Signal Loss on Cables?

[dmc83]

I am currently using a 75 ft RG 6 cable. According to https://www.wilsonamplifiers.com/blog/u ... ete-guide/ I am losing 6.225 dB on 800 Mhz and 10.1125 dB on 1900 Mhz with this cable. According to the same page, switching to a 75 ft Wilson 400 cable would basically half that. If I switched to a 30 ft Wilson 400 cable I would be down to 1.3 dB loss on 800 Mhz and 2.1 dB loss on 1900 Mhz. That is a drastic difference out here in the woods where i'm often flirting with the -120 dead signal range. I just want to make sure i'm getting this right before I buy the cable. Thank you.

[terryjett]

Looking at cable specs on this cable https://www.wilsonamplifiers.com/wilson ... le-952375/ (no clue exactly which cable you are talking about, so have to assume):

LOSS PER 10-FEET (800 MHZ) 0.45 dB
LOSS PER 10-FEET (1900 MHZ) 0.7 dB

75ft / 10ft = 7.5 x 0.7 = 5.25 dB

So Est loss for 75 ft @ 1.9GHz is 5.25 dB

That is HUGE difference if you are currently losing 10.1125 dB @ 1.9GHz (1900MHz)

[Didneywhorl]

RG6 cable isn't the right Ohms. LTE antennas use 50 Ohm coax, RG6 is 75 Ohm. Unless there's some RG6 out there that is 50 Ohm?

[terryjett]

RG6 cable isn't the right Ohms. LTE antennas use 50 Ohm coax, RG6 is 75 Ohm. Unless there's some RG6 out there that is 50 Ohm?

Correct, RG6 is 75 Ohm. Even though there is a mismatch of 25 Ohm between the two types of cables, many still use the 75 Ohm, especially in the ham radio world where everything is 50 Ohm (or 300 Ohm with open ladder). Main issue of the mismatch is heat from transmitter. It also drives the SWR up some.

I do not recommend others use 75 Ohm cable, but I do in many "roll my own builds". Do not do like me, it may cause harm to you equipment and vision

[Didneywhorl]

I think the bigger issue resides in the high frequency wave lengths are more effected by higher ohm cables. I'm DEFINITELY no expert though, lol.

[terryjett]

I think the bigger issue resides in the high frequency wave lengths are more effected by higher ohm cables.

Could be. No expert either. Started in radio electronics (microwave communications) way back in 1978 when joining the military and learned little bit.

Something to consider though: RG6 that is installed for satellite is rated to 3GHz. Good RG6U Quad Shield has a loss of about 10db @ 100 ft (based on 2250Mhz). So if I were to use 25 ft @ 2250Mhz would be about 2.5db loss.

Again not saying people should be using RG6. Only pointing out the loss. Stick with low loss 50 Ohm cable as all our equipment is designed for 50 Ohm cable.

[Didneywhorl]

I wonder if voltage plays a part? These little modems aren't using but what 3 volts? Satellite dishes and cable networks have to be using power supplied voltages of at least 12v?

You got me brainstorming why this does that and where it doesnt, blah blah blah. LOL

[terryjett]

I wonder if voltage plays a part?

Chart for the MC7455 Modem showing power requirments:

mc7455-power-requirements.png

Power supply output voltage has absolutely nothing to do with coax signal levels in this case. Input voltage is driving the electronics + modem. There is oscillating voltage associated with the signal level output (coax) though.

You are getting into transmission properties and it is a lot more complex that what the input voltage to equipment is.

I think we (or just me) are getting way off the original OP's question though:) Maybe we need to get together and talk about radio / transmission properties over a cold one, lol Matter of fact about that time now...

[SliverGT]

Can you install the modem in a weatherproof box and mount it close to the antennas?

[Didneywhorl]

Can you install the modem in a weatherproof box and mount it close to the antennas?

If your asking in general, then yes. IF your asking the OP, then I'll be quiet.