Hello all, I have a question I think I know the answer to, but being new to base station type scanner radios and outdoor antenna's I find myself second guessing so much that I do. I have a Diamond D-3000 discone antenna that's split between 2 radios I'm using a Strideberg active splitter to connect the 2 radios, I get mixed reception sometimes it's really good and other times I know I am missing calls be dispatched, I have a 50 ft run of RG-58 coax going to my antenna, but after remeasurement I think I can get away with using only 30ft. of coax. Is that extra 20 ft of coax hurting my radio signal strength and reception all that much ? I've read where it makes a big difference having too much coax and other articles say it's not a big deal could someone please give me their opinion on this coax issue ? I would greatly appreciate it. Thank You very much E.L.
Too much Antenna Coax ?
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rf_patriot200
Active Member
RG 58 can have a Lot of attenuation loss, especially at UHF and above. So, the shorter the better, OR invest in Lower loss cable like LMR 240 or RG 6 Quad Shield which will have lower loss figure than RG 58.
mmckenna
I ♥ Ø
All coaxial cable has loss. Loss is what reduces the amount of signal between the antenna and your radio.
Couple of things:
The longer the coax, the more loss.
The higher the frequency, the more loss.
Different types of coax have different amounts of loss. Cheap/small coax usually has more loss. More expensive/larger coax has less loss.
You want to reduce losses, if you can. Since you cannot change the frequency of the station you are listening to, you want to change the other two and/or add more antenna gain. Since discone antennas have zero gain, that's not helping you.
You didn't saw what frequencies you are listening to, that will play into the amounts.
RG-58 is a pretty lossy coax. It's fine for short runs, like in a mobile application. It's not great for base station use when you are trying to reach an outdoor antenna up on the roof.
If you are listening to an 800MHz radio system, you are losing almost 80% of the signal in the cable. Shortening it to 30 feet will result in about 60% of the signal being lost.
Stepping up to a better cable will improve things. How much improvement will depend on how much you want to spend.
From cheap to expensive, or cents per foot to dollars per foot:
RG-6, mentioned above, will result in a little less than 50% of your signal lost in a 30 foot run.
RG-8 will lose about 25% of your signal.
LMR-400 will lose about 23% signal loss
LMR-600 = 16% signal loss
1/2" Heliax = 14% signal loss
7/8" Heliax = 8% signal loss
1 5/8" Heliax = 5.5% signal loss.
If you are listening to lower frequencies, then the losses are even less.
You can calculate it yourself here: Coax Calculator
Couple of things:
The longer the coax, the more loss.
The higher the frequency, the more loss.
Different types of coax have different amounts of loss. Cheap/small coax usually has more loss. More expensive/larger coax has less loss.
You want to reduce losses, if you can. Since you cannot change the frequency of the station you are listening to, you want to change the other two and/or add more antenna gain. Since discone antennas have zero gain, that's not helping you.
You didn't saw what frequencies you are listening to, that will play into the amounts.
RG-58 is a pretty lossy coax. It's fine for short runs, like in a mobile application. It's not great for base station use when you are trying to reach an outdoor antenna up on the roof.
If you are listening to an 800MHz radio system, you are losing almost 80% of the signal in the cable. Shortening it to 30 feet will result in about 60% of the signal being lost.
Stepping up to a better cable will improve things. How much improvement will depend on how much you want to spend.
From cheap to expensive, or cents per foot to dollars per foot:
RG-6, mentioned above, will result in a little less than 50% of your signal lost in a 30 foot run.
RG-8 will lose about 25% of your signal.
LMR-400 will lose about 23% signal loss
LMR-600 = 16% signal loss
1/2" Heliax = 14% signal loss
7/8" Heliax = 8% signal loss
1 5/8" Heliax = 5.5% signal loss.
If you are listening to lower frequencies, then the losses are even less.
You can calculate it yourself here: Coax Calculator
mmckenna
I ♥ Ø
Just to be clear, this is -NOT- a complete list of suitable (and not so suitable) coaxial cables. It's a cross section of what is out there. Lots of variants above, below and in between these.
Ubbe
Member
Is it from the same system or frequencies that it varies that much? Then it can be desense that another strong transmitter interfere too much and your receiver looses sensitivity. What receiver/scanner do you use and can you set it to show digital bit errors that would be a great indicator to check receive quality.
It can also be a bad connector that moves when the wind caches a coax that hasn't been secured. Also if you receive systems above 500MHz a full size discone type antenna works much worse than a simple 1/4 electrical wire. RG58 can be used at VHF and lower frequencies and as short lengths when connecting to a scanner from multicoupler.
Another thing with Uniden scanners and their digital reception are that it can have bugs and its a beta firmware out that's being tested that seems to make digital decode much better to not skip calls, that has been an issue for ages.
/Ubbe
Hello there M Mckenna thank you for your response, I have a 30ft section of RG-8 that I wanted to substitute for that 50ft line I'm using now. I'm using 2 Uniden scanners(#1 SDS 200, #2 BCT15X) I listen to multiple frequencies the BCT15X is programmed with all analog conventional frequencies from 42.600 to 156.000 to 400MHz, on the SDS 200 I have several p25 systems programmed that go in to the 800MHz range, some is simulcasted, I seem to have my issues with the P25 systems(and its usually the system that's the furthest away about (30-35 mi), and short of increasing my antenna height another 10-15 ft I assumed using a shorter length of coax might be the easiest and least expensive way to help myself based upon what I have read. For 25 years I used handheld scanners and never thought twice about antennas or coax etc. Now that I have a bit more invested in radios I'm trying to get the best reception possible and with all I have read one minute I think I have it figured out what I need to do and the next I've read something else that's telling me something completely different. It gets a bit confusing. Thank You for your help E.L.
mmckenna
I ♥ Ø
It should improve your reception, if that cable is good. Just make sure you water proof -ALL- your outdoor connections.
If it'll improve it enough to fix the issue, if it is a signal strength issue, that will be something you'll have to figure out.
Glad we could help.
Hello M McKenna sorry to bother you again, I looked at my 30ft section of coax as I was sure it was RG-8, its not it is 5D-FB which I'm being told is equal to LMR 400 or LMR 300 , Is that correct ? Thank You again for all your help , E.L.
mmckenna
I ♥ Ø
No idea what that is. I'll try to look it up tonight.
unitdelta
Member
Specs don’t look overly great. Losses on the specs seems to be measured in meters…
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Ubbe
Member
It's spec are pretty much like a RG6 but can handle many kW of power. 30ft have a 2dB attenuation at 900MHz.
/Ubbe
/Ubbe
rf_patriot200
Active Member
RG8 Does have More shielding than RG58, so Yes that would be a better choice.
mmckenna
I ♥ Ø
So, looks like you got the answer. I've been on the road and haven't been able to check.
Since it sounds like you need to replace our coax, I'd start with the LMR-400. You can order custom lengths/connector configurations from a few dealers on line.
Get the correct connector to match the base of the antenna.
Don't forget waterproofing the connector if it's outdoors.
Don't connect LMR-400 directly to a scanner. Use a short flexible jumper. This stuff is stiff and will break radio antenna jacks.
G7RUX
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You can go bonkers with feeders but for most scanning/amateur radio use you probably don't need to go much beyond LMR400 or 600 unless you are looking at long runs or particularly high frequencies or powers, when you would need to start looking at something more serious. A couple of lengths of LMR400 would serve you very well for most purposes.
