Cable type

[CYUL]

I'm going to be changing cables for my VHF/UHF receivers & antennas. I was wondering what would be the best type for a cable run of less than 75 feet?

Thanks
CYUL

 

[hoser147]

There are several good coax cables you could use, just depends on what you want to monitor and what you want to spend. As a standard I wouldnt use anything less than RG 6 on the cheapest end of the scale and toward the higher end would be LMR400. If the stations you monitor are close you could use RG6 if you want to pull in more distant Rx or even local portable transmissions,then I would go with something like RG 11 or 9913 or LMR400. Hope this helps.............Good Scannin Hoser

 

[af5rn]

http://www.hamuniverse.com/coaxdata.html

 

[CYUL]

So if my cable run is let's say 50 feet. How do you calculate the loss factor? Do you simply cut it in half?

Example: 100 ft of RG58 at 400MHZ loss is 10.5 DB. Would 50 feet be 5.25 DB?


Thanks
CYUL

 

[hoser147]

Forget the RG58, Go with one of the above cables, At 50 ft its really not going to be an issue, You can get the RG 6 at wallyworld for a decent price under 20 bucks for 100ft run with good crimp and seal connectors. If you really want to check out cable loss just google it you will come up with several charts.............Hoser

 

[CYUL]

But RG6 is 75 ohm cabling, would that not result in a mismatch?

CYUL

 

[PHOENIX_SCANNER]

Use heliax! LOL.

No seriously, LMR-400 flex is the best bang for the buck in my view. It's just a tad more than 9913 around here, and better for the higher frequencies. I noticed a real difference monitoring a local PD who uses 900mhz trunking, going from 9913 to LMR-400, more than I had expected. But in that case the cable run was rather long. 9913 is the minimum respectable cable for 800/900 mhz use as far as I am concerned. RS RG8 is a joke. Might as well just run RG6. Scanners don't really care if you use 75 ohm cable. Impedance matching is a big issue for transmitting, not as much for receiving.

 

[n5ims]

But RG6 is 75 ohm cabling, would that not result in a mismatch?

CYUL

Yes, but unless you transmit, you'll only see it in very marginal signal levels (where better cable than RG-6 would be necessary anyway). Moving from RG-58 to RG-6 on a scanner monitoring an 800 MHz system would reduce signal loss by about 6.5db (about 2 s-units), including any loss due to the impedence mismatch. Now if you move from RG-58 to LMR-400 you would reduce the signal loss by about 10db (just over 3 s-units).

 

[k8tmk]

For those of you who cannot relate dBs, S-units, etc., a 3 dB loss would cut the signal strength in half. A 6 dB signal loss would cut the signal strength in half again. A 10 dB signal loss would reduce the signal strength to one-tenth.

Randy

 

[CYUL]

I'm working on getting some LMR 400 UF.

Thanks
CYUL

 

[cberk01964]

I bought what was advertised as LMR-400. I received the cable today. On the cable it reads "Commiscope 0623 WBC-400". Is this LMR-400?

 

[CYUL]

seems to have the same spec's:

http://docs.commscope.com/Public/0623.pdf

CYUL

 

[btritch]

LMR 400 is about the best I've found, I changed to this on my scanner recently from RG 6 and I could tell a HECK of a difference, That's what I would recommend to anyone!

 

[PHOENIX_SCANNER]

Unless one is planning on building a 200' tower in their back yard ( I probably would if I could), LMR 400 is all you need. The real work and expense will come when you put in proper grounding / static discharge. That will cost more than your cable, and is sooo important. Don't forget that part.

 

[CYUL]

I have installed my LMR 400 UF cable. What a difference!! I'm running it into my 20 yr old Icom AH7000 Discone that is about 27 feet up. So far I'm seeing much better reception on all bands. I'm going to push it up about 6 more feet next week.

Equipment:

ICOM R7000
ICOM R7100
2X PRO 2006

Paul

 

[hoser147]

Thats good glad to hear it keep in mind Phonenix Scanners advise................Hoser

 

[rfradioconsult]

For those of you who cannot relate dBs, S-units, etc., a 3 dB loss would cut the signal strength in half. A 6 dB signal loss would cut the signal strength in half again. A 10 dB signal loss would reduce the signal strength to one-tenth.

Randy

A common mis-conception; a 3 dB loss doesn't cut the signal strength in half; 6 dB is half signal strength. Receiver sensitivity is measured in microvolts not watts. A receiver with an S meter reads 6 dB difference between each S unit, example: a reading of S7 is 6 dB less than a reading of S8.

 

[tassie]

Lmr 400

I was wondering where you purchased the LMR 400 coax ? Canada or US?

Thanks

Tassie

 

[zz0468]

A common mis-conception; a 3 dB loss doesn't cut the signal strength in half; 6 dB is half signal strength. Receiver sensitivity is measured in microvolts not watts. A receiver with an S meter reads 6 dB difference between each S unit, example: a reading of S7 is 6 dB less than a reading of S8.

Be careful there. Your post COULD be interpreted wrong.

3 db is double, or half of POWER, depending on which way you go. 10 watts to 20 watts, for example. 10 DB is factoring POWER by ten... say, 10 watts to 100 watts.

rfradioconsult's comments about how receivers are measured, is correct. In voltage (or microvolts), a factor of 10 is 20 db. 1 microvolt is 20 db stronger than a tenth of a microvolt. So, in THOSE terms, it takes a relatively large change, in terms of DB gain or loss, to translate to a change that a person would notice. Especially an FM receiver like a scanner, doubly so one without an S meter.

If you were listening to a 10 watt transmitter that was S4 on a calibrated, reasonably accurate S meter, and then that transmitter was turned up to 100 watts. That S meter reading would go from S4 to barely over S5... after increasing the power by 90 watts.

 

[n8emr]

Back to the original question. RG6 is your best band for your buck cost. For VHF and UHF your going to be hard pressed to see a real world difference between rg6 and lmr-400 unless your doing some deep DXing. For the average scanner user they will never see it.

On top of that you can pickup 1000ft of quality quad shielded rg6 for $75, Your going to be lucky to get 50ft of LMR for $75

The 75/50 ohm mismatch will in most cases never been see for the average scanner user, Again unless your deep dxing its not going to make a difference


.