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Author Topic: Are there comparisons of portable QRP antennas?  (Read 7326 times)
NO9E
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Posts: 391




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« on: August 08, 2013, 12:17:18 PM »

Lots of info about QRP antennas for fast deployment in the field. However I have not found many comparisons. Wonder whether anybody did?

Assume we have a radio with a wideband antenna tuner. We hike and then want to operate. Any band that is open. Here are a few dilemmas.

Seems the lightest material is thin magnet wire, say 26 gauge or 0.4 mm. Does not really limit efficiency if the total length of the antenna is at least half wave. But probably should not touch branches. With touching, an insulated cable like Wireman slinky can do but it is a few times bulkier. We are still talking ounces, though.

The simplest antenna is vertical wire with one elevated radial. Does very well in DX close to salt water but may be poor when poor soil, many trees or obstructions. Also poor for closer contacts (low higher angle radiation).  The antenna may be half wave but then tuning will be finicky and the antenna would be half wave on one band only.

Another antenna may be a dipole fed by a flat TV line. But it is bulkier and needs two supports.

A magnetic loop is easily deployed. But it is harder to carry, heavier and tricky to tune.

Another option is inverted L or long wire with one or more radials.  Both low and higher angle of radiation but perhaps very complex radiation pattern. Also, needs two supports but not the feeder.

Most often I use a semi vertical with one counterpoise. At some QTH it works very well and in some poorly even though those QTHs look similar.

Ignacy, NO9E
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W1JKA
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« Reply #1 on: August 08, 2013, 01:28:27 PM »

   Another can of worms: There are probably only two types of portable Qrp antenna comps you will find, those are by commercial manufacturers that are some what biased and done in a specific location under some what controlled conditions then there are the many comps found in the Antenna, Qrp, Elmer Forum topics here on eHam  which are personal results and comments found by individual hams who have taken the time to experiment with some wire, coax or some type of twin lead and eventually found what works best for them in different situations for their specific operating needs, I can only suggest that it would be wise for you to do the same.
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KA0HVE
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« Reply #2 on: August 08, 2013, 03:26:03 PM »

FWIW, I use a W3EDP at home which is more of a portable type antenna; 84' main element with a 17' counterpoise.  I think it takes a 6.5' counterpoise for 20 meters but I'm usually on 40 meters so I haven't tried that one.

I check RBN pretty often and it hits several of the skimmers pretty well in multiple directions.

I only have the top of the main element up around 15' and it still works.  I've gotten out about 1,500 miles with 5 watts.  If I hit some good conditions I'd guess it would reach a lot farther.  Some more height would certainly help too.

It takes a tuner of course.

I made it from a 100' roll of really thin speaker wire that cost me about $11 and I had almost half of the wire left over.

It's working well for me but YMMV.
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K6AQ
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« Reply #3 on: August 08, 2013, 04:18:56 PM »

I use the EARCH 6-40 antenna with my KX3. I've found that to take a lot less space than the Buddipole that I was trying to use before. Plus, I don't even need a pole unless I'm going somewhere without trees (which, unfortunately, is a lot of summits around here). Seems to work well for me.
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W4KYR
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« Reply #4 on: August 08, 2013, 04:37:53 PM »

I got one of those Rainbow QRP tuners on E-Bay. The instructions say it is for an End Fed Antenna for 40 meters. The antenna is simple,  67 feet insulated and strung up and 34 feet for the counterpoise.  I haven't tried it yet but it seems simple.
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K5LXP
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« Reply #5 on: August 09, 2013, 06:06:01 AM »

67 feet insulated and strung up and 34 feet for the counterpoise. 

Why would you put a quarter wave radial on an end fed half wave?


Mark K5LXP
Albuquerque, NM
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W4KYR
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« Reply #6 on: August 09, 2013, 07:44:37 AM »

 
Quote
Why would you put a quarter wave radial on an end fed half wave?
Mark K5LXP
Albuquerque, NM


I'm going by these recommendations.


Here it says

http://www.njqrp.org/n2cxantennas/halfer/halfer.html

"The Halfer is a “minimalist” End-Fed Half-Wave Antenna for the 7 or 10 MHZ amateur bands intended to provide a very simple to erect yet effective portable QRP antenna.  It features are:

    ·  Light weight - about 7 ounces  
    ·  Small Size - fits in a quart zip-lock bag  
    ·  Efficient - same as a half-wave center fed dipole  
    ·  Effective - can be configured for local or DX operation  
    ·  Simple - single antenna wire and single counterpoise wire  

    ·  67 foot insulated antenna wire  
    ·  34 foot counterpoise  
    ·  Three antenna insulators  
    ·  Copy of  End-Fed Half-Wave Antenna article from 72 newsletter"



Another page mentions using 66 feet for the antenna and 33 for the counterpoise.

http://www.njqrp.org/Rainbow/worldradio.html

"One end of the 66-foot wire was hoisted to the top of the pine, while the other end sloped to the antenna post on the back of the Rainbow tuner. Meanwhile, the 33-foot counterpoise was connected to the Rainbow's ground post and stretched along the ground directly beneath the 66-foot antenna."


This has no mention of a counterpoise

http://www.njqrp.org/Rainbow/rb_descr.html

"Similarly, the Rainbow consists of simple tuner *and* LED display SWR bridge on a 2x3 inch printed circuit board that can be built in a another Altoids tin. A complete QRP station except for the key and a 67 foot antenna wire fits inside two Altoids tins"



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KB1GMX
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« Reply #7 on: August 09, 2013, 08:55:31 AM »

I believe the HFpackers site has comparisons.

Myself I use a PAR EF 40/20/10 and  for other bands in the 5-30mhz range a precut length
of #22 stranded hookup wire for it.  That and 100ft of 0.050 paracord to pull one or both ends up.
Its light small and works.

If the site has no trees or other high supports a fiberglass crappy pole of 20ft long seems to work.
Its light and only 4ft long closed up. 

I've tried and played int he yard with loaded antennas and they are low on efficiency.


Allison
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AK7V
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Posts: 251




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« Reply #8 on: August 09, 2013, 09:14:39 AM »

I've used the "67 ft radiator, 34 ft counterpoise" type antenna a lot doing QRP in the field.  My thought is that it's based on the same idea as an OCF (Off-Center Fed) dipole, which is generally fed at ~36% from one end -- as opposed to being based on a vertical with counterpoise.  Since the QRP version doesn't involve a feedline, and you probably can't put your radio up in the trees along with the antenna, you just leave the shorter end of the antenna on the ground.

The OCF dipole is supposed to produce an easily-matchable impedance in more than one ham band.  I think this QRP setup works pretty well.  I've never used an OCF dipole in its intended configuration, though.
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WB6BYU
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« Reply #9 on: August 09, 2013, 09:43:45 AM »

Quote from: NO9E

Lots of info about QRP antennas for fast deployment in the field. However I have not found many comparisons. Wonder whether anybody did?




Just about every ham has a different set of circumstances, requirements and trade-offs for
"fast deployment in the field".  While the electrical performance isn't difficult to analyze
based on modeling, side-by-side comparisons, etc., the practical physical solutions will
vary widely in terms of what hams have found most effective.

So you'll find a wide variety of recommendations, many of which are based on criteria other
than the actual radiation performance of the antenna.

(And this isn't limited to QRP antennas - the same principles apply regardless of the power
level.)


Here are some thoughts based on my portable operation over last 40+ years:


Quote

Seems the lightest material is thin magnet wire, say 26 gauge or 0.4 mm. Does not really limit efficiency if the total length of the antenna is at least half wave. But probably should not touch branches. With touching, an insulated cable like Wireman slinky can do but it is a few times bulkier. We are still talking ounces, though.



Magnet wire is not a good choice.  I used it for my first backpacking trip and immediately
went looking for an alternative.  If you are really desperate to save weight you can go as
low as #32, but solid wire kinks badly and is more prone to breaking.  I switched to stranded,
insulated hookup wire:  it may be just as curly as magnet wire when it comes off the spool,
but you can pull it and it will straighten without many kinks.  Magnet wire will kink and break
under the same stress.  (The plastic insulation adds a lot to the strength.)  I recently picked
up a spool of #26 stranded, insulated hookup wire in various colors, and that may eventually
replace the original #22 wires that have been in my standard dipole kit for the last 35 years.
That seems like a good combination of strength, flexibility and weight.

Even magnet wire has insulation on it.  I've never worried about touching branches, and my
antennas have been strung up in plenty of trees.


I like to experiment with antennas, so one requirement for my portable antenna kit is that
it can be used many different ways:  sometimes you find the perfect opportunity to try
a specific antenna.  My kit has dipole wires for each band that can be added as desired
to a center insulator attached to a chunk of RG-174 coax, which gives me the option to
combine the wires in other ways.  For example, a 40m quarter wave wire makes a full wave
loop on 10m (add one 18" clip lead for SSB, two for CW.)  I can use each wire as an end-fed
quarter wave plugged directly into the transmitter, or extend it to 3/4 wave when that
allows me to get more height.  I've even strung up the 20m dipole as a doublet between
two rock crags (with a 300' drop between them) and used the 40m and 80m wires to make
a balanced feedline for it to a spot where I could safely sit and operate.  It isn't just one
antenna - rather it is material to make lots of different antennas.


Some of the choice depends on what bands you like best.  On 10m and 15m it isn't difficult
to find supports to string a vertical half wave wire, but much harder on 40m and 80m (though
I've managed a 5/8 wave vertical wire on 80m using a kite.)  My favorite band is 40m, which
will color my preferences because high angle radiation is still useful for casual contacts, which
isn't the case on the higher frequencies (even on 30m.)  So a horizontal dipole at 15' works
much better on 40m than on 20m for my style of operating.  Similarly, when backpacking I'm
more likely to be operating during the evenings on 80m and 40m, with only occasional stops
during the day when the higher bands are open.  But if you are going to go to the park for
the day to operate, then 20m though 10m are likely going to be more important in your plans.



Quote

The simplest antenna is vertical wire with one elevated radial. Does very well in DX close to salt water but may be poor when poor soil, many trees or obstructions. Also poor for closer contacts (low higher angle radiation).



I haven't had very good luck with end-fed random wires of that type, though much of that
experience has been on 80m where the lack of a ground system greatly reduced the efficiency.
One problem is finding a tall enough tree for the lower bands.  This also requires an antenna
tuner - which I do NOT take with me on casual trips in order to save weight, space and bother.
Sometimes an end-fed long wire that slopes up to a tree (or horizontal if the ground is sloping)
can give pretty good results.  Others swear by such wires - a matter of personal experience
and preference.



Quote
 
The antenna may be half wave but then tuning will be finicky and the antenna would be half wave on one band only.



I hear lots of complaints about problems tuning an end-fed half wave antenna, but I
haven't had any problems with them, and a half wave or multiple there-of is my preferred
length when I do use an end-fed wire (usually as a long-wire antenna rather than vertical.)
A simple L-network does the job, and if you are always using the same piece of wire then
the settings for each band can be fixed rather than continuously variable.  (Something
like a band-switched inductor and a variable capacitor.)  A 65' or 130' wire is close enough
to a half wave on 10 / 15 / 20 / 40m (and 80m for the 130' wire) that further adjustment
of the length isn't necessary.

Some variants that I've used over the years include J-poles for 10m and 15m, and a coaxial
dipole (with braid from RG-58 slipped over the coax) for 20m.  Once tuned, those give the
same performance as a half wave end-fed wire, but don't require a tuner.  A J-pole made
using 1/2 wave of wire attached to 1/4 wave of twinlead may be easier to assemble than
the common EFHW approach using an LC circuit enclosed in PVC pipe at the feedpoint.



Quote

Another antenna may be a dipole fed by a flat TV line. But it is bulkier and needs two supports.



If you only have one support you can string it up as an inverted vee or a sloper (though
that may not be as good on the higher bands if the wires have too much slope.)

In practice finding a second support often isn't a problem.  In dense forest it may be
difficult to get the antenna strung up between them due to other trees in the way.
Again, this depends on the expected area you are going to be operating from - in some
areas trees may be too dense, other places they will be sparse or lacking altogether,
and that will factor into your antenna choice.

One way around the bulk of the twinlead is to use the same type of wire as your
antenna.  Twisted pair has a lower characteristic impedance, but if your center insulator
is wide enough then sometimes just putting a bit of tension on the line will keep the
conductors spaced apart.  One of the antennas I've built (but haven't used much yet) is
basically an 80m doublet with a sliding center insulator so I can adjust how much of the
wire is "antenna" and how much is "feedline".  That gives me more flexibility to adapt to
different situations, band choices, etc.

Or the same materials (twinlead and wire) can be used with a Zepp feed for a long wire.  
While a Zepp feed certainly has some shortcomings, sometimes it is a good solution to a
specific situation.  I operated Field Day one year from southeast Alaska using my Argonaut
505 and a Zepp-fed long wire with very good results, breaking pile-ups on KG4 and KZ5
(back when both were DX prefixes).  But the feedpoint was 50' up in a cedar tree
that leaned out over the tide flats, and the wire was tied off to a post that I erected
at low tide so, when the tide came in, I had a sloping long wire over salt water pointed
Stateside.


While I've tried lots of portable antennas, for casual operation I generally revert to my
dipole kit - that's the simplest thing I've found that works well.  I can install it for any
combination of bands that I want to use, and it doesn't require a tuner (even when
put up in some rather odd ways over the years.)  The 25' of RG-174 isn't all that bad
in terms of bulk, weight, or loss, and I have a spare length that I can splice on when
supports permit greater height.  (Even though I can toss a line over a branch at 60',
typical heights are usually 15' to 20'.)  The common method is to toss a rock over a
a branch and use that to hoist the center insulator, then tie off the wires in various
directions.  When I have more height I hoist it by one dipole wire to gain a bit of
effective height on that band.  By using the 40m dipole on 15m I've often put it up
for the 5 pre-WARC HF bands, and with practice it doesn't take too long.  (In
Tasmania it took me half an hour, in the dark, while holding a trout in one hand.)  That
gives me all that bands that my Argonaut covers without a tuner, while also providing
the flexibility for other arrangements when situations present themselves.


One of the secrets to any portable antenna system is optimizing the mechanical
aspects - winding the ropes and wires so they don't tangle, making connections simple,
knowing what knots work best for different uses and being able to tie them easily,
choosing wires that won't break when they kink, making sure there aren't any small
pieces such as nuts that can be lost, and designing the kit so it can be repaired in
the field with a pocket knife if needed.  Those factors often contribute more to the
enjoyment (or lack thereof) of operating in the field than the electrical design of
the antenna used.
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K5LXP
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« Reply #10 on: August 09, 2013, 09:47:17 AM »

based on the same idea as an OCF (Off-Center Fed) dipole, ... you just leave the shorter end of the antenna on the ground.

I'll agree, if you add a "counterpoise" it's no longer an end fed.  End feds are fed from the "end".

Extending the OCF analogy a step further, wouldn't that then be like putting part of the OCF on the ground?  Or does calling part of an antenna a "counterpoise" somehow negate ground losses in that instance?


Mark K5LXP
Albuquerque, NM
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AK7V
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Posts: 251




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« Reply #11 on: August 09, 2013, 10:10:21 AM »

based on the same idea as an OCF (Off-Center Fed) dipole, ... you just leave the shorter end of the antenna on the ground.

I'll agree, if you add a "counterpoise" it's no longer an end fed.  End feds are fed from the "end".

Extending the OCF analogy a step further, wouldn't that then be like putting part of the OCF on the ground?  Or does calling part of an antenna a "counterpoise" somehow negate ground losses in that instance?


Mark K5LXP
Albuquerque, NM


Yeah, that's how I see it -- an OCF with the short leg laying on the ground.  Definitely ground loss occurring.  But it's easy to deploy and does work in a pinch.  I had a "BNC to 2 binding post" adapter in the back of my K1 that I'd rig up just like this in the field.
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WB6BYU
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« Reply #12 on: August 09, 2013, 11:07:47 AM »

Quote from: AK7V

Yeah, that's how I see it -- an OCF with the short leg laying on the ground... 



An important distinction is the current distribution on the wire:  an OCFD is typically an
even multiple of 1/2 wavelength long on the bands where it works, so the feedpoint
avoids the point where either side of the antenna is close to 1/2 wavelength or multiples
thereof.  (That's why a 80m or 40m OCFD doesn't work well on 15m.)

The reason for using a quarter wave radial with an end-fed half wave antenna is to
provide an alternate path for the ground currents so they don't have to flow back
on the outside of the coax.  The actual current flowing in the radial is much lower than
it would be for an end-fed quarter wave wire, so its contribution to the total radiation
(as well as the maximum possible loss possible due to ground proximity) is relatively
small.

We can see how this works with some fairly simple math:  let's assume that a quarter
wave end-fed wire has an impedance of 30 ohms and an end-fed half wave has an
impedance of 3000 ohms.  Since I = square root ( P / R ) the half wave would have
only 1/10 of the current.  The same current flows in both the antenna wire at the
feedpoint and in the radial wire, and since power is proportional to resistance, only
1% of the transmitter power is radiated by the radial.

In practice there are a number of other factors, but the point is that the power radiated
by (or potentially lost in) the radial wire is relatively low when the antenna has a high
input impedance.  Because the current is relatively low we don't always notice the
effects of the common mode current (especially at QRP) if we don't have a ground radial
or some other alternative path for the ground current to flow.
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WB0FDJ
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« Reply #13 on: August 09, 2013, 04:23:23 PM »

As one fellow already mentioned, check out the HFpack website. They did a "shootout", (actually two, one was for vertically polarized antennas and the other for horizontally polarized) which compared several manufactured antennas to homebrew. They didn't included mag loops or anything more exotic. Granted we're not talking about a professional antenna range but the results are there for the looking.

Doc WB0FDJ
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AA4PB
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Posts: 12770




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« Reply #14 on: August 09, 2013, 04:59:22 PM »

Every end-fed antenna has a counterpoise of some type. If it didn't it wouldn't work just like a bulb won't light if you only connect one terminal to the battery. Many coax fed end-fed antennas use the coax shield for the counterpoise. If you connect an end-fed wire directly to a tuner then the case of the tuner, the radio, and everything connected to them becomes part of the counterpoise. End-fed wire antennas are often made 1/2 wavelength long because that minimizes the current flow in the counterpoise (but it can never be zero).

In the scenario of a tuner connected to an end-fed 1/2 wavelength wire, the 1/4 wave counterpoise wire connected to the tuner ground connection (if the wire is left floating above ground) will minimize the RF on the tuner case and radio case by minimizing the impedance of the tuner ground connection.
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