Getting 50 watts actually out of repeater

[WRYD530]

So 50 watts is the maximum allowed to transmit on GMRS.  If i setup a repeater with 2 radios  a duplexer and separate antennas for each radio and the best cable i may still lose about 10-20 watts correct? So is there a way to boost the 50 watt radios to actually get the 50 watts out of the transmission?

[OffRoaderX]

not really.. you have to push all the power before the duplexer, and cheaper/smaller duplexers eat a huge %% of the power. So you will either need to push more power into the duplexer (if it can handle it), or get a better duplexer that doesnt eat so many RF electricities.

HOWEVER - the difference between ~20 watts and 50 watts is probably not going to be noticeable.. I have tested my base setup at 40 watts vs 110 watts, and people at the outskirts of my range (around 60 miles) can't even hear a difference between 40 and 110W ..

[Guest]

I agree with randy. you’re not going to notice much change.  Heck I get 200miles from a 20w base station and a good antenna.   The key is the antenna and height and line of site  more then the wattage. 

[WRWE456]

Heck the furthest report I have heard with a hand held GMRS radio was 127 miles. That was hill top to a repeater at 7500 feet line of sight. KG-935G with a Nagoya NA-771G 15"whip. 5.5 watts.

[BoxCar]

10 hours ago, WRYD530 said:

So 50 watts is the maximum allowed to transmit on GMRS.  If i setup a repeater with 2 radios  a duplexer and separate antennas for each radio and the best cable i may still lose about 10-20 watts correct? So is there a way to boost the 50 watt radios to actually get the 50 watts out of the transmission?

You can't boost the output of the radio to overcome losses downstream from the radio. The FCC limited the radio's output to 50 watts so you have to eat the losses.

[SteveShannon]

11 hours ago, WRYD530 said:

So 50 watts is the maximum allowed to transmit on GMRS.  If i setup a repeater with 2 radios  a duplexer and separate antennas for each radio and the best cable i may still lose about 10-20 watts correct? So is there a way to boost the 50 watt radios to actually get the 50 watts out of the transmission?

If you use a separate antenna for each radio you don’t need a duplexer. The reason for the duplexer is to allow you to simultaneously transmit and receive using a single antenna.
Using separate antennas can be done but requires enough separation between the antennas to achieve a level of RF isolation. That’s usually done by separating them vertically.  I’m not recommending that you do that, just explaining that it can be done. It is one way to overcome the losses incurred by using a duplexer.

But everything Randy (@offroaderx) said is correct.  Better quality duplexers result in less loss and chasing those last several watts makes very little difference. As someone else said in a similar thread recently, many repeater owners run their transmitter outputs at reduced output to ensure long life. 

[WRYZ926]

1 hour ago, Sshannon said:

But everything Randy (@offroaderx) said is correct.  Better quality duplexers result in less loss and chasing those last several watts makes very little difference. As someone else said in a similar thread recently, many repeater owners run their transmitter outputs at reduced output to ensure long life. 

That is how our club does it. We are using a Bridgecom repeater and running it at a lower power. We do the same with our 2m and 70cm repeaters. Running a busy repeater constantly at full power will shorten the life of the repeater. 

Another thing to look at is the duty cycle of the radios or repeaters. The higher the duty cycle is the better.

[WSEL330]

Sooo...jumping after reading. I understand that more Watts doesn't necessarily ,equate to more fars. I realize from here that my repeater pushing 24 Watts will work almost as well as 50 Watts. My question is about Watts vs fars and obstacles. Is Watts vs fars linear, geometric, exponential? For example: 5W output on the repeater vs. 24W output more drastic improvement than 24W to 50W. Second part is: does more Watts afford more 'muscle' to propagate through foliage? (understanding that height and antenna is king here. I can not get above canopy but can get to about 70')

[SteveShannon]

2 hours ago, WSEL330 said:

For example: 5W output on the repeater vs. 24W output more drastic improvement than 24W to 50W. Second part is: does more Watts afford more 'muscle' to propagate through foliage?

24 watts compared to 5 watts will get you a slightly better signal at greater distance than the 5 watts. The difference between 24 watts and 50 watts will be less noticeable.

Yes, more power goes through foliage and walls better.

But the real secret to getting farther range is to put a very good antenna up as high as you can.

[Blaise]

1 hour ago, SteveShannon said:

But the real secret to getting farther range is to put a very good antenna up as high as you can.

I climb the tallest tree around before attempting to use my radio...

[marcspaz]

 

Well, lets address these separately.

 

21 hours ago, WSEL330 said:

Is Watts vs fars linear, geometric, exponential? For example: 5W output on the repeater vs. 24W output more drastic improvement than 24W to 50W. 

 

The answer is "none of the above".  It's logarithmic.  Calculating range verses distance in free-space (not accounting for the curve of the Earth nor obstacles) involves a complex formula, based on things like the distance between the antennas, the frequency, the gain of both the transmitting antenna and the receiving antenna, and the attenuation value of the atmosphere.  

If we assume that neither antenna has gain, at 465MHz (about the center of the GMRS frequencies), 1 mile of free space has about 90dB of signal attenuation.  At 10 miles, there is 110dB of attenuation.  At 100 miles, there is 130dB of attenuation.

So, lets say you are transmitting a 1 watt signal to a station 1 mile away.  Your signal will be reduced to 1 nano-watt, or about 224 micro-volts.  This is just a little higher than the 60% mark of receive sensitivity for most retail OTC radios.  That station can receive your signal, but its about 60% audio and 40% static.  It's usable, but a lot of static.  If you want a station 10 miles away you hear you just as well, you need to increase your power to 100 watts.  If you want to have a station 100 miles away be able to receive your signal at the same levels, you would have to increase your power to 10,000 watts.

As you can see, trying to increase your range by increasing your power becomes very impractical.  Most of the time we look at things like using antennas with high gain or increasing receive sensitivity and selectivity.  For example, if you use that same 1 watt with a 14dB gain beam antenna on both ends of the communication path, that would be like increasing your power to 630 watts and both antennas having no gain. 

 

21 hours ago, WSEL330 said:

Second part is: does more Watts afford more 'muscle' to propagate through foliage? 

 

To make life easy for yourself, to figure out how much more power you need, just estimate foliage loss using the 15–20 dB rule of thumb.  Increasing power does help penetrate through trees and buildings.  It does help fill-in hole and dead spots a bit too... but like free-space attenuation... more power has massively diminishing returns.

If you want to "know" actual numbers to calculate the RF power needed to penetrate foliage, you need to determine the signal attenuation caused by the vegetation.  You need to use the frequency, vegetation depth you want to penetrate, the water content in the leaves and trees, and the path geometry. The degree of angle to which the signal gets bent, as the signal passes through the foliage, affects the amount of attenuation.  Vegetation type and density affects signal scattering and absorption, too.

And did I mention this changes seasonally?  And the more dramatic the season changes, the more dramatic the variations will be.

[LeoG]

The legal way to get 50 watts out of the duplexer is to buy an all in one repeater.  The duplexer is internal to the repeater unit and the output on the antenna connection can't be more than 50 watts.  In order to do that you have to put 60-70 watts into the duplexer which is fine as long as the output on the connector isn't above 50 watts.  I'm running such a repeater.

[nokones]

You can go with a high gain antenna. There is no rule on the ERP with the 462 MHz main channels, but that will change your effective radiation pattern.

[WSEL330]

Fascinating stuff! Thank you all! 

Marc: In depth stuff, digging it. It is obvious now but didn't consider seasonality in that way.

Leo: Yeah, I'm loosing on the order of about 20W giving me 24ish Watts out of a repeater outputting 48W. I have the ability to have 2 separate antennas with separation over several wavelengths.

The rest of the crew: I hear ya, A solid, good/great antenna. I am working on that!

[LeoG]

Sounds like a crappy duplexer or it's not tuned correctly.  That' about a 3dB loss when it should be on the order of 1.5dB or less, 1.2dB being typical of a normal mobile 6 cavity duplexer.

[WSEL330]

3 minutes ago, LeoG said:

Sounds like a crappy duplexer or it's not tuned correctly.  That' about a 3dB loss when it should be on the order of 1.5dB or less, 1.2dB being typical of a normal mobile 6 cavity duplexer.

I was thinking that too.....I may update with the make and model when I get home.

[SteveShannon]

12 minutes ago, WSEL330 said:

I was thinking that too.....I may update with the make and model when I get home.

Unless you like spending money with nothing of consequence to show for it, I wouldn’t.  The difference in range between 24 and 48 watts will be nearly zero.  Think of it this way: if your radio has a signal strength meter that displays the strength of your received signal, one S-unit is equivalent to 6 dB.  In other words, to go from S8 to S9, you would have to quadruple your RF output power. 

Second, please tell us how and where you measured your output power and what kind of coax cable you have going to your antenna.  Specifically, have you measured your RF output right where the coax connects to the antenna? A lot of times people unintentionally convert their radio’s output power to heat by using the wrong coax for UHF.  So, how long is your coax and what type is it.

Also, sometimes placing your antenna below the canopy will get you through vegetation better than raising it up into the thick part of the vegetation.  

[marcspaz]

31 minutes ago, LeoG said:

Sounds like a crappy duplexer or it's not tuned correctly.  That' about a 3dB loss when it should be on the order of 1.5dB or less, 1.2dB being typical of a normal mobile 6 cavity duplexer.

 

27 minutes ago, WSEL330 said:

I was thinking that too.....I may update with the make and model when I get home.

 

3 minutes ago, SteveShannon said:

Unless you like spending money with nothing of consequence to show for it, I wouldn’t.  The difference in range between 24 and 48 watts will be nearly zero.  

 

I've been working with @LeoG to optimize his repeater setup by testing and tuning his duplexer.  We dramatically improved notching and the band-pass losses and SWR.  Leo seems happy with the way things are working, but I'm not convinced there is a noticeable improvement in coverage. He has reported improvements in some places and reductions in others.

I will say that improving tuning makes the radio happy.  Less overheating, better duty cycle will translate to longevity for your repeater.  Even if you don't get more usable range, it is still ideal to optimize tuning.

[SteveShannon]

7 minutes ago, marcspaz said:

will say that improving tuning makes the radio happy.  Less overheating, better duty cycle will translate to longevity for your repeater.  Even if you don't get more usable range, it is still ideal to optimize tuning.

I hadn’t considered that aspect.  I absolutely agree with that and if @WSEL330 is experiencing any of those problems a replacement duplexer, correctly tuned to the right frequencies could certainly be worth the investment.

[LeoG]

Yup, anything not getting out of the duplexer is heating the duplexer up.  I suppose same with SWR, but not as dramatic.  As for the tuning Marc had done for me the range didn't really increase that much but the clarity of the signal did.  And the sensitivity of the repeater receiver vs being able to receive the transmitted signal on the HT was affected.  The repeater could hear me but a lot of times I was just barely in range of the repeater.  Whereas before I couldn't even trigger the repeater.  I only moved up to a 100 watt duplexer because the transmitter pushes 71 watts at 13.8 volts and I have to reduce that to maintain below 50 watts after the duplexer.

I've hear that a 50 watt duplexer does well up to about 35 watts in and after that doesn't.  And I can say that a 50 watt duplexer doesn't do well with 65 watts in even though if you look at the specs it says 50-80 watts in.

[WSEL330]

3 hours ago, SteveShannon said:

Unless you like spending money with nothing of consequence to show for it, I wouldn’t.  The difference in range between 24 and 48 watts will be nearly zero.  Think of it this way: if your radio has a signal strength meter that displays the strength of your received signal, one S-unit is equivalent to 6 dB.  In other words, to go from S8 to S9, you would have to quadruple your RF output power. 

Second, please tell us how and where you measured your output power and what kind of coax cable you have going to your antenna.  Specifically, have you measured your RF output right where the coax connects to the antenna? A lot of times people unintentionally convert their radio’s output power to heat by using the wrong coax for UHF.  So, how long is your coax and what type is it.

Also, sometimes placing your antenna below the canopy will get you through vegetation better than raising it up into the thick part of the vegetation.  

I measured output power at the TX of my kenwood TKR 850. I also measured coming out of the duplexer at the antenna plug. I am using RG213 and/or KMR400 (swapping back and forth in testing). The cable length is 100'. My comment for increasing power was not for gaining distance as a know that does work that way. I was more interested in foliage penetration. This tree is above canopy but the lower portion of it's foliage is at the rest of the trees canopy thus wanting to penetrate better. I can not speak to the tune of the duplexer but my SWR meter says 462.702 (the Freq i want). I do not remember the sales facts but I will update later after work but I feel good about the tune for the seller. Audio quality does not appear to be an issue for this novice ear. Antenna is a HYT(T) whatever tuned to that freq. I think it is 3db gain?.

[LeoG]

You mean to avert losses in that cable.  100' is when you start getting into hardline.  Heck, 50, 60 feet is when you start getting into hardline for UHF.

[SteveShannon]

20 minutes ago, WSEL330 said:

I measured output power at the TX of my kenwood TKR 850. I also measured coming out of the duplexer at the antenna plug. I am using RG213 and/or KMR400 (swapping back and forth in testing). The cable length is 100'. My comment for increasing power was not for gaining distance as a know that does work that way. I was more interested in foliage penetration. This tree is above canopy but the lower portion of it's foliage is at the rest of the trees canopy thus wanting to penetrate better. I can not speak to the tune of the duplexer but my SWR meter says 462.702 (the Freq i want). I do not remember the sales facts but I will update later after work but I feel good about the tune for the seller. Audio quality does not appear to be an issue for this novice ear. Antenna is a HYT(T) whatever tuned to that freq. I think it is 3db gain?.

Okay, with 24 watts going into the duplexer end of 100 feet of RG-213 you get roughly 7.44 watts out of the antenna end of the coax.

With LMR400 (I don’t know how KMR400 compares) the output is better than 12 watts at the antenna end.

[marcspaz]

16 minutes ago, LeoG said:

You mean to avert losses in that cable.  100' is when you start getting into hardline.  Heck, 50, 60 feet is when you start getting into hardline for UHF.

 

Yep.  My home repeaters and my portable repeater are all capped at 50', using LMR400.  Hard line, even ultra flex, is too stiff for portable use.  So, I keep it short.

[WSEL330]

That seals it. Two antennas, done. separated by about 30'. I'll update as I test range and propagation.