scanner coax cable

[squad2lt]

I am using RG6u 75 ohm cable for about a 75ft run with a 36bd amplifier connected to a VHF loop dipole antenna that I have connected to the scanner in my office. Our radio guy told me I shouldn't be using that cable. I know usually 50ohm cables are used with scanners but if I switched cables would I notice any change in my reception? I do plan on changing the antenna to a multiband antenna eventually. I listen to UHF/700/800 primarily. Thanks in advance.

 

[bb911]

If your RG6u is good quality it is more than ok. In fact, changing to 50 ohm coax would likely cause your signal to weaken, unless you were to get an amp with 50 ohm input/outputs.

 

[mmckenna]

36dB is a LOT of amplification, and probably not doing you any favors. It's going to boost noise as well as the stuff you are trying to listen to.

RG-6 will work fine. Yes, its 75Ω cable, but unless you know for sure your antenna is 50Ω, then I wouldn't get hung up on it. Scanner antenna inputs are rarely 50Ω across their operating range.

If you are going to install a new antenna, it might be worth considering upgrading your coax. I'd ditch the amplifier and use lower loss cable. How much cable do you actually need to get from your antenna to your radio? Would it be possible to reduce that length?

 

[G7RUX]

The mismatch losses from using 75 Ohm coax nstead of 50 are not large at all…

 

[Ubbe]

with a 36bd amplifier connected to a VHF loop dipole antenna

I don't know of any amplifier that will do 36dB. What is the model and you just have the coax connected directly to your scanner with no splitters or extra attenuation? RG6 attenuates 6dB at a 100ft lengthusing 900MHz, so 4.5dB at 75ft and if any SWR a little bit more, like a 75 to 50 ohm mismatch will drop the signal 0.4dB

Usually a scanner can't take more than a 10dB increase in a very RF quiet environment far from any transmitters and that would be a 15dB gain amplifier with that coax and at 900Mhz. At VHF your coax has less than 2dB attenuation and a 12dB gain would be the absolute max.

/Ubbe

 

[merlin]

Your coax is just fine, you would not improve any to change that unless your run extends over 100 foot.
>>> Your preamp is way to hot. I use 15 Db preamp, and it usually stays off. If anything, I often have to turn on the attenuator.
That is with a discone with little gain.