Fancy speaker cable as feedline

[KI4NVL]

I'm currently using a hunk of radioshack twinlead (the stiff, foam filled black stuff) for my QRP portable operations... I have a spool of this:

http://www.monstercable.com/productdisplay.asp?pin=81

They call the conductors 12 gauge... they seem bigger to me though, and each is composed of LOTS of tiny copper wires, so this is very flexible cable, and fairly lightweight.

Anyone have any thoughts on how this will perform compared to my current RS cable? I plan to test it out this weekend...

Also, any suggestions for a lightweight, flexible, good performing parallel feedline for QRP/portable?

Regards,

Brian/KI4NVL

[WX7G]

The Monster cable will have a characteristic impedance around 100 ohms. I expect that it will work just fine. Give it a try.

[WA7NCL]

I know what you mean about the stiff cheap tv cable.  One thing I have done is use a leather punch and punch a bunch of holes between the wires in the twin lead to reduce the amount of dielectric between the wires and make it more flexable.

In the end I have decided to use RG-174 coax with a variable length dipole instead of the twin lead with a fixed length dipole.

The coax has the benefit of being able to toss part of it on the ground and is easier to get in and out of my back packing tent without worrying about it laying on the ground.  

I have various tap points on the dipole for various bands. I don't seem to need a tuner either since the swr is usually low.  The loss of 20 or 30 feet of RG-174 is acceptable on HF as well.  And... its very flexable.

[VK1OD]

I'm currently using a hunk of radioshack twinlead (the stiff, foam filled black stuff) for my QRP portable operations... I have a spool of this:

http://www.monstercable.com/productdisplay.asp?pin=81

They call the conductors 12 gauge... they seem bigger to me though, and each is composed of LOTS of tiny copper wires, so this is very flexible cable, and fairly lightweight.

Anyone have any thoughts on how this will perform compared to my current RS cable? I plan to test it out this weekend...

Brian,

Transmission line losses are mainly due to conductor loss and dielectric loss. For quality transmission lines at HF which typically use polyethylene (PE) or PE foam, dielectric loss is insignificant. For example, Loss components in practical transmission lines at HF shows that dielectric loss in RG213 is much less than copper loss over HF, and relatively insignificant.

PVC is widely used for insulation of power, audio, and telecommunications cables, and it is significantly lossy at HF.

K8ZOA characterised common ZIP cord (which uses PVC insulation), and the data is in TLLC. Taking a dipole at 14MHz (say feed point Z=60+j0), and 25m of ZIP feedline, the efficiency of the feedline is about 40%, whereas common inexpensive RG6 TV coax would have an efficiency of around 87%. By contrast with PE dielectric coaxial cable, the conductor loss in this case is relatively high, and dielectric loss is as high as the conductor loss by 30MHz.

See PVC insulated feed line on HF for a graphical comparison of RG6 and ZIP cord.

So, what you have will work, whatever 'work' means, but it is probably not insulated with a low RF loss dielectric, and losses may be quite worse than using a more conventional transmission line.

Thing is in this case that if you are running QRP, you are already behind an average station on EIRP, do you really want to chuck another 3.5dB away?

Sure it 'works', but the question you might ask is how well.

I don't know the detail of the stuff you have, and so it is not possible to be definitive other than to say that whilst you can't say with confidence that it will work poorly, you also can't say with confidence that it will work as well as a conventional  transmission line.

Owen

[K3GM]

The characteristics that give this wire is "suppleness" are its fine strands and loose twist.  The only observation I could offer is if you need a critical dimension in your antenna design, any tension placed on the wire will cause it to lengthen as all of the "air space" in the loose twist of the wire is taken up.  That's a problem with any twisted, multi-stranded conductor, and the primary reason Copperweld is a superior wire antenna material.

[N8EKT]

regular old lamp cord also has similar properties but since it's not manufactured for RF use,
there's no guarantee that any two pieces you buy will be the same.

[NR4C]

It will work.

i make my light-weight portable antennas from radio Shack 22ga Speker wire, (100 ft ~$11.00).  Provides a 134 foot doublet and 33ft of feedline.  Split the wire from one end down 67 feet and tie an Underwriter's knot.  the remaining 33 feet is feedline.

...bc

[AE5NE]

I would apply a twist to the zip-cord "feedline", for the same purpose as telephone pairs are twisted: external influences to the two conductors will average out and the pair will be less sensitive to induced noise.

I would expect the impedance of such a feedline to be around 100 to 150 ohms.