What is the practical difference between RG-58 and RG-400?

Morgan3820

Morgan3820

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Today My avionics guy found that I have RG-58. He says that this should be replaced with RG-400 for my 2 coms at about $1000 labor and material. I know that the center cable is bigger in cross section but what is the practical differences between the two.
 
Morgan3820 said:
He says that this should be replaced with RG-400 for my 2 coms
Click to expand...
What's his reasoning?

FWIW: On new installs especially GPS and ADS-B, RG-400 is preferred or required. I've never read/seen any requirement to replace RG-58 on face value only.
 
It’s a lower loss cable. Double shielded to better keep noise out and signal in, center conductor is larger gauge which results in less signal loss. I don’t know that I’d go out of my way to replace com/nav with it unless you are already in there. Many transponders are requiring it (ngt-9000, gtx 3xx etc) and most GPS require it as well (though due to the low loss there is often a minimum length on the GPS cable). If the plane is already torn apart and you are pulling lots of new wires it might be worth adding it on, but unless you are having issues or your rg58 has the green crusties I’d defer it if it’s going to require opening things up.
 
Bell206 said:
What's his reasoning?

FWIW: On new installs especially GPS and ADS-B, RG-400 is preferred or required. I've never read/seen any requirement to replace RG-58 on face value only.
Click to expand...
There really wasn’t a specific reasoning, just well that’s what they’re installing now. Com 1 is not as Clear as it could be. I think it was just more of a observation that the new installs go with RG 400
 
We use RG400 on all new installs, but would never change a Com cable unless we were having problems with it.
 
There is little loss on vhf on the length of cable that you are probably using.. if it’s a new instal then yeah change it..


Sent from my iPhone using Tapatalk
 
I believe the STC for the GNS430W specifies 400 for the connection to the waas antenna.
 
Agreed. The Garmin GPS's I've installed call out RG400. But replacing RG-58 for Nav/Com radios sounds like a moneygrab to me.

That said, when I was building, I put in RG-400 for everything just in case.
 
The 'practical difference' is $1000 in your pocket vs. not having it. Is there a problem with the current install like low output or intermittent signal loss ? Is the person suggesting that this 'should' be done an avionics tech ? Does he have a boat payment ?
 
According to a wire supplier, the key difference is not shielding, but insertion loss, i.e., attenuation for the transmitter. RG400 has heavier wire and a silver coating to improve its conductance a little.
https://www.wiremasters.net/about-us/blog/new-ads-b-systems-bring-coaxial-demands-rg58-vs-rg400

I would say that if the FAA says they are receiving your ADSB, then there’s no reason to switch cables. Even if you’re losing a bit of transmit power in a cable, you’ve got enough.
 
NoHeat said:
According to a wire supplier, the key difference is not shielding, but insertion loss, i.e., attenuation for the transmitter. RG400 has heavier wire and a silver coating to improve its conductance a little.
https://www.wiremasters.net/about-us/blog/new-ads-b-systems-bring-coaxial-demands-rg58-vs-rg400

I would say that if the FAA says they are receiving your ADSB, then there’s no reason to switch cables. Even if you’re losing a bit of transmit power in a cable, you’ve got enough.
Click to expand...

Does the ADSB equipment even touch the comms cables ? Isn't that all done via the transponder or UAT ?
 
weilke said:
Does the ADSB equipment even touch the comms cables ? Isn't that all done via the transponder or UAT ?
Click to expand...
depends....if the source is already installed....it's handled with a serial connection. If not, some transponders with built in GPS source require installation of the antenna and coax.
 
Practical difference for COM radios? Unless it’s a really long cable run, I’d say the difference is negligible. Don’t go down the rabbit hole of what’s recommended or required for GPS, transponders, or ADS-B.

If your COM 1 isn’t performing well, I’d look first at the antenna and it’s grounding, then at the quality of the crimped connections on the cable ends. RG58 is fine for VHF comms.
 
Depends on age. Old coax deteriorates and becomes lossy. That may be a factor.
 
Checkout_my_Six said:
depends....if the source is already installed....it's handled with a serial connection. If not, some transponders with built in GPS source require installation of the antenna and coax.
Click to expand...

Yeah, but would ADSB ever touch the VHF 120MHz comm wiring ? Its a 978 or 1090MHz signal that is broadcast and received via a transponder antenna. You could cut the coax to COM1 and COM2 and it would make no difference to your ADSB.
 
Now that I have a real keyboard, I'll continue from post 15:

$1000 sounds high. When I have been involved with changing out coax, it is a routine thing/no brainer to change out old coax but it is done when the airplane interior is at least partially opened up for some kind of avionics install or update.

The penalty for lossy cable to the navs and comms antennas is receiving range. You will never know exactly what you have lost and, when you can't pick up ATC or a VOR, you will never know whether it is because of lossy cable. I'm not sure I would spend $1000 to forestall this problem but in general I believe that it is silly to buy a bunch of expensive radios and then to deliberately reduce their performance by hooking up known-lousy or suspected-lousy cable. For example, the HF ham antenna on my roof is connected to my transceiver using LMR-400. Many would say this is silly, because there is not a lot of difference between cheaper RG-8 or even RG-58 and the better LMR-400 at HF frequencies. But why buy a $1000+ transceiver and then cheap out for a few bucks on the cable? And $1000 is dirt cheap compared to avionics radios.

Some people don't think this way. I also have a Comet discone antenna up there for VHF and UHF. It came with a pre-assembled RG-58 cable. Crazy. Huge losses at UHF. That cable is now in my junk box and the run from the antenna to the transceiver is more LMR-400.

So .. it's partially a philosophy thing.
 
For everything up to AND INCLUDING GPS (excepting transponder) the only difference you will notice is about $2 a foot. And, I've been using 58 on transponders for years at the power levels we talk about for part 91 aircraft without a hint of a problem.

As to deterioration over the years, yeah, soak it in avgas or cigarette smoke and it deteriorates. i've got some of the original 58 in my 50 year old 182 and it is working just fine.\

Jim
 
All good info. Yes, this shop is well known for 'upselling'. Knowing this, I held them off until I found out the real deal with you guys. For GP, the next time the panel is opened I may put a new terminal on the radio side but as it stands I am not going to tear up the interior to run new coax. Thanks all
 
I would be hard pressed to believe simply changing 58 for 400 would solve anything unless the 58 was in bad, bad shape.

Sounds as if you have a comm issue and my money says the 58/400 is simply their (expensive) first stab.
 
"What is the practical difference between RG-58 and RG-400?" Just signed up for an account to answer. Got no skin in the game.

"We require users to have more than 5 posts in order to include links in posts. This is used to prevent spam."
As you can see cannot post any link to any coax calculators on Google, will do best to explain.

Using 25ft RG-58 with a 10Watt Airband transceiver at 134.0MHz, only 7.7 Watts will reach your antenna.

Using 25ft LMR-400 with a 10Watt Airband transceiver at 134.0MHz, 9.2Watts will reach your antenna.

So that is the transmit (TX) side of the business. The receive (RX) side hides even murkier truths.

The shield/braid of RG-58 is like fishnet stockings, got lotsa big and plenty holes in it, **** poor shielding.

The shield/braid of LMR-400 has a tightly woven stranded wiring pattern, beneath this is an aluminum wrap that tightly adheres to the insulation carrying the center core.

The center core of RG-58 is a few strands of whimsical wire, whereas the center core of LMR-400 is a thicker solid single copper core.

The practical difference between the 2 is in TX and RX.

This is America, it's is entirely feasible to order a 25ft length of LMR-400 with correct connectors on both sides delivered to your doorstep to do the coax change yourself.

Truthfully I'd also look at changing the aerial to something resembling a dipole. Certainly also a cross needle SWR meter to turn the exercise into a fun activity.

YMMV

Victor
 
While that calculation is correct for a perfect SWR match, most small GA airplanes won't have a 25' run of coax to the COM antenna, methinks. With a 10' run, your transmit power is 9W, before adding in connector loss. I think the coax run in my plane is about 8' total to the COM antenna. I'd be surprised if most planes are actually radiating more than half the transmit power by the time you add in connector loss, mismatch, etc.
 
Rebelrabbit said:
"What is the practical difference between RG-58 and RG-400?" Just signed up for an account to answer. Got no skin in the game.

"We require users to have more than 5 posts in order to include links in posts. This is used to prevent spam."
As you can see cannot post any link to any coax calculators on Google, will do best to explain.

Using 25ft RG-58 with a 10Watt Airband transceiver at 134.0MHz, only 7.7 Watts will reach your antenna.

You are using 25 feet of coax to connect radio to antenna? What are you wiring, a 737? I've never used over 10' in my 60 year career in CessBeePipMoo aircraft. You might want to do the path loss calculation (you do know what path loss is, yes? If not www.rstengineering.com to my freshman engineering class gives a path loss calculator) says that a 1 watt transmitter and a 1 microvolt receiver have a range of a few hundred miles. Do you really think that you need ten watts to communicate? Then you have never designed a com radio.

Using 25ft LMR-400 with a 10Watt Airband transceiver at 134.0MHz, 9.2Watts will reach your antenna.

BFD

So that is the transmit (TX) side of the business. The receive (RX) side hides even murkier truths.

I'd like to hear the murkier truths as you see it. Other than power being proportional to the square of voltage, tell us more untruths.

The shield/braid of RG-58 is like fishnet stockings, got lotsa big and plenty holes in it, **** poor shielding.

The shielding at this frequency is approximately 98%. If you've got another number, I'm willing to put up my references.

The shield/braid of LMR-400 has a tightly woven stranded wiring pattern, beneath this is an aluminum wrap that tightly adheres to the insulation carrying the center core.

BFD

The center core of RG-58 is a few strands of whimsical wire, whereas the center core of LMR-400 is a thicker solid single copper core.

And I'm sure with your VAST (or is it half-vast) experience, you understand that RG-58 only has one variant with stranded; most of the 58 is solid core, and that is the one we use in avionics.

The practical difference between the 2 is in TX and RX.

That makes no English sense whatsoever, nor have you proven your point.

This is America, it's is entirely feasible to order a 25ft length of LMR-400 with correct connectors on both sides delivered to your doorstep to do the coax change yourself.

The first truth of this entire post.

Truthfully I'd also look at changing the aerial to something resembling a dipole. Certainly also a cross needle SWR meter to turn the exercise into a fun activity.

Truthfully, how in the hell do you get a dipole onto a metal ship? And in this country we call them antennas, not aerials. I see an ivory tower egghead that has never done an installation in his/her life. And most of us use Bird bidirectional wattmeters and calculate VSWR (not SWR with no reference). and you may think it is fun. The rest of us put the results into the logbook.

YMMV

Amen to that, especially if you listen to this clown.


Victor
Click to expand...
Jim .........
 
Jim, don't hold back, man. It's bad for the heart to bottle it all up. Tell us how you really feel. :)

I too was amused by the dipole thing. Nice trick, if you can do it.
 
DaleB said:
While that calculation is correct for a perfect SWR match, most small GA airplanes won't have a 25' run of coax to the COM antenna, methinks. With a 10' run, your transmit power is 9W, before adding in connector loss. I think the coax run in my plane is about 8' total to the COM antenna. I'd be surprised if most planes are actually radiating more than half the transmit power by the time you add in connector loss, mismatch, etc.
Click to expand...

Indeed so, the losses can increase even further unless a perfect match is present. The further away from 50 ohms the aerial is matched, the higher the losses. 50 ohm coaxial cable is designed to carry 50 ohm loads. The reduction in TX power reaching aerial is also another clue that your RX will also be similarly affected. Unfortunately connector loss is inherent across all types of coaxial cables employed, at least using a better coaxial cable can mitigate the losses.
 
"What is the practical difference between RG-58 and RG-400?" Just signed up for an account to answer. Got no skin in the game.

"We require users to have more than 5 posts in order to include links in posts. This is used to prevent spam."
As you can see cannot post any link to any coax calculators on Google, will do best to explain.

Using 25ft RG-58 with a 10Watt Airband transceiver at 134.0MHz, only 7.7 Watts will reach your antenna.

You are using 25 feet of coax to connect radio to antenna? What are you wiring, a 737? I've never used over 10' in my 60 year career in CessBeePipMoo aircraft. You might want to do the path loss calculation (you do know what path loss is, yes? If not www.rstengineering.com to my freshman engineering class gives a path loss calculator) says that a 1 watt transmitter and a 1 microvolt receiver have a range of a few hundred miles. Do you really think that you need ten watts to communicate? Then you have never designed a com radio.

Using 25ft LMR-400 with a 10Watt Airband transceiver at 134.0MHz, 9.2Watts will reach your antenna.

BFD

So that is the transmit (TX) side of the business. The receive (RX) side hides even murkier truths.

I'd like to hear the murkier truths as you see it. Other than power being proportional to the square of voltage, tell us more untruths.

The shield/braid of RG-58 is like fishnet stockings, got lotsa big and plenty holes in it, **** poor shielding.

The shielding at this frequency is approximately 98%. If you've got another number, I'm willing to put up my references.

The shield/braid of LMR-400 has a tightly woven stranded wiring pattern, beneath this is an aluminum wrap that tightly adheres to the insulation carrying the center core.

BFD

The center core of RG-58 is a few strands of whimsical wire, whereas the center core of LMR-400 is a thicker solid single copper core.

And I'm sure with your VAST (or is it half-vast) experience, you understand that RG-58 only has one variant with stranded; most of the 58 is solid core, and that is the one we use in avionics.

The practical difference between the 2 is in TX and RX.

That makes no English sense whatsoever, nor have you proven your point.

This is America, it's is entirely feasible to order a 25ft length of LMR-400 with correct connectors on both sides delivered to your doorstep to do the coax change yourself.

The first truth of this entire post.

Truthfully I'd also look at changing the aerial to something resembling a dipole. Certainly also a cross needle SWR meter to turn the exercise into a fun activity.

Truthfully, how in the hell do you get a dipole onto a metal ship? And in this country we call them antennas, not aerials. I see an ivory tower egghead that has never done an installation in his/her life. And most of us use Bird bidirectional wattmeters and calculate VSWR (not SWR with no reference). and you may think it is fun. The rest of us put the results into the logbook.

YMMV

Amen to that, especially if you listen to this clown.


Victor

Your behavior indicates you seem to have gone off the deep end here. To be honest I am not insulted easily, and perhaps I don't even view your comments as insults actually.

The best defense though is not via ad hominem but facts, and I like dealing with those, because the only thing that is valid ultimately is truth.

Your behavior has merely displayed what exists between your ears :)

Victor
 
There is no COM antenna which provides a perfect match at all frequencies you'll want to use, or even at any frequency as they come out of the box. If you're lucky you'll see an SWR of 1.5 over about a 4 MHz range, worse above and below. I tuned my com antenna for about 121 MHz, since I most often transmit on 118 - 123 MHz.

Old RG58 is often much better than the crap they sell today. CBers can get away with lousy cable at 27 MHz. Losses are much higher at VHF.
 
PW_Plack said:
There is no COM antenna which provides a perfect match at all frequencies you'll want to use, or even at any frequency as they come out of the box. If you're lucky you'll see an SWR of 1.5 over about a 4 MHz range, worse above and below. I tuned my com antenna for about 121 MHz, since I most often transmit on 118 - 123 MHz.
Click to expand...

Sure. A quarter wave whip over an infinite ground plane has a purely resistive impedance of 32 ohms, and since 50/32 = 1.56 you will in fact see about a 1.5:1 VSWR. Below resonance the complex impedance will be capacitive/resistive and above resonance inductive/resistive. At some point the complex impedance will be 50 +/- jx which may or may not drive certain bridges to null. It will NOT confuse a bidirectional wattmeter, which is why most professional antenna installers use one. All you really care about is how much of that hundred-dollars-a-watt power is heating up the atmosphere and not reflected back down the line to heat up the final transmitter stage.

Jim
 
PW_Plack said:
Old RG58 is often much better than the crap they sell today. CBers can get away with lousy cable at 27 MHz. Losses are much higher at VHF.
Click to expand...
Amen to that. The crap coming out of China most often isn't within spitting distance of constant impedance and I think they use rendered pig fat for the dielectric. Belden, on the other hand, I would gladly wire into a manned capsule on a moon mission.

Jim
 
weirdjim said:
Amen to that. The crap coming out of China most often isn't within spitting distance of constant impedance and I think they use rendered pig fat for the dielectric. Belden, on the other hand, I would gladly wire into a manned capsule on a moon mission.
Click to expand...
Bought a cheap pre-made RG-58 cable on Amazon to cut off the connectors and use for stock. Turns out the "braid" is aluminum foil.

Ron Wanttaja
 
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