Question about baluns and cables

[LIScanner101]

My old but “still new in box” Monitenna is, as many of you know, a wideband dipole, so it needs a 300-ohm-to-75-ohm balun in order to connect it to traditional RG-6 and F style connectors. This will be used for scanning ONLY (NO transmitting).

Since the cable is, as I suspect, old and inferior to what’s out there today I was considering upgrading to something like brand-new quad shield satellite TV cable. Then I thought – why stop there? Why not upgrade to something even BETTER, like LMR-400 or LMR-600? Less loss, right? Problem is, those are 50 ohm cables. What would happen if I connected these to the balun's output? Would I lose a lot of signal? Is it a “myth” that you have to use 75 ohm cable on a balun when you’re just scanning?

 

[n5ims]

My old but “still new in box” Monitenna is, as many of you know, a wideband dipole, so it needs a 300-ohm-to-75-ohm balun in order to connect it to traditional RG-6 and F style connectors. This will be used for scanning ONLY (NO transmitting).

Since the cable is, as I suspect, old and inferior to what’s out there today I was considering upgrading to something like brand-new quad shield satellite TV cable. Then I thought – why stop there? Why not upgrade to something even BETTER, like LMR-400 or LMR-600? Less loss, right? Problem is, those are 50 ohm cables. What would happen if I connected these to the balun's output? Would I lose a lot of signal? Is it a “myth” that you have to use 75 ohm cable on a balun when you’re just scanning?

Probably should just use some new quad shield RG-6. The loss will be acceptable for what you're using unless the run is way over 100' or so. The impedence will be correct. The connectors will be correct (no adapter loss). Installation will be easier than the thick and stiff LMR coax.

That said, if that last microvolt of signal (you may never see it, but still) is necessary for your situation, check with your local Cable TV folks to see if they have any end-of-reel runs of their thick and stiff stuff (not the drop coax, their pole to pole cable). That'll give you the right impedence and a bit lower loss, but will be harder to install than your typical RG-6QS.

You probably wouldn't notice the loss using the LMR-400 attached to your balun, but you'll probably have more loss in the required adapter than you'll gain using that coax over RG-6QS. Remember that it generally isn't that important to have the absolute most signal you can get (that can even make things worse). You only need enough signal to do the job, anything more is wasted or even overloading your receiver! Where the very low loss coax is important is when you have a very long run between your antenna and receiver.