Couple Questions Lumped into One

[Dealer]

Finally found some room to put up a Wire Antenna, at 35ft. on both ends,
using a 4 to 1 current balun on a 80 meter OCF dipole and using 100ft. RG8X.

Problem is that it goes across the house on the west end at a low point on
the roof which is about 20ft. so that makes it clear the roof with sag at balun
of say 10 to 12 ft.

Problem is TVI on that end of house, which of course is the area of the Great
Room and my wifes favorite haunt Damn TVs...
No problems at all on the east side where my shack is about 60ft. away.

Since I have not any problems of this nature, I am thinking that it is the antenna
radiation because of being close ? in that area.

Also the coax is temp laying on the roof until all is solved.

Any thoughts on a UnUn or a line isolator in the event it is common mode currents
on the coax ?

Also a question on a TEMP RF Ground using coiled Rat Shack wire from radio to
the base of my I-10k sharing same ground rod.

No transmatch is in line and very temp to see if grounding is of any help.

Only the OCF dipole is a direct connect to the Kenwood.


Thanks to any and all for suggestions.

KD5WJY
John

 

[W5LZ]

John,
I sort of doubt if the problem is going to be as simple as adding an unun, or a ground to the system. It sounds like it's a matter of the antenna being just too close to the TV (whatever else). Also doubt if the feed line laying on the roof is a 'biggy'. Maybe, but I doubt it. The easiest way to find out is to move the antenna further away. (And if you are in the same boat as most of us, that isn't going to be simple/easy or even possible, probably.)

An off center fed dipole isn't exactly the 'cleanest' radiating thing around. The feed point, and the ends of the antenna are the 'biggies', sort of, higher voltages present in most cases. They ain't exactly 'balanced', sort of. They are not bad antennas, just have different qwerks.
- 'Doc


PS - The 'Great Room' is the one with the radio stuff in it, not the TV! And that's the only statement in this post that I can be absolutely sure of.

 

[BJ radionut]

TVI

Other questions...TV "over the air antenna"? Cable? Sat?...I hope not Uverse AT&T they use 160m and 80M freq's on their data/video lines...Let's have some more info if possible...
Doc's also correct try moving things around and see what happens...
All the Best
BJ

 

[Dealer]

Other questions...TV "over the air antenna"? Cable? Sat?...I hope not Uverse AT&T they use 160m and 80M freq's on their data/video lines...Let's have some more info if possible...
Doc's also correct try moving things around and see what happens...
All the Best
BJ

Sorry to be so long in reply, so much going on and the answer is Yes to Sat. and
over the air antenna, but is a non issue at the moment as a storm tested the
short side and it came loose at the end guyed to a tree. I took it all the way down
and will relocate it.

I believe it was because of being to close to the fireplace stack just a couple of feet
to the side and and maybe five feet above it.

When I built this home it was decided since fireplace was to be in the middle of the house and the design was such that a full masonary fireplace was out of order.

Instead it has a metal tube enclosed in a wooden chimney like a lot of newer homes
these days. Also less expensive

Ten meters was fine, Twenty was just a bit on audio and the real problems were on
40 @ 80 meters. Doc, grounding did in fact help some..

My Wife and a higer power wanted it moved, So moving it is !!


John, KD5WJY

 

[Dealer]

Got the antenna moved a bit east, more towards the center of the house
where peak of the roof is higher.

Good 15ft above the roof and also used a messenger line to support the
balun and less srain on the wire overall...

Darn good job if I do say so myself and the numbers look good.

Guess What ?

Now I have RFI on my side as well good grief and we call this fun, and thats
not counting the 4 ridgecap shingles I pulled loose on the roof in the process.

I get nosebleed on a 4ft step ladder.

Problems are on 80 @ 40 meters only as 20 @ 10 are clean as can be ??

I am starting to think that these reviews that we read on eham and such is buy
people who really never had an antenna at all.. i.e Oooo just threw it on the roof
or better yet, strung it under the gutter down spouts or wraped it around a cedar tree
like christmas lights.

I turned off radio to move it and redo the temporary ground on the back of case and it
bit me some twice till it bleed off.

I think common mode currents on feed line at this point ?? Have yet to see a plot
of a wire antenna radiating downwards from a height of 35 to 40ft.

Antenna overload it could be I suppose, but I have never read that discussed regarding
a wire antenna at 200 watts or less.

To be in the clear as in "Clear would take 250ft of buryflex and thats taking the
fun out of it.

BTW, this is all on audio in my shack and not on picture or computer and for some
additional information, my I-10k is right over my head at 45ft. and at least 30ft.
or more from the wire...

Regards,
John - KD5WJY

 

[Justme]

Put an 1:1 balun directly at the feedpoint of the OCF
I use an OCF here, 1200 watts with no RF bleeding in any stuff here, and i live on the edge of the city.

That will prevent RF on the outside of the coax and that causes the problems you have now.
My feedpoint is 10 feet from the roof the rest of the OCF is flat top at 45 feet.

 

[W5LZ]

There were a couple of things that caught my eye right off...

"I turned off radio to move it and redo the temporary ground on the back of case and it bit me some twice till it bleed off."
---- I think I'd start looking for another source for that 'biting' thingy, RF feed back or common mode currents just don't hang around very long when the transmission stops. If it 'bit' you twice, I'd be willing to bet it ain't either of those two thingys.

"I think common mode currents on feed line at this point ?? Have yet to see a plot of a wire antenna radiating downwards from a height of 35 to 40ft."
---- When you talk about radiation patterns, and when you are -that- close to the antenna (top, bottom, sides, where ever), there basically just ain't no pattern to it, the signal is too strong, sort of fills in all those supposedly 'empty' places. Bad way of putting it, but it gets across what I'm trying to say. If you had a very discriminating meter that didn't worry about getting zonked because of the strength of the signal applied to it, it would probably show some very tiny differences in signal strength at distances of less than a full wave length from the radiating source. Those 'tiny differences' get larger, become more apparent/noticeable, as the distance from the source increases. And then before you know it, you got a real live radiation pattern of some sort of shape. But that close to the antenna (source), it's all radiation with very little difference in strength above, below, to the sides, where ever. Sort of like getting shocked from 1234 volts, or getting shocked by 1235 volts. Ain't enough difference to make any difference, sort of.

Since an OCF is not a balanced antenna to start with, a balun isn't going to do much good. An 'Unun', or a 'line isolator', or a 'choke', would make a bigger difference with out creating any additional differences because of that balanced/unbalanced thingy. (By 'choke', I mean a typical coil of coax.)
Is this a definitive answer? Of course not. But it's definitely a 'ball-park' one.
- 'Doc

(For a suitable fee I will dispatch my midget hula dancer to perform during antenna work. Fool proof method to correct any mistakes made during that antenna work. I don't make that offer to just anybody, so consider yourself privileged! Oh, by the way. She happens to like food and beer. Please don't make her mad, she makes things go the other way when she's not happy.)

 

[SR385]

A bit anecdotal, but....

A 102' doublet fed with window line right to my tuner and run parallel to the house but about 35' away from the house...no RF in the shack at all.

135' OCF fed with window line, RF *everywhere* (it was unbalanced....a learning experience) unusable.

135' OCF dipole with window line down to a 1:1 balun and coax into the shack, the antenna runs perpendicular to the house with one end about 25' above the desk in my shack just outside the wall. 100W, no RF anywhere. 1kW no RF until I get to 20m and then it's unusable.

My next trick...center feed that antenna, fed with window line, push the antenna back out at least 30' from the house...my bet, my RF issues go away again.

I can run a kW on my vertical that is 40' from the house all day on any band it will cover with no RF issues.

I think the proximity to the house, combined with it being an unbalanced antenna are aggravating your troubles.

It's all fun, frustrating, but fun when you get it working. I took the current OCF and tied the window line leads together and fed it against ground for 160m the other night and it made a nice improvement. Always interesting to see what happens as I make changes and keep playing.

 

[W5LZ]

Just for grins...

All antennas are frequency 'sensitive' to some point, usable on more than one band, but never all of them unless loaded/trapped in some way.
OCF antennas are not the 'cure-alls' that some might think they are. The feeding of the thing NOT at the center is only a means of finding an impedance compatible with the feed line, and in the process, loosing whatever benefits 'balance' contributes to the whole thing (that's sort of a long 'stretch', but still true).
If the thing is far enough from anything, it isn't going to make a huge difference if it does radiate 'weirdly'(RFI). Since having 40 acres isn't exactly 'normal' for the average person, especially in town, cleaning the antenna system up is a good idea. Typically, not the easiest solution, but nice.
Common type antennas are 'common' because they have some characteristic that's nice to have. Uncommon antennas are really only as useful as their 'uncommon' characteristic in particular circumstances. In other words Dealer, ditch the OCF antenna and try another kind. Unless!! there's a particular reason for using it, then do what you can to make it more usable. (Sort of what you're doing, huh?)
Another one of them 'pearls' of wisdom...
- 'Doc

(Pearls = small piece of grit stuck in an oyster's _ _ _ and getting larger over time. Nasty thought, huh?)

 

[Justme]

Symetrical fed antenna's can cause just as much trouble

If both legs are not precisely hung the same height, or one over an roof and the other over ground, the antenna is everything except symetrical.

I run the OCF because it was according the oldtimers the recipe for RFI and an bad antenna, so i wanted to know if that was true, not by hearing so, but to see for myself

I run it IN the city with 1200 watts PEP at 45 feet above ground, with no RFI whatsoever

I run mostly on our 80 meter net in Holland 100 watt, produce the same signal as most other peeps in the net with 400 watts or more, in symetrical antenna's

Is it an wonder anntenna?, no it is just an 1/2 wave dipole on the lowest frequency just differently fed so it will work on more bands
On those bands the SWR is low, so not much losses in LMR400 coax, i use an even better conterpart, all 60 feet of it.

I ran symetrical fed antenna's, full size loop antenna's for 80 meters,next project is an full size loop for 160 meters.

My pearl of wisdom, experiment, have fun, homebrew is cheap, and the antenna system is 90% of your station.

Cor

Homemade baluns for 2 to 3 kW , home made ladderline too.

 

[Dealer]

OK this is what has happen so far, I wanted to see if a air wound choke made
any difference.

A quick look in the cabinet of Stuff found a 18ft. length of RG8 ready made
and wound 10 turns on a flower pot just a bit of a taper in it and figured that that
would at least let me know if any results would be had.

In my shack it made all the difference and we are back to square one and all is good.

In the Great Room however, Opps I stand corrected !! the Den it is.
The problem still exist, so back to the drawing board on that one.

Not sure if winding another choke in different configuration will be of help or not.

I know one thing, and thats I want be putting my Ol butt on that hot roof
again thats for sure. The pitch is way to steep for me and bones at my age dont
heal so well.

Thats it for today.


Regards,
John - KD5WJY

BTW, I worked the taper out by hand...

 

[W5LZ]

The 'taper' in that choke isn't going to matter much, wouldn't worry about it. Adding another at the feed point might do some good, but it also might not. Wouldn't hurt to try I guess, since it should at least 'clean up' that part of the feed line between feed point and the other end. That doesn't do much for the radiation from the antenna being sort of close to the Den. Not much you can do about that except move it further away (the den or the antenna, your choice). Of course, moving the antenna 75 feet, or more, into the air (higher) would work too. And I'll hold my breath on that one, which will still be easier than what she's gonna tell you to do with that idea! Oh well, win some, loose some...
- 'Doc


Ooo! Ooo! Put a metal roof on the house and ground it!

 

[Dealer]

Doc, I typed a nice long reply with a little humor and then the router went on Blink
just as I hit the send button, spittttttt makes me so mad when that happens.

So recycled it and all that good stuff , So I will keep this short !!
Do you think I should wind choke for transmitter end the same as the other or not ??

Your reply regarding radiation has not fallen on deaf ears just not ready to
throw in the towel yet.

If it can be made to work, then I will make it work with help and advice from those
who came before me .

A few other things I have in mind, however I believe it best to take things one step
at a time..


Regards,
John---- KD5WJY

 

[W5LZ]

Dealer,
Chokes really are not that critical as to how you wind them, or what they are made of to some extent. If your normal feed line, whatever you're using to get from here to there is long enough, wrapping it a few turns around something of the appropriate size to give it shape ought'a work as well as anything 'special'. The main thing is to make the coils large enough so that the coax isn't bent too sharply, no conductor migration sort of thingy. I haven't run across any accurate way of determining the required number of coils needed for any particular frequency range. And if the antenna is used on more than one band, that 'right' size is sort of out the window anyway. A very rough rule of thumb is at least the same number of turns as in the first or first couple of numbers in the band (8+ for 80 M, 4+ for 40 M, etc. At least 4 or 6 for 10 meters). That rule of thumb breaks down real quick, so it's definitely not some kind of 'rule', you know? A few 'extra' turns won't hurt at all.
I may have misunderstood where you already have a choke. I thought you put one at the transmitter end already. If so, another one isn't going to do much good. One way of thinking about chokes is that they 'live' up to their name, they choke stuff off of the feed line from where they are to the 'other' end of the feed line. So the best place to put them is at the antenna end. That assumes that the transmitter is 'clean' to start with and doesn't 'contaminate' things going to the antenna, just any "re-radiation" coming back down the feed line... sort of (didn't say it was a good way of thinking about it, just another way).
About the computer 'glitching'. Wanna swap problems? I'd be tickled to get rid of the ones I have for the ones you have! Although, I have them at times too. Mine sort of takes a 'nap' at the most inopportune times (when I wanna use it). Takes sort of a long time to get awake, 'sluggish', and just stops like it has to think about what I told it to do. Got a feeling it's the antivirus program and firewall. I used a firewall called 'BlackIce' till they quit supporting it (10 years?), worked just dandy. Tried several others since, including 'MacaFEE' and 'Nortions", don't like them. But, what'a'ya gonna do? Then again, it may be something else, beats me. Oh well, if it weren't for the problems this 'C%@p' would be very boring, wouldn't it?
- 'Doc

 

[Beetle]

Dealer - if you do wind a choke for keeping RF off the outside of the shield, you might want to keep the diameter fairly large. A good rule of thumb is to shoot for a bend radius of 10x-12x the cable diameter. For RG8, which has an OD of 0.405", that would be a 4" radius, or an 8" diameter. In hot weather, if you flex a piece of coax too sharply, the center conductor can migrate right through the dielectric and contact the shield. This is generally considered ungood. Keep it loose!