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Author Topic: Speaker wire feedline?  (Read 14731 times)
KC8SLC
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Posts: 10




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« on: July 23, 2010, 09:31:56 AM »

Hello!! I'm wondering how well speaker wire will work as a feedline for a dipole. I'm looking for a lite weight, easy to rollup package to take backpacking,camping, etc. A single wire antenna straight from my ZM-2 antenna tuner with a counterpoise is another idea. Has anybody tried the speaker wire feedline? Please let me know, Tim.
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WB6BYU
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« Reply #1 on: July 23, 2010, 10:00:36 AM »

Yes, I've tried it, as well as zip cord.  I use RG-174 coax for my packpacking antenna kit
instead - it is also small and light, coils easily, and has a constant 50 ohm impedance.
It can also lay on the ground, etc. without adversely affecting performance.

The speaker cable I used had vinyl insulation, which has higher losses, and the
characteristic impedance is not as well defined.  On 40m the losses aren't too much
of a problem for short lengths, but my 25' feedline was just about 1/4 wavelength
and it transformed the dipole impedance out of the matching range of my rig.  On
20m the feedline is about half a wavelength so the impedance isn't as critical, but
the losses are higher.

If that is all you have available, it certainly will work.  But in my experience the
small coax is a much better solution for a backpack dipole kit.  I tuned up the
dipoles in my kit in a local park about 30 years ago and have never used a tuner
with it.  Still works fine after many miles in my backpack.
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W5FYI
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Posts: 1046




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« Reply #2 on: July 23, 2010, 11:13:28 AM »

It has had a lot of success for portable operators. Its characteristic impedance is very close to 70 or 75 ohms, so there's very little mismatch. Many hams will unzip the wire to the appropriate leg length, tie a knot at that point, and hang the antenna. It's cheap and easy. Have fun.
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WX7G
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Posts: 6148




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« Reply #3 on: July 24, 2010, 08:25:55 AM »

Measured parameters, #12 AWG speaker wire, clear insulation, looks like large zip cord:
7 MHz, 2 dB/100'
21 MHz, 6 dB/100'
Characteristic impedance 95 ohms
VF 0.64



« Last Edit: July 24, 2010, 08:51:16 AM by DAVE CUTHBERT » Logged
N3OX
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Posts: 8847


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« Reply #4 on: July 24, 2010, 02:18:34 PM »

Measured parameters, #12 AWG speaker wire, clear insulation, looks like large zip cord:
7 MHz, 2 dB/100'
21 MHz, 6 dB/100'
Characteristic impedance 95 ohms
VF 0.64

RG-174 has a bit less than 4dB/100' loss at 21 MHz and will weigh less than half the same length of 12AWG speaker wire line by my estimate... plus you get a good match.

Thanks for the data... seems like speaker wire is terrible.  Grin

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
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Posts: 13356




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« Reply #5 on: July 24, 2010, 06:40:32 PM »

If you are trying to save weight you are more likely to grab a spool of the Radio Shack
speaker cable - I think it is about #22 or so.  That is the stuff that I used.  It uses
solid wire instead of stranded IIRC.  I expect the losses are higher than the #12 stuff
that WX7G tested.

But if you get a 50' spool and unzip 32' for the antenna, that only leaves you 18' for
the feedline, and the losses won't be too bad in such a short length.  My biggest
problem was feeding the antenna - I didn't check the characteristic impedance but
I'd guess it is also around 100 ohms, causing a high SWR at the rig end of the cable.

That lead to one of my more frustrating times as a ham - I was camped high on a
ridge in the Salmon-Trinity Alps Primitive Area with my 40m dipole strung from a
tree, fixing dinner, watching the black bear wander by, and listening to KC4USA
booming in on 40m from the South Pole in the Novice Band on my HW-8.  But due
to the high SWR I couldn't raise him.  (He was easily working other operators and
was calling CQ with nobody answering - except my feeble attempts.)

After that episode I switched to RG-174 and now get a good match with a wide
variety of antenna installations.

I also switched to stranded, insulated hookup wire rather than magnet wire - the
latter was too prone to kinking and was lucky to survive its first trip.  By comparison
the original set of dipoles made from hookup wire have seen service in VK, ZL, KL7,
KH6, VE1 and a number of states over the last 30 years.

You live and learn...
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KE3WD
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Posts: 5689




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« Reply #6 on: July 29, 2010, 05:39:49 PM »

Somebody wi8ll come along and say why I'm lying or some other crap, but I've used common stranded zipcord for both dipole and feedline with some rather great results considering the fact that it was used as a portable antenna strung from whatever was high enough and reachable at campsites, etc. - even from motel balcony. 

At one point I even just soldered the two ends of the twinlead to a PL-250 and ran without a tuner on the 20 meter band, which that particular dipole was cut for.  At around the 70 - 75 ohm mark, the doggone thing worked remarkably well IMO.  Consider that the dipole itself is supposed to be 72 ohms at the feedpoint, at least, that's the way I explained the performance to myself that evening...

I would use the zipcord over the speaker wire. 

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WB6BYU
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« Reply #7 on: July 29, 2010, 07:34:25 PM »

Quote from: KE3WD
... but I've used common stranded zipcord for both dipole and feedline with some rather great results ...


So have I, both the speaker cable and zip cord.  I worked Minami Torishima on first call using a zip cord feedline and
my old Argonaut at 2 watts output.

But, having used various feedlines, I recommend the RG-174 because it has lower loss and is easier to use. 
25' of zip cord may work fine on 20m where it is close to a half wavelength and so doesn't transform the
antenna impedance, or if you are using a tuner.  And the efficiency difference with short feedlines is not that big.
You can still make plenty of contacts.  But if you are buying feedline specifically for lightweight portable operation,
and are planning to use half wave dipoles, the coax makes life simpler and easier on the trail.  A 25' piece costs
less than $10, so cost isn't a major issue.

Can you use speaker cable or zip cord?  Sure.  Is it the best option when you have a choice?  Probably not.
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K5UNY
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« Reply #8 on: August 01, 2010, 07:19:11 AM »

    WB6BYU,  I have used Speaker wire for both the antenna and feedline to my HB ZM-2 tuner and it "appears" to work well. My question is more of understanding what you are doing with the RG174. Are your dipole antennas fed with 174 cut for use as monoband antennas? so you have several of these made up for the band of interest?  I would assume so or you would be calling it a doublet and not using 174!!!
    My 20M version with 174 rolls up nicely and fits into a ziplock baggie for storage quite nicely.
    My apologies for going off on a tangent here with the question. 
    73  Alex K5uny
   
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WB6BYU
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Posts: 13356




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« Reply #9 on: August 01, 2010, 01:23:40 PM »

I've described my dipole kit a few times here.  I have about 25' of RG-174 with a center insulator on the end
(cut from a piece of radiator hose.)  I also carry a set of dipole elements for all bands of interest, cut from
#22 or #24 stranded, insulated hookup wire.  For each use I decide what bands I want to operate, tie the
appropriate set of wires through the center insulator and hook the ends under thumb nuts to connect them
to the feedline.  The other ends of the wires have loops for tying ropes.  I hoist the whole thing from a rope
over a tree branch, either by one of the dipole ends or by tying the rope to the center insulator.

So one feedline with multiple dipoles in whatever configuration I need each time.

Sometimes I set it up for all 5 HF bands that my Argonaut covers, using the 40m wire on 15m.  Sometimes
I set it up for just one or two bands, especially for a short stop.  (One of my favorites was a lunch in
Tasmania where I could hang a vertical 10m dipole from a tree branch over salt water within reach of
a picnic table.)  The whole thing - including enough rope to string it up - fits in a small nylon belt pouch.
I tuned it up initially at a relatively low height (12', with the ends at 6', I think) and have never used a
tuner with it.  Occasionally I get creative - a 40m wire makes a full wave loop on 10m with the addition
of one 18" clip lead for SSB or 2 for CW.

When ham radio is the main focus of the trip, such as Field Day or a QSO party, etc., I sometimes take
along a small tuner.  On one occasion I strung up the 20m dipole between two rocks and connected
the 40 and 80m wires together to make a parallel feedline that just reached to a safe spot where I
could sit and operate - the ground dropped off 300' in the middle of the dipole!  I can also use the
wires in other configurations - half square, long wire, etc., but for normal operations during the evening
on the trail I generally just throw up a dipole or two.
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KC8SLC
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« Reply #10 on: August 02, 2010, 05:17:42 AM »

Thanks for the input guys!! I have some speaker wire laying around, so I'll try that first. Tim  Shocked Shocked Shocked
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KU3X
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Posts: 144




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« Reply #11 on: November 20, 2010, 04:44:48 AM »

You may want to try LMR 100. It's about the same size as RG 174 but has less loss. I would not run out and make a switch if you are already using RG 174, but it is a good line to consider if you are just starting out. When running QRP you need all the help  you can get. Don't give up half of you power in the transmission line. Remember, if you give up 3DB in transmit you also give up the same amout in receive.

RF Connections has this line in stock.
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W3JJH
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« Reply #12 on: November 20, 2010, 07:21:48 PM »

300 ohm TV twin-lead is lower loss than any of the cables mentioned above.

300 ohm ladder line is even better.  (http://www.thewireman.com/antennap.html#balanced)  I've used it with an 80 m inverted-vee and a ZM-2 as a QRP antenna for Field Day and Boy Scout camping trips.
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AURICH
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Posts: 5




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« Reply #13 on: November 20, 2010, 07:42:31 PM »

Speaker wire isn't ideal, but it works. I used a simple speaker wire dipole when I was on vacation with my Yaesu FT-817 and wasn't able to bring along an antenna. I ran over to Wal-Mart and picked up a 100ft package of #24 speaker wire for less than $5. I hooked it up to the binding post adapter leaving about 10ft for feedline and then unzipped the other end until I had a resonant half wave dipole for 20m. In a V-configuration I was able to work coast to coast and into Canada from a valley in central Colorado. So like I said, it's not perfect and has its losses but if you keep things short and it's all you have available it works just dandy....
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KP4MD
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Posts: 6




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« Reply #14 on: April 09, 2011, 07:51:06 PM »

I first tried the cheap 24 gauge speaker wire but found it too lossy due to ohmic losses (the wire became warm to touch when running 100 watts). 
Also I could hardly strip the insulation on that wire without pulling apart the 4-5 hair thin strands of copper that were the conductor.

So I changed it for a 36 foot length of Pfanstiehl 18 gauge 18-AS/50Z PVC speaker wire bought at Fry's Electronics as an HF transmission line. 

Measured Characteristics
Impedance114 ohms
Vel. Factor0.66
FrequencyAttenuation
MHzdB/100 ft
1.82.2
3.53.1
5.33.8
74.4
10.15.3
146.2
18.17.1
217.6
24.98.3
288.8

Disadvantages: non-standard impedance, lower power capacity and somewhat higher attenuation than coaxial cable.

Advantages over coaxial cable: lighter, less visible, more available and more economical, may present less loss when operated at high SWR and is easily wound on a ferrite toroid core to form a common mode choke or 1:1 current balun.  (The 4:1 voltage baluns built into commercial antenna tuners are very lossy).

I've worked plenty of DX running 100 watts and using an MFJ tuner to feed a 36 foot length of this speaker wire as transmission line for my low profile station antenna.

73, Carol, KP4MD/W6
Sacramento, CA
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