[Repeater-Builder] Re: Can you hear 3db?
--- In Repeater-Builder@yahoogroups.com, "Chris Peterson" <[EMAIL PROTECTED]> wrote: > > Okay, now say I can find an antenna with exactly the same pattern, but 3DB > less gain. Some would say that nobody would know the difference and they'd > probably be right. However, to get that extra 3DB of gain, you have to > change the antenna's pattern. If this is done right, more of the antennas > gain is directed towards the ground, rather than up in the air where it does > no good. So users will probably notice the difference, because they're > noticing a more than 3DB increase in signal strength due to the antennas > major lobes being directed more to where the users actually are. Chris, just to comment on the above The users will not notice a "more than 3DB increase" in signal strength. Increasing the gain of an antenna by 3db will net a 3db increase in signal level. (Not talking about 4000 ft. mountains here :) ) Did I understand your comment as you intended, Chris? Laryn K8TVZ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Can you hear 3db?
--- In Repeater-Builder@yahoogroups.com, "Jim B." <[EMAIL PROTECTED]> wrote: "... Another thing to think about-the 3 dB power change ISN'T what you're hearing. To really compare apples to apples, you have to measure the sound output (SPL) change that the 3 dB change creates> Jim Barbour WD8CHL (yikes)" ___ Huh You must be stuck thinking SSB / AM Those 3dB are carrier power. What you are listening to is the quality of the demodulated signal at the target receiving unit. It is generally accepted industry practice for path reliability projection, e.g. Motorola Coverage Acceptance Standards, that 4dB C/N is the point at which an FM communications receiver delivers 12 dB SINAD and that 7 dB C/N is the point at which such a receiver delivers 20 dB quieting. Hence, it follows that a 3dB change in transmitter power [or increase in antenna gain OR reduction of path loss] which will result in a corresponding 3 dB improvement of received C/N would be sufficient to: A] take a received signal from 1 dB C/N [unreadable] to 12 dB SINAD. -OR- B] Take a received signal from 12 dB SINAD to 20 dB quieting - a very noticible audible improvement in DAQ [Delivered Audio Quality] - a metric that has been used extensively in radio coverage prediction and verification. Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Can you hear 3db?
--- In Repeater-Builder@yahoogroups.com, bradley glen <[EMAIL PROTECTED]> wrote: "I have noticed a various amoumt of personal perseption with regards to the remarks..." __ __ Personal perception? I'm more of a Joe Friday kind of guy myself. "Just the facts." Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Can you hear 3db?
Second, I see this 3 dB thing bantered about as the > smallest change that can be heard. I think this is > wrong, due to personal experience, and talking to > others. > Joe I agree. 3db is quite easily heard when I switch 3db in and out on my step attenuator. Laryn K8TVZ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Can you hear 3db?
--- In Repeater-Builder@yahoogroups.com, Bob Dengler <[EMAIL PROTECTED]> wrote: "...OK, so does this mean the noise temperature of a NBFM FM receiver can be approximated by measuring the 12 dB SINAD point & then subtracting 4 dB? ..." __ _ Essentially - yes. Given that it is generally accepted that: N=kTB and that N= -174 dBm/Hz [at room temperature] The 'accepted' value for the noise power in your receiver bandwidth will be -133 dBm. If your receiver has a measured 20 dB quieting of 0.35 microvolts [-116 dBm] and a corresponding 0.25 microvolt 12 dB SINAD [-119 dBm] then it follows that it has a Noise Figure NF = 10 dB [-119 minus 4 = -123, -133 minus -123 = 10] Keep this in mind when someone tells you they have a super pre-amp on their repeater receiver and their receiver sensitivity is better than a tenth of a microvolt - they are either using faulty measuring procedures or poorly calibrated instruments because 20 dB quieting would be on the order of 0.11 microvolts if the noise figure was zero. Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Can you hear 3db?
All, I agree. 3db is quite easily heard when I switch 3db in and out on my step attenuator. Laryn K8TVZ Neil J pretty much nailed this one: It is generally accepted industry practice for path reliability projection, e.g. Motorola Coverage Acceptance Standards, that 4dB C/N is the point at which an FM communications receiver delivers 12 dB SINAD and that 7 dB C/N is the point at which such a receiver delivers 20 dB quieting. Hence, it follows that a 3dB change in transmitter power [or increase in antenna gain OR reduction of path loss] which will result in a corresponding 3 dB improvement of received C/N would be sufficient to: A] take a received signal from 1 dB C/N [unreadable] to 12 dB SINAD. -OR- B] Take a received signal from 12 dB SINAD to 20 dB quieting - a very noticeable audible improvement in DAQ [Delivered Audio Quality] - a metric that has been used extensively in radio coverage prediction and verification. And this consideration by Roger is technically why 3 dB makes a big difference: The quieting curve of an FM receiver is very non-linear. 3 db will make a very noticeable difference if the signal is well into the noise, barely any or none at all if it's strong. Roger Grady K9OPO I choose to use 250 watts instead of 110 (roughly 3 dB) on my KQ3M repeater in Hay's Mill PA. I can tell you that 3 dB makes a big difference, in both the coverage and the electric bill. Believe me, if it didn't, I wouldn't pay the extra money each month. I hope this wraps this thread up... Thanks, Kevin Custer Yahoo! Groups Links To visit your group on the web, go to:http://groups.yahoo.com/group/Repeater-Builder/ To unsubscribe from this group, send an email to:[EMAIL PROTECTED] Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
Re: [Repeater-Builder] Re: Can you hear 3db?
Hi All I have noticed a various amoumt of personal perseption with regards to the remarks.Here is mine. Perhaps look at this scenario :When I do my repeater surveys I primarily look at the user requirements. Ant system is designed -for eg: mobile coverage or portable coverage. It has all got to do with "link budget "as a term we use now in GSM in my current job. If the up-link is the same as downlink the transparent coverage is achieved. My one ham repeater is only about 1 Watt into a 0dBm antenna.The reason for this is simple-the path link is sufficient for the Yagi antennas at all the repeaters to make up for any losses. I did some playing around and found that when one puts up a repeater -do your homework and do your installation as best as you can with quality products. If you really want to customise the repeater coverage first use 0 dBd (folded dipole ) in order to guage the coverage and make notes .From there you can then use higher gained antenna and make the notes. Too many people are bulldusted by "high gained antennas that really take coverage away from areas often where improvements are greatly needed. My golden rule with antenna specialising is thus :Energy can not be destroyed , only transferred. Good luck Bradley Glen ZS5WT South Africa Naturn UHF Repeater system --- nj902 <[EMAIL PROTECTED]> wrote: > > > --- In Repeater-Builder@yahoogroups.com, "Jim B." > <[EMAIL PROTECTED]> wrote: > "... Another thing to think about-the 3 dB power > change ISN'T what > you're hearing. To really compare apples to apples, > you have to > measure the sound output (SPL) change that the 3 dB > change creates> > Jim Barbour > WD8CHL > (yikes)" > ___ > > Huh You must be stuck thinking SSB / AM > > Those 3dB are carrier power. What you are listening > to is the > quality of the demodulated signal at the target > receiving unit. > > It is generally accepted industry practice for path > reliability > projection, e.g. Motorola Coverage Acceptance > Standards, that 4dB > C/N is the point at which an FM communications > receiver delivers 12 > dB SINAD and that 7 dB C/N is the point at which > such a receiver > delivers 20 dB quieting. > > Hence, it follows that a 3dB change in transmitter > power [or > increase in antenna gain OR reduction of path loss] > which will > result in a corresponding 3 dB improvement of > received C/N would be > sufficient to: > > A] take a received signal from 1 dB C/N [unreadable] > to 12 dB SINAD. > > -OR- > > B] Take a received signal from 12 dB SINAD to 20 dB > quieting - a > very noticible audible improvement in DAQ [Delivered > Audio Quality] - > a metric that has been used extensively in radio > coverage > prediction and verification. > > > > > > > > > Yahoo! Groups Links > > > [EMAIL PROTECTED] > > > > > > __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Can you hear 3db?
nj902 wrote: > > --- In Repeater-Builder@yahoogroups.com, "Jim B." <[EMAIL PROTECTED]> wrote: > "... Another thing to think about-the 3 dB power change ISN'T what > you're hearing. To really compare apples to apples, you have to > measure the sound output (SPL) change that the 3 dB change creates> > Jim Barbour > WD8CHL > (yikes)" > ___ > > Huh You must be stuck thinking SSB / AM No, I'm talking about noise... -- Jim Barbour WD8CHL Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Can you hear 3db?
Jim B. wrote: > nj902 wrote: > > >>--- In Repeater-Builder@yahoogroups.com, "Jim B." <[EMAIL PROTECTED]> wrote: >>"... Another thing to think about-the 3 dB power change ISN'T what >>you're hearing. To really compare apples to apples, you have to >>measure the sound output (SPL) change that the 3 dB change creates> >>Jim Barbour >>WD8CHL >>(yikes)" >>___ >> >>Huh You must be stuck thinking SSB / AM > > > No, I'm talking about noise... > btw-I was trying to be a bit tongue in cheek... -- Jim Barbour WD8CHL Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Can you hear 3db?
At 2/12/2005 06:34 AM, you wrote: >All, >> >>I agree. 3db is quite easily heard when I switch 3db in and out on my >>step attenuator. >> >>Laryn K8TVZ > >Neil J pretty much nailed this one: > >> >>It is generally accepted industry practice for path reliability >>projection, e.g. Motorola Coverage Acceptance Standards, that 4dB C/N is >>the point at which an FM communications receiver delivers 12 dB SINAD and >>that 7 dB C/N is the point at which such a receiver delivers 20 dB quieting. OK, so does this mean the noise temperature of a NBFM FM receiver can be approximated by measuring the 12 dB SINAD point & then subtracting 4 dB? That would mean that the amount of signal from the sig. gen. is equal to the total noise power at the front-end of the receiver within its pre-detection bandwidth (~16 kHz) at that level (0 dB C/N means C=N). I always thought that the 0 dB C/N level is the point at which a signal would be barely detectable. However, that point is more like 6 dB below the 12 dB SINAD level, at least on the receivers I've tried. >I hope this wraps this thread up... Sorry; at least I've steered it in a different direction. Bob NO6B Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
