Effects of leaves on UHF frequencies

[LeoG]

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://apps.dtic.mil/sti/tr/pdf/ADA048304.pdf&ved=2ahUKEwjn3cCT-dyIAxUeF1kFHa86GJUQFnoECCsQAQ&usg=AOvVaw06iZ047tec0lBcnnzoBaVK

 

I found this in there which could be somewhat relevant to any tree problems GMRSers may be having. The red line is mine at what I guessed is 462MHz which ends up at 0.1dB/Meter attenuation for tree leaves.

Now I see why I have such a big issue with receiving my repeater signal at my house.  My antenna height is in the thick of the leaves.  40' high at the base with trees at about 72' tall.

I was doing measurement calculations and I stopped when I hit 102dB of attenuation

 

[WRXP381]

What wattage radio do you have? How much  coax and what type? What antenna are you running? 

[LeoG]

You should know this already.

Repeater at the shop is 50w with 40w out of the duplexer.  50 feet of LMR400 to a Retevis MA-09 7.2dBi gain antenna that is currently at 40' at the base.

At the house I have a 20w Wouxun XS-KG20+ that outputs 25w.  84' of Messi and Poaloni Hyperflex 13 cable running into a copy of the 7.2dBi gain antenna at 42 feet off the ground.

The shop is 100 ft higher than my house.

Sometimes the signal is pretty strong 3/4 of the power meter.  Never full quieting.  Tonight it's running low, between 1/4 and 5/8 on the power meter.  Signal varies, tonight you can watch in swing up and down on the meter sometimes.

 

Most of the times I'm using the repeater with a 2w talkie inside the shop to talk to the little lady.  Other times I'm miles from the shop.  In the northern direction I can get pretty far but am limited by hilly terrain.

[WRXP381]

My only suggestion would be higher gain antennas since gain works both was in receive and transmit so a good tall higher gain like 9 or 12 may help with receive from the repeater 

[LeoG]

I already took your advice.  I ordered a Comet 712EFC GMRS 9dBi antenna.  It will be here tomorrow.  This is for the repeater site.  The antenna will eventually be put above the tree line using Messi and Paoloni Hyperflex 13 as I stated above.

[WRYZ926]

Yes foliage will affect UHF frequencies. Pine and cedar trees are the worst. A higher gain antenna won't help all that much to punch through the foliage. Yes you might see a small  improvement. But your best solution is to get both antennas above the trees for a more clear line of sight.

The route I take regularly has a lot of eastern red cedars close to the road. I have dead zones with UHF, both 70cm and GMRS, where the cedar trees are tall and close to the edge of the road. The GMRS repeater antennas are at 400 feet and the 70cm repeater antennas are at 900 feet. I am using a 20" Tram antenna tuned for GMRS and a Comet SBB-1 dual band for 2m/70cm. The radios I am using are a TYT TH-7800 and Wouxun KG-1000G, both are 50 watt radios. While I do get some static in the same area when on 2m, I can still be clearly heard on the repeater. All repeater antennas are on the same 900 foot tower. 

Line of sight is king when it comes to UHF.

[nokones]

Pine needles, especially wet pine needles, will have a tremendous affect and will fully antenuate the signal on 800 MHz.

[GreggInFL]

7 hours ago, nokones said:

Pine needles, especially wet pine needles, will have a tremendous affect and will fully antenuate the signal on 800 MHz.

Big time.

Our neighborhood was getting quotes for high speed internet and one vendor specialized in RF.  They took one look at the pines and no quoted.  We went with fiber.

[WRKC935]

102 dB of path loss isn't actually that bad.

If a repeater is putting out 40 watts that's 46dBm.

so 46 - 102= -56dBm.  That friend is a SCREAMING hot receive signal and will lay the needle in the needle in the corner so to speak.

When you get down to a -115 dBm signal level, then you will start to hear noise in most receivers.  By -119dBm the signal is going to be noticeably noisy and broken.

This doesn't take into account, antenna gain at either end OR cable loss at either end. 

But, if you know antenna gain, tower height (for cable length). The type of cable. The duplexer used, and you have a verified accurate antenna system with known cable loss and gain of the antenna.  You can calculate the RF power level being transmitted at the site. And be fairly close, like within ten watts.

[LeoG]

I stopped calculating at 102dB.  There was many more trees patches to go.  I basically stopped at 1000 meters of trees.  My signal at times can be adequate, but but it varies considerably.  I put the squelch up to 4 the other day and my wife couldn't here me during the day.  I dropped it back down to 1 to make sure that didn't happen again.

 

According to calculations the input into the antenna after coax losses are 32 watts and the effective radiated power is 102 watts.

 

Let me finish adding up the loss of the trees.

[LeoG]

OK, added it up and it came out to 166dB loss.  It was 1660 meters of trees.  That doesn't include houses that are in the way and the slight hill I'm on, but I think my antenna is up high enough so that isn't a factor. Only if I'm on a hand held.

 

102 watts is 50.09dBm - 166dB = -115.91dBm

 

Sounds about right the way the signal can act sometimes.  The best I've seen is 3/4 on my power meter on the mobile radio.  Worst is non existent signal but that's unusual.  1/4 on the power meter is usually as low as it goes.  I've never had full quieting on the signal.

[WSEM262]

Ive got the exact same issue at my location.

 

Maybe install an amplifier ?

Crank the output up to the point you have 50 watts leaving the duplexer... and upgrade the coax too.

 

I've gotten improvement just going from 35ft of LMR400 to 30ft of LMR600 on my repeater setup. My repeater pushes 48 watts into the duplexer (A Bp/Br cavity style), which sends 34 watts to the Comet GP6NC (9db gain) GMRS antenna.

 

[SteveShannon]

11 minutes ago, WSEM262 said:

FCC 50w maximum to the antenna.

That’s not the rule.

The limit applies to the output power from the transmitter.

§ 95.1767 GMRS transmitting power limits.

This section contains transmitting power limits for GMRS stations. The maximum transmitting power depends on which channels are being used and the type of station.

(a) 462/467 MHz main channels. The limits in this paragraph apply to stations transmitting on any of the 462 MHz main channels or any of the 467 MHz main channels. Each GMRS transmitter type must be capable of operating within the allowable power range. GMRS licensees are responsible for ensuring that their GMRS stations operate in compliance with these limits.

(1) The transmitter output power of mobile, repeater and base stations must not exceed 50 Watts.

But more to the point that won’t make much of a practical difference anyway.

[WSEM262]

So if we are to split hairs...  "transmitter output power" could be set to 10 watts and an inline amplifier could be putting out 100 Watts ?

The amplifier is not technically a "transmitter".

As that is written and possibly interpreted... the transmitter output falls squarely within the FCC rules @ 10 watts. Anything beyond the transmitter doesnt appear to be addressed by these rules. 

[LeoG]

Yep, I was gonna say the same thing Steve.  Out the back of the amplifier is where the 50 watts is measured.  If it's an all in one unit you get to have 50 watts out out of the duplexer if the duplexer is housed in the same case as the amplifier.

[LeoG]

If you didn't blab it on the internet and did that, would anyone ever notice?  No.  But I believe they meant 50 watts out of the transmitter which no matter if you want to call it an amplifier or transmitter is the main source of the signal going to the antenna without the hair splitting.

Need a thousand lawyers to write the regulations and still someone will be able to "interpret" them differently than was implied.

[SteveShannon]

11 minutes ago, WSEM262 said:

So if we are to split hairs... my "transmitter output power" could be set to 10 watts and the amplifier could be putting out 100 Watts ?

The amplifier is not technically a "transmitter".

As that is written and possibly interpreted... the transmitter output falls squarely within the FCC rules @ 10 watts. Anything beyond the transmitter doesnt appear to be addressed by these rules. 

 

1. An amplifier is still a transmitter (anything that transmits is), but there are additional rules regarding amplifiers.

2. Try finding an amplifier certified for part 95E.

[WSEM262]

1 minute ago, SteveShannon said:

 

1. An amplifier is still a transmitter, but there are additional rules regarding amplifiers.

2. Try finding an amplifier certified for part 95E.

Understood. 

[WSEM262]

5 minutes ago, LeoG said:

If you didn't blab it on the internet and did that, would anyone ever notice?  No.  But I believe they meant 50 watts out of the transmitter which no matter if you want to call it an amplifier or transmitter is the main source of the signal going to the antenna without the hair splitting.

Need a thousand lawyers to write the regulations and still someone will be able to "interpret" them differently than was implied.

Understood. 

I edited my post and will shut up now. 

[LeoG]