INV - L specs and help

[WB4AM]

Hello,

I have been watching this post too.  I agree with Kevin, but by adding a few more will help you that much more.

When I had built mine, I had 4 radials down just laying on the ground.  I kept my air variable capacitor in line and left it half close or half opened!  The only difference is I used aluminum pipe for the vertical section for about 57 feet.  I used 10 gauge strained wire for 105 feet long.  It was longer until I cut for best swr.

Each time I cut the wire I check swr and I also moved the air variable capacitor to see if there was any reaction.

I discovered it would allowed me to adjust the swr to use the entire phone band. 

But 1.1 swr did not come into play until about 24 radials were put down.  I was placing 4 to 8 radials each summer until I reached about 40 radials and then maybe I place 4 or 5 more a few years later.  Before this I might had gotten 1.5 swr using the air variable up and down the band.  I remembered the more radials I had put down the better the swr was.

One last thing.  I copied this plan with my uncle's 160 antenna with the same results.  However he didn't bury his radials.  He moved them to one side so he could cut what little grass he had living in the "Pines" in Jersey. 

One time I was over there and he said he cannot get a good swr on 160.  I tried to move the remote variable cap from inside the shack and sure enough high swr.  I went outside and found he forgot to spread his radials back around the antenna.  I told him that is why you have a high swr.  He didn't believe me.  We move the radials back around the antenna some what even and went inside to check the swr.  I didn't even touch the remote air variable and the swr was like 1.4 compare to 3.2 or so.  After adjusting the air variable we were able to achieve 1.1 swr.

For some reason he only had about 12 radials or so and he was able to get 1.1 swr.  I think this was due to the high water table surrounding his house and the sugar sand that also surrounded his home.

I live in Pa. where the ground is hard and rocky.

So hopefully some food for thought.

Ken

[K4BOF]

Data shows about 100kc of bandwidth on either side of the resonant frequency before it starts wigging out to 3:1 SWR.  That seems consistent with other INV-Ls, yes?

Am I correct in that as I increase my radial system, that the bandwidth will become more and more narrow?  And, the resonance will shift up or down in frequency?  Thanks

[KB2WIG]

I've still suffering from the lazies, so I haven't put up my 160m eL.

This site has some good dope r/e 160m eLs,

http://www.antennasbyn6lf.com/

He has these wiered things called "measurments". They seem to help explain things.... .. This guy is an IEEE fellow, so he may have someting to say. 

KLC

Maybee I'll do some antenna work tomorrow.

[WB4AIO]

Data shows about 100kc of bandwidth on either side of the resonant frequency before it starts wigging out to 3:1 SWR.  That seems consistent with other INV-Ls, yes?

Am I correct in that as I increase my radial system, that the bandwidth will become more and more narrow?  And, the resonance will shift up or down in frequency?  Thanks

Your bandwidth is wider than average in my experience.

Anything you do to increase efficiency will generally decrease bandwidth, to the extent that the inefficiency is due to coupling to lossy ground.

I find that you need very few radials to get good efficiency as long as the radials are eight feet or more above the ground. Four is ample. Two work pretty well too.

The loss from having one radial only is probably between 1 and 2 dB compared to two radials, so it's not huge in practical terms. You could gain another dB or so by making it 16 radials instead of 2 -- I decided that was too much work. But, on the other hand, rock-crushing signals are generally the result of carefully minimizing all losses, and all those hard-won decibels are cumulative.

Elevated radial length will indeed affect resonant frequency; longer will lower it, shorter will raise it. It doesn't matter so much when the radials are on or in the ground, but efficiency is dramatically lower for non-elevated radials.

In my setup everything is isolated from Earth ground as much as possible.

73,

Kevin, WB4AIO.

[WB4AIO]

I've still suffering from the lazies, so I haven't put up my 160m eL.

This site has some good dope r/e 160m eLs,

http://www.antennasbyn6lf.com/

He has these wiered things called "measurments". They seem to help explain things.... .. This guy is an IEEE fellow, so he may have someting to say. 

KLC

Maybee I'll do some antenna work tomorrow.

Nice find -- looks like some good reading for cold Winter evenings.

73,

Kevin, WB4AIO.

[K4BOF]

Your bandwidth is wider than average in my experience.



I currently have approx. 20 radials down on the ground at various lengths at the feedpoint.  Most are 65' in length.  1-2 are 132' long.  All are lying on top of ground (covered by grass through the years).  I have only 1 that is 132' long and elevated at 10-12'.  

With more radials (preferably elevated), will this decrease SWR across the 160m band and provide a more consistent match between 1.8-2.0mHz?  Or will it cause a decrease in bandwidth (less kcs of workable frequency)?  I am confused by your comment that my bandwidth is wider than avg.,...I would think that that is a good thing?  My ATU should be able to handle the entire band now with the current setup.  Thank you.    

[WB4AIO]

Your bandwidth is wider than average in my experience.



I currently have approx. 20 radials down on the ground at various lengths at the feedpoint.  Most are 65' in length.  1-2 are 132' long.  All are lying on top of ground (covered by grass through the years).  I have only 1 that is 132' long and elevated at 10-12'.  

With more radials (preferably elevated), will this decrease SWR across the 160m band and provide a more consistent match between 1.8-2.0mHz?  Or will it cause a decrease in bandwidth (less kcs of workable frequency)?  I am confused by your comment that my bandwidth is wider than avg.,...I would think that that is a good thing?  My ATU should be able to handle the entire band now with the current setup.  Thank you.    

More radials will reduce ground losses, and probably that will narrow your bandwidth, because ground losses are like putting a resistor in series with your antenna -- which broadens things out.

I don't know too much about the consequences of combining on-ground and elevated radials. I've only tried one or the other.

There are two ways to design antennas, as I see it. (This is an oversimplification, but there is a lot of truth in it.)

One is to design the antenna to match your feedline impedance, and let the efficiency and pattern fall where they may. (Sometimes they fall in a very good place, sometimes not.)

The other is to design the antenna to produce the pattern and efficiency you want, and let the impedance fall where it may. This usually requires a matching network.

All the best,


Kevin.

[Steve - K4HX]

If you already have 20 radials on the ground, I don't think adding one elevated will help much. It may have produced some of the the erratic readings previously.

[K4BOF]

Confused yet perplexed at the same time.  It was my impression that more radials the better, elevated being best.  In several books highlighting the W1BB 1/4 WL fame, it looks like he ties everything on the ground together, pipes, buried metal, fences, radials on the ground, radials in the air, and as many as possible, etc ,etc, etc.

I think, I'm just going to let this antenna eat with RF and see what happens.

[Jim, W5JO]

One thing I would suggest is the next time you want to trim the length of any wire antenna, simply fold it back on itself until you get the reading you want.  Then cut the length as desired unless you might use the wire in other projects later.  In that case just leave the extra folded back and wrapped around the conductor.

[Steve - K4HX]

Elevated radials done correctly (not a trivial process) can be effective. But they aren't always the best option.

http://www.w8ji.com/counterpoise_systems.htm

Confused yet perplexed at the same time.  It was my impression that more radials the better, elevated being best.  In several books highlighting the W1BB 1/4 WL fame, it looks like he ties everything on the ground together, pipes, buried metal, fences, radials on the ground, radials in the air, and as many as possible, etc ,etc, etc.

I think, I'm just going to let this antenna eat with RF and see what happens.

[WB4AM]

I have a 135' wire going vertically about 4' away from my tower for 40-45' then bends perfectly horizontal for the rest of the wire length.  I have it tied off to a far tree.  The wire is 13g.  

At the base of the tower I have a tuning network that is enclosed in a box.  From the feed point into the box, the center conductor goes to one side of a large multi looped coil that I can adjust the tap to, the other side of the coil has the wire that goes vertically up the tower.  Between the feed point and coil I have a Jennings Cap that is variable.  The other side of the Cap is attached to a ground rod and several radials that vary in length.  

Hello Bruce,

In case you want to try something different in your network at the feed point, I would place your Variable Cap in series with your coax going to the antenna.   In other words don't take the one end to ground at all.  I am also thinking in case your vertical wire might be to short, it might be worth leaving the coil in line between the Cap and the antenna.  That is, if you want to try something different !!!

My 160 antenna had a 1000pf Air Variable in series with the coax and the antenna.  My radials just connected to a stainless steel bolt that was bolted through an aluminum plate.  

*********Edited*******  Barrel Connectors*********

My two SO239 Barrel Connectors was also connected through this plate.  

I had two coax center conductors only coming from the Air Variable running to the SO239 Barrel connectors.  

Main coax from the shack went to one so239 and the other so239 went to the antenna.
I had driven a 10 foot ground rod right near the antenna and the Large PVC pipe that housed the Air Variable.  So I ran radials from the Aluminum plate as well as from the ground rod which was also tied into the aluminum plate.  

So again if you would like to try something different but similar to what your already doing, you might want to give this a try.  I hope this will give you some more food for thought.

One more thing, how high off the ground do you have the end of the inverted "L" tied off?

This also can affect your SWR.  If you lower it to the ground and check swr and then raise it farther away from the ground and check swr you will certainly see a difference in your SWR.  The higher you can get the end of the wire from the ground the better off you will be.  This was my experience...

Ken

[K4BOF]

I'm missing something in translation here,...
W1BB and several others have mentioned to tie all the grounds together ALONG WITH the radials (buried, on top of ground or even elevated) to the antenna system. 
The W8JI site and WB4AIO mention isolating the antenna system from ground / earth.  Which is it?

I can disconnect my earth grounds from the antenna system and just keep all the radials I have connected to the antenna system.  My radials are currently all connected to ground /earth too.   

In my previous testing of the 175' wire and series cap, I was connected to ground / earth, along with my radials. 

[KB2WIG]

" isolating the antenna system from ground / earth"



The following is from W8JI,     http://www.w8ji.com/counterpoise_systems.htm

""

Concentrating any field in a smaller cross sectional area of lossy media increases loss. Reduced field concentration is why large area (in terms of wavelength) radial systems have less loss than small systems, and why a big thick carbon rod with large end-plate contacts that spread fields has less loss than the same carbon rod with point contacts  concentrating fields. Unfortunately, space limitations and local obstructions often restrict counterpoise or radial system size. When restrictions force a small system, we can maximize available performance. There are three ways to reduce earth losses near a counterpoise:  


*The counterpoise can be made larger, with multiple cross wires. This allows fields to spread, rather than concentrate in lossy earth  

*The counterpoise can be elevated some height above from earth. This also allows fields to spread, rather than concentrate in lossy earth

*All earth paths, including the feedline, must be isolated or insulated from the counterpoise. This prevents conducted currents from directly entering lossy soil    

We sometimes hear radials or counterpoises need only be as long as the vertical is high. Truth is opposite this myth. Shorter verticals generally require larger and better grounds for peak efficiency. The sole exception to 20-30 radials "being enough" occurs more often when an efficiently designed and properly constructed vertical antenna is very short in terms of wavelength!  ""

klc

[K4BOF]

What is wrong with this pic?

klc-
Thanks for the attachment and I did peruse it.  I did read the definition at the beginning and it does make sense. 

[KB2WIG]

Nothing. I like to see "dots" where wires are connected.... .. 

That looks like a inverted eL.  Making the radiator a bit long gets the Z up closer to 50 ohms and adding the cap helps to tune things.
I'll let you know how it works here when I get it strung up.

klc

[K4BOF]

...the feedpoint is tied in to the ground rod, buried metal, water pipe and the radials.

[W3RSW]

 

[K4BOF]

These wires are not isolated from ground?

[K4BOF]

And another,...

[Steve - K4HX]

Just remember that as time passed, better ways of doing things are learned. Don't get caught up in old designs or articles as the gospel truth.

[K4BOF]

Completely understand.  I might be drinking too much Kool-Aid with these books, threads, etc (a.k.a. antenna gurus),...

I'm going to pull a 'klc' / Derb and tie in all the radials to one another with the Split Bolts.  I have multiple radials down on the ground, each approx 65', and a few 132', one is elevated.  That should be easy enough to do.  I'll unstrap the ground rods, water pipes, and tower ground from the system, keeping it isolated. 

Will report back. 

[Steve - K4HX]

Don't do that!

The odd item out is the elevated radial. Just get rid of it as it's probably not doing you much good.

The ONLY time you would want radials isolated from ground is when ALL the radials are elevated.

[WB4AM]

Hello Bruce,

I haven't seen any activity here and I was wondering how you are making out with your Inverted "L"?

Ken