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Ladder Line Entry to Shack
Hi Guys,
This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. The shield on the coax would float with no connection to any thing. This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? I would be interested in hear what has been tried! Tom, K8JRM in OKC |
#2
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Ladder Line Entry to Shack
In message , K8JRM
writes Hi Guys, This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. The shield on the coax would float with no connection to any thing. This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? I would be interested in hear what has been tried! Presumably, your ATU has a balanced output for the 450 ohm feeder. If you already have the two (presumably fairly short) pieces of coax lines already in place, I reckon that the first thing you should try is to ground the two shields to the case of the ATU (which I presume is your shack safety ground, and maybe also your RF ground). This should screen the inner conductors from other nearby conductors, and keep the feed balanced. If you don't ground the shields, you might as well not use coax. Obviously, using coax will change the impedance of the line for a short distance, and may affect the settings of the ATU (more on the higher HF bands, of course). But with luck, the ATU will still tune OK. The increase in feeder losses should be negligible. An alternative is to go from the ATU and through the wall using low impedance twin feeder. The spacing between the conductors will be much smaller than the for the 450 ohm feeder, and it should not have much opportunity to become very unbalanced due to the proximity of nearby conductors. It might be advantageous to twist it. I understand that, if the insulating material is suitable, twin mains power cable can be used as twin feeder, especially on the lower HF bands. The current rating of the cable will, of course, depend on what power you intend to run. Ordinary lighting twin flex should handle a couple of hundred watts. But, if you've got a bit of 50 or 75 ohm twin, all the better. -- Ian |
#3
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Ladder Line Entry to Shack
Tom,
Many configurations of the type you describe are widely misunderstood. To help you to analyse the configuration, keep in mind that for a coaxial cable in TEM mode, the current flowing on the outside surface of the inner conductor is accompanied by an equal magnitude but opposite phase current flowing on the inside surface of the outer conductor. Consider a break in the sheild as a circuit node with at least two connections, the inside surface of the outer conductor and the outside surface of the outer conductor. The configuration you describe will make essentially no difference to the common mode current, the feedline is not effectively shielded by the outer conductors. Owen |
#4
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Ladder Line Entry to Shack
On Mar 13, 12:22*pm, (K8JRM) wrote:
Hi Guys, This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? *Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. *When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! *I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. *The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. *The shield on the coax would float with no connection to any thing. *This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. *My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? *I would be interested in hear what has been tried! Tom, K8JRM in OKC Tom, you confuse me. Is the ladder line in the PVC tube all by itself? Or are there other conductors in the tube with the ladder line? If all by itself, then there has to be some metal conductor around the PVC. If the ladder line has to be in a PVC pipe with other wire, Stuff the PVC pipe full of rags or crumpled newspaper to fill the PVC and raise the ladder line as far away from the other conductors as possible. See if that helps. Another possibility is to put two 1/2 inch pvc pipes inside your 4 inch pipe, split the ladder line down the middle and run each wire through a 1/2 pipe. Some splicing will be necessary, but your antenna tuner won't care. My antenna is a 160 meter lazy quad (horizontal) fed at a corner with 225 ft. of 600 ohm feed line. This line comes through the wall of my mfg home (aluminum siding) and passes through a DPDT switch to 400 ohm ladder line to the antenna tuner. The wall insulators are ancient ceramic units made specifically for feed line through the wall. The tuner takes care of whatever matching is needed. Works great! Paul, KD7HB in Oregon |
#5
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Ladder Line Entry to Shack
"K8JRM" wrote in message ... This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! I can not get the antenna to tune with any of my ATUs. What about enlarging the hole and covering it with a piece of plexiglas with two bolts through it, spaced the same distance apart as the gauge of the ladder line. Connect sections of ladder line to both ends of the bolts -- under the bolt heads on one side and under the nuts on the other. MFJ makes something along these lines. Please see: http://mfjenterprises.com/Product.ph...uctid=MFJ-4602 Finally, have you tried tubes of material other than PVC? I ran some 300-ohm TV twinlead through an empty Sue Bee honey squeezer tube and the pictures were fine. (This was before I owned a signal meter, so I don't know if it had any bad effect.) "Sal" |
#6
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Ladder Line Entry to Shack
K8JRM wrote:
Hi Guys, This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. The shield on the coax would float with no connection to any thing. This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? I would be interested in hear what has been tried! Tom, K8JRM in OKC Tom, Sounds like your running the ladder line with some other conductors in the PVC. You never said how far the entry point was to the ATU, if its relatively short less than 15' or so I would recommend you run a piece of coax from the ATU through the PVC to a 1:1 balum located outside. there would be some loss in the coax/balum but it would be low on 160-30M and some what higher on 20-10 meters. I don not think you can quantify the amount of loss but I don't think you will see it via RST reports. I have successfully used this method over several years since I did not have the 4" PVC that you luckily have for the coax and other conductors. The above suggestion is made on the assumption that the ATU has a unbalanced output for coax and is not a balanced only tuner. With respect to the addition of two (2) pieces of coax as a feed through on the inside of the home the shields are connected together and then joined to the ground system in the shack. From the feed through point then you can continue with the ladder line to the ATU. I recommend the remote balum since it helps cut down on any coupling of RF to other conductors in the PVC. Use a good current type balum since the swr is likely to vary over the multiple band use. The length of ladder line from the balum to the feed point of the antenna is some what critical and there is lots of articles on the subject on the WEB, I believe DX Engineering has some excellent white papers on this subject for remote balums. 73 de Ron W4LDE |
#7
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Ladder Line Entry to Shack
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#8
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Ladder Line Entry to Shack
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#9
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Ladder Line Entry to Shack
"K8JRM" wrote in message ... Hi Guys, This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. The shield on the coax would float with no connection to any thing. This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? I would be interested in hear what has been tried! Tom, K8JRM in OKC Howdy Tom The two short pieces of coax with center conductor connected to either side of the ladder line is perhaps the best solution. It was covered in QST/The Doctor is In, June 2008. In the article it suggests using the best quality coax on hand, keeping the run to the absolute minimum and the coax shields should be tired at both ends and connected to the station RF earth. This configuration introduces a small section 100ohm nominal impedance transmission line into the antenna system which should have minimal losses, but most important is that it is still part of the balance transmission line. The losses for say RG213 at 4mtr would be almost nothing on 80mtr and perhaps up to 2db on 10mtr. Obviously the lengths of coax need to be exactly the same length. If you would like a copy of the article drop me email. Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
#10
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Ladder Line Entry to Shack
On Mar 14, 6:05*pm, "Peter" wrote:
"K8JRM" wrote in message ... Hi Guys, This is an age old question - what is the best way to get 450 Ohm ladder line into my shack antenna tuning unit (ATU)? *Here is my situation; I have two 4" PVC tubes inserted into the exterior wall that allow the entrance of coaxial cable into my shack. *When I run the ladder line into the shack through one of these ports, the multi-band wire antenna fed with the ladder line goes wild! *I can not get the antenna to tune with any of my ATUs. I have received several suggestions on how I can overcome this problem. The most promising one seems to be to use two short pieces of coax with center conductor connected to either side of the ladder line. These pieces of coax, in turn, would be fed through the PVC hole into the shack and the center conductors connected to the ATU. *The shield on the coax would float with no connection to any thing. *This solution sounds good; however, common sense tells me that ladder feed line will still suffer because of its proximity to other objects. Any thoughts on this solution? Another possibility is using a piece of Plexiglas place under a metal framed window pretty much as shown in the old hand books. *My problem with this solution is that the window is on the other side of the room from operating table, the two coax entry ports and AC power. Short of placing the tuner outside in the elements, is there a solution to my problem? *I would be interested in hear what has been tried! Tom, K8JRM in OKC Howdy Tom The two short pieces of coax with center conductor connected to either side of the ladder line is perhaps the best solution. It was covered in QST/The Doctor is In, June 2008. In the article it suggests using the best quality coax on hand, keeping the run to the absolute minimum and the coax shields should be tired at both ends and connected to the station RF earth. This configuration introduces a small section 100ohm nominal impedance transmission line into the antenna system which should have minimal losses, but most important is that it is still part of *the balance transmission line. The losses for say RG213 at 4mtr would be almost nothing on 80mtr and perhaps up to 2db on 10mtr. Obviously the lengths of coax need to be exactly the same length. If you would like a copy of the article drop me email. Peter *VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm Hi, Peter. I read the QST article and thought it was crazy and so I tried replacing the 5 ft length of ladder line from my antenna tuner up the wall to the two feed through insulators going through the wall to the 600 ohm feed line outside. With the 5 ft ladder line I could tune the antenna, a 160 meter lazy quad loop, to all bands through 15 meters. With the 5 ft section of double coax, just like the doctor said, the antenna would not tune for 20 meters or any higher band. I put the old ladder line section back. Remember what all the discussions say about keeping the feed line away from metal objects? Here we are introducing a 5 ft length of metal just 1/4 inch from the feed line. The extra capacitance just kills the feed line. Yes, I was using RG-213. So, the doctor in nuts, as far as I can tell. Paul, KD7HB |
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