Which coax to use!

[Luis650]

Hey all I'm looking to buy this Tram 1410 Discone antenna but I'm a bit confused about which coax to use for this antenna. I have my Bcd996p2 which has a BNC f connector I'm looking to use it for P25 systems which is in the 700-800 MHz and also 400mhz thank you very much.

 

[mmckenna]

The correct coax to use needs to take into account the length of cable.
As the cable gets longer, losses increase. So you need the appropriate cable that will keep those losses to a manageable level.
It also needs to fit in your budget.

So, how long is the run?

 

[Luis650]

not long maybe about 50ft ?

 

[prcguy]

A typical scanner Discone like the Tram 1410, Diamond D130, Radio Shack, etc, is not very good in the 700-800MHz range because the radiation pattern shifts way upward in that range causing about 10dB of degradation at the horizon.

 

[mmckenna]

not long maybe about 50ft ?

OK, so 50 feet.
So the length is half the equation.
The other part is that as the frequency goes UP, the losses go UP.

There are tools on line that will help you figure this out:

Coax Loss Calculator | KV5R.COM

Using that calculator, you can start entering info:
Line Length = 50 feet
Frequency = 855MHz (that'll cover you up into the 800MHz band)
Load SWR = Enter 1.0 since you are running a discone and not transmitting (it's close enough without complicating things)
Power In = I like to enter 100 watts, even though you are not transmitting, it'll make it easier to covert the loss into percentages

So, the variable you want to play with is the top line "Line Type"
RG-8 will give you 54% signal loss just in the cable
RG-6 will give you 65% loss. RG-6 is your standard, run of the mill, cable TV/satellite/TV coax cable you can get at Home Depot.
LMR-400 will give you about 35% signal loss.
LMR-600 will give you about 24% signal loss.

Your next step is to look at the costs of those cables. It's easy to say I want "the best", but truth is, you probably don't want to spend that much. Finding something that trades off the following characteristics is necessary:
1. Cost (If you have lots of money for this, you'd probably be getting something better than a Tram antenna)
2. Flexibility and ease of installation (bigger/more expensive cable gets hard to install as it won't bend as easy)
3. Loss. LMR-400 is probably a good place to be. 35% signal loss sounds like a lot, but if you get that antenna up high, you'll probably do OK.

You can order the cable with the correct connectors installed. This is a good thing if you haven't installed coax connectors before, or have the correct tools.

LMR-400 is kind of stiff, so you absolutely do not want to connect that directly to your scanner, it'll break the antenna connector off. Get a short jumper of RG-58 to make the final connection to your radio, and save yourself money on unnecessary repairs.

And I'd agree with what prcguy says. There are better antennas out there.

 

[Luis650]

OK, so 50 feet.
So the length is half the equation.
The other part is that as the frequency goes UP, the losses go UP.

There are tools on line that will help you figure this out:

Coax Loss Calculator | KV5R.COM

Using that calculator, you can start entering info:
Line Length = 50 feet
Frequency = 855MHz (that'll cover you up into the 800MHz band)
Load SWR = Enter 1.0 since you are running a discone and not transmitting (it's close enough without complicating things)
Power In = I like to enter 100 watts, even though you are not transmitting, it'll make it easier to covert the loss into percentages

So, the variable you want to play with is the top line "Line Type"
RG-8 will give you 54% signal loss just in the cable
RG-6 will give you 65% loss. RG-6 is your standard, run of the mill, cable TV/satellite/TV coax cable you can get at Home Depot.
LMR-400 will give you about 35% signal loss.
LMR-600 will give you about 24% signal loss.

Your next step is to look at the costs of those cables. It's easy to say I want "the best", but truth is, you probably don't want to spend that much. Finding something that trades off the following characteristics is necessary:
1. Cost (If you have lots of money for this, you'd probably be getting something better than a Tram antenna)
2. Flexibility and ease of installation (bigger/more expensive cable gets hard to install as it won't bend as easy)
3. Loss. LMR-400 is probably a good place to be. 35% signal loss sounds like a lot, but if you get that antenna up high, you'll probably do OK.

You can order the cable with the correct connectors installed. This is a good thing if you haven't installed coax connectors before, or have the correct tools.

LMR-400 is kind of stiff, so you absolutely do not want to connect that directly to your scanner, it'll break the antenna connector off. Get a short jumper of RG-58 to make the final connection to your radio, and save yourself money on unnecessary repairs.

And I'd agree with what prcguy says. There are better antennas out there.

thanks for this. Are those other better antennas pricey that would do the job

 

[mmckenna]

thanks for this. Are those other better antennas pricey that would do the job

If it was me, I'd get one of the multiband scanner antennas and a ground plane adapter and set that up. It'll give you some actual gain on UHF and 800MHz with a better radiation pattern.

Either of these two antennas:

EM Wave EM-M43002 - Triple Band Mobile Antennas

Tri-Band 150-162/450-490/763-870 MHz IP67 Rated Roof Mount Antenna

theantennafarm.com

Tri-Band 150-165, 450-470 & 806-940 MHz Mobile Two Way Radio Antenna Scanner

Tri-band antenna covers 150-165, 450-470 & 806-940, 100 Watts, Whip Length 16.5"

theantennafarm.com

And this NMO base station adapter:

Mobile Antenna to BASE Convertor VHF UHF Antennas TE Connectivity MBC

Mobile to Base Station Adapter Kit for NMO Mount Type Antennas. Includes bracket, clamps, radials and mounting bracket. Frequency Range 0 - 512MHz, SO-239 (UHF

theantennafarm.com

There are probably some other options, but for the price, that'll get you started.

 

[Luis650]

If it was me, I'd get one of the multiband scanner antennas and a ground plane adapter and set that up. It'll give you some actual gain on UHF and 800MHz with a better radiation pattern.

Either of these two antennas:

EM Wave EM-M43002 - Triple Band Mobile Antennas

Tri-Band 150-162/450-490/763-870 MHz IP67 Rated Roof Mount Antenna

theantennafarm.com

Tri-Band 150-165, 450-470 & 806-940 MHz Mobile Two Way Radio Antenna Scanner

Tri-band antenna covers 150-165, 450-470 & 806-940, 100 Watts, Whip Length 16.5"

theantennafarm.com

And this NMO base station adapter:

Mobile Antenna to BASE Convertor VHF UHF Antennas TE Connectivity MBC

Mobile to Base Station Adapter Kit for NMO Mount Type Antennas. Includes bracket, clamps, radials and mounting bracket. Frequency Range 0 - 512MHz, SO-239 (UHF

theantennafarm.com

There are probably some other options, but for the price, that'll get you started.

Great looking into this, would it be the same coax cable you mentioned used for the station adapter too ?

 

[mmckenna]

Great looking into this, would it be the same coax cable you mentioned used for the station adapter too ?

Yes.