Antenna height and length of coax hypothetical question.

[WRZI712]

Hello,

I'm relatively new to the GMRS world and I'm in the process of setting up a base station on the second floor of my house. I have two choices for antenna placement that would also affect the length of coax that I run. So here are the two options I have...which option would you choose and why. 

1) Antenna mounted 20' above the ground on the rear of the house with approximately 20' of lmr 400 coax to my radio. The top of the antenna will be approx 10' below the peak of the roof and partially obstructed by the house. 

2) Antenna mounted 30' above the ground on the peak of the roof with approx 35' of lmr 400 coax to my radio. The top of the antenna will be roughly 5' above the peak of the roof with no obstructions for 360

3) In this case just choose the easiest mounting method because the difference would be negligible. 

Thanks for all the input

Pete

WRZI712

[AdmiralCochrane]

4 hours ago, WRWE456 said:

Great! You will spend as much on the cable or more than the radio.

 

But it will be worth it. 

[SteveShannon]

10 minutes ago, WRZI712 said:

Hello,

I'm relatively new to the GMRS world and I'm in the process of setting up a base station on the second floor of my house. I have two choices for antenna placement that would also affect the length of coax that I run. So here are the two options I have...which option would you choose and why. 

1) Antenna mounted 20' above the ground on the rear of the house with approximately 20' of lmr 400 coax to my radio. The top of the antenna will be approx 10' below the peak of the roof and partially obstructed by the house. 

2) Antenna mounted 30' above the ground on the peak of the roof with approx 35' of lmr 400 coax to my radio. The top of the antenna will be roughly 5' above the peak of the roof with no obstructions for 360

3) In this case just choose the easiest mounting method because the difference would be negligible. 

Thanks for all the input

Pete

WRZI712

2, because in #1 your antenna is blocked and adding 10 feet of LMR400 will only cost you about 0.3 dB. 

[WRZI712]

3 minutes ago, Sshannon said:

2

A man of few words...short and to the point. Thank you. 

[WRYZ926]

I would go with option 2 unless you can get your antenna higher. And you won't have any problems with LMR400 over a 20, 35 or even 50 foot run.

[SteveShannon]

4 minutes ago, WRZI712 said:

A man of few words...short and to the point. Thank you. 

I went back and edited it to say why. 

[WRWE456]

I run 50 feet with no problems. Antenna about 10 feet above the peak with excellent results.

[WRZI712]

12 minutes ago, WRYZ926 said:

I would go with option 2 unless you can get your antenna higher. And you won't have any problems with LMR400 over a 20, 35 or even 50 foot run.

Thanks for the clarification. So in this case the height of the antenna outweighs the length of the coax. Would the opposite be true if you were to run a lower quality coax like RG8X? 

[kidphc]

Thanks for the clarification. So in this case the height of the antenna outweighs the length of the coax. Would the opposite be true if you were to run a lower quality coax like RG8X? 

Don't go with a higher loss cable coax. Additional height or additional gain from a higher gain antenna will be negated in the losses of the coax.

Sent from my SM-S901U using Tapatalk

[WRZI712]

1 minute ago, kidphc said:

Don't go with a higher loss cable coax. Additional height or additional gain from a higher gain antenna will be negated in the losses of the coax.

Sent from my SM-S901U using Tapatalk
 

Thanks...that's pretty much what I expected. 

[WRYZ926]

I have to agree with @kidphc on this one. You might not notice a difference in a 30 foot or shorter run but why hamper yourself.

With any antenna, height is king. Always use the best coax you can for the best performance. But height won't make up for the wrong type of coax.

[WRZI712]

1 minute ago, WRYZ926 said:

I have to agree with @kidphc on this one. You might not notice a difference in a 30 foot or shorter run but why hamper yourself.

With any antenna, height is king. Always use the best coax you can for the best performance. But height won't make up for the wrong type of coax.

I wouldn't be able to run the LMR400 straight to the back of my radio so what would be a suitable jumper coax to run and would the jumper have any negative affect? 

[WRWE456]

8 minutes ago, kidphc said:

Would the opposite be true if you were to run a lower quality coax like RG8X? 

It's not a quality issue it's a specification issue. Wrong kind of cable for the frequencies being used.

[BoxCar]

Go to https://timesmicrowave.com/documentation/lmr-guide/ for the Times Microwave guide to their coaxial cables.

[WRWE456]

A short length of RG8x will work fine as a jumper. I use a BNC adapter on my radios then a 3 foot length of RG8x with a BNC on the radio end and Type N connector on the other end. The 400 has type N connectors on both ends as do my antennas. Type N connectors are better for UHF (which is what GMRS is) and many antennas can be ordered with them installed. That is what I did.

By the way what radio are you running?

[WRZI712]

3 minutes ago, WRWE456 said:

A short length of RG8 will work fine as a jumper. I use a BNC adapter on my radios then a 3 foot length of RG8 with a BNC on the radio end and Type N connector on the other end. The 400 has type -N connectors on both ends as do my antennas. Type N connectors are better for UHF (which is what GMRS is) and many antennas can be ordered with them installed. That is what I did.

By the way what radio are running?

I picked up a Radioddity DB20-G new for about $85. I figure it's just enough to send me down the "Rabbit Hole" 

[WRZI712]

13 minutes ago, BoxCar said:

Go to https://timesmicrowave.com/documentation/lmr-guide/ for the Times Microwave guide to their coaxial cables.

Thanks for the link

[SteveShannon]

12 minutes ago, WRZI712 said:

I picked up a Radioddity DB20-G new for about $85. I figure it's just enough to send me down the "Rabbit Hole" 

I bought two of them. They’re decent little radios for the price. 

[WRWE456]

Great! You will spend as much on the cable or more than the radio.

 

[WRZI712]

19 minutes ago, WRWE456 said:

Great! You will spend as much on the cable or more than the radio.

 

I'm quickly finding that out...which kind of led me to the question I posted. Quality cable ain't cheap.  but now I understand why.