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Author Topic: Not too sure of my issue 40M horz wire  (Read 1795 times)
LOSTINTHEWOODS
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Posts: 13




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« on: April 16, 2013, 07:58:36 AM »

Hello all. 

I'm new to the HF realm of ham radio but I've finally gotten a radio and get to be on the air.  I suppose that my question is two fold.  My radio is a Kenwood TS440S (an oldie but a goodie, for me) the radio also has an internal antenna tuner.  I have a 65' wire hung horizontally out back, the wire is fed via 25' of RG8 coax.  I have made a few contacts on this wire (all stateside) and have gotten good signal reports from this antenna.  If I tune the radio to this antenna the needle on the radio will drop to about 1.5-2 SWR while the tuner is running.  I then turn off the tuner and switch over the meter selector switch to SWR and key the mic and the reading very closely resembles the reading taken while the tuner was tuning.

Before I get into my next question, I know there is no silver bullet antenna for all bands.  However, I have read about lots of folks using a single wire for multi band operation.

Last night I ran the dial up to 20M and listened.  I could hear several DX stations (Ukraine, Mexico, Italy) as well as several western states (the home QTH is EM89, SW OHIO).  However, when I tried to tune to my wire on 20M in an attempt to make my first DX contact.  I turned on the antenna tuner and the needle showed about 1.5-2.5 SWR while the tuner was running.  Afterwards I switched over the meter selector to SWR (same as before) and the new reading was BLOWN UP!  It pegged the needle to the right, and while transmitting the power meter was only just bumping 1-10W.

I suppose my question is, should my tuner be able to tune this wire for 20M, or am I living in a fantasy land hoping for that?  Do you think maybe my internal tuner may be faulty?

Any advice?

Thanks in advance!

73,
KD8MKP
Lowell
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M6GOM
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Posts: 945




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« Reply #1 on: April 16, 2013, 08:25:21 AM »

Your tuner is in no way wide ranged enough to tune it for 20m.

You might want to try 15m as it is a third harmonic of 40m. That should be well within the range of the internal ATU and give surprisingly good performance.
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AA4PB
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« Reply #2 on: April 16, 2013, 08:33:03 AM »

The internal tuner has a very limited range (probably 3:1 SWR max). It is intended to fine tune a nearly resonant antenna, for example a 40M dipole on the edges of 40M or on 15M. Trying to load a 40M dipole on 20M is well beyond its capabilities.

People who effectivly tune a doublet wire antenna on all bands do so with the following:
1) Use a wide range external tuner
2) Make the doublet at least 1/2 wavelength long on the lowest band you want to operate (often 80M)
3) Center feed the doublet with open-wire or ladder line feed (not coax) in order to minimize the loss. The SWR on the feed line itself will be very high on some bands and this will cause a good deal of loss in coax. Remember, tuners do not change the SWR on the feed line between the tuner and the antenna. They only lower the SWR on the feedline between the tuner and the transmitter.
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AC2EU
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« Reply #3 on: April 16, 2013, 08:35:47 AM »

Yeah, I think you are expecting too much from a random wire, especially if its fed with coax and with no balun.
The impedance can vary widely on the "end" depending on the frequency.
If you want to stay very basic, try using an external tuner that is designed for random wires ( no coax!) and ground the radio.

Better yet, get a copy of the ARRL antenna book...
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WB2WIK
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« Reply #4 on: April 16, 2013, 09:12:49 AM »

Hello all. 

I'm new to the HF realm of ham radio but I've finally gotten a radio and get to be on the air.  I suppose that my question is two fold.  My radio is a Kenwood TS440S (an oldie but a goodie, for me) the radio also has an internal antenna tuner.  I have a 65' wire hung horizontally out back, the wire is fed via 25' of RG8 coax.
 

You didn't say "how" it's actually fed.  How is the RG8 coax connected to the 65' wire, and where is it connected?
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WB6BYU
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« Reply #5 on: April 16, 2013, 09:17:35 AM »

What are you using for a ground connection at the antenna feedpoint?
That is, what is connected to the coax shield at that point?

Without an effective ground / radial / counterpoise system at the feedpoint,
end-fed wire antennas can be quirky.  That's because the coax shield ends
up being part of your antenna, and you can get RF feedback to the rig, etc.
(A common symptom in my shack is that the keyer continues sending after
I let go of the paddles.)

Also, the coax will be operating at a high SWR, which, depending on the
coax length, may likely be outside the range of your tuner.  While the
auto-tuner in the TS-440 has a wider matching range than many modern
tuners do, it still has limitations (assuming it is similar to the one in my
TS-450.)


I've used a number of end-fed wire antennas, and I actually prefer ones
that are a multiple of half wavelength.  But there are a few tips that will
tend to make such an installation work better:

1)  provide some place for the ground currents to flow at the feedpoint
other than back down the outside of the coax.  A quarter wave wire (for
each band of operation) is a good start, or a ground rod or large metal
object connected to the shield.  (I've used an aluminum pack frame while
backpacking, but larger would be better.  A metal window frame seems
to work well.)

2) Put the antenna tuner at the feedpoint.  If necessary, this may mean
bringing the end of the wire into the shack, but this has actually caused
fewer problems than trying to match such an antenna through coax.

3)  End-fed half wave antennas (and those that are a multiple of 1/2
wave, such as your wire used on 20m) have a high feedpoint impedance -
around 2000 ohms is a good guess, with significant reactance when they
aren't exactly resonant.  A simple "L" network tuner (coil and capacitor)
can match this easily, but when feeding with coax instead the SWR will
be very high and losses can be significant.  If you need to use coax between
the antenna and the tuner, some sort of pre-match network at the
feedpoint may lower the SWR on the coax to reduce losses and improve
the chance of the tuner being able to match it.  Sometimes an untuned
transformer will work for this, or a fixed network that just gets you close
to a match.

4) Just because your tuner can match the impedance at the end of the
coax doesn't mean that the antenna will work effectively, especially if it
involves coax cable operating at a high SWR.
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LOSTINTHEWOODS
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« Reply #6 on: April 16, 2013, 11:51:11 AM »

WOW!!!

Thank you for the responses!

A few points that I neglected in my original post.

1.  I have ordered the ARRL wire antenna book and anxiously await it's arrival. 
2.  The 65' wire is center fed.  Center conductor is tied to one leg of the wire (that is actually 2 pcs I suppose) and the shield is tied to the other leg.  I guess a better description is my antenna is to 32.5' wires joined in the middle.  It is assembled as outlined here: http://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf.  With that being said, I suppose the correct name for the antenna is a 40M dipole?  My apologies for the confusion.

Ok, now that we have those points clarified, does that help my chances of success any?

73,
Lowell
KD8MKP
« Last Edit: April 16, 2013, 12:05:32 PM by LOSTINTHEWOODS » Logged
AC2EU
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« Reply #7 on: April 16, 2013, 12:53:55 PM »

WOW!!!

Thank you for the responses!

A few points that I neglected in my original post.

1.  I have ordered the ARRL wire antenna book and anxiously await it's arrival. 
2.  The 65' wire is center fed.  Center conductor is tied to one leg of the wire (that is actually 2 pcs I suppose) and the shield is tied to the other leg.  I guess a better description is my antenna is to 32.5' wires joined in the middle.  It is assembled as outlined here: http://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf.  With that being said, I suppose the correct name for the antenna is a 40M dipole?  My apologies for the confusion.

Ok, now that we have those points clarified, does that help my chances of success any?

73,
Lowell
KD8MKP

The good news is that you have a 40M dipole, which is a very good thing. You may have success tuning the 3rd harmonic on 15 meters, otherwise the impedance mismatch and coax losses become untenable.
80 meter dipoles are a bit more versatile with the harmonic tuning, IMO, but it wont do 40 well ,if at all.
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W1JKA
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Posts: 1770




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« Reply #8 on: April 16, 2013, 01:03:35 PM »

  Now we know that it is a dipole just refer back to Reply #2.
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AA4PB
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« Reply #9 on: April 16, 2013, 01:21:55 PM »

The original post sort of implied that it was a 40M dipole because it's stated length is approx 1/2 wavelength and the SWR was reasonable on 40M. Had it been end fed the SWR would be upwards of 10:1 on 40M without some type of matching section at the feed point.

Anyway, what you have is called a 40M 1/2-wavelength dipole antenna.
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WB2WIK
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Posts: 20611




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« Reply #10 on: April 16, 2013, 01:30:25 PM »

WOW!!!

Thank you for the responses!

A few points that I neglected in my original post.

1.  I have ordered the ARRL wire antenna book and anxiously await it's arrival. 
2.  The 65' wire is center fed.  Center conductor is tied to one leg of the wire (that is actually 2 pcs I suppose) and the shield is tied to the other leg.  I guess a better description is my antenna is to 32.5' wires joined in the middle.  It is assembled as outlined here: http://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf.  With that being said, I suppose the correct name for the antenna is a 40M dipole?  My apologies for the confusion.

Ok, now that we have those points clarified, does that help my chances of success any?

73,
Lowell
KD8MKP

Sure, that's just a 1/2-wavelength 40m center-fed dipole.

If you move the feedpoint away from the center, you shift the feedpoint impedance that can be a more reasonable compromise on more bands.  A common approach with a 65' doublet is to feed it 21-1/2' from one end (making the "other" side of the doublet 43' long).  At the feedpoint, do not connect coax directly, but use a 6:1 (or even 4:1 can work) balun as a matching transformer.

Some easy-to-understand theory behind this is here: http://www.w8ji.com/windom_off_center_fed.htm

A power point presentation that's kind of fun is here: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&sqi=2&ved=0CEMQFjAC&url=http%3A%2F%2Fwww.yccc.org%2FArticles%2FAntennas%2FN1IW%2FOCFD_basic.ppt&ei=s7NtUd6TG8jXigL16oD4CA&usg=AFQjCNHfWn-0DE-cK-bztlDbeKcro0ArDw&sig2=Epu261hkS_6pZnJk0FtCtw&bvm=bv.45218183,d.cGE

More ideas here: http://www.hcra.org/2012/09/06/home-made-off-center-fed-dipole/

More fun reading here: http://w0hc.com/ocf-dipole/

It's a very old idea and well used in amateur circles for a long time.
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K5LXP
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« Reply #11 on: April 16, 2013, 01:42:22 PM »

Careful with what loads you connect to internal ATU's.  They're meant for only a limited impedance range and it is possible to zorch them trying to match an extreme Z antenna.

If your plan is to operate a single wire across multiple bands you need to consider an external ATU up to that task.  Most transceiver internal tuners can't handle that.  They're meant only to "touch up" an already nominal 50 ohm antenna.


Mark K5LXP
Albuquerque, NM
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WB6BYU
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Posts: 13335




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« Reply #12 on: April 16, 2013, 01:58:14 PM »

The 40m dipole should work well on 40m and 15m.  On 20m and 10m I'd expect the
SWR to be too high to match with the tuner in the TS-440 (which has much wider
range than many modern built-in tuners, as it has motor-driven variable capacitors
rather than relay-switched fixed values.)

Even if it can get a match, you'll likely end up losing half your power in the coax -
certainly not the end of the world, and you'll still make contacts, but probably
worth fixing.

One simple solution is shown at the end of the article you referenced:  cut a second
set of dipole wires for 20m and connect it to the coax along with the 40m wires.
Then you'll have one antenna with one coax that works 40m, 20m and 15m.
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K0ZN
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Posts: 1553




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« Reply #13 on: April 16, 2013, 03:08:09 PM »

Respectfully, pick up a copy of the ARRL Antenna Book and put in a little study time on antenna basics. The time and effort will repay itself many times over in reduced frustration (I.e. more fun) and better success on the air. The cold fact is that Amateur Radio is a technical hobby, consequently the more you know the better you will do. Antennas and basic theory is not complex, but it is pretty unforgiving of assumption, guesses and myths. Your antenna is what connects your station to the world, so it is well worth your time to maximize your knowledge in this area. You can pick up an older copy of the ARRL Antenna Book (the "real" antenna book, not one of the collections of various antenna projects) off of EBay cheap and the information and theory is still totally correct. Again, the foregoing comments are respectfully to help you have more fun and success on the air.

73,  K0ZN
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