Signal Loss vs Cable Length

fritodog · EVDO Newbie Joined: 19 Apr 2006 Posts: 8

I'm using an amp and have a 50 ft cable run to an outside antenna. I think I can reroute the cable and cut the distance in half (down to about 25 ft). I'm in a fringe area and currently get 3 bars on Verizon's EVDO network...max receive rate is ~ 500 kbps, but average is 300-400. Can anyone tell me if I will see much difference in signal strength and receive rate by shortening my cable run?

Tks,
FritoDog

JT · EVDO Fledgling Joined: 23 Apr 2006 Posts: 24

If you can shorten the cable it's always better. Only run as much as you need and never coil up any excess, it's a signal killer.

Scott · Posted: Fri Jun 16, 2006 5:31 pm Post subject:

Generally speaking, less loss from cables provides more signal to the card, or in your case amplifier. Since you use an amp, signal obviously would be much better even with 100 feet of coax.

Still, my take is that signal gone is signal lost. Amplifiers don't make signal magically appear... they just increase what is there.

You don't mention what type of coax you're using. 100 feet of RG58U isn't 100 feet of LMR600. There is less improvement realized by shortening if you have really good cable to begin with.

What is your actual signal level in VZAccess Manager? When hovering the lower green signal indicator when connected you should see either percentage or a negative number in dBm (for Windows only, percentage for the V620, dBm for the KPC650 & PC5740. AC580 or PC5220 depends on which connection software you're using -there may not be a way to check).

In Windows you can also look under Help>About VZAccess Manager to poll the card for signal details. For Macs it under VZAccess Manager>About VZAccess Manager...

WPSANTENNAS-MATT · Posted: Sat Jun 17, 2006 5:59 am Post subject:

If you have the ability to get the antenna up higher in elevation I would entertain that before re-routing the cable to decrease the length. The difference between using 25 or 50 feet of low loss cable in conjunction with an inline amplifier is negligible. It is extremely important that you connect the powered amplifier and/or external antenna to the card when it is powered down and then power up the card.
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fritodog · EVDO Newbie Joined: 19 Apr 2006 Posts: 8

Thanks for the feedback!

I'm using RG8X cable...will not be able to get the actual signal level in VZAccess Manager until Monday, when I am back in my office.

In terms of getting the antenna to a higher elevation, I'm on the ridge peak of the building about 15 ft off the ground and can't get higher without putting up a mast, which I don't really want to do.

WPSANTENNAS-MATT · Posted: Sat Jun 17, 2006 5:14 pm Post subject:

Is the card being used on a desk top model or a portable notebook computer?

Is there any way that you can connect directly to the antenna that is on the roof?

With RG8X your loss is almost 10 dB on the cable alone not including any couplers you may be using
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fritodog · EVDO Newbie Joined: 19 Apr 2006 Posts: 8

The card is in a notebook and I could take it up on the roof and connect directly (without the amp)...it would require climbing up a ladder with notebook in hand, but could be done.

I take it you are thinking this will give me a benchmark of what is possible without the 50 ft cable run. How does the amp play into this test? Or should I try both setups with the amp out of the equation?

Lastly, when you say the loss is almost 10 dB for the 50 ft cable run, does that mean a 0.2 dB loss for each foot? In other words, if I shortened the cable run to 25 ft, would my loss be cut in half...down to 5 dB?

WPSANTENNAS-MATT · Posted: Sun Jun 18, 2006 8:07 am Post subject:

The shorter cable length will help in compensating for the cable loss.

Here is a cable coax loss calculator that is very helpful in determining cable loss.

http://www.timesmicrowave.com/cgi-bin/calculate.pl

I would do the test on the roof with and without the amplifier and run several speed tests.

I would also try the speed test with no external antenna or amplifier connected (while on the roof) so you can find out what your “baseline” signal is. Do you have the ability to get the actual dB reading from the card or just the signal bars?

The cable may not have that much effect on the speed so I would hate to see you invest time in shorting the run to find out that it was a waste of time.

The RG8X cable is quite a bit higher loss than the LMR-400 so if you find a big increase in the signal when you connect it directly to your rooftop antenna I would even consider replacing the run with a higher quality cable.
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