 2-4 dB after feedline loss unless your feeding a very old numb receiver.
Okay, thanks for the confirmation, It is a cheaper LNA anyway, which is good. Oh yeah, a band pass filter is a good idea, thanks, I am wanting to allow TV frequencies through for this project, at least channels 2-6 anyway, I would want to reject anything much above 85MHz and probably anything below 50MHz though. I will have to research if there are such band pass filters for <50~53MHz and >83~88MHz.

Thanks also for the attenuator suggestion, I will have to research one of those as well, it would be nice to find a high quality attenuator that I can vary the level, I don't think I will need massive gain anyway.

I just used one of my spare ZX60-P103LN+ preamps as a UHF repeater master receive front end feeding several repeaters and its working really well, but its got a filter in front of it that is a good 55dB down 5Mhz either side of my operating frequency.
You have a lot of good stuff. I currently have two other projects I would like to do/finish, #1 the air band antenna you helped me get some information on not too long ago and #2 a few months ago I found links you posted to an excelent satcom antenna that can be built with parts from the hardware store. That is something I would like to try to build in the near future, I am interested in listening to satcom satellites. I have done some initial sourcing of hardware for the airband antenna and now I may think about adding a band pass filter for the FM band to use with the air band antenna whenever I finally get that built. I am still waiting on a better version of the NanoVNA to come out per this post here: Re: Nanovna-v2 4 inch display availability I'm not sure how much longer that will take, I would like to get something to test antennas soon so I can get going on the air band antenna after I finish this project I'm working on.
 

prcguy

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Several companies make scanner type log periodic antennas that will cover 50MHz and up in frequency, Create is one company and there are also military surplus Log Periodics that cover 30 to 76MHz or 30 to 90Mhz.

Yeah, I wish it was wider 50MHz-85MHz bandwidth but that is the best I could find for what I want to do. It is very difficult to find an antenna that covers this range that is not made for amature radio bands only. I would have liked to have more versatility in receive frequency range but this should accomplish what I want to do, I think. . . I don't want high gain or directivity I just need something that will "look" in one direction not omnidirectional.



Okay, thanks for the confirmation, It is a cheaper LNA anyway, which is good. Oh yeah, a band pass filter is a good idea, thanks, I am wanting to allow TV frequencies through for this project, at least channels 2-6 anyway, I would want to reject anything much above 85MHz and probably anything below 50MHz though. I will have to research if there are such band pass filters for <50~53MHz and >83~88MHz.

Thanks also for the attenuator suggestion, I will have to research one of those as well, it would be nice to find a high quality attenuator that I can vary the level, I don't think I will need massive gain anyway.



You have a lot of good stuff. I currently have two other projects I would like to do/finish, #1 the air band antenna you helped me get some information on not too long ago and #2 a few months ago I found links you posted to an excelent satcom antenna that can be built with parts from the hardware store. That is something I would like to try to build in the near future, I am interested in listening to satcom satellites. I have done some initial sourcing of hardware for the airband antenna and now I may think about adding a band pass filter for the FM band to use with the air band antenna whenever I finally get that built. I am still waiting on a better version of the NanoVNA to come out per this post here: Re: Nanovna-v2 4 inch display availability I'm not sure how much longer that will take, I would like to get something to test antennas soon so I can get going on the air band antenna after I finish this project I'm working on.
 

Merovingian

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That sounds good. I'm needing something that has enough directivity to "look forward" but be able to receive from a very wide angle. An antenna with a reflector or a reflector and one director. Can that be accomplished with a log periodic?

After looking up the antenna it does seem to be semi-wide angle 120° X 65°, still a little bit narrower that I would like but not too bad. I will give it some more thought.

Several companies make scanner type log periodic antennas that will cover 50MHz and up in frequency, Create is one company and there are also military surplus Log Periodics that cover 30 to 76MHz or 30 to 90Mhz.
 
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Merovingian

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:(:(:(

Yes, I have many strong FM signals here, 2-3 stations in particular are stronger than the others, they are above 100 MHz. For this project I would want to reject the entire FM band as much as possible. I thought I had found the perfect solution. . . :(

That filter offers almost no rejection in the FM broadcast band. Do you have any strong signals there? I would look for a filter that has at least 30dB attenuation at 88MHz and more throughout the FM band.
 

prcguy

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This is the best FM band stop filter I have found, Its got between about 44dB and 55dB attenuation in the 88 to 108MHz range and it just starts allowing the VHF air band through at 118MHz. It will eat into your VHF low range starting about 65MHz and up.


Otherwise most Minicircuits filters have really broad skirts and roll off very slowly. You need something with really sharp skirts that will allow reception to 85MHz then drop immediately so that 88MHz is down 30dB or more. That's expensive to make.


:(:(:(

Yes, I have many strong FM signals here, 2-3 stations in particular are stronger than the others, they are above 100 MHz. For this project I would want to reject the entire FM band as much as possible. I thought I had found the perfect solution. . . :(
 
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Merovingian

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There seems to be a big drop between 70 and 88 MHz, a large part of the frequencies I want to have the ability to receive. It does do a good job everywhere else though but too much is lost where I want to receive.

I've been doing some research. . . My new plan is this: Use the band pass filter Mini-Circuits in addition to this notch filter HPN-30118 Combined Notch Filter | Scanner Master to better suppress the FM band, it looks like the HPN-30118 rolls off more sharply toward 88 MHz per this link FM bandstop filter comparison . I think that should work better.

Idealy I would like to have something that starts to roll off at 87 MHz and drops off a cliff at 88MHz but that is probably not practical I imagine. . .

This is the best FM band stop filter I have found, Its got between about 44dB and 55dB attenuation in the 88 to 108MHz range and it just starts allowing the VHF air band through at 118MHz. It will eat into your VHF low range starting about 65MHz and up.

 

Ubbe

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You got a 90dB filter here FM Notch Filter 88-108 MHz Band Excellent Rejection -97dBm RTL SDR FM trap. | eBay
It says it has a 6dB attenuation at 82MHz. If you can solder you can put a jumper over C4 or L4 and it will raise that -6dB point to 86MHz. The filter I bought from that place attenuate 60dB and not 90dB but can be some leakage in my setup as the signal levels measured are very low compared to the test signals level.

/Ubbe
 

Merovingian

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Interesting! I will definitely consider that. I probably will have to do some soldering if I use that, I wouldn't want attenuation until 86 MHz. Hopefully that wouldn't affect other frequencies much.

Thanks!

You got a 90dB filter here FM Notch Filter 88-108 MHz Band Excellent Rejection -97dBm RTL SDR FM trap. | eBay
It says it has a 6dB attenuation at 82MHz. If you can solder you can put a jumper over C4 or L4 and it will raise that -6dB point to 86MHz. The filter I bought from that place attenuate 60dB and not 90dB but can be some leakage in my setup as the signal levels measured are very low compared to the test signals level.

/Ubbe
 

prcguy

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It looks like that filter has over 2dB insertion loss everywhere, not including the FM band attenuation. If you changed any parts you would need a way to sweep it to see the results.

Interesting! I will definitely consider that. I probably will have to do some soldering if I use that, I wouldn't want attenuation until 86 MHz. Hopefully that wouldn't affect other frequencies much.

Thanks!
 

Merovingian

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That is unfortunate. Yeah I would want to test that before I used it permanently. I'm hoping the band pass and notch filters I was thinking about using would do a good enough job to not need anything else. But I would still keep the filter in mind.

It looks like that filter has over 2dB insertion loss everywhere, not including the FM band attenuation. If you changed any parts you would need a way to sweep it to see the results.
 
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