Requesting 800 MHz Preamp (Mounted at/near antenna) Suggestions

[KC1UA]

Hello,

The topic pretty much spells it out. When spring arrives I have a tower mounted project in mind for an 800 MHz yagi which will be mounted on a side arm L type bracket with a lightweight rotor. I normally don't use preamps but I want to give one a try to maximize DX reception on this band. I've tried doing some research on inline and/or mast mounted preamps that are powered on the coax by a power injector. The antenna will potentially be used by multiple receivers/scanners and as such won't benefit from the bias tee output of an Airspy or RTL device.

Obviously I'm looking for the lowest noise best bang for the consumer buck solution specifically for this band. I did find the Stridsberg 700/800 preamp. I can weatherproof with the best of them but I'm not sure that this would be the best option. We have discussed that Stridsberg devices work well but don't have the lowest noise figure; this one shows a 3.5 dB noise figure and 18 dB gain. Something that is completely inline on the coax run would be ideal, but at least something that is built to be mast mounted would work. I do have a five site 800 MHz simulcast analog TRS here and a forthcoming multi-site Phase II P25 system to consider as possible contributors to overload, but hopefully the fact that the antenna will be on a rotor can minimize some of that if it's an issue. Most of the radios that will be in use with this antenna have variable attenuation, to include an IC-R8600 and numerous SDRs.

I'm continuing to search but any constructive suggestions would be appreciated.

Thanks!

 

[prcguy]

If your in a fairly low RF level area for the 700-900MHz range here is a preamp targeting 800MHz with good noise figure and moderate signal handling capability. New price is about $69 and they show up sometimes on eBay for about half that. I tried one on a 900MHz amateur repeater and it worked well but there was a lot of front end filtering to protect the preamp from everything except the specific frequency range I needed.

You can find inexpensive bias Tees on eBay to remote this or any preamp and this particular one runs off 5v. Low Noise Amplifier, 824 - 960 MHz, 50Ω | ZX60-0916LN-S+ | Mini-Circuits

 

[KC1UA]

That's definitely in the ballpark of what I'm looking for. Ideally I can find something similar with N connectors but I can also plan accordingly with the cable run. Thanks for this info. As to filtering it is definitely my intention to find and use a good band pass filter as well as there are other areas of the spectrum in this area that can be hellish.

 

[prcguy]

Here is a cheap filter that can be retuned to the roughly 851-866MHz range of the 800MHz public service band. I have a similar filter that I retuned to the 900 amateur band and the insertion loss is very low and the skirts are very steep. You would want an outdoor NEMA box to hold the preamp and it just needs to be larger to hold a filter like this. SMA connectors on the amplifier are no big deal since you would be transitioning to something else to feed through the box.

What exact frequency range would you be looking to receive with the Yagi and preamp?

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That's definitely in the ballpark of what I'm looking for. Ideally I can find something similar with N connectors but I can also plan accordingly with the cable run. Thanks for this info. As to filtering it is definitely my intention to find and use a good band pass filter as well as there are other areas of the spectrum in this area that can be hellish.

 

[btt]

You can find inexpensive bias Tees on eBay to remote this or any preamp and this particular one runs off 5v. Low Noise Amplifier, 824 - 960 MHz, 50Ω | ZX60-0916LN-S+ | Mini-Circuits

That amp has a very average/low OIP3. A nearby LTE tower is going to hammer it. A good rule of thumb is to look for an amp with an OIP3 20-25 dB above P1dB compression.

 

[prcguy]

If your going to run without a front end filter I prefer an IP3 above 45dBm or greater but you take a big hit in noise figure. If the OP only needs to receive the typical 800 band public safety range of 851-866Mhz a single filter is fairly easy and should protect the smaller amp.

That amp has a very average/low OIP3. A nearby LTE tower is going to hammer it. A good rule of thumb is to look for an amp with an OIP3 20-25 dB above P1dB compression.

 

[KC1UA]

Thanks for the responses and info, understood on all. I am primarily looking for coverage as stated in the 851-860 MHz area at this point in time.

 

[btt]

If your going to run without a front end filter I prefer an IP3 above 45dBm or greater but you take a big hit in noise figure. If the OP only needs to receive the typical 800 band public safety range of 851-866Mhz a single filter is fairly easy and should protect the smaller amp.

lol. So your advice is that it is ok to run without a preselect filter at all? After you incorrectly trashed my design over and over for this? Even after I told you multiple times I had a pre-select filter on there? You think designing a narrow bandpass UHF filter is easy, but you admit you are not a filter designer? I can tell you now that some UHF filters take hundreds of hours to design. Like this 902-928 MHz filter I designed. GitHub - tvelliott/jPCBSim_demos: demo simulation and validation files for jPCBSim It is very close to one I designed to save someone else from a very big mistake (it saved the contract). I'll stop now, but I had to point it out.

 

[prcguy]

I use mast mounted preamps with preselector filters which worked very well until recently where some huge 700MHz stuff sprang up. I mentioned this many times but maybe you forgot. The 50Mhz to 1GHz preamps that I recommend for some in low RF areas work fine on a broad band Discone without any preselection, gain is 10dB IP3 is 46dBm. I can't use that here but some can in their low RF level areas. Not everyone has 700/800MHz interference.

A few posts up I pointed out a surplus 8 section interdigital filter that is $39 and can be easily retuned to what the OP needs 851-860MHz with well under 1dB insertion loss and probably 60dB down 10Mhz from the band edges. That filter with the lower level lower NF MiniCircuits preamp would do him just fine. If he chooses to buy that filter I'll retune it for him for free.

I am not a filter designer but I suspect over my 45yr career I've specified, tuned, aligned and installed a bunch more filters than you probably have (through 94GHz) and even being retired about 10yrs I still do it as a hobby. I wouldn't say I trashed your design but it is backward putting any filter after the LNA, the whole purpose of filters is to protect the LNA, unless of course the receiver its feeding is one step above a crystal detector and folds up just looking at an antenna. Placing filters after the LNA is about the same as putting a vehicle air filter after the muffler.....

lol. So your advice is that it is ok to run without a preselect filter at all? After you incorrectly trashed my design over and over for this? Even after I told you multiple times I had a pre-select filter on there? You think designing a narrow bandpass UHF filter is easy, but you admit you are not a filter designer? I can tell you now that some UHF filters take hundreds of hours to design. Like this 902-928 MHz filter I designed. GitHub - tvelliott/jPCBSim_demos: demo simulation and validation files for jPCBSim It is very close to one I designed to save someone else from a very big mistake (it saved the contract). I'll stop now, but I had to point it out.

 

[sonm10]

@Ubbe turned me onto this one PGA103 Low Noise Amplifier 2GHz ESD protection + Gain Stabilization + USB cable | eBay

40DB IP3
0.5Db Noise figure

Not sure if this can be powered with a bias-tee or not???
Just have to find a weather-proof box to put it in.

 

[KC1UA]

@Ubbe turned me onto this one PGA103 Low Noise Amplifier 2GHz ESD protection + Gain Stabilization + USB cable | eBay

I'm actually using a version of a PGA103 as a part of a homebrew multicoupler I created. It works well overall but it does have varying gain across its coverage. I'm trying to stick with a band-specific amp this time around and as stated a band specific bandpass filter as well. Good point on the SMA connectors prcguy, as it would have to be in a box, so not an issue.

 

[KevinC]

We had enough of the my filter is bigger than yours in the other thread. So let’s please get back to helping the OP.

 

[merlin]

I robbed the filters from a BDA and retuned them for my 800/900 Mhz project.
They are tight and stretching to the low end rolls off quick.
An alternate project is ceramic filters. Find a 3 element just below your desired frequency and they can be
shaved up to what you want. (No, they don't go down) so takes care in tuning.
Something like the above works well with the PGA-103 preamps.
Everything in the weather proof box is SMA to bulkhead 'N' with seals.