Upgrading Output power on repeater

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 7:14 am

Hello. If I currently had a license that allowed my repeater to transmit 45 watts, would I have to go through all the hoops in coordination to increase that to about 75 watts? When we got our repeater license we paid a guy 350 bucks to do ours so I have no clue what to do about coordination, who to talk to, anything. thanks in advance.

motisking · Post by **motisking** » Tue Apr 20, 2004 7:35 am

No a lot of hoops.

I have a few questions to help answer this question better...

Is this a public saftey or industrial/business freq?

Does the license expire soon?

Are you against paying to have the license modified?

Are you looking to increase the ERP from 45 to 75 watts ? (Effective Radiated Power)

nmfire10 · Post by **nmfire10** » Tue Apr 20, 2004 7:42 am

Side Note: Many licences I've seen have no ERP listed, just a power output. Does that mean it is unlimited or just not specified but still limited by some normal factor?

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 7:44 am

I dont know. I know it is a business frequency and the license expires in november or december

here's the callsign you can look up the info

WPPG753

hope this helps

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 7:46 am

we have a 45 watt radio and im sure after the duplexer its less than that, but we're looking at a near 100 watt setup and of course after the duplexer it would be somewhat less than that.

we could theoretically go up to 125 but im afraid that may be too much power
we just need more penetration in the low spots and buildings not too far away

motisking · Post by **motisking** » Tue Apr 20, 2004 7:57 am

nmfire10 wrote:Side Note: Many licences I've seen have no ERP listed, just a power output. Does that mean it is unlimited or just not specified but still limited by some normal factor?

Transmit power was the old way of assigning power and ERP is the new better way.

Say you had a license for 45 watts of TRANSMIT POWER for a repeater. After the duplexer, connectors and lets say 100 feet of transmission line going to a 3 dB gain antenna the EFFECTIVE RADATIED POWER would be 30 watts.

Using the ERP method you could use as MUCH POWER as is needed to achieve 45 watts ERP.

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 8:01 am

okay, so would i have to go through coordination to have the ERP increased from 45 to say 75 watts or so?

motisking · Post by **motisking** » Tue Apr 20, 2004 8:06 am

Good news!!

Callsign WPPG753 is licensed for 130 watts ERP.

What type of antenna are you using? (3dB gain 7dB gain more?)

What type of transmission line? (RG213, Hardline?)

How many feet of trans line is in use?

P.S. Are portable radios able to get into the repeater in these weak areas?

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 8:14 am

We have a ASP 685 Antenna with 7/8 hardline on a 190 foot tower
portables dont do too bad, but they could be better.
we're wanting to put an amplifier on our mobile we use as a transmitter and use an advancedreceiver gasfet preamp on the receive
maybe that will help?

thanks for looking

motisking · Post by **motisking** » Tue Apr 20, 2004 8:29 am

The ASP685 is rated at 5.25 dB gain.

With 200 ft of 7/8 and connectors your “net gain” is +3.3 dB.

With your 45 watt transmitter your ERP is 58.6 watts.

You could increase the TX power to 100 watts and not need to modify your license.

So adding a TX amp and an RX preamp will help.

How far do you need to talk...
North ?
East ?
South ?
West ?

An antenna change, less gain, might help aim the signal down. Improving coverage.

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 8:34 am

Well, its not really a setup that I can control. Our county government lets us use their setup as long as they can use it as a backup.

its a great setup, really.

our county government built a setup about a year or two ago that is three vhf repeaters on a 300 foot tower using three antennas and a combiner.
our setup does better than it does, ive spent maybe 1500 bucks and them 60,000 dollars

thanks for your help, i'll be looking at an amplifier soon

motisking · Post by **motisking** » Tue Apr 20, 2004 9:06 am

If you talk a lot, get an amp that can handle the work.

TPL makes good amps. Motorola sells their stuff with the M logo on it, so it must be good!

10 Inch Rack mount = TPL part # PA3-1FE-RXRF is 15-40 watts in with 80-120 watts out. $926.00
Mobile amp = TPL part # PA3-1FE is 15 – 40 watts in with 80 to 120 watts out. Draws 14 amps. $505.00

If you purchase a mobile style amp put a cooling fan on it when you install it to keep it from giving you problems in the future.
A little $10.00 dollar "muffin" fan can do a lot.

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 12:11 pm

Way ahead of you on that one, we have an MSF5000 cooling fan already on the transmitter now. We talk a lot. it is basically a BS repeater anyways. thanks

motisking · Post by **motisking** » Tue Apr 20, 2004 12:29 pm

COOL!!

If and when you add the AMP let us know if improves your coverage.

Post by **wavetar** » Tue Apr 20, 2004 2:32 pm

Just a note on TPL amps. Make sure you get it factory tuned for the proper TX frequency. We had to change the frequency for 3 repeaters, about 1-meg from the tuned frequency. The TPL amp looked fine going straight into a service monitor w/spectrum analyzer, power output seemed unaffected. BUT, once you tried running it through a duplexer, the signal became incredibly 'dirty' & spurious, looked like the NY City skyline on a spectrum analyzer! Retuning wasn't too big of a deal & everything's fine now, but it's best to know about these things beforehand.

Todd

RKG · Post by **RKG** » Tue Apr 20, 2004 4:52 pm

Note that in most cases, it is far more economical (and often more effective) to upgrade the antenna than to increase transmitter power. For instance, doubling transmitter power only gives you 3 dB on the xmit side and no benefit on the receive side. You could get the same kick on xmit and a big bonus on the receive side by upping the base station antenna to 8 or 10 dB.

motisking · Post by **motisking** » Tue Apr 20, 2004 5:55 pm

For instance, doubling transmitter power only gives you 3 dB on the xmit side and no benefit on the receive side. You could get the same kick on xmit and a big bonus on the receive side by upping the base station antenna to 8 or 10 dB.

I think dog pecker gnat is already running to much gain. Not enough of the antenna is looking downward close to the tower.

nmfire10 · Post by **nmfire10** » Tue Apr 20, 2004 6:00 pm

On the same token, adding antenna gain may make the TX radiation pattern differ in such a way to make it even worse. All the ERP in the word does no good it is blasts over you and into the horizon.

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 7:44 pm

I guess I'm not getting it on the gain issue. I understand what you're saying, that I'm "Overshooting" my hopeful coverage area, but I've always been under the impression that gain is good.
I really think thats the mindset of everyone around here.

I mean I cannot change out the antenna, that's not a possibility. It does extremely well for what we do, we have great coverage compared to much more substantial systems, even better coverage. All of the local sheriff deputies have to switch over to our repeater when they cant get out on their tower 100 foot higher, with 60 more watts, and running through a combiner with a preamp. We can get mobile coverage for 35-50 miles radius pretty much guaranteed, and portable 15-20 miles with no big issues.

What we're having a time with is penetration. We go into a building and its like you walked into a lead room. Or when you top that hill you go down the other side you lose the signal for a second. I know thats just how it goes sometimes but if you can help it out a bit that might make all the difference.

I guess there's just some things you're not supposed to understand sometimes!

Thanks for the help!
Brian

nmfire10 · Post by **nmfire10** » Tue Apr 20, 2004 8:13 pm

Adding gain don't just expand the radiation pattern equally. It stretches it out so to speak. A normal 0 gain 1/4 wave antenna for the sake of demonstration has a round vertical pattern. It goes up, down, and out equally. When you apply gain, it is like squishing it front the top and bottom making it buldge at the sides, kind of oblong. With enough gain, you end up losing you propogation towards the ground or up over obstacles but you have a high strength signal blasting out in a straight hosizontal line from the height of the antenna. It is hard to type, I will try to draw something later. Gain is good up to a point. It will eventually become counter productive.

motisking · Post by **motisking** » Tue Apr 20, 2004 8:19 pm

dog pecker gnat wrote: What we're having a time with is penetration. We go into a building and its like you walked into a lead room. Or when you top that hill you go down the other side you lose the signal for a second.

VHF as a rule does not have penatration. Especially when your talken a portable in a building. (OK, someone disprove this. Because, yes it's a rule but all rules can be bent even broken.)

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 8:37 pm

I get what you're saying. I'm having to think of a beam antenna, the radiation pattern on that. YOu have to give a little to get a little more. Basically, to get gain, you must have loss in a sense.

That makes sense, if I'm following you correctly.

You just dont think about that when you look at an "omnidirectional" antenna

dog pecker gnat · Post by **dog pecker gnat** » Tue Apr 20, 2004 8:39 pm

I dont know if you would term it as penetration but when we went from a 25 watt to a 45 watt radio, signal could be received better in our firestation on portables. I understand that UHF or 800 or whatever may have better penetration, but I'm talking if you up the power and increase the reception capabilities, it just seems like there would be no way it wouldnt help somewhat

nmfire10 · Post by **nmfire10** » Tue Apr 20, 2004 8:53 pm

Here is a picture of the possible negative effects of too much gain on transmit. This is exagerated and disproportionate for the sake of understanding. My drawing skills are not so hot, this is the best your going to get from me. If it is any consolation, I had the same misconception that you did, as does pretty much everyone else that isn't "into this stuff" all the time.

I can't give you an answer as to how much of an improvement you will get by boosting the power. I guess it can't hurt and will probably improve some places. It's tough to predict.

motisking · Post by **motisking** » Tue Apr 20, 2004 9:04 pm

That is a work of art!!! A perfect diagram of high and low gain.

You should use that as your avatir!

RKG · Post by **RKG** » Wed Apr 21, 2004 3:27 am

Gain is good; gain is always good. The issue is how you achieve it.

The so-called "lighthouse effect," i.e., the notion that a high gain antenna with a narrow vertical beamwidth would shoot a strong signal at the horizon over the heads of a systems field units while being so weak closer to home that the units could not get in, is overstated.

For instance, consider the difference between a 5.25 dB UHF A/S Stationmaster vs. a 10 dB UHF A/S Stationmaster. The 5.25 antenna has a specified vertical beamwidth of 14 degrees, which means that the lower 3 dB radius is 0.15 miles (or 264 yards) from the station. At all points from 264 yards away to the horizon, the antenna sends (and receives) with 3 dB of gain, or more. Switch to the 10 dB antenna with a specified vertical beamwidth of 7 degrees, and the lower 3 dB point increases to only 0.31 miles (or 545 yards). The only users who would see an overall reduction in system efficiency would be those who operate between 264 and 545 yards from the base station antenna. In both cases, the radio horizon is 14 miles away, which means that as user distance increases from about 500 yards from the station to 14 miles from the station, the user will see an increasing amount of system performance enhancement. (Calculations done with RFS Celcalc.)

Which brings us to the question of downtilt. A zero downtilt antenna (used for foregoing calculations) shoots its max gain at the nominal horizon, while an antenna with downtilt aims a bit lower. As you can see from the calcs, for most installations, downtilt is not much of a factor, since all you would gain is a couple of hundred yards in a region where a unit can communicate with the base over a coat hanger.

In fact, downtilt is a value primarily with the unusual installation where the antenna is mounted on a high-rise building or TV antenna site, between 500 and 1,000 feet AAT. (If we used our 10 dB Stationmaster at 1,000 feet, the lower 3 dB point would be more than 3 miles from the station, while if we specified the antenna with 2 degrees of downtilt, that value is brought into about 1 mile from the station.)

Where there is a problem, if there is problem, is uptilt. This is not publicized by the antenna manufacturers (and may not be revealed at all), but most stacked collinear antennas are sensitive (with respect to beamtilt) to where in their bandwidth the antenna is used. For instance, the 10 dB 450-470 A/S Stationmaster , specified for zero downtilt, actually ranges between 2 degrees of downtilt at 450 mHz and a hair over 1 degree of UPTILT at 470. This would move the lower 3 dB point out to 1.09 mi. (or 1920 yards). So when buying an antenna, be sure to have the manufacturer specify the actual tested beamtilt at the actual frequency over which you intend to use it.

There is some discussion about building penetration. Absent the use of in-building repeaters or BDAs, the penetration of a base station signal into a building is generally a function of multipathing and aperture penetration. As someone noted, though VHF tends to propigate better than UHF in free space, all other things being equal, VHF tends to go around objects that UHF might multipath from, and VHF requires a wider building opening in order to enter it. However, for any given path between base station and field unit, the more effective radiated power you can send down that path, the better the signal strength will be on the other end.

All of which is academic, since the poster says that changing out his antenna is not an option.

dog pecker gnat · Post by **dog pecker gnat** » Wed Apr 21, 2004 5:10 am

wonderful food for thought though. sometimes you just dont even realize the most important aspects!

thanks!

anyways, you never know when something might happen and we have to relocate or replace the antenna due to lightning. good information to know