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Author Topic: Will I be okay to encircle the house?  (Read 10804 times)

linkclan

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Will I be okay to encircle the house?
« on: April 04, 2015, 03:55:54 PM »
So, my dream of a log periodic is a ways out and you guys have got me going on QRP as a fun alternative to spending large amounts of cash. Very unlike the folks on the other popular forms.

I already have a 135ft flat-top dipole up and it works pretty good except, well, you know, we hams must keep tinkering.

My question is: Can I safely surround my house with a 1060ft loop?

I have 6 trees picked out that will give me about 40ft in elevation on a slope to the east. One just happens to cross the feed point of my 135 which would come down and I could reuse the existing 450ohm feed line. I don't expect to ever put kilo-watts on this thing but, all the descriptions I have seen shows the loop off to the side of their home or shack. This configuration however would put the house smack dab in the center of it.

I believe my lightning protection is good with two rods 30ft apart at the balun, connected to three at the shack entrance 6ft apart and bonded through a sub panel ground to the primary electrode. Entrance consists of a NEMA 3R can with bulkhead buss and lightning arrests on each incoming coax.

I don't believe I would have to buy anything as my shop is full of wire and PVC pipe.

Thanks,
Paul


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Re: Will I be okay to encircle the house?
« Reply #1 on: April 04, 2015, 05:37:11 PM »
I have not tried it so I can't speak from experience, but a few years ago I mentioned doing that to another member of this forum.  He advised me that when he tried a loop around the eaves of his house his family objected strongly to the interference to their personal electronics when he keyed up.  It seems field strengths inside the loop were relatively strong and his experiment was quickly abandoned to preserve household harmony. I was after mounting convenience and didn't need the stealth feature so I dropped the idea.

FWIW and YMMV,
Wally

KK0G

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Re: Will I be okay to encircle the house?
« Reply #2 on: April 04, 2015, 08:48:25 PM »
I've never played with a loop but I always wanted to, everyone I've talked to that has one raves about them. I know the feeling of always wanting to experiment with different antennas, I've built many different ones over the years but for the past several years I haven't done any. It's probably a combination of the fact that my twinlead fed 140' dipole works so well and that I'm just plain lazy. Maybe one of these days I'll get around to finally building a loop.


Personally I wouldn't worry about lightning, it sounds like your protection is far more adequate than mine........ I figure that's why I pay insurance LOL.


Let us know how it works out.
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

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linkclan

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Re: Will I be okay to encircle the house?
« Reply #3 on: April 04, 2015, 11:50:30 PM »
I would really like to do this but my big concern is the amount of RF exposure we will encounter being inside the loop. There are a bunch of people limited to dipoles in the attic (ha, toys in the attic) I just wouldn't want to sleep in an upstairs bedroom directly under one of these while they are pumping kilowatts in an attempt to get a signal out. It will be 100ft away from the house at its closest point and we haven't had TV to interfere with in over 15 years. A terrible discovery is however that I will have to abandon the current feed point as it is in too close to get the whole 1060ft. I guess this means that I have to buy some coax. Dang it!

Sure wish my 135 worked better, it really only has a few resonant points and the majority is well over 5:1 so basically, its just cooking cable and relays. I might try adjusting the 450ohm feed length first to see if I get any improvement before I tear it down.

Paul-K6PLE

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Re: Will I be okay to encircle the house?
« Reply #4 on: April 05, 2015, 12:19:36 AM »
I would really like to do this but my big concern is the amount of RF exposure we will encounter being inside the loop. There are a bunch of people limited to dipoles in the attic (ha, toys in the attic) I just wouldn't want to sleep in an upstairs bedroom directly under one of these while they are pumping kilowatts in an attempt to get a signal out. It will be 100ft away from the house at its closest point and we haven't had TV to interfere with in over 15 years. A terrible discovery is however that I will have to abandon the current feed point as it is in too close to get the whole 1060ft. I guess this means that I have to buy some coax. Dang it!

Sure wish my 135 worked better, it really only has a few resonant points and the majority is well over 5:1 so basically, its just cooking cable and relays. I might try adjusting the 450ohm feed length first to see if I get any improvement before I tear it down.

Paul-K6PLE


A couple of comments;
1. The huge emphasis that the FCC has placed on RF exposure in recent years is ridiculous. At HF, unless you're holding on the antenna, you're perfectly safe, even at VHF and UHF there's very little if any real danger. Microwaves and higher can present some danger but with the low power transmitters most hams are capable of cobbling together, even they pose little risk. I'd worry far more about actual risks like getting in a car accident than RF exposure.


2. Not that I want to discourage you from experimenting with a loop, but why does your current antenna not work? A 135' dipole should work gangbusters if mounted at even a modest height. You mentioned relays, what exactly do you have for an antenna?
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

KK0G

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Re: Will I be okay to encircle the house?
« Reply #5 on: April 05, 2015, 02:00:28 AM »
Ditto what KK0G said; you may have to play with lengths and feedline configurations to get it to work on 40 meters but it should be fine on 80 and 20.  An alternative is a fan dipole.  Several years ago I put up a coax fed #12 stranded wire fan dipole with 80/40/20 meter legs with a center point up about 50 feet.  It worked very well until it deteriorated to the point where now only the 135ish foot 80 meter legs are still in the air.  It still works fine on 80 and 20 but doesn't want to match on 40 because of the length.  I put it up quickly so my lengths were not cut precisely, I got it close and let the antenna coupler take care of the difference.  I will be replacing it in the near future, but it worked fine for a long time.

Wally



linkclan

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Re: Will I be okay to encircle the house?
« Reply #6 on: April 05, 2015, 12:36:17 PM »
Lets see if I can compose a logical train of thought on the 135....

Strung between three trees at +-30ft with 2in grey pvc shoved up a middle tree for the center support. The 30ft seems to be okay as it is on a hill side and broadside to the east it probably thinks it is at 60 or 70ft. To the west, I'm sure it is all NVIS. If we redo it, I will go to 40ft in the center. The first mistake I believe is the grey pvc as I have heard that it is not quite RF invisible. Second mistake is the 450ohm ladder line attached to the grey pvc with zip ties and in full contact with the pvc and the oak tree. I have a little time today and think I will try to remedy this and cut all the zip ties and rout the ladder line away from the tree.

While we are on the subject of ladder line, I believe therein lies another problem. The acceptable lengths for 80M are 34-40 and 90-102ft. And for 40m it would be 42-52 and 73-83ft. After futzing with it initially at several different lengths (new, pre-licensed and without a SWR meter), I finally went with the full 100ft that came with the kit and strung the line back and fourth from the tree to the shack and miraculously the tuner stopped clicking and I was able to call out on 75m. The only thing I changed since then was the addition of a balun with a switch to toggle between 1:1 and 4:1 as it seemed that the tuner could latch into the higher frequencies at 4:1 except 20, 15 and 17 which are all 10:1 across the band no mater what. Now, I have a meter and am horrified at the terrible matching throughout the bands. Something must be done!

My thoughts have also been to build a fan dipole with a fat 75/80 wide band at the top and a 40 at the bottom cut for the CW portion. This should be pretty efficient and I could eliminate the ladder line and matching network. Then I would put up a separate way smaller fan dipole to cover the other daytime bands I'm interested in.

A giant loop would still be in the cards as it should also make a great receiving antenna.

73-K6PLE

« Last Edit: April 05, 2015, 01:12:20 PM by K6PLE »

KK0G

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Re: Will I be okay to encircle the house?
« Reply #7 on: April 05, 2015, 01:25:58 PM »
It sounds like you have ladder line running to a balun of some sort, then coaxial line from there to a tuner? Personally I'd eliminate the balun and run ladder line direct to the tuner - assuming your tuner has a 4:1 balun for balanced output. This will accomplish two things, first of all it eliminates the need for any specific length of feed line - however long it is from the antenna to the shack is the length it needs to be. Second, eliminating the coaxial feed line will also make any high SWR a moot point since there is negligible loss in balanced feed line with a high SWR. I've been running cheap 300 ohm TV twin lead directly to my 140' dipole from the tuner for years and it works awesome. No doubt there's a sky high SWR on my feed line on several bands, but as I said, with the balanced line there's practically no loss so as long as I can "tune" it with my tuner to make the transmitter happy, all is well, that's the beauty of balanced feed line.


I highly doubt your feed line attached directly to PVC is having much effect, the tree though?.....maybe. Your 30 foot height should work fine, raising it another 10 feet wouldn't be a bad idea if you can easily do it, but it probably won't have a dramatic effect on performance.


Another thing; the theoretical broadside figure eight pattern that all the books show for a dipole is exactly that - theoretical. It seldom works out that way in the real world. Rarely can we as amateurs get the antenna more than fractions of a wavelength height above ground and in the clear. When I put up a dipole my concern is not orientation for directivity, but the best and easiest way to mount it as high as I can with the feed point in a convenient location. However it ends up oriented is how it ends up, you won't get that textbook pattern anyway.


« Last Edit: April 05, 2015, 01:29:10 PM by KK0G »
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

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linkclan

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Re: Will I be okay to encircle the house?
« Reply #8 on: April 05, 2015, 02:53:47 PM »
Ladder line does go to a balun (switchable 1:1 and 4:1) the tuner is an unbalanced Z-Pro11 and this shack I speak of is actually a solar battery shack 35ft from my office/shack with RG-213 underground from here to there. The tree/center support is 15ft from the battery shack which gets my tuner and non outdoor rated balun out of the elements. There happens to be lots of 12vdc available in there also! Tuner was suppose to be a MFJ(Mighty Fine Junk) 9930 remote outdoor tuner but it arrived DOA and has been in their possession for about 3 months.

Today, I think I will work with what I have.

Just cut ladder line at 48ft

75/80m no longer resonant anywhere. Drops to 1.2:1 all the way out at 5100kHz
40m, 10:1 across the band
30m, 2:1 @ 10.125 with great bandwidth.
20m, Phone segment has several points below 2:1 and CW section starts at 4:1 and climbs from there.
17m, infinite across the band.
15m, 8:1 @ 21.000 and is beautifully resonant with 1:1 @ 21.450 right where I don't want it.
10m, 1:1 at 29.700 goes to infinity and beyond as we approach the CW segment.

Going to cut at 42ft next.

Paul

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Re: Will I be okay to encircle the house?
« Reply #9 on: April 05, 2015, 04:19:30 PM »
Ladder line does go to a balun (switchable 1:1 and 4:1) the tuner is an unbalanced Z-Pro11 and this shack I speak of is actually a solar battery shack 35ft from my office/shack with RG-213 underground from here to there. The tree/center support is 15ft from the battery shack which gets my tuner and non outdoor rated balun out of the elements. There happens to be lots of 12vdc available in there also! Tuner was suppose to be a MFJ(Mighty Fine Junk) 9930 remote outdoor tuner but it arrived DOA and has been in their possession for about 3 months.

Today, I think I will work with what I have.

Just cut ladder line at 48ft

75/80m no longer resonant anywhere. Drops to 1.2:1 all the way out at 5100kHz
40m, 10:1 across the band
30m, 2:1 @ 10.125 with great bandwidth.
20m, Phone segment has several points below 2:1 and CW section starts at 4:1 and climbs from there.
17m, infinite across the band.
15m, 8:1 @ 21.000 and is beautifully resonant with 1:1 @ 21.450 right where I don't want it.
10m, 1:1 at 29.700 goes to infinity and beyond as we approach the CW segment.

Going to cut at 42ft next.

Paul


Exactly how and where are you measuring SWR? As I said before, the 8:1 and 10:1 SWR readings should not be a problem at all. The high SWR will be on the balanced line and since high a SWR has little effect on the loss of balanced line, it's a moot point as long as the tuner will handle that much mismatch to make the transmitter happy. I'm not familiar with the Z-Pro11, is it not capable of matching that high of an SWR?
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

KK0G

linkclan

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Re: Will I be okay to encircle the house?
« Reply #10 on: April 05, 2015, 04:39:06 PM »
I am measuring at the end of the ladder line with a 1:1 current balun. I have given up on the dual as 4:1 is getting me nowhere. The LDG Z-Pro will match 8:1 with much clickety clack but I would much rather get the SWR centered or at least close to the band area I want to operate. This is all for efficiency's sake, you know:-) I am finding that the longer the ladder line, the closer i get to the frequencies I want. I wonder if it is proportional with the element length. I notice you have yours cut at 140ft which is a bit intriguing and I am now thinking that that 468# puts everybody up in the phone section for their first antenna.

BTW, its up at 40ft now and looks really silly sticking up 15ft out the top of the tree!

Paul

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Re: Will I be okay to encircle the house?
« Reply #11 on: April 05, 2015, 05:05:08 PM »
I am measuring at the end of the ladder line with a 1:1 current balun. I have given up on the dual as 4:1 is getting me nowhere. The LDG Z-Pro will match 8:1 with much clickety clack but I would much rather get the SWR centered or at least close to the band area I want to operate. This is all for efficiency's sake, you know:-) I am finding that the longer the ladder line, the closer i get to the frequencies I want. I wonder if it is proportional with the element length. I notice you have yours cut at 140ft which is a bit intriguing and I am now thinking that that 468# puts everybody up in the phone section for their first antenna.

BTW, its up at 40ft now and looks really silly sticking up 15ft out the top of the tree!

Paul


It will be far easier to use the 4:1 balun to match the 450 ohms to the 50 ohms the transmitter wants to see to be happy. One of the reasons I'm not a big fan of most auto tuners is because they generally don't have near the matching range of even a bare bones basic manual tuner but to each his own, I prefer being able to match my transmitter to pretty much everything including the kitchen sink if need be.  8)


My 140' dipole is no magic number, it just so happens that's how much wire I had on hand and it conveniently fit where I wanted to hang it.


In my opinion way too much emphasis is placed on antenna resonance and especially on SWR. For decades hams had no practical way of measuring SWR, hell most had never even heard of SWR and yet they got along just fine making contacts the world over. It wasn't until after WWII when the use of cheap surplus coaxial cable became common practice that it even became much of an issue.
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

KK0G

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Re: Will I be okay to encircle the house?
« Reply #12 on: April 05, 2015, 05:39:24 PM »
Paul, here is a little write-up on balanced feedline vs coax.  The thing to remember is balanced line is much less sensitive to mismatch (SWR) than coax is - coax works well for a mono-band resonant antenna or fan dipoles, but not multi-band single wire antennas.  Multi-band single wire antennas are not resonant in more than a few spots.  Pruning antennas for minimum SWR to use coax is a huge pita, and the results vary depending on whether your trees have leafed out yet or how much other vegetation, structures or obstructions are in the immediate vicinity.

Take a look at this article for some background:
http://www.qsl.net/kk6mc/FeedLinePrimer.txt

Wally

linkclan

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Re: Will I be okay to encircle the house?
« Reply #13 on: April 05, 2015, 07:19:31 PM »
Okay, I have 17m now!

I added 6ft to each side of the dipole and cut the ladder line to 56ft and that put 80, 40, 17 and 20 right in the middle of the CW portion of each band.

4:1 balun didn't work at all but the 1:1 put it right on the money.

Paul

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Re: Will I be okay to encircle the house?
« Reply #14 on: April 05, 2015, 08:28:13 PM »
It's probably getting too late for 17 meters tonight but if you want to try it out tomorrow I'll be around the shack from around noonish and on.

Radio Preppers

Re: Will I be okay to encircle the house?
« Reply #14 on: April 05, 2015, 08:28:13 PM »