Refracted signal question

[chad_96]

So, I've done some looking around, but can't find an explanation to a question on signals that are refracted.

The question I'm curious about is, Are refracted signals picked up better by raising an antenna, also? or is it going to be pretty much the same outcome with refracted signals without line of sight?

in summary, the valley I live, I'm picking up refracted signals, as there is no way to achieve line of sight without an extremely high mast/tower, that's not possible.

So just curious, would raising an antenna in this type of scenario help get better signal with height, or is the signal basically going to be the same with height as it's refracted signals?

 

[Ubbe]

So just curious, would raising an antenna in this type of scenario help get better signal with height

Probably yes. The closer you are to line of sight the less the signal has to change its angle and will have more signal left to it. If it needs to make a sharp bend then that's less likely to happen when it bounces of tree leafs and other objects.

There are signal level prediction softwares you can use and it shows a higher signal level the higher up you have your antenna behind a hill or mountain that totally blocks line of sight.

/Ubbe

 

[chad_96]

Probably yes. The closer you are to line of sight the less the signal has to change its angle and will have more signal left to it. If it needs to make a sharp bend then that's less likely to happen when it bounces of tree leafs and other objects.

There are signal level prediction softwares you can use and it shows a higher signal level the higher up you have your antenna behind a hill or mountain that totally blocks line of sight.

/Ubbe

Interesting, I didn't know of any other resources or software. I just used This RF Line-of-Sight Tool. Need to be 53' to have line of sight, and getting fair signal at 18' currently, but it's been determined that the mesa in-between me and the site and the small valley I'm situated in, is causing refraction to be how I'm most likely receiving the signal I get.

Was looking for an answer to this as I don't want to buy more 5' mast pieces and all the guying accessories if raising it in the refraction condition most likely wouldn't help unless I was in that 50' range, as that's just impossible.

Anyways, thanks much for the response Ubbe!

 

[lamarrsy]

Depending on the frequency band we’re talking —UHF and higher being easier to refract— you may not need to raise the antenna, maybe a better aiming toward the refracting surface would give even better results.
I’ve seen situations where in the broadcast we were to get an UHF temporary studio feed to the studio, with no direct line of sight and the best result was attained by pointing the UHF yagi toward an almost vertical (rock) mountain side to reflect the signal.
Same thing later with cell phone signal out in the boonies : the guy was trying to use a signal booster (which boosted noise also), but eliminating the booster, replacing it with a small yagi and pointing the cell yagi toward a cliffside nearly 90 degrees off, got almost full scale signal.

So, depending on a few factors, you may get better results with directing a signal to bounce off hard surface than raising an antenna.

 

[prcguy]

In So Cal there was a GMRS repeater in the flat lands of Los Angeles area with its antenna on about a 2 story building. A friend and I had several GMRS repeaters on mountain tops surrounding Los Angeles with one at about 1,000ft altitude and several at the 5,000ft altitude on the same frequency. When traveling outside the "LA Basin" area we could hear the flatlands repeater out in the So Cal Desert and on the other side of the mountain ranges that surround Los Angeles where our mountain top repeaters would not reach. And that flatland repeater with a business on it would never shut up.

So signal refraction can depend on many things, some which may not be completely predicable.

 

[chad_96]

Depending on the frequency band we’re talking —UHF and higher being easier to refract— you may not need to raise the antenna, maybe a better aiming toward the refracting surface would give even better results.
I’ve seen situations where in the broadcast we were to get an UHF temporary studio feed to the studio, with no direct line of sight and the best result was attained by pointing the UHF yagi toward an almost vertical (rock) mountain side to reflect the signal.
Same thing later with cell phone signal out in the boonies : the guy was trying to use a signal booster (which boosted noise also), but eliminating the booster, replacing it with a small yagi and pointing the cell yagi toward a cliffside nearly 90 degrees off, got almost full scale signal.

So, depending on a few factors, you may get better results with directing a signal to bounce off hard surface than raising an antenna.

I am strictly monitoring 800mhz signals in my rural area. Not sure of anything that hasn't moved to the 800mhz band. Very limited.

I was told I should consider This Yagi linked here, as it would be great for pointing towards the site, high gain, and specifically cleaning up 800mhz signal as the description reads for it.

Problem is a Yagi won't work for me. I have 2 sites monitored. One east and in line of sight and clear, and one to the west/southwest, behind a mesa.

So, kinda in a dilemma on what to do next, and considered buying more 5 foot mast sections. Currently at 18' and get fair signal from the high possibility I'm getting signal from refraction. But I don't want to throw money at it if it's deemed to fail or impossible to get any better signal unless I'm at that 53' line of sight, that's impossible for me to get near or even at.

As far as what it's bouncing off of, I couldn't even begin to guess. But I do have to use the attenuator on the SDS200 to get best signal without garbled audio. But signal is obviously changing frequently which is causing garble, filters being changed, attenuator off to on and so on..

Kind of a very technical deal for me to even begin to figure out or what step to take in getting better quality signal.

 

[pb_lonny]

Do you have to listen to both sites? You might be better focusing on the one that is the most important...

 

[chad_96]

In So Cal there was a GMRS repeater in the flat lands of Los Angeles area with its antenna on about a 2 story building. A friend and I had several GMRS repeaters on mountain tops surrounding Los Angeles with one at about 1,000ft altitude and several at the 5,000ft altitude on the same frequency. When traveling outside the "LA Basin" area we could hear the flatlands repeater out in the So Cal Desert and on the other side of the mountain ranges that surround Los Angeles where our mountain top repeaters would not reach. And that flatland repeater with a business on it would never shut up.

So signal refraction can depend on many things, some which may not be completely predicable.

Yeah I am definitely learning this.

My area is just odd with a mesa in the middle of flatlands and the little valley crevice I'm in. The refraction definitely works in my favor it seems, as I have to use the attenuator most time to get best quality signal that I am getting. But, what to do as far as trying to receive the signal quality better is a true toss-up, without just throwing money at it to buy more mast sections. Line of sight is 53' and I will never be able to get or near that anytime in my lifetime.

Then again, with the refraction, i don't know if getting higher up will be certain either. Just a true toss up I suppose is where I'm at currently, with no next step to try and better the quality.

 

[chad_96]

Do you have to listen to both sites? You might be better focusing on the one that is the most important...

I don't think both sites are truly needed. However the site that carries the bulk of all my monitoring is the problem site I speak of.

 

[Ubbe]

Problem is a Yagi won't work for me. I have 2 sites monitored. One east and in line of sight and clear, and one to the west/southwest, behind a mesa.

But I do have to use the attenuator on the SDS200 to get best signal without garbled audio. But signal is obviously changing frequently which is causing garble, filters being changed, attenuator off to on and so on..

A Yagi antenna are not totally deaf in other directions, it has side lobs, so if that other site are much stronger then it will probably be picked up anyhow. Some Yagis from Amazon are great and if you have a portable scanner you can go up on your roof and hold the antenna in your hand and see what kind of signal improvement you can get compared to the scanners own antenna. If it doesn't seem to improve anything then simply return the antenna. I would first lock a scanner to analog mode and listen to the data signal, how clean it sounds and also look at its signal strength.

I live in a valley and have no transmitter sites in line of sight and have to use the most gain I can get from a Yagi pointing at a ridge. There are some reflections from houses when I point the antenna at other directions but not as much signal as from the ridge. Holding the antenna in your hand you can easily try different directions and instantly see the result on a portable scanner. If it seems to work then you can install that antenna on the mast.

Having to use the attenuator to get a clean signal doesn't sound good as it has a nominal attenuation of 22dB that are more than 100 times. It doesn't seem to be lack of signal strength that are the issue then but instead some sort of interference? Also try to enable IFX on the frequency, it's done to one single frequency so will have to be done to all voice channels in a trunked system, or actually only the ones that have issues.

When using only reflected signals to monitor will have that phenomena that the signal strength varies a lot depending of the weather situation and how the wind blows if the signal has to go thru trees. Using a SDS scanner for weak signal monitoring are not suitable as it has a lot of RF issues and other signals many MHz away will have an impact on reception. If this is not a simulcast system then try another digital scanner as you then don't need to handle different filters and interferences as it will have a more solid receiver performance.

/Ubbe

 

[WA0CBW]

As "Ubbe" said using the attenuator to get better signals wouldn't be a "weak" signal problem. That sounds like you have too much signal. Using a Yagi may actually make it worse.
Bill

 

[wtp]

how far away are the transmitters ?
at some point the answer is "i can't get that one all the time".

 

[chad_96]

A Yagi antenna are not totally deaf in other directions, it has side lobs, so if that other site are much stronger then it will probably be picked up anyhow. Some Yagis from Amazon are great and if you have a portable scanner you can go up on your roof and hold the antenna in your hand and see what kind of signal improvement you can get compared to the scanners own antenna. If it doesn't seem to improve anything then simply return the antenna. I would first lock a scanner to analog mode and listen to the data signal, how clean it sounds and also look at its signal strength.

I live in a valley and have no transmitter sites in line of sight and have to use the most gain I can get from a Yagi pointing at a ridge. There are some reflections from houses when I point the antenna at other directions but not as much signal as from the ridge. Holding the antenna in your hand you can easily try different directions and instantly see the result on a portable scanner. If it seems to work then you can install that antenna on the mast.

Having to use the attenuator to get a clean signal doesn't sound good as it has a nominal attenuation of 22dB that are more than 100 times. It doesn't seem to be lack of signal strength that are the issue then but instead some sort of interference? Also try to enable IFX on the frequency, it's done to one single frequency so will have to be done to all voice channels in a trunked system, or actually only the ones that have issues.

When using only reflected signals to monitor will have that phenomena that the signal strength varies a lot depending of the weather situation and how the wind blows if the signal has to go thru trees. Using a SDS scanner for weak signal monitoring are not suitable as it has a lot of RF issues and other signals many MHz away will have an impact on reception. If this is not a simulcast system then try another digital scanner as you then don't need to handle different filters and interferences as it will have a more solid receiver performance.

/Ubbe

Thanks for the information Ubbe! That clarifies what I had read somewhere, but couldn't relocate the thread, about a possibility of a Yagi still hearing the other site (my local site) if I had it pointed the opposite direction, and the signal was strong enough to still be picked up.

Those are great ideas to try some testing. I do have a sds100, that I have a remtronix 820S antenna on, and ultimately have the filters set, and have no issues, like I'm having on the outdoor antenna, which is a dpdproductions 800 mhz vertical omnidirectional antenna. So, very strange that my indoor sds100 that's in what I would consider the worst location of the house hanging on a wall mounted clip doesn't have issues.

1 thing I've considered, and the only thing I can even possibly think is that I have the incoming powerline close to my outdoor antenna. It's probably 7-9 feet away. However, ive been told that powerlines wouldn't cause any interference. Problem is, I've never seen anything that factually says it won't. Another issue, the powerline is "in-line or level" with the antenna on height currently. So I am curious if raising it higher would get it above the powerlines height and do any better..? Not sure.

Other than that, I'm on the plains of Colorado. Really just flatland other than this valley I'm in and the mesa that's around 2 tenths of a mile behind my home and in-between the site and I. No trees in the way or even around really other than 1 in my yard, and farmground.

It's just way beyond me that my SDS100 with the remtronix is having no issue or problem indoors in a weird area, and a huge vertical antenna outdoors also tuned to the 800 mhz band is having the issues. I don't really want to do a yagi unless I absolutely have to due to pointing it at 1 site and not my local site, but thr other site has more of my listening as the range of it is way further than the database reflects. And it carries all but 2 talkgroups, which I would like to keep monitoring. So basically I'm stuck on what exactly the next step should be.

I have heard the Uniden BCD536HP is an excellent scanner. That's my goal is to purchase it next, if the reviews are correct. But that will be quite awhile down the road, so the ol' lady don't send me and my scanner packing.

The attenuator having to be on is hot and miss. Somtimes on, sometimes off. But due to the signal quality issue, the filter has to be changed fairly often. I just assumed from what I've read that if the attenuator had to be on, then that would mean signal is great despite needing to be at 53' on line-of-sight. But, nothings ever verified of that's a correct assumption or not. I have tried IFX also, it doesn't help or do anything for me.

Anyways, thanks again for all the advice and information, it helps tremendously!

Edit- for clarification I've been recommended THIS Yagi for my situation. I am strongly considering it.

 

[Ubbe]

It's just way beyond me that my SDS100 with the remtronix is having no issue or problem indoors in a weird area, and a huge vertical antenna outdoors also tuned to the 800 mhz band is having the issues.

As you also have to sometimes use the attenuator indicates that you are interfered by another transmitter that gets too strong for the scanner using an external antenna. Perhaps some nearby cellular tower can be the cause of the overload issue. The guy that came up with the concept for the SDS scanners knew very well that it didn't had the best receiver performance and gave the advice that if you didn't suffer from simulcast issues then you would probably be better off choosing another scanner model.

I don't really want to do a yagi unless I absolutely have to due to pointing it at 1 site and not my local site

Edit- for clarification I've been recommended THIS Yagi for my situation. I am strongly considering it.

A yagi can be a good choice to focus on the signal you want to receive and attenuate signals from other directions that could interfere. That would help a poor receiver to perform better but you would probably need to reduce the signal level from the antenna, using a variable 0-20dB attenuator would be the best thing to use to be able to set the perfect level where you still receive your signal but attenuate everything else as much as possible, the same way you would do when receiving simulcast systems using an ordinary scanner to only receive one single site.

The Antenna Farm has some kind of blocking filter since 2-3 years ago that doesn't allow me to access their web page.

/Ubbe