Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: running back a random wire for tuning purposes?  (Read 2114 times)
K7RNO
Member

Posts: 279




Ignore
« on: June 11, 2013, 06:46:48 PM »

I am setting up an end-fed random wire in my backyard primarily for the 40 - 30 - 20 m bands, but also for lower bands. My max. length is about 15m. While I have an ATU, I would ideally like to tailor the wire to approximately 1/4w (and in any case add radials of the same lengths too). I am using an insulated 14 gauge copper wire.

To taylor the lengths, I could remove insulation at the 10m/7.5m/5m lengths from the top, fold and run the wire back at that point and connect the interim length to the TRX. Would the folded-back wire mess up my 1/4 wave? I would have to either roll up the extra length and tie it down at the fold, or run the extra length back on the wire toward the top, attaching it with plastic clips.

Which way would be the preferred way, and would any of that even be beneficial, with the ATU available?
Outside of the ATU tuning, I would not be transmitting, only receiving!

Thanks for your expert help.

73,

Arno
Logged

73,
aRNO
NAQCC #6870, SKCC #11131
K0ZN
Member

Posts: 1560




Ignore
« Reply #1 on: June 11, 2013, 07:59:56 PM »

A 45 ft. piece of wire is about 1/4 wavelength at about 5.2 Mhz.  At that frequency the "load" would roughly in the area of 37 ohms and not reactive....again at
5.2 Mhz, but that is not a ham band (well.... it is close to the 60 M band if you are interested in 60M).  On any ham band the impedance load presented by that wire will be complex and probably not too "friendly". Depending on the range of your ATU, it may or may not be able to deal with it. Don't be surprised if it can't find a match.

Also, remember that feeding an antenna directly out of your tranceiver makes the tranceiver chassis, mike cord, coax, wires to the power supply, essentially PART of the
antenna ground system, which is why you want a decent/effective earth ground or counterpoise. This can increase the possibility of RF bothering the rig or power supply etc. if the power is very high.  If ALL you want to do is listen, then there is very little concern....that wire will "pick up stuff" on almost any frequency you want to listen on; it should work pretty well for casual listening. Transmitting into that wire (which the ATU has to do to find a match) is a very different situation.

Again, if the ONLY thing you want to do is receive, then making the ATU "happy" is not much of an issue.  Adding a ground or counterpoise wire may or may not
increase the strength of received signals. You can experiment with that to see what works best and it may change by band; just look at the S meter and see what
works best.  Also, if you want to you could cut the wire at places where there is a 1/4 wave length (or 3/4) on various bands and then "jumper" them as necessary
for the various bands, but I suspect that on receive-only, just the wire will work just fine. I would try the simple solution first!

73,  K0ZN
« Last Edit: June 11, 2013, 08:12:41 PM by K0ZN » Logged
K7RNO
Member

Posts: 279




Ignore
« Reply #2 on: June 11, 2013, 08:21:01 PM »

K0ZN,
Thank you for the detailed information. I understand what you are saying. I also agree with you on the ARRL antenna book, I will get one and study it (there are several, which one would be best to cover these topics (building wire antennas to set up and break down again)?

For now, I am just anxious to start gettin something out of my new KX3 other than white noise Smiley

73,
Arno

Logged

73,
aRNO
NAQCC #6870, SKCC #11131
K7RNO
Member

Posts: 279




Ignore
« Reply #3 on: June 11, 2013, 10:23:43 PM »

For books, if I could only get one, which of these three would be the best for an antenna beginner:
* ARRL Antenna Book 22nd ed. (looks very comprehensive but seems to be too advanced for me)
* Basic Antennas (looks just right to me, for my basic needs—for now)
* Practical Wire Antennas 2 (possibly the opposite of the ARRL Antenna Book: too little theory, too much How To, not enough Why).

Which other antenna book(s) should be on that list, or even at the top?


Logged

73,
aRNO
NAQCC #6870, SKCC #11131
KA4NMA
Member

Posts: 354




Ignore
« Reply #4 on: June 11, 2013, 10:27:05 PM »

I would keep the antenna straight and long.  A true random wire antenna does not have a specific length such a 1/4 wl.  You did not mention what type of atu you will be using.  Must internal ATU do not have enough of a tuning range.  If all you want to do is to receive, skip the ATU and go directly to the radio.  You will not be able to transmit.  Don't forget some sort of counterpoise.  I would also agree that you need to the get the latest ARRL Antenna Handbook.  It is a lofty volume and a hefty price, but is worth it. Also does your radio have a dedicated receive only connector? If so, use that.  Another idea for receive only is to strip the end of the wire and insert it into the antenna connector.  Cheap, and easy receive only.

Randy ka4nma
Logged
K7RNO
Member

Posts: 279




Ignore
« Reply #5 on: June 11, 2013, 11:28:07 PM »

Randy,
I have an Elecraft KX3 with built-in ATU. Why not use it?
Counterpoises will be used, if they improve reception.

Yes, random wires don't have specific lengths, but if I could significantly improve reception on some bands, why not de-randomize mine for those, if I can? Can I? That question is still open  Wink

I will be connecting via a stackable binding posts adapter.
Logged

73,
aRNO
NAQCC #6870, SKCC #11131
K0ZN
Member

Posts: 1560




Ignore
« Reply #6 on: June 12, 2013, 08:38:42 AM »

Hi, Again....

Re: the Antenna Book.  If money is not an object, it is nice to have a new copy, but not that critical unless you are into some more advanced projects.  
Frankly, some of the older ones, such as in the late '60's, 70's or 80's, which can be found very cheaply on Ebay, etc. are every bit as good for basic antenna theory.
The basic technical theory is about 99% unchanged. About all that has changed is that we now have more advanced tools and modeling to work with antennas.  What you are seeking is some of the graphics about basic antennas, current distribution, impedance as it relates to wavelength, etc. Seeing graphic explanations really makes a lot of stuff come together. The old books are fine for that and some of them actually have some graphs that are not in the newer ones. Remember, "back then" most hams built their own antennas, so the old books are just fine for DIY. Another really excellent book, if you could find one of the earlier copies cheap, is ON4UN's book "Low Band Dx'ing". It is really an antenna book for the most part....and lots of other good stuff in it; well written.

I am not familiar with that Antenna Basics book, but it sounds like a good place to start. I am sure there is some good stuff in it.

Antennas and antenna theory are NOT particularly complicated, but there is a fair amount of "stuff" related to them that is not intuitive and a good book
with graphic explanations, graphs and pictures makes things a lot easier to understand. Another problem existing in the antenna world is a lot of myths and misconceptions.....and a known accurate source of technical info like the ARRL Antenna Book or other good book avoids those.

I have been flamed on here a couple of times for recommending that people make the effort to open a book and study antennas, but it is simply because that is the RIGHT answer in the long run: knowledge. The hard fact is you just cannot cover an issue as broad as antennas in a few paragraphs on an internet site. Maybe I am old fashioned, but I kind of assume most hams want to know WHY something works or works better. No radio station is any better than its antenna. A $5,000 radio connected to a crappy, poor antenna is still a poor station! .....whereas a QRP rig connected to a well built, highly effective antenna can be amazing.

Bottomline:  any time and effort you put into learning about antennas and basic antenna theory WILL pay off in a better signal and more fun.

Good luck &  73,  K0ZN
« Last Edit: June 12, 2013, 08:41:56 AM by K0ZN » Logged
WB6BYU
Member

Posts: 13461




Ignore
« Reply #7 on: June 12, 2013, 09:01:25 AM »

Quote from: KG7BJM

Yes, random wires don't have specific lengths, but if I could significantly improve reception on some bands, why not de-randomize mine for those, if I can? Can I? That question is still open  Wink



Depending on the angle of the wire, you are likely to get slightly better results using
the full wire length rather than trimming it to 1/4 on each band.  The longer wire
generally will have a higher input impedance, so slightly less ground loss.  And if
the longer wire allows you to get more of it higher in the air, that may improve your
angle of radiation.

The details depend on the exact arrangement of the wire, the ground conductivity,
distance to the stations you want to listen to, etc., so it is difficult to say for sure
either way.  You could always put up both wires and compare them to see which
seems to work best for you.  But I'd suspect that the longer wire generally will
be at least a bit better, and, n cases where the quarter wave wires happened to have
a slight edge, it won't be enough to make it worth changing the lengths, especially
just for receive.
Logged
K3VV
Member

Posts: 13




Ignore
« Reply #8 on: June 12, 2013, 09:13:42 PM »

A couple of suggestions.

First, I'd recommend the longest length L less than your garden's dimensions that satisfies this property:  L is not near a half-wavelength (or half-wavelength multiple) on 40, 30 or 20 meters.  Here's a page that lists some lengths satisfying that constraint.

http://www.hamuniverse.com/randomwireantennalengths.html

There are several lengths near 15 meters that will work.   The KX-3 tuner should have no trouble matching an end-fed antenna that satisfies the foregoing constraints.  (At least my KAT1, KAT2, and KAT100 have no problems matching such a wire.)  As you've already acknowledged, you'll need counterpoises for each band.

The antenna described above will work on the three bands of interest at least as well as the one you proposed originally and it will work with a lot less fiddling and fooling around.

I have over a dozen antenna books and my favorite for quick antenna solutions is "Practical Wire Antennas" by John Heys, G3BDQ.  You should, as others have said, get a copy of the ARRL Antenna Book eventually, but Heys' book gives you the information you need to put effective wire antennas aloft in almost any situation.  It's a marvel of clear-headed and clearly voiced technical writing.

http://www.amazon.com/Practical-Wire-Antennas-John-Heys/dp/0900612878


Logged
K7RNO
Member

Posts: 279




Ignore
« Reply #9 on: June 12, 2013, 09:45:37 PM »

Great info, K3VV, thank you.

Looking at the length info chart, I am afraid mine is in the vicinity of the bad ones (but I still heard stations from TX, VT, WI, PA, NC and others this evening, mostly on 20m—with just the aerial, no counterpoises or ground yet).

Going to do some exact measurements tomorrow...and am after one or two antenna books now  Smiley
Logged

73,
aRNO
NAQCC #6870, SKCC #11131
G0VKT
Member

Posts: 64




Ignore
« Reply #10 on: June 13, 2013, 04:12:28 AM »

I am in complete agreement with K0ZN. You can't beat books. Yes, the internet is a fantastic sorce of information, but a book tends to focus my mind more.
Can I recommend "HF Antennas for all Locations" by Les Moxon G6XN. A very informative read.

Paul.
Logged
WB6BYU
Member

Posts: 13461




Ignore
« Reply #11 on: June 13, 2013, 08:38:15 AM »

Quote from: KG7BJM

Looking at the length info chart, I am afraid mine is in the vicinity of the bad ones (but I still heard stations from TX, VT, WI, PA, NC and others this evening, mostly on 20m—with just the aerial, no counterpoises or ground yet).



The lengths that are multiples of 1/2 wavelength will still work fine on receive, but some
automatic antenna tuners won't handle the high impedances on transmit due to the high
voltages that can be developed across the contacts of the switching relays.

In fact, just about any wire will pick up signals on receive, because efficiency generally isn't
an issue.  The signal to noise ratio stays fairly constant because most of the noise is picked
up by the antenna along with the desired signals, and both go up and down similarly when
there are losses.

The only real advantage of using the antenna tuner on receive is that, when properly tuned,
it may help to reduce strong out-of-band signals.  (When NOT properly tuned, signals will be
much weaker than when the wire is connected directly to the receiver without being tuned.)
Logged
KA4NMA
Member

Posts: 354




Ignore
« Reply #12 on: June 13, 2013, 07:57:56 PM »

You will need to check the specifications on the Elecraft ATU.  What SWR range does it work with.  Many of the rig based antenna tuners only cover 3:1 and under. Some work with a limited range of impendences.  With a random wire, you will need a wide ranging ATU to cover all the different scenario's. 

Randy ka4nma
Logged
W0FM
Member

Posts: 2056




Ignore
« Reply #13 on: June 14, 2013, 12:04:27 PM »

Arno,

In your original post you stated that "Outside of the ATU tuning, I would not be transmitting, only receiving!"  Please keep in mind that, as insignificant as it might sound, even a brief transmission while tuning an antenna tuner (automatic or manual) on a band that you are not licensed for will, technically, be a violation of the FCC Rules and Regulations.

Be careful out there.

Terry, WØFM
Logged
K7RNO
Member

Posts: 279




Ignore
« Reply #14 on: June 15, 2013, 11:42:31 AM »

Thanks again for the info. Am taking everything into account.

(The General test is this coming week).
Logged

73,
aRNO
NAQCC #6870, SKCC #11131
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!