Why "More Power" Isn't The Answer

[marcspaz]

I have seen a few posts talking about getting more distance out of UHF gear, such as the GMRS equipment we use. It looks like the common theme is, many immediately want to go for more power, assuming they can brute-force their way through issues. I am hoping myself and some of the other people who have some training and practical experience can use this thread to help new users understand how to make life better without more power.

 

I want to start with handheld transceivers. HT antennas use your body as a counterpoise. Depending on how you are dressed, how tall you are, how you are holding the radio, the radio position, the distance of the radio from your body, what direction you are facing, all impact performance. Even how much fat, salt and water your body is retaining at the moment impacts how an HT antenna works, because those things vary the conductivity of the human body. In all seriousness, forget about more power... or even more range from a typical HT.

 

If you want more range out of your HT, your best bet is to find higher ground, figure out where the best place to stand is, and what general direction to be facing when compared to the receiving station provides the best communications path.

 

 

Mobile antennas are often several wavelengths+ in overall height and the body of the vehicle is typically a much better reflective counterpoise. There is a lot that can be done in the mobile and base antenna world that can help, but for now, lets continue to focus on why 'more power' likely isn't the right answer.

 

 

 

There is a standard in radio communications about intelligibility of radio communications. It is called the 5/9 scale. 0 to 5 for voice clarity and 0 to 9+ for signal strength in s-units. It is said that while a 2/1 signal provides partially usable comms, the lowest "reliable" communications happens at a 3/2 (or 32) and the best is a 5/9+ (often called 599, 59+20, 59+40).

 

With that in mind, you have to quadruple your power to impact a receiver 1 s-unit. So, if the other party is receiving a signal at 1/2 s-unit while you are using 4 watts, you need 16 watts to go to 1 s-unit. You then need to jump to 64 watts for 2 s-units. Finally a third jump in power of 256 watts to get to 3 s-units and possibly getting a reliable communications signal (a 2/3 or 3/3). Depending on the modulation of the carrier signal and bandwidth, you may need to jump to 4 s-units, requiring well over 1,000 watts.

 

Now, lets say the same receive condition exists, but now you are already using 20 watts for that 1/2 s-unit. Now your power jumps are 80 watts, 320 watts, 1,280 watts for 3 s-units and possibly needing 5,120 watts for 4 s-units. Well, the first bump you made already seriously violates power restrictions in GMRS.

 

AND, this is under hypothetical perfect conditions, assuming nothing else changed in the environment. Which almost never exists.

 

Chasing better performance by boosting power typically doesn't give you any truly desirable results. The top 3 items that will help improve comms in almost every band is elevation, elevation, and elevation. From there its antenna tuning (and beams) filters to reduce interference and lowering the noise floor, as some examples.

 

 

 

So, for our technically skill folks... Would anyone like to contribute some general advice for new users to benefit from?

 

General advice on what to do or not to do?

[WRAF213]

Absolutely, finding higher ground should be the first step towards improving a setup. Running more power only matters on fixed setups where the antenna is already as good as it can get, or on mobile operation where there is no 'finding a good spot'. Even then, there's not a huge difference between 15 and 40 watts.

 

Here's my first piece of advice for new users (and I have a bunch, fair warning): use scan mode on a radio that will tell you the active CTCSS tone or DCS code if you're looking for repeaters to use. RTL-SDR is also a good tool, and makes the entire 462 MHz band visible with good sensitivity and excellent selectivity.

 

Especially on fixed setups, grounding is important. Noise will get picked up along the coax and travel up to the antenna, where it enters the receiver. The effect is very apparent on SDRs, where the noise floor is directly visible. When grounding a setup, check for ground loops with a multimeter.

 

Learn to recognize the busy-channel indicator on your radio. When the radio detects any activity on the channel, regardless of correct CTCSS/DCS, it'll turn on the busy-channel indicator. It'll help you to know if you have the correct CTCSS/DCS for a particular system. Some repeaters use multiple CTCSS/DCS, so this indicator can be useful on those repeaters to make sure you aren't interfering with a different conversation. On Baofeng's radios, this is the green LED on top of the radio. On Motorola's commercial radios, this is a blinking red or green LED near the antenna; on their FRS/GMRS radios, this is the red LED above the display.

 

Some repeaters transmit CTCSS/DCS back to you, but only while someone is transmitting to it. If you're hitting the repeater but can't hear it come back to you once you finish transmitting, this could be a possible cause. Use the monitor feature on your radio or check the busy-channel indicator to check for the repeater's tail.

 

Don't be afraid to try simplex. If you hear a callsign with variable signal strength, they're probably not going through a repeater. It's rare to find contacts that way, but that's largely because hardly anyone calls for contacts on simplex. 462.5625 (channel 1), transmit and receive CSQ; and 462.6750 (channel 20), transmit CTCSS 141.3 and receive CSQ are good places to try calling CQ.

 

People who use MDC-1200 on their radios don't actually have to hear the data bursts, the radio can detect the burst and mute it. It gets annoying so most people with MDC-1200 radios have their radios like that.

 

This forum sure does love their Kenwood TK-880s and Motorola M1225s. They're great radios, but terrible general-purpose radios. Virtually all commercial radios can only be programmed by computer software, so you have to know ahead of time what you're going to talk to. Speaking of commercial radios, used Motorola HT1000 radios are incredibly durable and inexpensive. They use the same programming

 

Don't waste your money on the BTech GMRS mobiles, the quality control is practically absent. The GMRS-V1 is apparently alright and Part 95 accepted. Use CHIRP for programming; it will save a lot of time and headaches, while allowing for named channels.

 

When buying a used radio online, make sure the frequency range actually includes 462-468 MHz. For handheld radios, make sure that you are getting (or already have) a charger and antenna. The battery is probably shot, so include a replacement in your budgeting. I like to have at least one spare battery, so I can continue using the radio while a battery is charging. Don't transmit on a handheld radio while it's charging.

 

Counterfeit antennas are a thing, especially with Nagoya. Buy from trusted sources, or find a friend with an antenna analyzer or VNA who'd be willing to show you how to see if an antenna is good or trash. Be willing to learn how to use test equipment, or at least be aware of what that test equipment is testing. It'll help greatly in the future when you are faced with new problems.

 

GMRS isn't ham radio, but it's often used pretty similarly to 70cm. Ham radio clubs are still a useful resource where you can make lots of friends with lots of knowledge. If you don't have a ham license, they'll pressure you to get one. A Technician-class license is easy to get, costs much less than your GMRS license, and you may even be able to use the same antenna for 70cm. Different clubs have different focuses, so don't get discouraged if you don't feel a particular club is right for you. Depending on the area, hams may not like GMRS for one reason or another; but recognize the common interest in establishing reliable communications between licensed operators.

 

There's a 30 MHz gap between 70cm and GMRS, so most 70cm antennas with appreciable gain don't work on GMRS (and remember you're usually transmitting at 467 MHz, not 462 MHz). Check your antenna's documentation to see how much bandwidth you have. Most handheld antennas are broadband enough, and most commercial-band antennas actually work better on GMRS.

 

Don't put up a repeater until you know exactly what you're doing. There's enough deaf GMRS repeaters out there. Don't take on the task alone, either. The more support you have, the better (and, for you, cheaper) the repeater can be. Even a low hilltop provides significantly more coverage than a rooftop repeater. Sites cost money, but can cost a heck of a lot less if you get to know some repeater folk and can make a good sales pitch. Don't use LMR-400 for repeaters.

 

Getting above the roofline makes a big difference in suburban areas, particularly when trying to work hilltop sites. For more rural areas, try to get above the treeline if possible. If you're the only one-story house in a block of two-story houses, ouch.

 

Be it ham radio or GMRS, remember that the radio hobby is about communication. This includes, but is not limited to: rag chewing, technical talk, emergency communication, repeater building, proselytizing the wonders of properly configured radios, and being willing to help the confused. A lot of people out there try to assert their dominance over a channel and run around with a better-than-thou mentality, and over the course of your license you'll find at least one of them. They aren't out to improve either service or what each service stands for, so stay away from them. Don't let them change your perception of the radio hobby, either.

 

If you hear confused FRS users on channel 1 that can't get their radios to talk to each other, offer to help. Transmit CTCSS 67.0 and receive CSQ. They'll probably need help configuring CTCSS on their radios. Ask for the model number and look up the manual on Google. Stuff like this happens more often than I'd like to admit, and half the time those people spent a lot of money on those radios. Be a good citizen.

 

Some repeaters will beacon out their callsign. That doesn't mean there's anyone using it. Repeaters aren't supposed to do that, but not everyone has a good repeater controller. It's almost universally agreed upon that such repeater behavior is super annoying.

 

Not all repeaters identify, and that can make it a pain in the rear to figure out who owns the repeater. It's usually private repeaters that don't identify, and some legally don't even have to. It's another fact of life that makes frequency coordination difficult for repeater owners.

 

The FRS channels, especially 1-14, are flooded with business users. They're allowed to be there, and aren't looking for conversation. Let them be. They're close enough together (a few hundred feet, typically) that they won't even notice you're on the same frequency as long as you're on a different CTCSS/DCS code.

 

Not everyone is following the rules. Report egregious violators to the FCC, but don't expect enforcement action. Report criminal activity (eg. terroristic threats, use of radios in a crime) to law enforcement, not the FCC. If you happen to know who the perps are, tell the FCC as well. You probably won't encounter any such activity.

 

If you start getting involved in the commercial radio users crowd, be it on 70cm or GMRS, you'll see a lot of brand loyalty. I'm a Motorola guy, since those are the first commercial radios I got involved with and those radios meet all of my needs. We have a lot of Kenwood folk on here, and boy do they love their TK-880s. Both make rock-solid commercial radios. There's other brands out there, too. Stay away from cheap Chinese radios, those are markedly not rock-solid radios and may not have any type-acceptance whatsoever. It's generally accepted that radios with commercial (Part 90) type acceptance are fine for GMRS (Part 97E) operation, since Part 90 requirements are more stringent in terms of RF performance. While the FCC is yet to make an official exemption, they allude to it frequently in the 2017 rule change discussion.

 

Directional antennas (mostly Yagis or log-periodic antennas at these fequencies) are terrible general purpose antennas, since you need to know the direction towards the stuff you want to talk to. Commercial omnidirectional antennas covering 460-470 MHz at a minimum make the best general-purpose antennas. Browning's BR6157 is a good starter antenna, with some gain and a wide bandwidth. If you spend more than $60 on one before any sales tax, you've overspent.

 

Use FakeSpot when shopping for radios or accessories on Amazon. Don't get ripped off by fake reviews.

 

Monitor channel 1 (again, transmit CTCSS 67.0 and receive CSQ) during disasters. You may save someone's life. Prioritize your safety highest; you're still a victim.

 

Don't be a dillweed on the air that hides from consequences behind a microphone; respect is reciprocal. Not everyone you'll meet understands this.

 

When you got your GMRS license, your whole family just became GMRS licensees as well. Come up with a separate simplex channel for them and them only. It's useful when outdoors, communication between vehicles on road trips, or during disasters. Having a nationwide license to operate a radio without frequency coordination, and with unlicensed operators on FRS, is a beautiful luxury we have on GMRS that you will get nowhere else. Make sure to test your channels ahead of time, and check them regularly if you don't use them often.

 

I mentioned it earlier, but I'll elaborate on it: RTL-SDR is an excellent tool for GMRS. All of the output channels are visible with a spectrum analyzer-type visualization. Interference becomes easy to spot and identify. CTCSS and DCS decoding is straightforward and nearly instant, and works with hardly any signal strength at all. Signal strength readings can be calibrated against an absolute scale (dBm), which allows for comparison between antennas and locations. A fancy setup of them, Kerberos SDR, can do direction finding with real-time map plotting, but requires some technical knowledge. SDR is fairly recent, and there's plenty of user groups online (like Reddit's r/RTLSDR). When shopping for RTL-SDR, don't spend more than $30 for a bare unit, and don't buy anything that doesn't have a 1.0ppm TCXO or better. If the item description doesn't say TCXO, it doesn't have one.  RTL-SDR Blog v3 is a good unit, and the Nooelec NESDR SMArTee performs the same. Throw the RTL-SDR Blog 20dB LNA on there as well, life will be much better. Use a USB 2.0 extension cord with SDRs.

 

Talking on a handheld radio while driving a vehicle is illegal in California under the cell phone laws. Mobiles, with a simple PTT-only hand mic, are fine.

 

Don't get a 16 or 48 channel radio as your first real commercial or commercial-grade radio. Go for something with at least 128 channels and a screen. Get the programming software and cable before you get the radio so you aren't stuck with a paperweight. Don't give money to HamFiles.

 

If you have a lot of long conversations but all you have is your handheld radio, get a mobile radio and a power supply. Use a proper antenna (as discussed earlier) and some low-loss coax (RG-8, LMR-240, or better). PL-259/SO-239, also called the UHF connector, is a terrible connector at UHF. Avoid it wherever possible. Use TNC or N for permanent or semi-permanent connections, and BNC for connections you switch out a lot. Keep your connectors clean and seal any outdoor terminations. Assume each adapter adds 0.5-1dB of loss, so use as few adapters as possible. Get your coax terminated in whatever connector your antenna has; don't leave the adapter outdoors. Mastic tape gums up over time and future you will hate present you. If you use cheap non-outdoors coax like I did, it can get water ingress. SWR will still show a rather normal reading, but the wet insulator will suck up all your RF (easily 99% of it).

 

Good coax is thicker than you think. Take that into consideration.

 

Folk at your local ham radio club, or GMRS club if you live in an area with one, have done enough fixed radio installations to be able to help you with yours. Don't go out alone and do it, but take some notes so you can eventually help others. Honestly, they're not that hard.

 

If you're in a place that gets thunderstorms more than a few times a year, lightning protection is a real concern. Nothing will stop a direct strike, so unplug your equipment during such inclement weather. That's another reason to keep portable radios around.

 

Repeaters almost always use hardline instead of flexible coax. Hardline is expensive and requires special tools. Good feedline is critical on repeaters because you usually have a 40-watt transmitter on the same antennas as a sensitive receiver. Slight non-linear effects, even a rusty fencepost nearby, can cause issues with receiver performance.

 

If you have an opportunity to visit a hilltop repeater site (an opportunity you may get if you're involved with repeater groups), take it. The first trip to one is an experience, and you'll get to see a variety of real-world installations. Hilltop sites are surprisingly dirty; nobody's up there keeping the floors clean. Some sites are cleaner than others. It's often a long drive and fair distance from civilization, so bring a lunch and go to the bathroom before the trip. Some sites require four-wheel drive and an experienced driver to get to. Buy their dinner.

 

Flat areas can get significant coverage from a low-level repeater. Rooftop repeaters actually have decent performance in those environments.

 

Even on rooftop antennas, your simplex range to a five-watt mobile/portable can be as short as two miles. GMRS is heavily influenced by line-of-sight propagation. Building penetration is better than MURS or 2-meters. 

[gman1971]

Wow WRAF213, amazing info, thank you! 

[RCM]

... you have to quadruple your power to impact a receiver 1 s-unit. So, if the other party is receiving a signal at 1/2 s-unit while you are using 4 watts, you need 16 watts to go to 1 s-unit. You then need to jump to 64 watts for 2 s-units. Finally a third jump in power of 256 watts to get to 3 s-units and possibly getting a reliable communications signal (a 2/3 or 23). Depending on the modulation of the carrier signal and bandwidth, you may need to jump to 4 s-units, requiring well over 1,000 watts.

 

Now, lets say the same receive condition exists, but now you are already using 20 watts for that 1/2 s-unit. Now your power jumps are 80 watts, 320 watts, 1,280 watts for 3 s-units and possibly needing 5,120 watts for 4 s-units. Well, the first bump you made already seriously violates power restrictions in GMRS.

I would like to add that it generally takes 2 s-units to hear an appreciable difference in signal strength. So as long as your 1 watt is enough to be heard without dropouts, it will take 16 watts to make any real difference.

If your signal is readable at a 1 watt "low" setting, there is no reason to switch to "high" power as that will only drain your battery faster. The 4 or 5 watt setting only has any relevance in a case where the low setting is strong enough to be heard, but is dropping out.

 

In my experience, there is zero reason to seek out the 40-50 watt "H" version of a particular mobile radio. It really won't do anything noticeably better than the standard 25 watt radio. But it will use more battery power, get hot faster, and find any substandard connections in your wiring faster than the lower power radio. It will also subject you and any bystanders to more RF exposure. And it is more likely to negatively affect the computer and other electronics in your car or home. That's much more prevalent than you might think, too. The manufacturer of your vehicle or home computer couldn't care less about your 2-way radio activities.

[Durake]

Very well written.. Good information.

[mstephens]

Nice writeup(s), Thank you.  Super informative.

I'm new to GMRS. I have been monitoring Public Safety channels alot, but never heard anyone in my area talk on GMRS. I am 4 miles away from our Local Repeater (Cowee Bald, North Carolina). Should be hearing something, but nothing yet.  Learning allot before jumping in on a First GMRS Radio. Looking at some of the ebay Kenwoods.

[JLeikhim]

I am going to throw out some ideas for those who are repeater operators. It is an area I am exploring.

 

By now everybody realizes that a 5 watt portable talking through a 50 watt repeater will have its range limited to the ability of that 5 watt portable to "make" the repeater, lets say 8 miles. If that 5 watt portable is talking through the repeater with another user with a 50 watt mobile some 20 miles further distant, that is an inherent accomplishment of the technology.

 

In the public safety arena, UHF 5 watt portables are the critical users. Users want that portable to work everywhere. Public safety seeks to design systems to 97% reliability within a jurisdiction (town/country/statewide). Reliability is the name of the game. A TIA document TSB-88 describes how such systems are designed and tested.

 

For example, if you wish portable coverage throughout a large city or county, the use of satellite voting receivers has long been the solution. Each of these voting receivers has a reliable footprint where a 5 watt portable can be received.  Lets say that a small city has three satellite receivers at various locations and where the city boundary is reached, the coverage from any single receiver is 97% reliable. However in other areas within the city, the coverage drops to 70% reliable , if the other two receivers in the system overlap those areas and are also 70% reliable or greater, then > 97.3% "Joint Probability" is attained when the voter switches between strongest signals.

 

 

For the typical GMRS repeater operator, constructing such a system would require having antenna towers at various locations and a means to bring the signals back to a voter by phone line or other circuit. The towers alone would be costly to build, rent or maintain.

 

However, the hardware, satellite receivers and Voters are readily available on the surplus market and can be pressed into use in a much different way on one site, preferably a rooftop..

 

All three receivers can be co located on the same tower or rooftop and be used to facilitate multiple receiver diversity reception.  Diversity reception can work with two repeaters, but we will use three in this example.

 

If your repeater had 70% reliability out at 8 miles, you could improve the reliability to 97.3% in theory by adding two more receiver antenna branches.

 

To get maximum return, there is a need for the antennas to each receive uncorrelated signals from that distant portable. In a hilly or urban area that may easily be the case. The antennas will have to be physically separated many wavelengths from each other on the tower or rooftop to yield diversity gain. A caveat is that the additional two receivers will need bandpass / notch filters to filter out the transmitter, just as a duplexer would do for a singe receiver station..

 

I will provide an excel file "Joint probability example" to anyone interested.  I was unable to attach it.

[RCM]

I am going to throw out some ideas for those who are repeater operators. It is an area I am exploring.

 

By now everybody realizes that a 5 watt portable talking through a 50 watt repeater will have its range limited to the ability of that 5 watt portable to "make" the repeater, lets say 8 miles. If that 5 watt portable is talking through the repeater with another user with a 50 watt mobile some 20 miles further distant, that is an inherent accomplishment of the technology.

 

In the public safety arena, UHF 5 watt portables are the critical users. Users want that portable to work everywhere. Public safety seeks to design systems to 97% reliability within a jurisdiction (town/country/statewide). Reliability is the name of the game. A TIA document TSB-88 describes how such systems are designed and tested.

 

For example, if you wish portable coverage throughout a large city or county, the use of satellite voting receivers has long been the solution. Each of these voting receivers has a reliable footprint where a 5 watt portable can be received.  Lets say that a small city has three satellite receivers at various locations and where the city boundary is reached, the coverage from any single receiver is 97% reliable. However in other areas within the city, the coverage drops to 70% reliable , if the other two receivers in the system overlap those areas and are also 70% reliable or greater, then > 97.3% "Joint Probability" is attained when the voter switches between strongest signals.

 

 

For the typical GMRS repeater operator, constructing such a system would require having antenna towers at various locations and a means to bring the signals back to a voter by phone line or other circuit. The towers alone would be costly to build, rent or maintain.

 

However, the hardware, satellite receivers and Voters are readily available on the surplus market and can be pressed into use in a much different way on one site, preferably a rooftop..

 

All three receivers can be co located on the same tower or rooftop and be used to facilitate multiple receiver diversity reception.  Diversity reception can work with two repeaters, but we will use three in this example.

 

If your repeater had 70% reliability out at 8 miles, you could improve the reliability to 97.3% in theory by adding two more receiver antenna branches.

 

To get maximum return, there is a need for the antennas to each receive uncorrelated signals from that distant portable. In a hilly or urban area that may easily be the case. The antennas will have to be physically separated many wavelengths from each other on the tower or rooftop to yield diversity gain. A caveat is that the additional two receivers will need bandpass / notch filters to filter out the transmitter, just as a duplexer would do for a singe receiver station..

 

I will provide an excel file "Joint probability example" to anyone interested.  I was unable to attach it.

When you mentioned rx diversity on a single tower, I immediately pictured Yagis pointed in different directions.

[WRAF213]

If your signal is readable at a 1 watt "low" setting, there is no reason to switch to "high" power as that will only drain your battery faster. The 4 or 5 watt setting only has any relevance in a case where the low setting is strong enough to be heard, but is dropping out.

 

Going from 1 watt to 4-5 watts makes a fairly substantial difference (about 10dB more quieting; I'll test it later) when 1 watt is barely understandable, because the signal gets about 6-8dB stronger. Going from 25 to 40 watts is only a 2dB increase, the same as going from 1 watt to 1.6 watts. There are times when that 2dB advantage makes a difference, but it's so rare that it's not really worth it. FM sees a pretty strong rate of SNR improvement with carrier strength increase when it's close to or just above demodulation threshold, but once the signal reaches a good level of quieting there's almost no improvement that can be made using higher transmitter power.

 

[edit] Here's actual, on-air performance between low and high power near threshold.

[RCM]

Going from 1 watt to 4-5 watts makes a fairly substantial difference (about 10dB more quieting; I'll test it later) when 1 watt is barely understandable, because the signal gets about 6-8dB stronger. Going from 25 to 40 watts is only a 2dB increase, the same as going from 1 watt to 1.6 watts. There are times when that 2dB advantage makes a difference, but it's so rare that it's not really worth it. FM sees a pretty strong rate of SNR improvement with carrier strength increase when it's close to or just above demodulation threshold, but once the signal reaches a good level of quieting there's almost no improvement that can be made using higher transmitter power.

 

[edit] Here's actual, on-air performance between low and high power near threshold.

Near threshold is exactly what I was talking about when I said "low power is strong enough to be heard, but is dropping out." In that case the 6db increase from 1 watt to 4 watts can be enough to make a difference.

[JLeikhim]

When you mentioned rx diversity on a single tower, I immediately pictured Yagis pointed in different directions.

While you could do this. For example a sectorized array of antennas. However, I think the theoretical diversity gain would be better letting all antennas see the subscriber. A lot would depend on the topography being served and where portable and mobiles are expected to travel.

 

As I said, this is an experimental idea that I have. In fact the parts are in my lab right now, looking for an  appropriate site to test from. I might try three corner reflectors approximating 120 degree sectors to compare. One important thing I want to try is a fourth omni antenna in horizontal polarization.

 

I need some funding and a rooftop!

[JLeikhim]

Going from 1 watt to 4-5 watts makes a fairly substantial difference (about 10dB more quieting; I'll test it later) when 1 watt is barely understandable, because the signal gets about 6-8dB stronger. Going from 25 to 40 watts is only a 2dB increase, the same as going from 1 watt to 1.6 watts. There are times when that 2dB advantage makes a difference, but it's so rare that it's not really worth it. FM sees a pretty strong rate of SNR improvement with carrier strength increase when it's close to or just above demodulation threshold, but once the signal reaches a good level of quieting there's almost no improvement that can be made using higher transmitter power.

 

[edit] Here's actual, on-air performance between low and high power near threshold.

Excellent demonstration. FM capture of the noise floor is pretty evident. Also when in multipath, there are significant nulls of signal strength where additional power is beneficial.  TSB-88 parameters used in modeling coverage predictions account for signal strength in estimating coverage at a particular reliability and delivered audio quality thresholds. Viewed on a coverage contour, even small amounts of signal power reduction most definitely affects reliability and signal quality.

[JLeikhim]

OP Marc is correct ultimately that elevation is everything in this game.

[gman1971]

I just made this new thread, trying to explain the whole CCR situation from a receiver standpoint, and why those things aren't that great.

 

https://forums.mygmrs.com/topic/1661-the-definitive-ccr-thread-why-you-wont-really-save-anything/

 

G.

[RCM]

I just made this new thread, trying to explain the whole CCR situation from a receiver standpoint, and why those things aren't that great.

 

https://forums.mygmrs.com/topic/1661-the-definitive-ccr-thread-why-you-wont-really-save-anything/

 

G.

Just on the off chance that we don't notice your thread, huh?

[gman1971]

Absolutely! One can never be too careful

 

Just on the off chance that we don't notice your thread, huh?

[Radioguy7268]

OP Marc is correct ultimately that elevation is everything in this game.

 

Not entirely true.

 

Your transmit coverage will always look better when you model a higher elevation, even at lower power... BUT...   at some point, the repeater is just part of a System, and any repeater system that does not receive as well as it transmits, is mostly a one-way paging transmitter. 

 

If you want the mobile/portable users to talk back in, then having a clear and clean receive frequency matters, and having a well tuned receiver matters. If I stick your receive antenna high in the sky, the good news is that you might hear transmitters 100 miles away. The bad news is, you're going to hear stuff 100 miles away that wasn't part of your system, and if those transmitters interfere with your ability to receive desired transmissions, then you're back to having a deaf System.

[marcspaz]

Not entirely true.

 

Your transmit coverage will always look better when you model a higher elevation, even at lower power... BUT... at some point, the repeater is just part of a System, and any repeater system that does not receive as well as it transmits, is mostly a one-way paging transmitter.

 

If you want the mobile/portable users to talk back in, then having a clear and clean receive frequency matters, and having a well tuned receiver matters. If I stick your receive antenna high in the sky, the good news is that you might hear transmitters 100 miles away. The bad news is, you're going to hear stuff 100 miles away that wasn't part of your system, and if those transmitters interfere with your ability to receive desired transmissions, then you're back to having a deaf System.

While I agree with you... my comments are generalized. People with HT's and mobile radios aren't going to walk/drive around with massive tuning cans and massive narrow resonance antennas for improved noise filtering.

 

Also... a hug majority of complaining and questions I see/hear is "I can't reach a repeater" and "how do I get more range out of my radio?"

 

Most people building repeaters are likely educated and experienced enough that the don't need my advice.

[gman1971]

Yep, I can certainly vouch for that. Since putting a super high gain antenna high up, the analyzer was reading a massive noise threshold.... needed 2 cans (cavities) to bring it down to an "acceptable" level.

 

I think the radio range these days, aside from more TX power, is also limited by receiver being overloaded by RF noise; b/c after finding out the noise threshold at my location I was blown away how high it was... so if you don't have a radio that has a tight front end you won't receive signals from very far...

 

Don't sell yourself short, Marc, you are being helpful to others, and nobody knows everything.... point is that sometimes little tidbits like that are the eureka moment that makes it, even for knowledgeable ppl.

 

G.

[marcspaz]

Yep, I can certainly vouch for that. Since putting a super high gain antenna high up, the analyzer was reading a massive noise threshold.... needed 2 cans (cavities) to bring it down to an "acceptable" level.

 

I think the radio range these days, aside from more TX power, is also limited by receiver being overloaded by RF noise; b/c after finding out the noise threshold at my location I was blown away how high it was... so if you don't have a radio that has a tight front end you won't receive signals from very far...

 

Don't sell yourself short, Marc, you are been helpful to others, and nobody knows everything.... point is that sometimes little tidbits like that are the eureka moment that makes it, even for knowledgeable ppl.

 

G.

 

Thank you for the kudos... much appreciated, my friend.

[RCM]

Yep, I can certainly vouch for that. Since putting a super high gain antenna high up, the analyzer was reading a massive noise threshold.... needed 2 cans (cavities) to bring it down to an "acceptable" level.

 

I think the radio range these days, aside from more TX power, is also limited by receiver being overloaded by RF noise; b/c after finding out the noise threshold at my location I was blown away how high it was... so if you don't have a radio that has a tight front end you won't receive signals from very far...

 

Don't sell yourself short, Marc, you are been helpful to others, and nobody knows everything.... point is that sometimes little tidbits like that are the eureka moment that makes it, even for knowledgeable ppl.

 

G.

Good points, but not everyone lives/works in an area with such a high noise floor.

[WRAF213]

Yep, I can certainly vouch for that. Since putting a super high gain antenna high up, the analyzer was reading a massive noise threshold.... needed 2 cans (cavities) to bring it down to an "acceptable" level.

 

I think the radio range these days, aside from more TX power, is also limited by receiver being overloaded by RF noise; b/c after finding out the noise threshold at my location I was blown away how high it was... so if you don't have a radio that has a tight front end you won't receive signals from very far...

Cavity filters don't actually make noise go away, they just reduce out-of-band interference. You should have no difference on your noise floor power (aside from filter loss) on GMRS after installing properly tuned cavity filters. Are you measuring out-of-band transmitters as being part of your noise floor? Those would be interference sources, not noise, in the grand scheme of things; noise sources would be unintentional radiators or some malfunctioning transmitters. A noise power exceeding -60dBm over 100 kHz bandwidth would be nonsensical, but it's pretty sane to have a -60dBm signal somewhere within a particular 100 kHz bandwidth on a fixed setup.

 

[gman1971]

I used the wrong words, sorry. I usually call noise, wrongly, to anything that doesn't let me hear the signals I need. And Having a giant 1400 foot tall tower 2 miles away from my house, with 8 different TV stations, NOAA radios, police dispatch, and who knows what other fire breathing RFIs coming out of it... the cavities did indeed help with the receiver being swamped with garbage from all over the spectrum. 

 

G.

 

 

Cavity filters don't actually make noise go away, they just reduce out-of-band interference. You should have no difference on your noise floor power (aside from filter loss) on GMRS after installing properly tuned cavity filters. Are you measuring out-of-band transmitters as being part of your noise floor? Those would be interference sources, not noise, in the grand scheme of things; noise sources would be unintentional radiators or some malfunctioning transmitters. A noise power exceeding -60dBm over 100 kHz bandwidth would be nonsensical, but it's pretty sane to have a -60dBm signal somewhere within a particular 100 kHz bandwidth on a fixed setup.

 

[gman1971]

I understand that, and that is good, b/c living in this kind of area sucks for radio comms.

 

G.

 

Good points, but not everyone lives/works in an area with such a high noise floor.

[WRAF213]

Yeah, being within that distance of a broadcaster is the real problem at hand. Based on your symptoms, I'm assuming there's UHF TV broadcast on that tower in the 500 MHz band (which is almost all that's left of UHF TV). TV typically runs tens to hundreds of kilowatts, and any internal or external mixing products of TV broadcast may resemble noise due to the DTV modulation. FM is more easily controlled and the harmonics aren't in-band (fourth harmonic ends at 432.2 MHz), but that still requires strong filtering. To do an actual check of your RF environment and noise floor, you'd need a good spectrum analyzer that stays linear up to at least 10dBm; most quality equipment is rated up to +30dBm.

 

If you've got noise that appears to be in-band but cavity filters improve the situation, you've probably got intermod going on. Band-reject filters near the antenna can help with that. If filtering near the receiver doesn't improve in-band performance to a satisfactory level, PIM may be at play. Right now, intermod and overload effects could mask a generally crap noise floor from unintentional radiators; don't expect to dive in with hundreds of dollars of equipment and hit thermal noise floor (though you'll have to spend a little bit more to avoid PIM and ensure linearity of any active components). A noise power of -125dBm/16 kHz is pretty typical for a quiet area, compared to thermal noise floor at -131dBm/16 kHz. HDMI/DVI are particularly egregious noisemakers on UHF LMR bands, especially with AliExpress-quality cables. LMR-400 would make a mess of your RF environment.

 

Overload effects don't cause CCRs to not be heard, it simply knocks out their ability to hear. Any RDA1846 design will show desense on almost any rooftop antenna anyways; they're meant to be used with unity-gain antennas attached to the unit and work rather well in that scenario. Desense on the stock antenna or equivalent is only encountered in rather exceptional RF environments.

[RCM]

I understand that, and that is good, b/c living in this kind of area sucks for radio comms.

 

G.

Man, I bet it does.