LMR vs. RG-6 cable

[ansky]

I have my HP2 connected to an outdoor antenna with 50 feet of RG6 cable. I use it specifically to pull in a couple distant frequencies. One comes in with 3 of 4 bars, and the other comes in with 1 of 4 bars on my signal meter. If I switch to LMR do you think it would have any noticeable improvement in reception? LMR cable isn't cheap so I don't want to spend the money if it won't make much difference.

Also, does LMR cable have the same coax connector as RG6 cable, or would I need some type of adapter?

 

[mikewazowski]

LMR what? LMR comes in various types.

 

[KevinC]

Here's a good coax loss calculator...

Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator

Enter your coax type, frequency and coax length and see for yourself what the difference would be.

And they use different connectors.

 

[KE0GXN]

I have my HP2 connected to an outdoor antenna with 50 feet of RG6 cable. I use it specifically to pull in a couple distant frequencies. One comes in with 3 of 4 bars, and the other comes in with 1 of 4 bars on my signal meter. If I switch to LMR do you think it would have any noticeable improvement in reception? LMR cable isn't cheap so I don't want to spend the money if it won't make much difference.

Also, does LMR cable have the same coax connector as RG6 cable, or would I need some type of adapter?

Not sure on the adaptor question.

But here is a thread I started a while back that has some good information on coax stuff by some real knowledgeable members that helped me out:

http://forums.radioreference.com/scanner-receiver-antennas/320122-mobile-base-converter-kit.html

Hope that helps.

 

[cavmedic]

Use some RG11. It is less loss than RG6 and will be cheaper than LMR 400.

 

[Blackswan73]

Use some RG11. It is less loss than RG6 and will be cheaper than LMR 400.

If he is wanting to maximize his reception, the last thing he wants is 75 ohm coax to feed a 50 ohm radio. Depending on how long your feed line is, you might good good improvement with the least cost, with RG 8, or RG 8x also known as mini 8. However at UHF freqs, the LMR400 will deliver the most signal at the least loss.

 

[jack103]

Here we go again ! No difference on receive only!

 

[ridgescan]

I love the LMR240. Most folks don't know of it. Good cable.

 

[Blackswan73]

Here we go again ! No difference on receive only!

For most, that is true, but the OP is talking about boosting fringe reception. Depending on the length of his coax run, using a 50 ohm coax instead of a 75 ohm coax could indeed make a difference. Since the impedence of the radio is 50 ohm, using a 75 ohm coax is already starting with a 1.5 :1 mismatch. Add that to the loss of a long cable run, say over fifty feet, and fringe reception will definitely be affected.

 

[KE0GXN]

I love the LMR240. Most folks don't know of it. Good cable.

I agree, but I ended up replacing my LMR 240 25 foot run with a 15 foot run of LMR 195UF. The LMR 240 was a bit to stiff for my liking and I feared the stress it may have been putting on my SMA antenna connector on my scanner. If I could do all over again I would have gone with LMR 240UF or just got the 195UF to begin with. I also didn't need the 25 feet run, the 15 foot run I got now works for my application. Live and learn...

With that said, maybe I was freaking out for no reason, but to me the LMR 240 seemed like it could stress my antenna connection if I was not careful all the time. I am using a mobile base kit that I move around from room to room in my house, so at the end of the day I felt more comfortable with the 195UF. With such a short run, I loss no reception what so ever that I could tell either. ..

If I were the OP and I used either the 400 or 240, I would consider a 195UF or RG58 pigtail for the foot or so run to the actual scanner.

That's me though....for those that run LMR 240 or more to their scanners, more power to you.

 

[cavmedic]

For most, that is true, but the OP is talking about boosting fringe reception. Depending on the length of his coax run, using a 50 ohm coax instead of a 75 ohm coax could indeed make a difference. Since the impedence of the radio is 50 ohm, using a 75 ohm coax is already starting with a 1.5 :1 mismatch. Add that to the loss of a long cable run, say over fifty feet, and fringe reception will definitely be affected.

Standing wave ratio / power reflections happen from transmitting RF not receiving it.


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[AK9R]

Standing wave ratio / power reflections happen from transmitting RF not receiving it.

Standing waves can occur any time RF power is transferred. It doesn't matter whether that RF power is 50 watts or 0.5 milliwatts. There is still a power transfer and you need to minimize impedance mismatches to maximum power transfer.

 

[popnokick]

There are two things that could be critical and were not in the OP:
1) What are the "distant frequencies" the OP is trying to receive?
2) What exactly is the antenna being used?
If the intent is to improve the distant signals it may be more cost and performance effective to look at the entire system rather than simply changing the coax.

 

[jackj]

Why not?

Here we go again ! No difference on receive only!

If impedence mismatch makes a difference on transmit then it makes a difference on receive. Remember that you are talking about a mismatch at both ends of the cable. If it makes no difference on receive then why not use 124 ohm coax and get even less loss?

 

[cavmedic]

You are assuming he is using an antenna with a 50 ohm feed point.

Some scanner antennas use a 300/75 ohm transformer at the feed point such as a " scantenna"


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[dsalomon]

I usually go to DX Engineering for my coax needs. They're not the cheapest guy on the block, but the DX Engineering version of matching LMR or CNT spec cable is typically just a little bit better (lower loss) and usually less expensive than the name brand (but usually not by much). I've bought a LOT of stuff from DX Engineering over many years and I strongly vouch for them as a great company. If they have what you want in stock, it almost always ships the same day. Their support is great. If you need something you don't see on their website, they always answer the phone and are very helpful. Over the years, I've stumbled on a few companies that are great to do business with, DX Engineering is one of those companies. No, I'm not an employee or contractor, just a fan based on many excellent experiences.

Now, having said that, they sell their own version of some popular coax sizes / types. When I've needed good low loss coax, I've bought this before: DX Engineering 400MAX Low-Loss 50-ohm Bulk Coaxial Cable DXE-400MAX - Free Shipping on Most Orders Over $99 at DX Engineering. Their "400MAX" is LMR-400 equivalent, but a little less expensive. They also sell it in pre-made lengths: DX Engineering 400MAX DX Series Low-Loss 50-ohm Cable Assemblies - Free Shipping on Most Orders Over $99 at DX Engineering.

If you have the money, go for LMR600 or a good LMR600 replacement. For my discone and my 2 meter Winlink gateway antennas, I use CNT-600, which I got from Cable X-Perts (Coax Cable assemblies |RF 50 OHM| RFID Cables | Custom coax assemblies). They are also a very trustworthy company. I go there instead of DX Engineering because DX Engineering doesn't carry LMR-600 (or other brand of LMR-600 type) coax. Both of those antennas needed a 150' run. At those frequencies, the coax is the weak link in the chain. You're better off spending more money on better coax than on signal amplifiers.

Just FYI, CNT-600 is tough stuff to work with. It's thick, doesn't bend easily, and requires a different connector than the typical N connector you use for LMR-400, RG8, etc. Unless you're very comfortable with working with this stuff. I'd advise that you get pre assembled lengths (N connectors already connected on each end). For my needs, I got 2 150' CNT-600 cables from Cable X-Perts and am very happy with that purchase. It was worth the money. If you go with a CNT-600 / LMR-600 type cable, you should also go with N connectors. Use an adapter if you need to, but put N on the coax assembly - it's lower loss.

73 - David, AG4F

 

[prcguy]

Excellent point since the OP did not provide info on his antenna. I'm a stickler for using 50 ohm cable for a 50 ohm rated antenna, but for a Scantenna or other thing that is intended to use 75 ohm cable I would upgrade to low loss foam type RG-11.

For any other antenna rated at 50 ohms like a Discone or multiband ground plane, the antenna should provide close to a 50 ohm impedance on its design frequencies and you want to use the lowest loss 50 ohm cable you can afford. If you have a certain but known performance with RG-58 50 ohm coax and you upgrade to LMR-400, the improvement will be very predictable and you can figure it out from coax loss charts. If you go from RG-58 to RG-11 with a 50 ohm rated antenna all bets are off and some frequencies may have less loss and others could be way different than you expect.

Published coax loss is based on a matched system where the source and load are the same as the inherent impedance of the coax. When the source or load (antenna or radio) are a different impedance than the coax, then the coax loss goes beyond the published spec.

Bottom line is, if you have a 50 ohm rated antenna, use a good 50 ohm coax and your done. You never have to think about it again. Also be aware that most antennas (besides a Discone) will only have a good match on fairly narrow regions around where they are designed to work if the mfr is somewhat legit. Many scanner antennas are not much more than some coat hanger bits cobbled together and there is no real design behind them, so the 50/75 ohm coax argument may not apply.

An actual Discone like the RS, Icom, Diamond, Comet, Workman, etc, and not a Hustler or Centerfire, etc, will have a good match over the roughly 100 to 800MHz range and will provide a good match to 50 ohm coax over that range. This is really important if your going to use a preamp because many preamps will have oscillation problems if not terminated with a reasonable match over their entire operating range.
prcguy

You are assuming he is using an antenna with a 50 ohm feed point.

Some scanner antennas use a 300/75 ohm transformer at the feed point such as a " scantenna"


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[Blackswan73]

I guess I have been out of the loop so long I didn't even know they made a scanner antenna with a 75 ohm feed point. I have to wonder why the designers did that, unless they wanted to be able to utilize cheap 300 to 75 ohm baluns. Still, for very weak signals, that isn't going to to be a good choice for a receiver with a 50 ohm impedence. But, if the OP does have a scantenna and wants to get the best signal transfer, I would suggest replacing the the cheap TV style 300 to 75 ohm balun with a good 6:1 balun and a low loss 50 ohm feedline

 

[blackbelt76]

I have my HP2 connected to an outdoor antenna with 50 feet of RG6 cable. I use it specifically to pull in a couple distant frequencies. One comes in with 3 of 4 bars, and the other comes in with 1 of 4 bars on my signal meter. If I switch to LMR do you think it would have any noticeable improvement in reception? LMR cable isn't cheap so I don't want to spend the money if it won't make much difference.

Also, does LMR cable have the same coax connector as RG6 cable, or would I need some type of adapter?

I use LMR 400 bury cable, excellent in it's longevity over RG6 as well as lower loss, esp in the 800Mhz region.

It does not matter if one is transmitting or receiving, a micro-volt signal impinging from feed point to your HP is still transmitting a signal.

Get the proper connector.Although .RG6 connectors will work; the O.D of the cable is different. Times Microwave sells the proper connectors.
Be ready for some challenging times when stripping LMR 400 as it is dual shield, braid+aluminum.

 

[prcguy]

LMR-400 strips easily with a box knife or single sided razor blade, just go slow and be careful not to nick the center conductor. I've used many of the cheap $3 Chinese crimp connectors for LMR-400 and they are just fine. Some are even silver plated.

I've also used the Chinese screw/clamp on types similar to the older versions of N connectors for RG-213, etc, and they work great. I would not use the Chinese connectors for any critical stuff above maybe 1500MHz, but for HF/VHF/UHF use they are just fine. The clamp on types can be assembled by anyone with a razor blade, diagonal cutters and a couple of crescent wrenches and this is great for someone only doing a few connectors that doesn't want to invest in crimpers, etc.
prcguy

I use LMR 400 bury cable, excellent in it's longevity over RG6 as well as lower loss, esp in the 800Mhz region.

It does not matter if one is transmitting or receiving, a micro-volt signal impinging from feed point to your HP is still transmitting a signal.

Get the proper connector.Although .RG6 connectors will work; the O.D of the cable is different. Times Microwave sells the proper connectors.
Be ready for some challenging times when stripping LMR 400 as it is dual shield, braid+aluminum.