Cell Signal Boosters

[k0ua]

I understood it while reading it but could not explain it to anyone. Here is my math-idiot practical understanding: our cell phone reception is measured in negative dB. A great signal would be around -60 dB. No signal would be around -115. But, because it is logarithmic, an improvement from, say, -100 dB to -75 dB is a much greater improvement that 25%. Also, the longer the coax I use to set up my signal booster the greater the dB loss will be.

Oh, and I have booked a room at the Holiday Inn for tonight.

Yes, the longer the coax the more loss, BUT it possibly could be offset by getting your directional antenna up higher to capture more signal. As an example lets say that RG6 cable has a loss of 14db per hundred foot at 1.9ghz (calculator here)

That is a pretty significant loss, and lets say you are now using 50 foot so a 7db loss. But you decide to stick you antenna up another 50 foot higher in the air to get over a ridge blocking the signal. Although you lose another 7db in signal, perhaps the extra height go you over the ridge into line of sight with the tower and could easily gain another 30 db in signal by clearing the ridge. These are all just hypothetical scenarios of course. But it could work out that way.

 

[k0ua]

To get a feel for how significant the loss of 100 foot of RG6 coax is at 1.9ghz (1900 Mhz) is lets look at what would happen if we put 100 watts in one end of the coax, we could expect to see less than 4 watts come out the other end. The other 96 watts would be lost in the form of heat inside the coax length. From this we can conclude that RG6 is a poor choice of coax for this frequency if a length of 100 feet is needed.

 

[k0ua]

To get a feel for how significant the loss of 100 foot of RG6 coax is at 1.9ghz (1900 Mhz) is lets look at what would happen if we put 100 watts in one end of the coax, we could expect to see less than 4 watts come out the other end. The other 96 watts would be lost in the form of heat inside the coax length. From this we can conclude that RG6 is a poor choice of coax for this frequency if a length of 100 feet is needed.

Now lets look at this exact same scenario of of 100 foot of RG6 coax but instead of 1.9Ghz lets look at a much lower frequency of 1.9Mhz. Just above the AM broadcast band in the middle of what we call the 160 meter amateur band. Now our loss per hundred foot is about .3db per hundred at this frequency, and if we pumped in 100 watts into one end we could expect to get about 92 watts out the far end at this frequency. A much better scenario than the one above.

 

[k0ua]

I understood it while reading it but could not explain it to anyone. Here is my math-idiot practical understanding: our cell phone reception is measured in negative dB. A great signal would be around -60 dB. No signal would be around -115. But, because it is logarithmic, an improvement from, say, -100 dB to -75 dB is a much greater improvement that 25%. Also, the longer the coax I use to set up my signal booster the greater the dB loss will be.

Oh, and I have booked a room at the Holiday Inn for tonight.

You seem to have a pretty good understanding of the concepts at this point. You are well on your way to becoming an RF systems engineer, just a couple more weeks at the Holiday Inn and you can call yourself "expert".

 

[k0ua]

You seem to have a pretty good understanding of the concepts at this point. You are well on your way to becoming an RF systems engineer, just a couple more weeks at the Holiday Inn and you can call yourself "expert".

We can get into SWR (Standing Wave Ratios), conjugate matching and additional losses from mismatches at a later time.

 

[aczlan]

So, what would be a better cable than RG6?
I hear some of the local hams talking on the repeater for hours about SWR, Baluns, etc. I get about 20%, but the rest goes right over my head.

Aaron Z

 

[RedNeckGeek]

k0ua, thanks for the in depth explanation. I think I got it, as logs aren't exactly news to me, and they way you presented it makes sense. The examples are especially helpful. Now I feel like I'm ready to go back to the Wilson guys with a few measurements of the ambient levels of signal strength available here and get some straight answers on whether or not one of their antenna systems would help pull in the new 4G network. Fingers crossed.

Oh, and I have booked a room at the Holiday Inn for tonight.

I'm afraid that won't help much: It has to be a room at a Holiday Inn EXPRESS! :laughing:

 

[k0ua]

So, what would be a better cable than RG6?
I hear some of the local hams talking on the repeater for hours about SWR, Baluns, etc. I get about 20%, but the rest goes right over my head.

Aaron Z

Almost any cable that is larger will have less loss than RG6. BUT that said some other things have to be taken into consideration. For example RG11 which is also a 75 ohm coax like RG6 will have to have different connectors to accommodate its increased physical size. and if you need to terminate it with an F type connector you will need an adaptor. As coax cable becomes larger, it's cost increase also, as well as its rigidity and its ease of working will go down. Also you must consider what is going to go onto the ends of the coax and the impedances that this equipment is manufactured to work with. For example RG6 is a 75 ohm coax, which means that the equipment is manufactured to "look" into a 75 ohm impedance as well as the antennas are made to match the 75 ohm characteristic impedance of the coax. Remember this discussion I alluded to a couple of posts back about SWR and mismatches? Do you wish for me to go there?

 

[k0ua]

As a tidbit of information: You mentioned the word "balun" This is a contraction that stands for the term "balanced to unbalanced"

As an example coax is a type of "unbalanced" line and 300 ohm Television twinlead is a type of balanced line. If we us a "balun" we can effeciantly transfer power from a balanced to unbalanced transmission line. Also in typical TV transmission line systems we use a 75 ohm coax line RG6 or RG11, or the balanced 300 ohm twinlead. But baluns can also have an impedance transformative function in this case a 4 to 1 impedance transformation of the 75 ohm to the 300 ohms. So the typical little twinlead to coax balun you have seen for years does two things at once, transforms the mismatch in impedances and also matches balanced line to unbalanced coax.

 

[k0ua]

k0ua, thanks for the in depth explanation. I think I got it, as logs aren't exactly news to me, and they way you presented it makes sense. The examples are especially helpful. Now I feel like I'm ready to go back to the Wilson guys with a few measurements of the ambient levels of signal strength available here and get some straight answers on whether or not one of their antenna systems would help pull in the new 4G network. Fingers crossed.



I'm afraid that won't help much: It has to be a room at a Holiday Inn EXPRESS! :laughing:

I am glad to have helped a bit.