ELEVATED RADIAL SAG

[K5UJ]

Thanks Vic.  Well there's one NEC plot that seems to say that when radials are 5 meters above ground that results in 2.5 dB gain over having them on the ground.  The frequency was 7.2 MHz so 5 meters would be a significant height.  One thing I like about these papers is he actually built an antenna to use for tests instead of only doing modeling.

73

Rob

[flintstone mop]

I like that part too Rob. I think TOM JJ has modeled and built and reported. I think someone else here.
It really helps us common folk out.
Fred

[Steve - WB3HUZ]

Unless I missed it, in those two articles, all measurements were done at 7.2 MHz and above.

Rob,

There are several references to elevated radial tests.  One is on page 23 of this link:
http://rudys.typepad.com/files/qex-ground-systems-part-6.pdf

Also some info here:
http://rudys.typepad.com/files/qex-ground-systems-part-3.pdf

I have not reread this series of articles -- just skimmed them.  If you have time,  it is nice to find all 7 QEX artcles on his site.  My first post implied that there was only one QEX article.  I attended his presentation at the hammy convention.  And so on.

73  Vic

[K5UJ]

Unless I missed it, in those two articles, all measurements were done at 7.2 MHz and above.

That was my impression.  So you have to scale things to the low bands.    To possibly achieve the plotted performance from the data for the elevated radials 5 meters high on 40, you'd have to go to 10 meters high on 80 and 20 meters high on 160.  he's actually testing a bit higher than the 0.1 lambda fraction I gave at the beginning of the thread. 

My hunch is (assuming all radials are 1/4 w. long and the vertical is also 1/4 w.) there is a rough ratio relationship of height of radials and number of them that has to be maintained to achieve an acceptable gain figure, IOW 4 radials at 0.1 lambda and as you decrease height, the number of them has to increase at some number per meter of lost elevation until you are on the ground with 60 to 120 of them.

[flintstone mop]

I'll report from the trenches what happens.
Better match?, known contacts previously made from the old design?, SSB contest in FEBRUARY!!!

I gots some 10 foot high plastic condit and a tulip planter on my battery drill and start stringing the radials. And fight the tuner at the base.

Fred

[KM1H]

The world changes at 160 and lower, what that article says at 40M likely has no bearing.

Read thru the various BCB data of where stations replaced their rotting out buried radial fields with 10' or so high elevated radials and had to reduce power to conform to their original proof of performance. The FCC started allowing elevated radials a decade or so ago on an experimental basis and I believe they are now allowed as needed.

[Mike/W8BAC]

A Cristian broadcast AM transmitter site near Lincoln Park (South of Detroit) has an impressive nine tower sight with an elevated ground plane. The wire appears to be .375" stainless steel stretched as tight as a piano wire with very few supports. The elevation above ground is about 15 feet.

Mike

[flintstone mop]

Impressive Mike,
Everything seems to point to get them high to avoid getting hung up in them. And 10 feet was a number from a broadcast antenna installation.

There were other links Don provided where some were 35 feet high and the feedpoint raised condsiderably also.

I'll try to start my adventure this weekend.

Fred

[flintstone mop]

PICS coming tomorrow. Hopefully I remember to take them before we go to darkness.

I have 3 up so far and much easier to install than ground mounted. Effectiveness will be checked this Winter.

Thanks or tuning in.
Fred

[flintstone mop]

OK with the USA time change madness I will post a pic sometime this weekend of the finished project. It would take special photo technique to see the magnet wire I used. #18 AWG

Easy to install and changed characteristics of antenna drastically......MA160 Cushcraft top loaded,capacity hat,30 feet tall.
At least the SWR is reasonable 2:1, 10kc BW and single digit reactance.
The Rx signals are as quiet as the dipole. Usual drop in sig level going to Vertical. close in stations would be lower RX sigs.............more listening and more use is needed to evaluate this new system.
All of those 10 foot high poles look weird out there. I hope the deer don't get tangled
FRED

[KD6VXI]

Hello all, and long time no been here (Great grammar)

I can report some semi-interesting results from doing a vertical here, too.

I had 4 radials mounted at the ground level.  Remote tuna located at feedpoint, and 100 feet of wire in an Inv-L config....  40 feet (running parallel to the 40 foot tower) and then cutting off at diag level to a point about 20 feet off the ground.

I could get a decent match anywhere (Using a HULL electronics remote marine tuna), had RFI in the shack problems (the antenna was 15-20 feet away), but couldn't work anyone...  Maybe 10 contacts in 2 days....  6 meters seemed to work well with it as well.

Spoke with a friend who works 75 AM here on the west coast, he mentioned elevating them as high as I could get...  I figured I'd use the roof   So, I'm about 10 feet off the ground on my radials now.

Worked almost 60 countries in the next week, 30++ over CQWW.  Matching is a LOT different now, sometimes the best I can do is 1.7-1.9.  Antenna is slightly better than a dummy load above 21 mhz....  I've worked some 15 meters and some 2 meters, but nothing compared to when on the 11 meter vertical at 40 feet....  I even broke a couple pileups, I was surprised.

'Got my name called' on 20 AM once.  14 watts of carrier, not bad.

I'm going to increase it to 8 radials next, I have to get some poles to lift some of the ends up.  Radials all cut for 80 meter resonance now, I forget the exact length, but in the upper 60 foot range.  I also increased the length when possible a couple feet to couple them to the poultry netting that covers my fence (fences approximately an acre).

--Shane
KD6VXI

[KM1H]

Dont expect the SWR to improve with more radials, just the radiating efficiency. A 1/4 wave vertical with no loss is around 26 Ohms so with a few more radials you should be at the 2:1 point.

Yep, elevated radials really do work.

[KD6VXI]

Carl (and others).

I have an idea for a vert....  I picked up an 80 foot tower and have a 31 foot aluminum monopole I was going to mount on top of it and then feed it as a base fed vert.

BUT, that was before playing with the elevated radials.  I did a bit of reading, but came to nothing conclusive on this, so:

Can I run the radial network 10 feet up the tower?  If so, would be it better to ground the base of the tower, or leave it isolated electrically?

I also HAVE to run guy wires...  I was reading about people feeding towers as verts that some isolate the guy wires, break them up, etc., while others use them as capacitive hats....  Since their would be a "stinger" above the tower, would it be better to isolate and separate them, or use them as cap hats?

I guess another 'issue' would be power handling capabilities.  I'm not looking to do anything near the mobile, but you know I LIKE QRO....  Which would be the best method of feeding with 'available' components (like 4CX5000).

--Shane
KD6VXI


* Don't mean to hijack the thread, but one question led to another to another *

[flintstone mop]

Finally unveiling of the elevated radials at MOP radio.
I'll see what happens with this antenna this Winter.
I found out that with about 150PF in series that 40M is ready to go. Almost entire band.
Thanks for looking.

[flintstone mop]

Picture 005 was supposed to be a view of a radial leaving the ground rod heading to the first 10 foot pole about 20 feet away.

Im trying to show the general layout of the poles. The magnet wire #18 is too small to see with the camera. I'm not a very good photographer.

Fred

[KM1H]

 

have an idea for a vert....  I picked up an 80 foot tower and have a 31 foot aluminum monopole I was going to mount on top of it and then feed it as a base fed vert.

Will that be an insulated or grounded base?  With an insulated base you can slope the radials up fast and then run horizontal but putting down a ground screen as Ive mentioned a few times will probably help.

With a shunt feed you can use any point to establish a ground reference.

BUT, that was before playing with the elevated radials.  I did a bit of reading, but came to nothing conclusive on this, so:
Can I run the radial network 10 feet up the tower?  If so, would be it better to ground the base of the tower, or leave it isolated electrically?

Id ground it for lightning protection and static bleed.


I

also HAVE to run guy wires...  I was reading about people feeding towers as verts that some isolate the guy wires, break them up, etc., while others use them as capacitive hats....  Since their would be a "stinger" above the tower, would it be better to isolate and separate them, or use them as cap hats?

At a prior QTH I had 90' of tower with 4 el for 10/15/20 stacked on top. Guys were Phillystran which suck. The large amount of top loading resonated the tower down around 1700 KHz and required a big cap to tune out the reactance, I needed 1/4" spacing to keep from arcing with 1200W and the bandwith was only around 35-50 KHz. Luckily I soon moved to here and went with the elevated radials phased verticals sloping off the tower guys for 160.  You can easily do a 4 square on 75 with your proposed setup.

I guess another 'issue' would be power handling capabilities.  I'm not looking to do anything near the mobile, but you know I LIKE QRO....  Which would be the best method of feeding with 'available' components (like 4CX5000).

If it needs a tuning network then youre into a big vacuum and tubing coils. If its just a phased array its simple to do just with coax and each antenna only takes part of the power. I never bothered with those fancy phasing boxes, the F/B was only 15-20dB but I use Beverages to receive most of the time anyway.

Carl

[flintstone mop]

The little vertical that could............proving to be a performer on 160M. I'll try      some A-B comparisons with my full length dipole / VEE at 70 feet.
 Some surprises that it's the Cushcraft 27 foot top loaded vert for 160M.
Fred

[KD6VXI]

I don't have a choice on the grounded or not, it HAS to be grounded because of ice issues:  If I insulate it, then 3-4 months out of the year a good 15 days each of those months, it's unusable because it will be shorted.  Ice forces it.  I lost a 300 dollar ground plane antenna today due to ice, nice reminder.

I'm with you on the static bleed and lightening safety.  Although I've not had a strike here, near me, or anywhere I can find (other than Google earth lol), I DO have an issue with static electricity here....  It's the high desert.

I had tried a commercial ground plane.  It came down in the ice today.  SO, I'm back to doing things KISS.

You answered my main question:  Can I have the base of the tower GROUNDED, but also have my ground plane ELEVATED.  And the answer is yes.

Should prove to be interesting the v/i relationships below the ground screen / above the actual ground....

Thanks for the info..  I knew it would be necessary to go to vac caps and large diameter tubing....   It's going to be fun playing this far down low

The remote tuna is working great, but the noise is through the ROOF today, ground plane wire is +14 ga....  And it's measured at 3/8 inch about 2 hours ago in thickness in the vertical plane.  That's a buncha ice buildup!  The sag is pretty good, too, but the antennas still workin!

--Shane
KD6VXI