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Author Topic: Ladder line connection to transceiver  (Read 4645 times)
KC2UVX
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Posts: 26




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« on: December 21, 2009, 01:34:05 PM »

New to ham radio. Trying to make a dipole with ladder line. How do I connect the ladder line to the tuner? I know I have to attach it to a PL259 connector, but how do I do that? I know this may seem a silly question but I would appreciate any help or direct me to some site. Thanks to all.
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K5UNY
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Posts: 11




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« Reply #1 on: December 21, 2009, 01:37:41 PM »

Well I think you need to divulge what sort of tuner you will be trying to use??
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G3RZP
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Posts: 4742




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« Reply #2 on: December 21, 2009, 02:05:39 PM »

Take a length of RG8, about 20 odd feet long. Coil it up into about 6 turns, around 12 inches to 1 foot diameter, and tape the turns with plastic tape. Connect one end to the ladder line and the other end to a PL259. Use a tuner that can handle the power and a VSWR of 10;1 or more.
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KD8GEH
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Posts: 473




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« Reply #3 on: December 21, 2009, 02:17:49 PM »

Welcome!

You will need to tune the antenna to resonance on designed band with the ladder line attached to the coax choke as the previous op noted. You can avoid some possible RF issues if you leave some length (20-30 ft)of coax from the tuner to the ladder line connection. Always solder weather-proof that connection. You can also use PVC pipe or an old plastic coffee can for the choke and run the turns side by side, more efficient.
Feel free to contact me direct if you need help.

73,
Dave KD8GEH (@arrl dot net)
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WB6BYU
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« Reply #4 on: December 21, 2009, 04:25:17 PM »

Some tuners have terminals on the back for balanced line.  Just
connect the ladder line there and use the internal balun.

Or you can use an external balun, either in a box or home made.
These typically are in the form of a box with two terminals on one
end for the ladder line and a coax connector on the other. 

While you can make a choke balun by coiling up coax cable, I
wouldn't recommend it in this case because the SWR on the coax
may be very high.  You can easily lose half your power in that
30' of coax, and it can also transform the impedance to something
that is difficult for your tuner to match.  A 1 : 1 current balun
wound on a ferrite core is a better approach for this application.


Or, if you are in a hurry to test an antenna, you can do what I did
this weekend.  I found a short piece of coax (less than 1 foot) that
had a connector on one end and simply stripped back an inch or
so off the far end, separated the braid from the center connector
and twisted them to the incoming twinlead.  Crude?  yes, and it
doesn't necessarily maintain the feedline balance.  Some day
perhaps I'll put a proper balun in there, but it allowed me to test
my receiver with a temporary wire antenna, which was the primary
objective.
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N1LO
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« Reply #5 on: December 21, 2009, 05:32:22 PM »

Sounds like your tuner has no balanced line connectors. Yes, you *do* need a balun. I recommend a switchable ratio 1:1/4:1 *current* type balun from either Elecraft or MFJ.

The balun will have 2 terminals on one side for your ladder line, and a UHF jack on the other. Use a short (3-5') coax jumper to connect the ANTENNA jack on the tuner to the UHF jack on the balun.

Using ladder line will allow you to use your new dipole efficiently on many bands. Use whichever balun ratio is easiest for your tuner to match. When setting up such a system, you may have to add or subtract 5-10' of ladder line to arrive at just the right length that allows you to tune all bands, so don't get discouraged if your first 'cut' doesn't deliver all bands.


This is a terrible place to use a large coax choke coil, as 'BYU pointed out. Coax choke coils are not very broadbanded, and when multibanding on frequencies where the antenna is not resonant, there can be large losses in that 20-30' section of coax.

--...MARK_N1LO...--
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N4JTE
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Posts: 1158




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« Reply #6 on: December 21, 2009, 05:45:13 PM »

If the dipole is for one band than direct coax hookup is the way to go assuming antenna cut to 1/2 wl for the band. If you are trying to multiband an antenna by using lower loss ladderline it will work best at freqencies above the original design.
The easiest way is to install a 1 to 1 current balun near shack entrance than run a piece of 52 ohm coax to your tuner for multi band use.
regards,
Bob
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K0ZN
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Posts: 1553




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« Reply #7 on: December 21, 2009, 07:33:49 PM »

Hi,

Short answer to your question: You cannot and SHOULD NOT connect ladderline to a coax connector. They are totally different types of transmission line and the principal and theory under which they each work are quite different. You must provide some device, usually a Balun(Balanced-to-Unbalanced) transformer, between those two types of line. Coax is a 50 ohm UNbalanced line and ladderline is 450 ohms BALANCED. Connecting them together is kind of like the "square peg into a round hole" situation.

Respectfully, BY FAR, the best investment you could make in your station at this point would be a copy of the ARRL Antenna Book....and put in a couple of hours of study on antenna and transmission line fundamentals. They are not complex, but something you really do need to understand in order to enjoy this hobby and avoid a lot of frustration and problems. There is a lot more to antennas than you can pick up in a few threads on an internet site. This is a technical hobby; no way around it. Picking up a little knowledge will improve your signal and the amount of fun you have.

Pick up a copy of the ARRL Antenna Book....it will be a great asset to your station. An older copy picked up off of Ebay cheap will still be totally correct on basic theory.

Welcome aboard and good luck.

73,  K0ZN
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G3RZP
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Posts: 4742




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« Reply #8 on: December 22, 2009, 01:45:35 AM »

20 feet of RG8 has a loss of 0.2dB at 30MHz when matched. If the SWR was as high as 20:1, the loss would only be 1.5dB. Not really noticeable at all in reality. On the lower bands, there would be even less loss.
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K9IUQ
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Posts: 1982




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« Reply #9 on: December 22, 2009, 03:27:56 AM »

"You cannot and SHOULD NOT connect ladderline to a coax connector"

My first antenna was a 40 mtr doublet fed with used (free) cheapo 300 ohmn tv twinlead. I did not know what a tuner or balun was. I soldered a PL-259 right on to the twinlead and plugged it into my Eico 720 (which I built from a kit). Used this antenna on 40 AND 15 mtrs.

I did not have someone tell me it wouldnt work.

I used this setup for a couple of years, got WAS and gosh knows how much DX.

It was 1960 and I was just a dumb teenager.

Stan K9IUQ
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G3TXQ
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Posts: 1529




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« Reply #10 on: December 22, 2009, 07:59:33 AM »

20 feet of RG8 has a loss of 0.2dB at 30MHz when matched. If the SWR was as high as 20:1, the loss would only be 1.5dB. Not really noticeable at all in reality. On the lower bands, there would be even less loss.

The problem with a "coiled-coax" choke balun is not its loss, it's its poor choking impedance over a wide frequency range. I've yet to see a design which manages better than a 4:1 frequency range at Z>500ohms.

Of course, 4:1 may be a sufficient frequency range for the OP - it's interesting how much advice he's been given when he hasn't yet mentioned what bands he is interested in Wink

73,
Steve G3TXQ
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G3RZP
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Posts: 4742




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« Reply #11 on: December 22, 2009, 12:15:16 PM »

At a previous QTH in the early 1980's, I had a doublet about 20 feet high at one end, and 28 feet at the other. About 80 feet long - that was the length of the garden. The open wire line (made of stranded hook up wire and spacers from HV cable) was 23 feet long as that was the length that fitted through the dining area and the lounge when I made it. That went to a 6 turn, 18 inch diameter, 14mm thick 60ohm coax balun (because I'd got some 60 ohm coax!) hung on the fence between us and the neighbours, and then via 10 feet of RG8 coax to the tuner.  With a Drake TR3, I worked the old 80 to 10 bands and went from 105 to 185 countries in 3-1/2 years. Not all on CW either.

So the high SWR and possible poor current balance from the balun didn't stop things working..
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WB8YYY
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Posts: 159


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« Reply #12 on: December 22, 2009, 12:33:16 PM »

Welcome to the hobby, and join us as we continue to learn as well.  Balanced line is nice for multi-band antennas - so it solves the matter of interfacing wire to transmission line.  But the bi-product is that it creates a new problem at the rig!  While I have a ladder line fed antenna, I would recommend most hams start with coax fed antennas for a few bands.  By now you have probably discovered tuners made to interface with balanced line, or found a suitable balun.  Best if your antenna is suitably sized for your lowest operating band, meaning you will only be able stretch it a little when its smaller than a half wave.  If you already have the balanced line fed antenna built or up in the air, and you have a new tuner or balun on the way - be patient as you figure out how to use it.  I recommend turning your transmitter power as low as possible while tuning the antenna, just as a precaution.  73 Curt
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KD5PME
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Posts: 32




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« Reply #13 on: December 22, 2009, 12:34:43 PM »

New to ham radio and you already have an Extra license. Way to go.

Now, I suggest you might want to do some research on antennas and transmission lines as others have posted here. Most would think an Extra would know a little bit more about this subject.
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KE3WD
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Posts: 5689




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« Reply #14 on: December 22, 2009, 01:10:33 PM »

"New to ham radio and you already have an Extra license. Way to go."

-... .-. .. -. --.  

- .... .

-.. .- -- -.

-.-. .--

- . ... -

-... .- -.-. -.-


The argument, IIRC, was that CW had nothing entirely at all to do with learning the ins and outs of RF, operation, etc.  

This old ham gotta point that out.  

Now, one can indeed connect a twinlead to an SO- plug or jack and get away with it.  

Especially if that twinlead is common AC electrical zipcord, which comes in around the 70-75 ohm mark.  

Incidentally, so does the feedpoint of a dipole.  

But for this poster's situation, get a proper balun to go between the SO and the ladderline.  NOT a coax balun, even though you can get away with that one, too, but this is a situation where, if you have to ask the question, you shouldn't try that!  

MFJ or DX Engineering make 'em.  

Get one and follow the directions in the box.
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