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Author Topic: QRP and antennas  (Read 26495 times)
VK3YE
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Posts: 32




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« Reply #30 on: October 17, 2014, 05:34:47 AM »

For casual operating I use an end-fed wire about 20m long.  It gives good results on 40m up to about 1000km.  It also works for DX on the higher HF bands.

If I want to mainly aim for 20m DX I often use a vertical over salt water.  This can either be a vertical dipole or end-fed.

Even better is Moxons and half squares. However these take longer to put up and being lazy don't often bother.
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ZENKI
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Posts: 989




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« Reply #31 on: October 18, 2014, 06:13:30 AM »

QRP operators are most just obsessed with just putting up any piece of wire like its putting on a pair of shoes. If you were going mountain climbing you would think hard and long about the type of shoes you going to wear climbing a mountain. QRP antennas are no different. You need to think hard and long about what you going to do and what you want to try to work with your antenna.

Take off angle gain  is the biggest determiner of antenna performance for portable or QRP operation. The worst antenna QRP operator could use would be a beam at a very low height. This would be especially true when you have a choice of a dipole that can be installed higher than a beam or use vertical with a low takeoff angle like a vertical that can be installed near the seawater's edge.

For my QRP/manpack operation I always think about the take off angle at all times. I am obsessed about take off angle because when I go portable or do QRP operation I want to work DX. When you cant put up a beam then the best bang for buck is a low take off angle. That generally means a vertical with a decent ground radial system. Now if you operating from home you can lay out radials.  If you operate portable my 2 best performing antennas are the vertical delta loop fed 1/4 wave down from the top on one side and a half wave end fed vertical  grounded with a ground rod. You can put both of these antennas up on a light fiberglass pole.

If stationery QRP work is your aim another fantastic antenna for home use is the G3LDO magnetic slot antenna fed with open wire feedline. Its one of the best home QRP antennas you can use. It has a very low angle of radiation. Another fantastic antenna is a horizontal 80 meter loop fed with open wire feedline. Or even a 40 meter vertical delta loop fed with open wire feedline for a combination DX/LOCAL antenna.

Bits of end fed wire and antennas like the Fuchs are poor performing  and mostly  a big waste of wire. I prefer to cut  long wire antennas up into a 40 meter doublet fed with open wire line. For monoband work you cant beat a resonant dipole  especially if its at 0.6 wavelengths above the ground. On 20 and 40 meters you cant beat resonant coax fed dipoles. Its as good as its going to get.

Another fantastic high performance  single or even multiband antenna is a Bisquare antenna for 20 meters fed as a all band loop. Raised high on a fiberglass pole I can run pileups with 25 watts QRP.

There are really 2 rules.

Height for horizontal antennas equates to a mighty signal.
Low takeoff angle for vertical polarized antennas also produces a mighty single.

A big waste of time  is using kite and balloon and extra long wires, just a waste of effort and energy most of the time. Most of the time when I am just in a hurry I use a  vertical dipole that is  fed with open wire feedline for all bands. I use a S9 pole  with wire and I can erect this pole in 5 minutes and be working all bands chasing DX  with good reports.
Compared to the Buddy pole contraption a open wire feed vertical dipole leaves it for dead and ease of use. Ever tried to go out at night changing taps on a coil near a mosquito  infested swamp? You will soon appreciate open wire fed vertical dipole of modest length.

When thinking about antennas, regardless of what antenna you going to use  the best one is always the antenna which has the most gain between the angles of 3 and 20 degrees. If you only interested in local short skip NVIS work then a loop or low dipole is hard to beat. High angle single hop propagation has very little path loss and anything will work, even a dipole laying on the ground. Determine the required takeoff angle then decide which antenna is  the best match for that angle, no secrets really its very simple.

Its TakeOff Angle,  TakeOff Angle,  TakeOff Angle!

Obviously, QRPers are minimalists when it comes to power. Does the same hold true for antennas? Do most QRP operators tend to use simpler, lower profile antennas, or is the percentage of them using beams and towers about the same as for QRO operators?

73 John AF5CC
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KB1GMX
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Posts: 827




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« Reply #32 on: October 18, 2014, 12:01:33 PM »

Zenki makes some good comments.

Size the antenna for the "mission".  Possible missions include Field day, a few hours in a park or public lands,
One day hike up a hill, or an extended back pack trip, mobile trailer.   It is also dictated by the bands one might
use or prefer.

 For example a Dipole on the top of a mountain  with no trees means dragging poles and ropes to hold it up.  
Maybe a tall vertical with 4 surface radials would be nearly as good but easier to setup if there is nothing
but rocks.

EFFECTIVE Gain is everything as is is the intersection of takeoff angle and efficiency.  Gain you can't use
 is wasted typically due to takeoff angle with unreasonably poor gain resulting.   A low (less than 1/2wavelength)
dipole has a poor takeoff angle.  It could have higher gain than a vertical but the signal is mostly up not out.  
 Horizontal antennas with loading coils  close to the ground do not perform well. Better to make it a vertical
with radials.  A 11FT collapsible whip and a suitable loading coil will win if there are four radials of at least
11ft on the ground better is if they are tuned.  Reason even though its lower efficiency the signal is closer
to the horizon where its useful.  This also varied with band choice at 10 or 15 meters 1/2 wave high is 11ft
where on 40 that's 66ft!   What that means is on 10M a dipole wins, on 40 the vertical with radials may be better.

I use two antennas for QRP mostly.  One is the PAR EF140/20/10 as I can size the wire for any
frequency from about 5 to 29.99 mhz.  As delivered its 40ft long.  Its easy to erect and tuned
needs no tuner.  Common setups using it are  Flat top, inverted V, inverted L, Sloping, and
vertical.  If the site is tree limited or no supports I may bring a 20ft fiberglass crappy pole as that
can do the inverted V or for 20M or higher a sloper or vertical.  Makes a very compact kit.

Where supports are an issue a 10ft bungee whip (mil style) or a 11ft collapsible whip with loading
coil works well if there are ground radials.  Again easy to setup without supports like trees.  There
are taller whips or use Buddipole or similar extension rods to make the whip taller.  The longer the
vertical the less fussy the sweet spot on the loading coil.  

Those work for my portable ops.  Others I've tried include 7-8ft moble whips (monoband) with
ground radials (when not on the truck) and these work well enough and can be fast setup.
Small loops never worked for me.  Full sized ones do work but space and size are considerations.
If the supports exist full size (1 wave length) loops are very good.

At home or for field day were setup time is small compared to operating time the par EF40/20/10
is one antenna that gets much use.  The other is a K6STI rectangle suspended from a tree limb
25ft high.  For 10M that antenna does better than a dipole at 30ft every time in the chosen direction.
At 40M an inverted L with a few radials is a winner every time over a dipole at 30ft.

Resonant vs non resonant.  For QRP its about what gets radiated,  Non resonant antennas
are less effective radiators with uncontrolled or unknown for the band radiation angles.  Good
enough for Emcom work where range is less an issue and rapid setup or rough conditions are
a factor.  Even then a better antenna be it a dipole, end fed half wave or loaded tall vertical
is often as easy.

Tuner vs no tuner.  Tuner is nice but always begs the need for SWR measurement.  If it has the
swr indicator built in that's handy.  At low power the Elecraft T1 autotuner is a good bet.  But at
more than 10W its likely to be a manual tuner.  For trips that require packs and are weight sensitive
a tuner is just more stuff.  Your back, your consideration.

Everyone has different preferences but mine are based on easy setup, radiation angle, acceptable
efficiency and my pet is no tuner if possible.   For portable I'd rather carry more battery as I can run
longer or at higher power than drag more antenna stuff.

Then again that's for HF.  At VHF (and high HF) the story changes as height is not a radiation
pattern problem and gain is everything.   Even at 15M antenna height and length are very small.  
At 10M and above loaded antennas are unneeded as  a quarter wave is now around 100Inches
and shrinking.  A dipole at 16ft and 16.5ft is a very efficient antenna for 10M and at 6M that
shrinks to 115 inches.  If working from a hill or mountain with good line of sight consider these
bands even during the off peak sunspot years.

 My two rules are simple as well.

  * If you want a bigger signal put up more metal.  For vertical that means less load coil and more
    whip and ground radials.  For others that often means a full wave loop or even a half rhombic.

  * If you can't use more metal, put the metal you have higher.  Dipole work best when over
     1/2 wavelength high.  Or you might consider a vertical dipole hanging from a limb.  It also
     suggest the top  of a hill/mountain is better than the valley.
    

Allison




« Last Edit: October 18, 2014, 12:05:14 PM by KB1GMX » Logged
VK3YE
Member

Posts: 32




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« Reply #33 on: October 18, 2014, 01:11:04 PM »

Good observations above.  I'll elaborate on my comments above. 

A lot of antenna choices come down to (i) what you want to work, (ii) how much weight you're willing to carry, and (iii) your location, including facilities for mounting antennas.  These are often very personal decisions related to one's own location, circumstances and interests.  Here's some of mine.

1. What you want to work

This comes down to operator preferences and operating culture on each band.  I most prefer the more conversational operating style of 40m but occasionally like the DX excitement of 20m and the volatility of the higher bands, again for DX.  40m nearly always gives contacts at times that higher bands are dead or wall to wall contests (contests can provide good contacts but only if the rules allow contacts between anyone - not just to a selected country).

On 40m there's a good number of amateurs within 1000 - 1200km and a much lower number up to 3000km.

On 20m from here there's a few stations within 3000km but they're mainly working DX. So the emphasis here is very long haul (15 000km) DX.

2. Weight to carry

I'm lucky enough to be a few minutes walk from parks and beaches so want to hand-carry everything.  And I might go into shops on the way there and back.
So there's some size and weight limitations.

3. Operating location

The beach is a huge asset that I'd be stupid not to exploit.  There's a choice of being on the sand but near fences and seats (which one can lash a telescopic pole to),
on the sand nearer the water (no supports so need a sand spike for a pole - but need to be mindful of other people) or in the water. 

Another choice is fixed portable or pedestrian mobile.  Surprisingly, pedestrian mobile is not actually a compromise on 7 MHz and up, provided you're in salt water with a vertical antenna.

A half-wave end-fed with high-z coupler works very well on 40m for distances up to about 500 - 600km (with 5w SSB).  It's performance drops off so that by 800km your signal is often
marginal, especially in the middle of the day. And 1000km + contacts are very rare (unless it's around dawn or dusk).

In contrast even if it's not full size (eg a centre loaded whip 5m long) I've found a vertical works extremely well for about 500km - 1000km on 40m during the day. That's provided you're over
the water, and your ground wire makes contact with it (I use a contact ring tied to my ankle - look up 'Wadetenna' for various links and videos).  Luckily its under 500km performance is still good enough for it to be considered a good all round antenna.  Provided it's warm enough I now prefer to be in the water rather than on the land with an end-fed half wave (it's a terrible performer out of the water).

Shorting the loading coil provides a full quarter wave on 14 MHz and the antenna appears to deliver good low angle performance with many DX contacts made.  Some have been made on higher bands but they're less frequent than 14 MHz.

I think people are still right to be suspicious of short vertical antennas with limited ground systems.  For a beginner at home a full sized dipole is likely to provide more predictable performance and possibly less noise, especially for short and medium distances.  But I've learnt in the last year or two that there are circumstances that they do work and if you're in the water they're unbeatable.

A few notes and links to videos on portable antennas, including the Wadetenna mentioned above, is on my website at www.vk3ye.com
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KF7ATL
Member

Posts: 59




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« Reply #34 on: October 18, 2014, 03:58:57 PM »

John,

When operating portable, I use an end-fed half wave wire with counterpoise fed by a qrpkits.com SOTA tuner. When rolled up it will fit into a ziplock bag, so it is very portable. When at home, I use my standard antenna.

Garth, KF7ATL
« Last Edit: October 18, 2014, 04:29:07 PM by KF7ATL » Logged
VK4FFAB
Member

Posts: 37




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« Reply #35 on: October 18, 2014, 04:19:16 PM »

I have 2 antenna that I use portable, a Buddistick and an end fed vertical and 9m squid pole with 6 radials. Which I use depends on how far away from the car I wish to operate and how rough the terrain is.
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W7ASA
Member

Posts: 268




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« Reply #36 on: October 18, 2014, 08:00:37 PM »

I am always concerned when a person has a new 'tiny' transceiver, they immediately buy a tiny antenna: wrong. Efficiency in radiating to the desired target is the key.  Antennas depend upon desired distance.  My 'Mother' station was usually within NVIS distance and I was almost always in trees, so a horizontal wire antenna, such as a dipole cut for our sked freq was a good choice, in a pinch I could use a slantwire and tuner, but that looses a lot of signal. The longest regular sked I maintained while in a wilderness area was 1,000 miles and again, a dipole up HIGH worked quite well, providing 100% comms with mt 'Mother' station at 1,000 miles during the several weeks I was back there.

Zenki is right-on: 'take-off angle'!  Low angle for DX, HIGH angle for NVIS and medium take-off angle for middling distances. Always got for maximum efficiency, balanced against what you can reasonably carry and set-up.  To paraphrase the wisdom of W7ZOI: " When faced with the choice of a prime mountaineering activity or ham radio, choose the mountain."


73 de Ray
W7ASA ..._  ._
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