if you had to choose where to mount a 2m / 440 vertical?

[mr_fx]

I have a 2m / 440 8.5 foot tall vertical colinear antenna.

If you had to choose:

- 40 feet high, in an oak tree, surrounded by branches and leaves, using RG8x (mini), this will require a 60 foot run of feedline

OR

- 20-25 feet high, on an asphalt single roof, using either RG-214 (basically RG-213 with silver coated center silver coated double shield), this will require only a 35 foot run of feedline

also I MIGHT have some left over LMR400 that will be long enough for the roof install... maybe

NOTE: this will be used mainly for my 2m APRS station, and occasionally used for 2m and 440 repeaters (I rarely use 440 repeaters)

 

[Captain Kilowatt]

The leaves will degrade the 440 side somewhat but the 60 feet of mini coax is a killer. If it were me I would do the lower install witb the better cable if you only have those two choices since you are just looking at APRS and repeaters which I am assuming are fairly local.

 

[Robb]

Roof install with the LMR - most def . . .

 

[2RT307]

One of our club classes had a presentation from some TimesMicrowave reps. They had a slideshow with a graph for frequency and loss with different coax. Things get ugly QUICK with VHF/UHF. Definitely the shorter/better coax would be my choice.

73,
Brett

 

[mr_fx]

well it seems I have enough LMR400 to install in the oak tree as well...

so how do I decide if the tree creates more problems than the benefits of being around 20 feet higher?

 

[2RT307]

Try it and see? I used an Antron A99 in a tree for years without any problems. You might see a difference though with VHF/UHF.

73,
Brett

 

[Captain Kilowatt]

HUGE difference between 27 Mhz and 440 Mhz. Foliage attenuation is noticeable at 440 but virtually non-existent on 27.

 

[C2]

Your use is primarily 2m and rarely 70cm. You could quantify the benefit from the height and weigh that against the additional cable loss. If your area is relatively flat there will be less benefit from the height unless you are working the horizon. Are you running an iGate and want to maximize your range, then the tree may be a better compromise, but it's getting to splitting hairs from the guessing chair?

I would make the run to the tree if the cable was available and then just move the antenna to the roof and compare with some fixed stations - but I suspect the roof top will be just fine.

 

[The DB]

I did some modeling and playing with numbers. Ignoring the effect of the leaves, the additional height of the tree will net about 0.9 dB gain over the lower height. There was no significant change in the take off angle, if you are a believer in that sort of thing.

If comparing LMR-400 for both run lengths you would have an additional 0.4 dB in losses. So using LMR-400 for the higher antenna, you would have a net gain of 0.5 dB in gain over the lower antenna. This is not enough of a change to be noticeable in the real world.

However, if you have to use RG-8x for the higher antenna, you will have a net loss for the higher antenna in the range of 1.8 dB loss if the lower antenna is using LMR-400, and 1.4 dB in loss if the lower antenna is using RG-214.

These numbers are based on modeling gains of 2 meter antennas at said heights and numbers from the Time Microwave Coaxial Cable Data page.

Long story short, just go with the lower height


The DB

 

[C2]

That there is an informed guess. Nicely done!

 

[mr_fx]

Based on what DB is saying I might even GAIN something by mounting on the roof by the time you count in loss due to foliage

 

[Robb]

.9db isn't much at all compared to the amount of loss you may get with the leaves/tree loss. Remember, that is <point> 9; not 9db. Huge difference.
Think he was saying that you would be no better off by such a small figure compared to the possible losses . . .

 

[mr_fx]

.9db isn't much at all compared to the amount of loss you may get with the leaves/tree loss. Remember, that is <point> 9; not 9db. Huge difference.
Think he was saying that you would be no better off by such a small figure compared to the possible losses . . .

\that is what I gathered as well

 

[Robb]

Hey; that 1 1/4" OD electrical conduit is cheap everywhere; IIRC it is like $8 per 10ft piece. That should get you higher on the roof. What antenna are you going to put up?

 

[mr_fx]

What antenna are you going to put up?

Tram 1480, a 2m/440 colinear that is 8.5 feet tall