Question about coax cable and length

[petbytes]

I’m looking at purchasing an Icom R75 receiver and a LF Engineering H-900 Probe Antenna. http://www.lfengineering.com/downloads.htm

This is my first SW base receiver so I’m starting out with the basics.

I have restricted antenna placement so my plans are to mount the antenna outside on the roof edge my house at the highest point.

I’ll run the coax through the side of the house (stucco) and drop it down into the wall. The whole run will be about 25 feet (about 8 feet of the coax will be outdoor but mostly below the roof overhang).


The antenna comes with 50ft of RG-174/U with an RCA coax lead-in.

Is it Ok to shorten it?

Will the RG174U be Ok for my set up?

Thanks much!

 

[W4KRR]

I’m looking at purchasing an Icom R75 receiver and a LF Engineering H-900 Probe Antenna. http://www.lfengineering.com/downloads.htm

This is my first SW base receiver so I’m starting out with the basics.

I have restricted antenna placement so my plans are to mount the antenna outside on the roof edge my house at the highest point.

I’ll run the coax through the side of the house (stucco) and drop it down into the wall. The whole run will be about 25 feet (about 8 feet of the coax will be outdoor but mostly below the roof overhang).


The antenna comes with 50ft of RG-174/U with an RCA coax lead-in.

Is it Ok to shorten it?

Will the RG174U be Ok for my set up?

Thanks much!

Yes, it's okay to shorten the cable. RG-174/U is very small coax, and I'm not sure why they would include that type of coax with an antenna. That coax would have an unacceptably high signal loss at VHF and UHF frequencies, but for shortwave, it might be okay, especially if it's under 25 feet.

 

[n5usr]

According to this coax loss calculator:
http://www.ocarc.ca/coax.htm

50 feet of RG174 will have roughly 2dB of loss at around 25MHz, dropping to 1dB around 7MHz. Not too bad, actually. You could cut that loss in half by using RG58, so if you aren't hearing weak signals well you could switch and still have a fairly thin and unobtrusive cable.

Edit: And I just realized the antenna COMES with 50 ft, and you want to use 25. At 25 feet, the losses are cut in half, so 1dB@25MHz and 0.5dB@7MHz. Even nicer.

 

[elk2370bruce]

For receiving purposes, this will do because the length of the antenna is far less critical than for transmitting and the coax run is rather short. If you are unhappy with the sensitivity, you can easily experiment with a length of RG-8x at minumum cost so long as you avoid RatShack coax (but that is another topic). The Icom R75 is a nice receiver and you'll have loads of fun with it. I've used a random length wire antenna wrapped around a couple of trees for SWL of about 100 feet and had a ball for many years. The amateur radio transceiver antenna is an entirely different kettle of fish that requires calculation and tweaking.