Coax Antenna lead in

[Blueliner]

OK, I'm just the odd day here and day there SWL listener with two antennas. One is a MLA 30+, the other a long wire SWL Endfedz by Virbroplex. I just manually connect and disconnect these with a Coax feed line going into my basement office / sometimes "radio shack".

I've been using SDRplay Uno and a little bit of their newer SDR Connect both of which are great in my opinion.

Here is my dumb question:
I have very thin coax that was supplied with the MLA 30+ that seems to work just fine. However, the SWL Endfedz came with a length of RG 8x lead in.
Am I losing anything on the MLA 30+ by using the thin coax supplied or is there any real difference. My radios are about 25 to 30 feet away from the antennas outside of the concrete block basement wall.

And if you could, what is the difference between the thin coax and the RG8X in terms of it being used for SWL listening purposes.

Thanks in advance for any and all comments.

 

[mmckenna]

There are online coax cable loss calculators that will let you compare different cables.

Coax loss goes UP as length goes UP
Coax loss goes UP as frequency goes UP

So, just ball-parking things here:

25MHz. 300 feet of cable.
Your "thin coax" may be RG-174.
Losses for that is about 1.2dB, or about 24% signal loss.

For the RG-8X:
Losses about 0.45dB, or about 10% signal loss.

As you go DOWN in frequency, the loss numbers will improve.

So, the RG-8X is performing a bit better.
However, before you start replacing coaxial cable, it gets pretty hard to notice some of these small differences. You might put money/effort into changing out the RG-174 and not notice any perceptible difference in the signal. Or you might….

Also, when changing out coax, try to change everything out. Don't add coaxial adapters to make the wrong ones work. Each connector adds a bit of loss on its own.

Coax Loss Calculator | KV5R.COM

 

[Blueliner]

Thank you. Not sure I am going to try full replacement, as the thin coax enters the weathertight MLA box without n external connector.
Haven't had complaints about it but wondered about the differences in these two types of coax.
Thanks for the explanation, very helpful indeed.

 

[mmckenna]

Thank you. Not sure I am going to try full replacement, as the thin coax enters the weathertight MLA box without n external connector.
Haven't had complaints about it but wondered about the differences in these two types of coax.
Thanks for the explanation, very helpful indeed.

Yeah, I wouldn't mess with it. At the low frequencies those antennas cover, coax loss isn't as big a deal as it is on the higher frequencies.

 

[WA8ZTZ]

So, just ball-parking things here:

25MHz. 300 feet of cable.
Your "thin coax" may be RG-174.
Losses for that is about 1.2dB, or about 24% signal loss.

only 1.2db loss per 300' of rg174 @ that freq seems kinda low ?

 

[Blueliner]

I only use about 25' of this thin stuff, and the antenna just doesn't get much of anything on the higher frequencies, so not much consequence.
Again, appreciate the comments they are helpful.

 

[mmckenna]

only 1.2db loss per 300' of rg174 @ that freq seems kinda low ?

Typo. Meant 30 feet. Sometimes the fingers go faster than the brain.

 

[mmckenna]

25MHz. 300 feet of cable.

This should have said "25MHz. 30 feet of cable."

 

[WA8ZTZ]

Typo. Meant 30 feet. Sometimes the fingers go faster than the brain.

OK, got it... just didn't seem right to me initially.

 

[WA8ZTZ]

Yeah, I wouldn't mess with it.

Agree, not worth messing with it if it's only 30' on an active antenna for HF SWL.

 

[mmckenna]

Agree, not worth messing with it if it's only 30' on an active antenna for HF SWL.

Right, often the "active" antennas have an amplifier in them that are design to overcome coax losses. Unless you needed to add a lot more cable, it's probably working as designed.

 

[Blueliner]

I think I'll just try to raise the height of this existing MLA 30+. Right now it is about 12' off the ground on a PVC pole. It is on the down hill side of my house outside the walk out basement's wall, the base being about level with the basement floor. Hillside slopes away significantly, and slopes up significantly around the corner of the house. So the loop is at about mid high in the upper part of the house. I can gain at least another 10' just by moving it around the corner of the house where the hillside slopes up quite a lot. Would be almost the same lead in, maybe another 5 to 10 feet.

Thanks for the comments and suggestions.

 

[merlin]

Why I use ladder line feed. 100 foot, just under a Db loss.

 

[Dovebar1]

I think I'll just try to raise the height of this existing MLA 30+. Right now it is about 12' off the ground on a PVC pole. It is on the down hill side of my house outside the walk out basement's wall, the base being about level with the basement floor. Hillside slopes away significantly, and slopes up significantly around the corner of the house. So the loop is at about mid high in the upper part of the house. I can gain at least another 10' just by moving it around the corner of the house where the hillside slopes up quite a lot. Would be almost the same lead in, maybe another 5 to 10 feet.

Thanks for the comments and suggestions.

On Youtube if you look up DX Commander
he has videos on small square loops on the ground. That might be worth trying.