Coax Location Issue

[n3lrx]

 Well, I *was* able to get my SWR down as low as 1.19:1 without a tuner. With exact placement of coax. If I move coax an inch or touch it the SWR changes again, usually for the worst. If I touch the analyzer the ratio changes, again for the worst. The same goes if I attach the coax to the tuner and read the SWR from there. At this point it seems my tuning is totally up to coax and the particular placement thereof. I can't lengthen or shorten the antennas and make any change for the better. Grrr. It's really annoying.

 Does this mean the coax is just too short? I've only got 25 feet between the analyzer and the antenna. I'm going to order more anyway, I need the longer length so I can close the door at least most of the way, this means I'll have coax coiled up on the deck but I don't care. Most of it has to be left coiled on the deck anyway to keep the SWR down.

 I'm probably praying on a miracle to get on the air anyway. I hope I don't go through all this work to get on the air and get in trouble for blowing away someones TV.

Frustrating  

[K1JJ]

Hi Randy,

What is that short vertical using for a ground plane?  Looking at your picture from another thread, it's not clear.

From all the symptoms you've described - stray electrical noises, coax sensitive to placement, swr moving around, it sounds like the coax is hot and has unbalanced shield currents. The coax is acting as part of the radiating antenna which is NG. My guess is you will take out your neighbor's electronics if you run 100 watts.

Lets go back to basics.  You might try to duplicate the layout of a good car mobile whip layout for 75M.  Ideally, the 11' whip has a large coil at the base or center and is positioned vertically on top of a car or truck roof. It is fed with 50 ohm coax and matched for ~10 ohms at the base of the whip using a shunt capacitor to ground.  

This proven system works FB on 75M and 40M, so there is no reason why you can't do something similar using radials to simulate the ground plane and use the shunt capacitor match.  


T

[K4RT]

Are you testing with just the analyzer? If so are you able to ground the analyzer?  Have you tried reading SWR transmitting with your radio?

What antenna did you put up?

73
Brad

[W4EWH]

From all the symptoms you've described - stray electrical noises, coax sensitive to placement, swr moving around, it sounds like the coax is hot and has unbalanced shield currents. The coax is acting as part of the radiating antenna which is NG. ...

Lets go back to basics.

Ditto. As a first step, try winding three or four turns of coax right next to the feedpoint, to form a choke and reduce current on the shield. If you have to run the coax away from the antenna at a right angle, instead of straight down from the radiating element, then I suggest you bury it to reduce RF pickup on the outside of the shield.

HTH. GL!

Bill, W1AC

[KA0HCP]

If this is a vehicle mounting, check out Alan's website. Everything you want to know about mobile installations.

Obviously you have common mode on the coax.  Magmounts are notorious for poor ground coupling.  As suggest either air wound coax or a some turns on a torroid may help.

www.K0BG.com

[Pete, WA2CWA]

Maybe you guys should read Randy's other article including antenna picture:
http://amfone.net/Amforum/index.php?topic=36904.msg283151#msg283151

[K4RT]

Thanks Pete. I had not looked at the earlier thread. Single threads that are updated are good.   From the photo it looks like a dipole made with two hamsticks over Randy's deck and I see maybe 20 turns of coax for an RF choke.

[n3lrx]

 The antenna is a pair of 75m hamsticks in a dipole config. (I take the obstructions down when I try to use it, they are currently down.) I tried it on the transmitter and I get 3:1 tuned, 5:1 untuned. But if I situate the coax in a specific way I can get down to 1.19:1 on the analyzer. But as soon as I disturb the coax it goes haywire again. I can't get a decent SWR with the door closed, which will come in handy during a Michigan winter. I ohmed the coax and there are no breaks.

 I also have that ugly balun attached which has done a great job at killing the common mode current. Before I could not even touch the transmitter or the tuner without getting zapped, there is zilch on the chassis now. (Unless the SWR is way high) I've also got another ferrite choke but the coiled coax works best. I also did not know until after the fact that the ferrite choke was not to be used with high SWR applications until after I bought it. (ebay) I have no idea what it's made of it, it's inside PVC. I like what I can see and a coil of coax seems to do the job.

 I'm in a 3rd floor apartment and I don't have access to a decent ground other than what's available from the AC wall plug.

 I'm beginning to think I'm battling a lost cause here because my receive is not up to parr where I'd like it to be either. I can't even hear the east coast power stations much at all. There seems to be no Michigan or any other short range activity. Basically I get s3 of noise and the occasional s5 signal. There's only one person to get s9 or better and that's Don, K4KYV. I'm not looking for DX but it would be nice to have someone to talk to, I don't care if they're on the other side of the street.

 100w in my situation might be a bit excessive but unfortunately that's as low as she goes. It's a legal limit transmitter and I'm trying to squeeze QRP level carriers out of it. With the current SWR situation I don't get much more than 50-60w out on the meter anyway. On the dummy load I get 100w.

[K1JJ]

OK, I see now. That's a shortie helically loaded dipole fed with coax at the center. I did look at the other thread picture before, but thought the other element half was a cable of some kind, thus a single element vertical..

Questions: If you disconnect the coax from the center and measure the dipole impedance at the junction, what does it show?    Maybe a better solution would be to feed it with open wire line and go directly into a balanced link coupled tuner that is configured for low impedance.  You could  even mount the tuner at the center of the dipole and connect it with a foot or so of open wire.  This would give you a better isolated 50 ohm coax feed to the rig.

What's behind the ceiling wood where the dipole is mounted? Is there electrical wiring, metal plumbing or other metallic objects within 2' to 10' away?  How about those Xmas bulbs and wiring hanging in front of the dipole?  They can't be too good for the pattern and coupling into your AC power system..

T

[flintstone mop]

thanks Pete
That arrangement for antenna ain't gonna work. No way..
Fred

[n3lrx]

The xmas bulbs and the lanterns are down. As far as I know the ceiling is just wood. I don't believe there is anything metal within it, or any metal within 2 feet, but there is an aluminum soffit vent about 2 feet away to the front of the antenna,  the door frame and door to the rear, but it seems like they are vinyl to me, and it's at least 2 feet away. Both are way out of resonance (too short), so won't they be semi-transparent?

As Fred said, this situation is probably hopeless.

[KB2WIG]

I feel your pain. I've done the indoors ant / apartment thing on 10m and 20m.

If I remember, the powers that be said no external antennas. There is something called 'night' that may be of help.

I'd look into using the 'stick as designed for a mobile operation. Clamp it to the railing at around a 45* angle, and run some radials.   Something small, that will not cause much injury if it falls. You'd get it a little farther away from the house/wires, which can't hertz. You could even go so far as to buy some cheep sheet metal from homely despot, and use that as part of yer car body. During the day, pull it in, and go on 10m.

( Read the ground section   http://bama.edebris.com/manuals/johnson/viking2/)

You could unwind the coil part from the fibreglass, and rewind a coil thats less lossie. Check this out.

http://www.w5dxp.com/bugstick.htm

If i were to do this, I'd also place a small matching coil at the base.

klc

[n3lrx]

At this point I wish I had at a 160~10m rig. Unfortunately I don't. My transmitter is a fixed 160-80m am transmitter. I'll just have to save up and buy a mobile all band rig like a IC706 or 857D.

[W1ITT]

If you go with the KB2WIG method, using one of the hamsticks in a pseudo-mobile configuration, consider using chicken wire as a counterpoise.  Get a piece big enough to carpet your entire deck/veranda.  It will simulate a good sized vehicle body and provide a counterpoise, of sorts.  You could either roll it up when not operating, or cover it with some outdoor carpet.
You can get some fairly inexpensively at Tractor Supply or your local feed store.  Solder some braid on and that will be your "ground" at the feedpoint.

FYI, years ago, when I was an impoverished college student living in a fire-trap apartment, I hooked my wide range homebrew tuner to the red and green telephone wires that left my second floor apartment and directly crossed the street.  I didn't strap, but I got out.  Not recommending this, of course....

[KB5MD]

It may not be all the problem, but that aluminum soffett vent is a little close to the antenna for comfort.

[WB2EMS]

I never had much luck with the 75 meter hamsticks. They were so inefficient that they weren't even a good receive antenna. On 40 meters and up they play ok with a good ground plane under them, but on 75 I only ever made one contact and he was 5 miles away. The two of them in the dipole configuration are going to have a really low impedance, nowhere near 50 ohms. That's probably a goodly part of the SWR problem.

I would consider building something like the 'bugstick' that was posted, maybe using the existing hamstick as a base. Or consider something made to clamp to the rail and extending out further. The Buddipole folks make a fairly pricey, but handy, set of elements and coils which pretty much make up an antenna 'erector set'. I've used the low band coil and the long black whips with a couple of base sections several times on tripods for verticals. But you could make something electrically as good far simpler with a couple of sleeved sections of aluminum tubing and a big homebrewed coil at the base. QST many moons ago had an article about a simple L network tuner and a 12-18' piece of aluminum pole mounted to a piece of plywood with the pole facing out a window at a 45 degree angle. The window shut on the plywood to hold it and seal for weather. Run that with a counterpoise wire run around the railing and maybe over the side down to the ground when in operation. It won't be as efficient as a real dipole, but if you make it reasonable sized with a decent coil and counterpoise, it will be much better than a typical screwdriver mobile antenna on 75 meters, and I've made many fine AM contacts with those. Hang a flag off it and say it's your flag pole.  

Another approach might be to look into homebrewing a multiturn magnetic loop that can be hung over the side when in use. It's hard to make a good loop below 40 meters a reasonable size, but you can use multiple turns to keep the dimensions down and still have some efficiency. It's also a good receive antenna to reject some noise.

Just some thoughts. It's not hopeless, just challenging.

[n3lrx]

 The soffit vents are about 5 ft long, and not connected together. There is about a half in gap between sections.

I've got some 'bigger' 75m ham sticks but that means they will extend into the neighbor's air space. I doubt she would be too willing to allow it if she knows I could wipe out her TV with it.

 I guess I should start saving for an all band/mode rig. 40 and or 20 even 10, the way it's been open lately, are probably my only hope. I don't know if there's any AM activity on 15 or the WARC bands. Probably, I've never used the WARC bands. I've used 15m on field day that's my experience there. I guess the WARC bands are cool No Freakin' Contesting.

 I think I can get away with clamping an antenna to the railing. A screwdriver might be a good investment. The only problem with that is 40m is open in daylight. That doesn't provide any stealth operation. 20 I guess is pretty much open to somewhere 24 hours a day (at least from what I've experienced during field day).

 Anyway, I'll start saving up for an all band, all mode HF rig. That means no giving in to the seemingly impossible challenge to get on 75 with my present apparatus. 

[flintstone mop]

Where do you park your vehicle? Install a nice real antenna on the vehicle and run a long line of coax to your shack. Even if it is not a perfect 1:1 match; the losses in the coax are not noticeable on HF.
That would be a nighttime operation or during the day when everyone is at work.
80M and up would be pretty good with a mobile antenna. Forget 160M
Fred

[n3lrx]

No can do. I'm in the back of the building the lot is in front of the building. I'm screwed as far as working 75/80m it seems.

[steve_qix]

This is probably a dumb question, but if you're on the 3rd floor, and I see from the pictures that there are a LOT of trees out the back, why don't you just run a wire (or 2 wires) out to one or more of those trees?  Then the antenna will be up in the air and away from the building.

You would be able to get on 75 meters quite well if you could string 121 or so feet of wire out the window as an end fed half wave.  Feeding such an antenna at the voltage point works very well even with relatively weak grounding available.  I have run end fed half wave antennas in the past and they worked well.  But, it really needs to be truly a half wave (or some even multiple of quarter waves so you're feeding a voltage point).

[n3lrx]

The office says no outside antennas. I don't want to get into more trouble than the possibility of interference to other tenants. I don't know what the office will say if I cause grief to my neighbors. Stringing a wire out to the trees would definitely draw attention. Especially since they said no. So I have to be as stealth as possible.

 Believe me I would love to set up an end fed or a inverted L. I've already got the hook threaded into the wall outside my balcony. It was my plan to shoot a wire out to the trees this winter when the leaves drop off (so I can see what I'm doing). Alas the powers that be are strongly against it, and eviction is not what I want to face.

[flintstone mop]

Randy
I do not know what your situation was when you moved to this place; but was there any research done for the use of your station, permission to have outdoor antennas, the landlord's rules about Amateur radio, etc,etc??
It might be best to be looking for another place to live. A small house to rent, that is in your financial capability, will give you so much freedom to operate your station.
Fred

[steve_qix]

Huh!!  No outside antennas.  That's a pain.  Did you already ask?   If not, you could probably put up a "stealth" outside antenna made of thin wire.  I've done this myself many years ago.  If someone says something, you can always "beg for forgiveness" which is a whole lot easier than "asking for permission", so to speak.  And you can stress the public safety aspect of what you're doing  - something like "what I'm doing could save lives and property in an emergency" blah blah blah...

I had a friend in a similar situation who had a "stealth" antenna up for years.  No one ever said anything!!

[n3lrx]

 Well, I did what I thought was the right thing to do and asked for permission and they said no. Absolutely not. I had nice plans for an end fed zepp, a carolina windom, or some other OCF antenna stretched out to the trees with very little impact on their property. I don't want to sneak anything and risk getting busted and kicked out. This apartment is a Godsend compared to the box I was living in.

 People put up flower pot hangers and bird feeders and mount them to the wall. My project would be about equal impact on their property as far as that goes. I guess they don't want neighbors complaining about interference. Which I can see their point.

 Judging the response I got when I asked I got the feeling that it wasn't open for discussion so I didn't press the issue further. I'll wait until I'm not the new guy in the building and ask again, and maybe explain my case a little.. Or wait until some property comes up that I can afford and buy a house.

 Theres also the possibility of moving to Texas. I have 2.5 acres promised to me there. It's just the internet thing that keeps me here. It's out in the hill country where my brother lives and there is no broadband. (Satellite sucks.) I need broadband for work, I can't get by on dialup or on a mobile phone hot spot. Around release time I can burn up a mobile or satellite bandwidth per month cap in one day. Besides my mother lives here in Michigan and she's not healthy so I'd like to be here for her. I don't know how much longer she'll be around.

 I think after she goes I'll move south and hope Time Warner or the other company makes it to his area. They are supposedly moving slowly towards that area but have no fire under their ass. It's too far from a CO for DSL.

 We'll see. If worst comes to worse I can save some money and buy a mobile rig and work mobile for the time being, or put up an antenna on the railing and remove it when done. The railing should be a nice 20m ground plane. 40 would be a bit awkward, I don't want the antenna sticking out in broad daylight. 100w PEP shouldn't be too much of an impact. Most everyone in the building who has TV has cable.

 If I can't squeeze out a signal on one band, I'll try the next. Something will come up.

[WB2EMS]

What is the structure of the building made of? I've seen a number of articles about loop antennas being operated indoors in wood frame houses with reasonable results at QRP levels. A QRP loop is pretty simple to build and they are surprisingly effective antennas if the ohmic losses are kept down. I have read a number of articles about folks on 80 meter cw with them. AM would be more of a challenge, but maybe you can work split mode with a modern rig and transmit slopbucket for efficiency and receive AM. I've done worse. 

If people hang planters, then a clamp on 'flagpole' to the railing with your favorite flag on it might be something you could start playing with and use the pole as the radiating element.

Or come up with some fanciful thing involving two loops about 4-5 foot diameter hanging over the rail - maybe hang bird feeders on the loops or flower baskets, and feed them in series as a magnetic loop. ala http://www.qrz.com/db/KB0YH first antenna pictured.

I've also seen a loop built under the round top of a plastic patio table.

20/17/15 meters all seem productive at this point in the sunspot cycle and 17 is a nice band in particular. I've heard AM on all 3, and work 21.430 when mobile on a regular basis.

As far as invisible antennas - in college I was in dorms for the first couple of years. I used to make antennas from unwound yoke coils, about #28-30 wire, with bits of Clorox bottle cut out as insulators. It was easy to run 75 feet or so out to a nearby tree and you couldn't see the 'yak hair' wire unless the sunlight glinted just right, or ice started hanging off it. Fell down from ice loading from time to time, but I never got caught. But you have to manage your risks.

Buddipole makes a nice long 10' black whip antenna that could be rigged out at night from a clamp mount and a loading coil. Set it up to operate and remove when not. http://www.buddipole.com/lotewh.html

Hi-tech, find a used TS2000 and D7 and run the TS2000 in the car with a mobile whip remotely from the D7 with the Skycommand system. Or via a wifi system with a laptop in the car with a radio.

I think you're going to have to run near QRP levels with any antenna in or near the building to keep out of your neighbor's gear. That leads to some simpler antennas, but not real conducive to AM.