Need Help Selecting an Omnidirectional Antenna for 860 MHz Reception in Hilly Terrain

[sstephenson]

First off, let me say that I'm a complete novice to the world of antenna selection, so I'm looking for some guidance and helpful suggestions.

I'm planning to purchase an omnidirectional base antenna for monitoring the 860 MHz San Diego City and County digital trunking systems. I live in a canyon with large hills bordering me closely to the east and west (maybe a quarter of a mile away on each side) and large mountains farther away (several miles) to the north and south. Needless to say the terrain around me is very uneven. Complicating things further is the fact that the San Diego County RCS system is divided into north and south regions, both of which carry communications unique to those regions as well as some transmissions that are simulcast on both. The closest transmitter to me is maybe two miles away to the south on a mountain peak, but this is for the RCS south system only. I also receive transmissions from RCS north, but the closest transmitter is not line of sight. San Diego City broadcasts from another transmitter (somewhere). That's why I've chosen to go omnidirectional rather than directional. I've been looking at antennas like those on this site:900 800 MHz Fiberglass Base Station MFB Omnidirectional Antennas PCTEL. Based on the versions offered, I'm looking at these two models.

MFB8583 806-866 MHz 858 MHz 3 dB 30 MHz 40°
MFB8585 806-866 MHz 858 MHz 5 dB 20 MHz 22°

I really have no idea which would be better in my situation; the 3dB gain 40 degree vertical beamwidth model, or the 5dB gain 22 degree vertical beamwidth model. Any help would be greatly appreciated!

 

[benbenrf]

sstephenson

Either of them could do the job - it depends on how far you are from the surrounding geographical features and how high those features are, relative to your base height, that is going to determine the beam width that is going to give your antenna the coverage required to cover the tops of the surrounding features - from where the signals are by & large going to be coming from. That said, at 860Mhz there is a fair chance a lot of signal reflection and bouncing around off canyon walls is going to be present (actually, you want to restrict antenna sensitivity to these reflected signal pick-up as much as possible - they amount to presenting the receiver front end with signals out of phase that just mess up your SNR).

The other consideration is how high [up on a pole?] you would be raising your antenna. Its a math trig calculation - as I'm certain you are aware of.

I don’t think I can suggest any particular antenna (i.e. manufacturer or brand name), but this beam-width consideration thing is important. I don't know what you know about vertical beam-width in omni-directional antennas, but it is a characteristic which can have a significant impact on antenna performance. I would like to share some ideas & theory with you that you may be able to put to use in selecting a suitable antenna.

By omni-directional you mean something that is going to receive equally well from all directions (?). Well, a lot of folk are generally not aware of beam-width as mentioned above, but while so-called omni-directional antennas tend to demonstrate pretty broad & even omni-directional receive coverage in terms of azimuth (on the horizontal or H plane), in terms of elevation or E plane coverage, things can be quite different.

An excellent diagrammatic representation of “directionality” or beam-width in omni-directional antennas can be seen in the series of diagrams at the bottom right hand side of Page 2 the following on-line PDF document.

http://www.ntecusa.com/docs/R&S_HE309_info.pdf

Notice how the E or elevation pattern changes – it (and therefore so does Gain) breaks up as frequency changes.

This is because omni-directional antennas tend to only demonstrate good circular receive coverage with equal receive gain on a single frequency. The further away from that frequency (the resonant freq) they are used at, the more broken up the pattern tends to become, and the more sensitive the antenna tends to become to the “angle of arrival” from which a signal comes.

In short: omni-directional type antennas tend to display variation in their sensitivity to signals, depending on the elevation angle from which that radio signal arrives from. One type of vertical omni-directional antenna may display poor sensitivity to signals arriving from say, between 5degrees – 7.5degrees above the horizon, but display 3dB, 6dB or even more sensitivity to signals arriving from say between 15degrees - 20degrees above the horizon …. and the complete opposite is equally possible using another omni-directional antenna, which may display good sensitivity to signals between 5 – 7.5degrees above the horizon and poor sensitivity to signals arriving from between 15-20degres above the horizon. An example of this can be seen in some antennas placed on top of skyscrapers, offering coverage to the surrounding urban area and been designed to offer greater sensitivity to signals arriving from low or even negative azimuth angles i.e. street level.

The point is: with careful choice you can take advantage of this often overlooked quirk in omni-directional dipole/whip/vertical type antennas – especially if you are located in a canyon or valley where antenna gain on a given freq at a low elevation (i.e. straight into the side of the canyon or valley wall) would be a complete waste.

In short, if you are really low down in a valley with high surrounding canyon or valley walls that are proportionally close in, your best bet is going to be an antenna with universal azimuth gain (H plane), but which displays good sensitivity to signals arriving from high angles and poor sensitivity to signals arriving from low angles. This may mean choosing an antenna that may not be resonant for 860Mhz, but that’s no problem as the loss incurred through using a no resonant antenna is addressed by way of adding an inline band-pass filter for 860Mhz (located right up against the antenna – on the pole if at all possible), followed by a narrowband preamp. Generally I am against the use of pre-amps, but this is one of the few examples of an application in which a pre-amp could offer significant gains

With careful choice and planning you could achieve omni-directional receive coverage with as much as 4dB - 6dB if not more, passive gain (i.e. before adding a pre-amp) while maintaining a good signal to noise ratio (SNR). Add a band-pass filter and, depending on just how saturated the ether is where you are based, it wouldn’t surprise me if you achieved receive signal quality with this omni-directional setup that typically could only otherwise be enjoyed using a passive directional antenna setup.

 

[WA1ATA]

One approach is to use an antenna that is optimized for the most difficult-to-receive transmitter that you want to hear.

Even with a highly directional antenna pointed elsewhere, the mountaintop transmitter 2 mile away will come in strong.

 

[sstephenson]

Thanks benbenrf for the very informative reply. Looks like I've got a little homework to do in order to choose the model with the appropriate gain and vertical beamwidth. I plan to mount the antenna on a mast on my fireplace chimney. I'm guessing that height above the ground will be about 20 to 25 feet. This should get me maybe 10 feet above my rooftop. Let's say that I measure the angle from the H-plane to the top of the mountain showing the greatest incline angle. I'm guessing that this would be about 15 to 20 degrees above the horizon. E-plane slightly less. Anything above that would be open sky. One other variable that I should mention is that my house is situated on a small hill up above the canyon floor, so I would think that there might be some signals coming from as much as 10 degrees below the E-plane. I think that I'm missing something very basic here, and I probably am. Given my example, I would think that I should choose choose the antenna with the 22 degree vertical angle and 5dB gain because I would think that most of my signals would be coming from an angle at or below the angle of the highest peak. If I understand correctly, I think that you're suggesting that I should try to take advantage of signals arriving from higher angles, and have less sensitivity at lower angles. Please help me understand the where I've gone wrong in my thinking.

Also, you have mentioned the possibility of using an antenna with a resonant frequency other than 860 MHz. Any suggestion what that resonant frequency should be? I don't have a good enough understanding of the principles behind this to make a choice here. Are you saying that perhaps I should choose something like the antenna below with a resonant frequency of 915 MHz with unity gain and a 75 degree vertical beamwidth so that I can take advantage of very high angle signals? Is that too extreme an example?

MFB9150 902-928 MHz 915 MHz Unity 20 MHz 75�

Also, I have only a very basic understanding regarding preamps, so I might be inclined to follow your advice if you think that this would be the way to go, but I don't really understand what the advantage is in this scenario vs. others.

Thanks!

sstephenson

Either of them could do the job - it depends on how far you are from the surrounding geographical features and how high those features are, relative to your base height, that is going to determine the beam width that is going to give your antenna the coverage required to cover the tops of the surrounding features - from where the signals are by & large going to be coming from. That said, at 860Mhz there is a fair chance a lot of signal reflection and bouncing around off canyon walls is going to be present (actually, you want to restrict antenna sensitivity to these reflected signal pick-up as much as possible - they amount to presenting the receiver front end with signals out of phase that just mess up your SNR).

The other consideration is how high [up on a pole?] you would be raising your antenna. Its a math trig calculation - as I'm certain you are aware of.

I don’t think I can suggest any particular antenna (i.e. manufacturer or brand name), but this beam-width consideration thing is important. I don't know what you know about vertical beam-width in omni-directional antennas, but it is a characteristic which can have a significant impact on antenna performance. I would like to share some ideas & theory with you that you may be able to put to use in selecting a suitable antenna.

By omni-directional you mean something that is going to receive equally well from all directions (?). Well, a lot of folk are generally not aware of beam-width as mentioned above, but while so-called omni-directional antennas tend to demonstrate pretty broad & even omni-directional receive coverage in terms of azimuth (on the horizontal or H plane), in terms of elevation or E plane coverage, things can be quite different.

An excellent diagrammatic representation of “directionality” or beam-width in omni-directional antennas can be seen in the series of diagrams at the bottom right hand side of Page 2 the following on-line PDF document.

http://www.ntecusa.com/docs/R&S_HE309_info.pdf

Notice how the E or elevation pattern changes – it (and therefore so does Gain) breaks up as frequency changes.

This is because omni-directional antennas tend to only demonstrate good circular receive coverage with equal receive gain on a single frequency. The further away from that frequency (the resonant freq) they are used at, the more broken up the pattern tends to become, and the more sensitive the antenna tends to become to the “angle of arrival” from which a signal comes.

In short: omni-directional type antennas tend to display variation in their sensitivity to signals, depending on the elevation angle from which that radio signal arrives from. One type of vertical omni-directional antenna may display poor sensitivity to signals arriving from say, between 5degrees – 7.5degrees above the horizon, but display 3dB, 6dB or even more sensitivity to signals arriving from say between 15degrees - 20degrees above the horizon …. and the complete opposite is equally possible using another omni-directional antenna, which may display good sensitivity to signals between 5 – 7.5degrees above the horizon and poor sensitivity to signals arriving from between 15-20degres above the horizon. An example of this can be seen in some antennas placed on top of skyscrapers, offering coverage to the surrounding urban area and been designed to offer greater sensitivity to signals arriving from low or even negative azimuth angles i.e. street level.

The point is: with careful choice you can take advantage of this often overlooked quirk in omni-directional dipole/whip/vertical type antennas – especially if you are located in a canyon or valley where antenna gain on a given freq at a low elevation (i.e. straight into the side of the canyon or valley wall) would be a complete waste.

In short, if you are really low down in a valley with high surrounding canyon or valley walls that are proportionally close in, your best bet is going to be an antenna with universal azimuth gain (H plane), but which displays good sensitivity to signals arriving from high angles and poor sensitivity to signals arriving from low angles. This may mean choosing an antenna that may not be resonant for 860Mhz, but that’s no problem as the loss incurred through using a no resonant antenna is addressed by way of adding an inline band-pass filter for 860Mhz (located right up against the antenna – on the pole if at all possible), followed by a narrowband preamp. Generally I am against the use of pre-amps, but this is one of the few examples of an application in which a pre-amp could offer significant gains

With careful choice and planning you could achieve omni-directional receive coverage with as much as 4dB - 6dB if not more, passive gain (i.e. before adding a pre-amp) while maintaining a good signal to noise ratio (SNR). Add a band-pass filter and, depending on just how saturated the ether is where you are based, it wouldn’t surprise me if you achieved receive signal quality with this omni-directional setup that typically could only otherwise be enjoyed using a passive directional antenna setup.

 

[popnokick]

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Put up your antenna first without the preamp and see if you get what you want to hear. You can always add it later should conditions warrant.

 

[jack103]

How about a Grove Scannerbeam with a tv rotator.

 

[sstephenson]

How about a Grove Scannerbeam with a tv rotator.

From the Grove website: "For example, at low band (30-50 MHz) it's essentially omni-directional with virtually no favored direction, but as you increase in frequency, it becomes sharper and sharper (more and more gain). At high band VHF, I'd say that it's probably at least 45 degrees wide for decent reception, while at 800 MHz, the reception drops off conspicuously after about 10-20 degrees."

I'm still confused about what my target verticle bandwidth should be. Should I avoid the area near the horizon since the mountains near me are 15 to 20 degrees above the horizon (and thus avoid stray reflected signals) or is the area between 0 and 20 degrees what I want to target because that's where most of my signals will come from? The quote above says that 800 MHz reception drops off after 10-20 degrees.

 

[popnokick]

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An earlier reply mentioned that 800 mHz signals are going to arrive at your location from unpredictable directions due to reflections off of the mountains near you. If you get a highly directional antenna instead of an omni you may miss a usable reflected signal by being aimed in the wrong direction. Stick with an omni antenna to maximize these reflected signals. If by chance you end up with out of phase multipath signals you can deal with that more easily than no signals from the agency you want to hear.
Do you have (or can borrow) a handheld scanner? Take it up to your roof and check out what you can receive, knowing that an omni that has some gain is likely to improve things vs the handheld omni whip antenna. You may also find that the vertical beamwidth on an omni is much less critical due to reflected signals reaching your rooftop location.

 

[benbenrf]

Steve

Yes – you want an antenna that is going to offer greater gain (sensitivity) to signals arriving from high angles as opposed to low angles.

Using an antenna with a res. frequency other than 860Mhz?
Yup, it’s a possible option - as said in my earlier post, the moment an omni-directional antenna is used on a frequency other than that for which it is tuned or resonant, it’s coverage pattern starts to break up and spike in certain directions more so than in other directions (as in the attached diagrams in my first reply). It looses its’ uniformity and starts to show more sensitivity to radio signals arriving from certain directions/angles, than to signals arriving from other directions/angles. It’s this characteristic you can try to take advantage of.

Unfortuneatly, the only way to know what those directions or angles are going to be is to have access to the antenna radiation pattern, diagram or graph – or access to a lab with some pricy instruments like vector analyzers and other hardware with the ability to undertake measurements like S-parameter and so on, so you can calculate them yourself for different frequencies for any antenna.

Professional antenna manufacturers should be able to offer the radiation diagram for any particular antenna they have designed and put on the market.

As a side note: radiation patterns are the result of voltages & currents (and their associated electrical phase) which occur along an antenna element when it intercepts a transmission from the atmosphere, or when it is transmitting a signal fed to it by a transmitter. How these voltages/currents change in position/location and amperage along the length of the antenna element (which determines radiation pattern), is a function of the antenna size (its element length) in relation to the frequency it is transmitting or receiving on.

In any event – so yes, it is possible that an antenna resonant for a higher or lower freq than 860Mhz could have a current/voltage distribution along its length resulting in greater sensitivity to/from a particular direction/angle at the expense or loss of sensitivity to/from some other direction or angle. But that’s okay – it’s fine, in fact its exactly what you want i.e. reduced low angle sensitivity in the direction of the canyon walls for the benefit of greater sensitivity from higher angles towards the peaks of the surrounding geographical features.

This is not the same as beam-width.
A beam-width of say 75degrees for an omni-directional antenna should be defined against a diagram (as illustrated in the diagrams attached to the notes above). Without that background diagram or circular plot, the question is: is the beam-width been measured from a polar 90degrees (i.e. 50% each side of the vertical 90degree plot), or is it been taken from the horizon and is it all above the horizon, or is it some of the beam-width below the horizon or below 0degrees). A beam-width figure by its self for a verticly polarized omni-directional antenna means nothing – you need to know where the beam-width angle starts before you can work out whether or not its’ going to give you the coverage you want.

The 2nd point to keep in mind regards beam-width as it’s usually provided by an antenna manufacturer, is that they tend to provide it for a specific frequency which is usually the resonant frequency of the antenna. Use the antenna at any other frequency for transmission or reception and that beam-width will change both in terms of uniformity as well as angle – it will also start to break up and “spike”, exactly as is illustrated in the diagrams attached to my earlier note. So, by all means take note of any info given in the sales bumpf attached to an antenna you are considering, but make sure that you understand the conditions for which that beam-width is given. It may turn out to be ideal, it may also turn out to be exactly the information you need to determine the antenna is not the best choice.


You often find that antennas with a resonant frequency of say somewhere around 700Mhz – 750Mhz, or, at the other extreme, somewhere around 900Mhz – 950Mhz just happen to demonstrate a broken up E-plane pattern with strong spike at 860Mhz at just the angle you want when you study their radiation patterns for frequencies other than their resonant frequency. If this was a 860Mhz resonant antenna to start with, the chances are that you wouldn’t be finding any spikes in or around 860Mhz, but rather a solid beam-width, if not totaly circular on the E-plane and which varied no more than 3dB (the industry standard). But in any event, so long as that beam-width (what ever it is) is high enough above the horizon or low enough below the Polar angle of 90degrees to cover the angle you want to have covered, then fine, go for it if you wish.

In summary Steve, what I been trying to share with you is the possibility of using an antenna that perhaps is not resonant for 860Mhz and does not offer a solid 3dB beam-width at 860Mhz but rather, an antenna resonant for some other frequency but which demonstrates a gain spike at 860Mhz on the ideal angle you want coverage for, and which is stronger/longer than any surrounding beam-width coverage illustrated on graph. If you can find an antenna which fits this criteria then you could potentially achieve antenna performance not far off that which would be achieved using a low/medium Gain directional antenna. This improvement in performance would come about not only by way of increased signal strength fed to the receiver/scanner front-end, but also by way of the huge improvement you would realize in improved SNR.

….. which leads me on to Preamps and filters – in my humble opinion a band-pass filter in your situation is almost certainly going to be a big plus. You not only want to maximize received signal strength, but you also want to reduce out of band noise as much as possible. My experience now-a-days is that scanners and receivers tend to have plenty sensitivity (that’s easily and cheaply built into a scanner or receiver), but they are poor when it comes to selectivity, because decent filtrs take up volume/space and they are expensive to construct and include in consumer type off-the-shelf scanners/receivers. Improving the signal to noise ratio (SNR) of the signal you feed your scanner/receivers’ front-end with, with a band-pass filter, almost always results in cleaner and clearer demodulated audio than you would otherwise experience by way of increasing signal strength with a preamp. A 3dB improvement in SNR will equal a 6dB or even 9dB increase in signal strength – if not more in many cases.

By all means use a preamp – but not before the band-pass filter. Always reduce noise levels before you boost the signal strength, because pre-amps do not only boost signal strength, they also boost noise level! So, stop the noise at the antenna – before it gets to the receive front-end and saturates the IF stages and increases inter-modulation – and the best way to do this is with an antenna pole mounted cavity type band-pass filter with around 4 or 5 poles inside. A Chebyshev type filter will give you a good balance between filter shape, roll off and ripple if you can restrict the band-width to not much more than around 10Mhz – maybe 15Mhz, but beyond that and I would think ripple is going to start to be a problem as well as roll-off.

Right …… nuff’ said – time for a cup of coffee.

Is it any clearer now – hope it helps.

 

[benbenrf]

From the Grove website: "For example, at low band (30-50 MHz) it's essentially omni-directional with virtually no favored direction, but as you increase in frequency, it becomes sharper and sharper (more and more gain). At high band VHF, I'd say that it's probably at least 45 degrees wide for decent reception, while at 800 MHz, the reception drops off conspicuously after about 10-20 degrees."

I'm still confused about what my target verticle bandwidth should be. Should I avoid the area near the horizon since the mountains near me are 15 to 20 degrees above the horizon (and thus avoid stray reflected signals) or is the area between 0 and 20 degrees what I want to target because that's where most of my signals will come from? The quote above says that 800 MHz reception drops off after 10-20 degrees.

Steve

Should you avoid the area near the horizon - you mean that angle which lies at roughly 0 degrees to your antenna location (i.e. on the same plane), or that does horizon mean here that area up near the peaks of the surrounding geographical features/hills/tops of canyon cliffs etc etc ....?

Yes - if measured as been on the same horizontal as your antenna, but no if you mean the tops of the surrounding geographical area.

The area low down contained in the valley is where you will be picking up a lot of reflected signals. these will arrive at your antenna out of phase (at different times to each other) and then present your receiver front-end with increased noise levels & inter-modulation levels to have deal with - so, reduce coverage of these low angles in as much as it is practical to do so

Don't worry too much about the drop off in signal strength at 800Mhz for the Grove antenna - that is not important here, what is important here is, as I explained in the post above: what angle does this 10-20degree beam-width lie at? Is it 10-20degrees off the vertical or above the horizon, that is what is important. That said I am afraid in either case although 10-20degrees is nice and tight and would do great if it could be measured off the top of the surrounding geographical features, this is not likely to be the case - it's going to be too low or too high I suspect as I suspect the Grove antenna beam-width at any frequency is measured off the horizontal i.e. level with the antenna. Check this, I may just be wrong - better still, ask Grove if they can provide you with an antenna radiation pattern for the antenna chosen at 860Mhz. It may well turn out to have a nice strong spike at just the angle you want.

Regards the drop off in sensitivity any antenna experiences as you move away from its' resonant frequency - this too is not a problem in many cases as signal strength can often be boosted with a preamp so long as the noise levels can be restrained - hence the importance of using good filtering when you use a preamp. I discussed this in detail in my post above.

Try to get a grasp of what I, and others have shared with you, but ultimately keep this in mind: there is seldom a perfect antenna for any given application unless one sets out to design an antenna specifically for the application. More often than not it comes down to having to comprimise - and I suspect that this is exactly what is going to have to happen in your case. Still, you should have no prob's in achieving pretty decent to pretty good reception - I've dealt with far more tricky antenna situations in my professional days!

 

[rbm]

I didn't see where cost was your limiting factor, so here's what I've done........

I have several 800-928 MHz antennas.
I've been using them for at least 15 years and they've held up well.

They're all Antenex 6db gain models. (FG8066, FG8966, FG9026)
Pick the one that most closely matches your frequencies of interest from the links.

Here's a link to one vendor.
(You'll also need the FM2 mounting hardware which is around $25)
FG8066 Antenex Laird 806-866MHz Fiberglass Omnidirectional Antenna 6 dbd Gain

On each of mine I have a Downeast Microwave 915LNAHC low nf preamp (tuned to my freqs of interest) mounted RIGHT at the base of the antenna and a second one inside at the end of the coax.
(I called and talked with them so I could get them tuned to the specific ranges I wanted)
http://www.downeastmicrowave.com/PDF/915lna.PDF

If there's ANY RF at all in those ranges I can hear it.

Rich

Specs for the various models are here:
http://lairdtech.thomasnet.com/view...ntennas?pagesize=100&sortid=&sortorder=ascrl]

 

[sstephenson]

Thanks all for your help. I genuinely appreciate it. Being new to the hobby and a biologist by trade, radio theory and practice are not my strong point (understatement). I like to pick up as much as I can though!

Benbenrf, thanks again for putting all the theory in terms that I can mostly understand :^)
Very helpful.

Rich, thanks for the info on your setup. I've taken a look at the Laird website, and I think I'm ready to try and pick an antenna. I noted that the 806-866MHz antennas are all centered at 813.5MHz. Based on the suggestions here, I'm guessing that's fine for use in my application. The San Diego City and County systems are in the 857-869MHz range. So you use twp pre-amps? What does that do to S/N ratio? One indoors and one outdoors? Can you buy them pre-tuned? Will I also need a band pass filter?

The 6d Gain model has a 17 deg vertical beamwith. The 3dB gain model has a 33 deg vertical bandwidth. The 0 dB gain model has a 75 deg vertical beamwidth. I'm thinking that in order to pick up more than reflections from the mountains that I should go with the 3dB or 0dB gain model?

Any comments/suggestions appreciated.

 

[rbm]

Steve,
If you have no very strong rf sources nearby, I would install something like the FG8066 antenna with just the pre-amp at the antenna.
(Maybe an FG8966 antenna if you have a need for the frequencies over 900 MHz)
It's easy enough later to add a second pre-amp inside if you choose to.

You can call Downeast Microwave and talk to them about the coverage you require.
That's what I did and the amplifiers were tuned to my specific frequency range.
They were very willing to help with my requests.

A band pass filter shouldn't be required.

With my setup and two pre-amps, the signals are either full quieting, or not there at all.

The pre-amps I use have a noise figure around 0.7 dB.
The gain spec is around 16 dB but mine are a little less because they're tuned wider. (Around 12 dB gain.)

As for supplying power to pre-amps at the antenna, you can refer to my old post here:
http://forums.radioreference.com/sc...wering-versus-remote-powering.html#post860180

Rich

By the way, the amplifier to the left in the photo is a Mini-Circuits ZQL-1900MLN and would work very well over a wide frequency range also. (From around 400 MHz through 2 GHz)
Here's a photo showing the frequency response of the one in that photo.

They were $265 or so new but I've seen them on ebay for a lot less.

Update: I just checked ebay and there's a ZQL-1900MLNW available for $59.99 right now plus $7 S&H!
Not a bad price at all! (Around 1.6 dB noise figure and 23 dB gain)
If I didn't already have four of them, I'd buy it myself!

 

[sstephenson]

Hi Rich,

If I were to purchase this eBay pre-amp, would it have to be "re-tuned" or is it good to go?

P.S. - Ahhh.... I see now. I would need one in the 800-900MHz range.

 

[rbm]

Hi Rich,

If I were to purchase this eBay pre-amp, would it have to be "re-tuned" or is it good to go?

P.S. - Ahhh.... I see now. I would need one in the 800-900MHz range.

The screen capture of my amplifier above has NOT been retuned.
The amplifier response is as shown.

It works well from around 400 MHz to around 2 GHz as is.

The only requirements are a 12volt dc supply and two coax adapters from SMA to the connectors you use.

Rich

 

[sstephenson]

Excellent. I just bought it. Thanks very much.

Now my next question. I see that there's a 3dB gain 824-896 MHz antenna centered at 835 MHz (my target range is 857-868MHz) available at a very reasonable price. It has a 40 degree vertical beamwidth. Is this good, or am I better off holding out for one with a narrower vertical beamwidth and higher gain. My terrain is very hilly with peaks up to 15 to 20 degrees above the horizon in some directions.

 

[rbm]

I should state two obvious details.

If there is no RF at all, no antenna and no amplifier will help in the least.

If there is a strong nearby signal, you could wind up with overload. (Though that can be corrected to 'some' extent with attenuation.)

Rich

 

[rbm]

Excellent. I just bought it. Thanks very much.
.

Good move. You saved me some money.
If it was still there tomorrow, I was gonna buy it!
I don't need it but it was just too good to pass up.

About the antenna, there's no telling where the rf would be coming from after it bounces around the hills.
In a situation like that, I buy what I like and give it a try. I've rarely been disappointed.

Rich

 

[sstephenson]

Thanks Rich.