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Author Topic: LNR End Fed + antenna tuner?  (Read 1679 times)
K8DJW
Member

Posts: 32




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« on: April 30, 2013, 11:24:21 AM »

I'm just curious if it is possible to get a tuner to match one of these antennas on a different band efficiently. The reviews for these antennas are outstanding on here, but they all say "no tuner" - I'm curious if I could get the 40-meter version (rather than a multi-band) and get it to tune on 20, or even 30, or does the matching network make this impossible...? Radios are Elecraft KX1 and K2. I've used several homemade antennas with these rigs but I'm really attracted by the good reviews.

73, Dave
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WB6BYU
Member

Posts: 13026




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« Reply #1 on: April 30, 2013, 11:43:34 AM »

It won't work any better than the equivalent length of a wire fed directly
with a tuner.

The base tuner is an "L" network (series coil and shunt capacitor).  You can still
match it on another band by adding a tuner between it and the rig, but the added
components may reduce the efficiency slightly due to higher matching losses.
But if your added tuner will match that length of wire, there is no reason to keep
the original base tuning network in line:  the antenna performance is based on the
wire length, not the matching method.


Then you need to consider the radiation patterns:  a 40m vertical wire used on
20m will have a high angle of radiation, which is going to waste much of your RF.
But if it slopes it may be usable.  A 40m end-fed half wave used on 17m no longer
has a high feedpoint impedance, and would want a better ground system.  (In
spite of claims, you still need some sort of ground/radial/counterpoise system
even with an end-fed half wave antenna:  if you don't provide an explicit one
then the RF currents will flow on the outside of the coax instead.)

So, to answer your question:

1) yes, you can use a tuner to operate it on another band, though it may not
be optimum.  That assumes the tuner has enough matching range, of course.

2) You need to consider the radiation pattern of the wire when used on a
different band.

3) Don't expect a commercial end-fed half wave antenna to work any better
than a stray piece of hookup wire of the same length fed directly from your
tuner.
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K8DJW
Member

Posts: 32




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« Reply #2 on: April 30, 2013, 12:04:13 PM »

It won't work any better than the equivalent length of a wire fed directly
with a tuner.


3) Don't expect a commercial end-fed half wave antenna to work any better
than a stray piece of hookup wire of the same length fed directly from your
tuner.

Thanks for your reply - I guess #3 is what I'm afraid of. What, then, is the point of the L matching network in these types of end fed antennas? I mean, I know it's to get the impedance down. But why wouldn't this work better than just a random wire of the same length? It's hard to argue with the 5/5 rating of this antenna.

I've made several homebrew dipoles for my setup, fed with ladder-line, coax, different types of crappy baluns, and have had varying success. I'm now planning on operating out of a shed in the corner of my property, so a traditional dipole isn't really an option. The biggest angle I could get on a dipole between the elements is about 60 degrees. 
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WB6BYU
Member

Posts: 13026




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« Reply #3 on: April 30, 2013, 12:28:04 PM »

Quote from: K8DJW

What, then, is the point of the L matching network in these types of end fed antennas?

 


It provides a match in a small space that doesn't require a separate tuner.  That's
the convenience factor:  plug in your coax and operate.  You can build your own and
it will work just as well, even if it doesn't have the high quality of workmanship.



Quote

But why wouldn't this work better than just a random wire of the same length?



If the wire is the same length, then it isn't actually random, is it?

The wires are specifically chosen to be a half wavelength long because that
presents a high impedance (which many auto-tuners won't match because
of the high voltage it puts across the relays).  That reduces the need for a
good ground system, as would be required for good efficiency with a quarter
wave wire.

Needless to say, such a wire is only 1/2 wavelength long on one band.  Use
it with a tuner on any other band and it is no longer an end-fed half wave
(though it will still have the high input impedance on harmonics of the original
band.)

A half-wave wire will work about the same regardless of where or how you feed
it.  And it happens to be a reasonably efficient antenna in many cases, though
not necessarily that much better than some other lengths.



Quote

 It's hard to argue with the 5/5 rating of this antenna.



Not necessarily...

There are a lot of antennas with similar ratings that don't work particularly well.  Remember
that most reviews are posted by those who bought an antenna, which rules out those who
didn't because they knew that any piece of wire would work as well.  That's not to say that
end-fed half wave wire antennas can't work well, or that the LNR antennas aren't well built.
But looking at the reviews in general, they don't exactly represent a random sample of
hams.  And to someone who has never used a full-sized HF antenna, the performance of such
a simple wire antenna can be pretty amazing.


Quote

I've made several homebrew dipoles for my setup, fed with ladder-line, coax, different types of crappy baluns, and have had varying success. I'm now planning on operating out of a shed in the corner of my property, so a traditional dipole isn't really an option. The biggest angle I could get on a dipole between the elements is about 60 degrees. 



Personally, if I had a support high enough for a vertical half wave wire, I'd string up an
inverted vee from it instead, as it can be expected to provide better performance.  I used to
use 130' end-fed wires for my portable operation, but now generally prefer dipoles instead.
(But that is a function of the bands I tend to use.)  In your case, an end-fed wire with a
reasonable ground system may work as well as anything else if that is the best you can
manage.

While many autotuners won't match them, I happen to like using end-fed wires that are
a multiple of 1/2 wavelength (like the 130' length), and there is no reason why you couldn't
choose, say, 65' (half wave on 40m) as a wire length from your shack.
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K8DJW
Member

Posts: 32




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« Reply #4 on: April 30, 2013, 12:49:39 PM »

Again, thanks, and yeah, I definitely understand your comments on reviews. It's easy to get sucked into all that.

I'm severely height-limited due to the proximity of power lines (both pole-pole and pole-house.)

Actually I'm looking more closely at the tri-band version now, as it's only 39 feet long which is about the perfect length for my needs. I could get a half wave (@40m) about 30 feet off the ground at one end, but if it broke loose from the house side, it could come into contact with my power line... possibly.

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KD2CJJ
Member

Posts: 369




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« Reply #5 on: April 30, 2013, 01:00:08 PM »

Don't confuse a long wire antenna with a 1/2 wave end fed... the LN PAR end feds are 1/2 wave end feds not long wire end feds thus have greater efficiency for that specific band over a long wire end fed.  The matching network could be damaged using a tuner on other bands as it will create higher voltages at the feed point possibly damaging the matching network.

With that said, I have the 20/40 antenna - it is resonant on BOTH bands and does not require a tuner except on the edges of 40 meters to tweak the SWRs (3:1 match) but on 20 meters its below 2:1 across the entire band.  I do use a tuner on other bands with no issues but I also stay at 100 watts for SSB, at or below 30 watts for a constant carrier mode.  

With with that said, it performs excellent on 20 and 40 if its your only antenna.  I can tune my mini beam on 40 (its NOT a 40 meter beam but it tunes) and the end fed beats it by 3s points (makes sense since the end fed is a 1/2 wave on 40)... On 20 meters the mini beam almost always beats it (the end fed is a full wave but up 40 feet where my mini beam is at 33 feet)....  On 80 its not bad either (tunes to a 1:1,1:2)....  160m not all that good, even on receive...  On 17 and higher it gets destroyed by my Mini Beam no comparison...

What does that mean?  I would suggest getting the resonant length end feds for the 40 meters and lower and for 20 meters and higher use a dipole...  If you have an option to use a dipole, use a dipole...

I do not have experience with a 1/2 wave 80 meter end fed tuned on 40 meters...  It could work well but it could damage the matching network (I doubt it if you don't drive it hard)... It will create nulls on 40 meters but also dB gain on 40 meters being longer than a 1/2 wave.  

One last thing, there will be common mode current with all end feds that dont use a counterpoise...  Use a current balun right before it enters the shack (NOT AT THE ANTENNA) as it uses the coax as a counterpoise... using a balun at the antenna will reduce the effectiveness of the counterpoise (ie coax) reducing its performance...

It won't work any better than the equivalent length of a wire fed directly
with a tuner.


3) Don't expect a commercial end-fed half wave antenna to work any better
than a stray piece of hookup wire of the same length fed directly from your
tuner.

Thanks for your reply - I guess #3 is what I'm afraid of. What, then, is the point of the L matching network in these types of end fed antennas? I mean, I know it's to get the impedance down. But why wouldn't this work better than just a random wire of the same length? It's hard to argue with the 5/5 rating of this antenna.

I've made several homebrew dipoles for my setup, fed with ladder-line, coax, different types of crappy baluns, and have had varying success. I'm now planning on operating out of a shed in the corner of my property, so a traditional dipole isn't really an option. The biggest angle I could get on a dipole between the elements is about 60 degrees. 
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73

Mike
KD2CJJ
KB1GMX
Member

Posts: 713




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« Reply #6 on: April 30, 2013, 02:15:39 PM »

Best answer not said...  Because the manual says don't.



Allison
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GILGSN
Member

Posts: 199




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« Reply #7 on: May 02, 2013, 09:37:11 AM »

I used a BetterQRP end-fed half-wave tuner with an LNR Trail end-fed wire and choke (40/20/10m). Works great, and you get the little LED SWR indicator. Of course, for other bands between 15 and 40m, you need another half-wave wire. I plan on cutting wires for 15m and 30m..

Gil.
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KB1GMX
Member

Posts: 713




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« Reply #8 on: May 02, 2013, 03:48:23 PM »

<<<a BetterQRP end-fed half-wave tuner with an LNR Trail end-fed wire and choke (40/20/10m). Works great, and you get the little LED SWR indicator. Of course>>>

Why?  The match box supplied with it works find for 40/20/10, At least both of mine do.  Of course you still
need different wires for 15 and WARC.


Allison
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K3VV
Member

Posts: 13




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« Reply #9 on: May 02, 2013, 06:18:08 PM »

John Huggins, K4XO posted a teardown, schematic and parts description for the PAR 10/20/40.  (Not the trail version.)

http://www.hamradio.me/antennas/lnr-precision-ef-102040mkii-examination.html

The PAR black box contains a toroid wound as a ~3:20 step-up transformer. The first three turns are bifilar-wound and one of the bifilar wires is used as the primary.  There's a ground return so that the coax shield, rig and operator can be used as a counterpoise.  In my opinion that's not a particularly elegant counterpoise design, though it saves a little wire and it works to a degree.   

I have a six-year-old 10/20/40 and have compared it in A/B fashion with 35- and 87-ft end-fed wires using a step-cut multi-wire counterpoise that provides 1/4-wave CP's on 40/30/20/17 wires.

Both the 35- and 87-foot wires tune with the K1/KAT1 and K2/KAT2 on 40/30/20/17 meters.  The 35-foot wire plays about as loud as the PAR and the 87-foot wire is 3-6dB better.  Again these are direct A/B comparisons.

The 35- and 87-foot antennas need a common-mode choke.  I use a binocular choke made of 16 (2 x Cool FT-43-90 toroids.  FT-61 or FT-73 might be a better choice, but I used what I had.  It's wound with 5 turns of RG-316.  Obviously you don't want to use the choke with the PAR unless you provide appropriate counterpoises attached to the SO-239 shield on the antenna side of the black box. 

The 35- and 87-foot wires also tune (using the KAT1 and KAT2) on 30 and 17 meters.  I've not tried them on 10 and 12 meters.  I didn't try to tune the tune the PAR on 30 and 17. 

IMO the PAR offers no advantage over the other two antennas. 
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GILGSN
Member

Posts: 199




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« Reply #10 on: May 02, 2013, 06:40:08 PM »

Quote
Why?  The match box supplied with it works find for 40/20/10, At least both of mine do.

Yes, it works great. I have the regular 40/20/10. The reason to use the BetterQRP tuner was because of the SWR indicator. My Weber MTR doesn't measure SWR like the LNR Mantiz does. So, I wanted to be sure that my SWR was ok before transmitting. With a properly stretched antenna, the LNR match box would be just fine, but I wasn't sure I would be able to deploy it properly, so the SWR indicator was an extra safety..

Gil.
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