dual band 80/40 homebrew vertical... what a waste of my day

[mr_fx]

well about noon I started working on this... laid down 30 random length ground radials, built the mounting plate, shot an 80m, and a 40m 1/4 wave aerial into the tree (so there are 2 aerials)

got everything hooked up, best match I could see was about 2.4 swr... well I added a coax choke, soldered all my connections... 2.2swr

Then I figured that I could try it without the 40m aerial, so I dumped it... then the swr went up to nearly 3:0 on 80 (well more like 3.1, but close)

But maybe the issue is that the antenna rides VERY close my 100ft tall oak tree

the funny thing is I once built a 160/80/40 version of this antenna, and only laid down 3 ground radials, and the funny part is it TALKED, had a half way decent match, but it also had 3 ground rods... this new antenna does not, I FIGURED that the 30 ground radials would take care of that

I give up... I think I will convert the G5RV into an 80/40 fan dipole, then convert my 10m dipole into an 20/40 fan dipole... then maybe set my Maco v58 into a 6m 5/8 wave ground plane

 

[W5LZ]

I wouldn't doubt that tree has some affect on your antenna(s) but the 'random length' radials will have more of an affect. How much shorter than about a 1/4 wave on 40 meters are they? Lots of 'shorter' than 1/4 wave length radials can be workable, but longer ones would be -more- workable. The length of those vertical elements can also make a fairly large difference on the lower HF bands. Did you find a 'low' SWR point on either band, or which ends of the bands seemed to be lower? Treat it like you would with a mobile antenna compare SWR at the low, mid, and high ends of the band(s) to see which way to go with it.
- 'Doc

 

[mr_fx]

I used an analyzer, I did no find a decent match ANYWHERE, and I checked from about 2.5mhz through 20mhz ...

as for the radials, a few are around 6 feet(maybe5 of them) but the rest of them are 20 to 50ft

 

[wavrider]

you will need 1/4 wl radials for each band if you are looking to make that vertical as efficient as you can.

Say around 24 radials should work pretty well,

the oak tree at 3.8 and 7.2 mhz will not really effect your antenna.


I built a 80 meter vertical, then put a matching network at the base for 40 meters. Relay controlled so at the flip of a switch I could be using that vertical for a 1/2 wl on 40 or a 1/4 wl vert on 80.

keep experimenting and have fun

 

[Justme]

Radials in or on the ground need some serious copper there.
My inverted L ( 77 feet high) is mounted to the back of the house, has 3000 feet of copper radials in/on the ground ranging from 35 feet to 250 feet.
Fed by an autotuner the L is too long on purpose, 77feet high alu tubing 3/12 inch bottom to 1/1/2 top and copper wire 77 feet to a mast in a tree at 45 feet up.
That way it won't be a 1/2 wave at 80. the tuner will tune the L from 160 - 10 without a hickup, MFJ 998, running 1000 watts in there.
Elevated radials 1/4 wave you need just 4 no option here... so i had to dig the lot in.

Using an homebrew amplified loop for recieve or the lengthened OCF ( Fritzel FD-4) for recieve on 160 in the noisy area here.

Regularly work the USA on 160 Ukraine 6000 miles out etc, phone is main mode.
THe L also does a good dx job on 80/40 low angle of radiation.
On 20 it's a toss up between the L or OCF at 45 feet up.
For the higher bands i use another vertical on top of the house or the OCF.
I can use on all bands a vertical or horizontally orientated antenna that way switch over in a heartbeat too.

 

[BJ radionut]

http://www.iw5edi.com/ham-radio/files/novice-multiband-antenna.pdf

FX: I have used a bunch of Verticals over the years...The link is a "Dandy"....

For 40/15m Start with about 33ft(maybe 32.5 ft) and use EMT conduit or Alm tubing instead of wire...1 1/2"...1 1/4" to 1" to 3/4" (one 10 foot piece each size) or whatever you may have to get it to stand up on it's own....
And then (4) "Tuned" radials (same length 33ft') and go from there....I think you will find it will fall right in....
They do well....used that set-up many Field Days with very good results....
Once you get this working you can "switch" in a coil for 75m as done with the Novice Antenna
GL
All the Best
BJ

 

[hookedon6]

actually the lenght of "tuned" ground placed or buried radials is not that much of a factor, the close proximity to the earth will detune them.

believe it or not,.... using more radials will cause the observed VSWR to increase,..... but the efficiency of the antenna will increase.

I have 3 500 foot spools of buried radial wire under my ground mounted (trapped) BTV

 

[Captain Kilowatt]

actually the lenght of "tuned" ground placed or buried radials is not that much of a factor, the close proximity to the earth will detune them.

believe it or not,.... using more radials will cause the observed VSWR to increase,..... but the efficiency of the antenna will increase.

I have 3 500 foot spools of buried radial wire under my ground mounted (trapped) BTV

That's right about the number of radials versus SWR. Most prople add radials until they see a perfect SWR and then stop. That just means they have about 35 ohms radiation resistance and about 15 ohms ground losses. Continue adding radials and the SWR will increase as yoi lower tbe ground losses. The best efficiency is when groind losses are as close to zero as possible and the radiation resistance near the nominal 35 ohms of a perfectly matched 1/4 wave. SWR would be about 1.5:1 but more efficient.

 

[mr_fx]

actually the lenght of "tuned" ground placed or buried radials is not that much of a factor, the close proximity to the earth will detune them.

believe it or not,.... using more radials will cause the observed VSWR to increase,..... but the efficiency of the antenna will increase.

I have 3 500 foot spools of buried radial wire under my ground mounted (trapped) BTV

That's right about the number of radials versus SWR. Most prople add radials until they see a perfect SWR and then stop. That just means they have about 35 ohms radiation resistance and about 15 ohms ground losses. Continue adding radials and the SWR will increase as yoi lower tbe ground losses. The best efficiency is when groind losses are as close to zero as possible and the radiation resistance near the nominal 35 ohms of a perfectly matched 1/4 wave. SWR would be about 1.5:1 but more efficient.

So are you saying I need to remove some of the radials?

 

[Justme]

No, add raadials till your groundlosses are as close to 0 as you can get within reason, after 3000 feet of copper i saw no more changes.
Accept the SWR you see then around 35 to 37 Ohms or 1.5, the little loss that produces will be more the offset by the efficiency the antenna system has now with low ground losses.
Or do as i did add autotuner, and tune it flat on several bands.

 

[Captain Kilowatt]

You can never have too many radials under a vertical. That combined witb trimming the vertical length should make for a decent SWR and a really good performing antenna.

 

[mr_fx]

I just can no afford to spring for a tuner right now, just out of the question...

the last 'vertical' I built was basically an Inverted L (well three inverted Ls on one feedpoint, it worked well, never got a good match on 80m, but it worked well, only had 1 radials on the ground per band but it did work well and was pretty loud to boot

 

[wavrider]

Ground mounted verticals on the low bands work well.

you have a 100 ft oak tree. If you can get a 80 meter piece of wire. roughly 60' at 3.9mhz and four raised tuned radials on it, sloping a a 45 degree angle you will have about an 50 ohm impedance.

OF course at 100" with a 60' vertical you will not be able to angle your ground radials at a 45 degree angle. try as best as you can to get the ground radials sloping and it will work well for you.

If ground mounted 24 radials will work. you can add more and the old saying is true, the more you add the better efficiency you will have.

I put the vertical up add 10 tuned ground radials and check the input impedance with the analyzer. Keep adding more until you get around 33 to 35 ohms on the analyzer. Should be between 16 and 36 radials depending on your soil.

With that 100' tree I would have multiple slopers coming off of it in all directions.

Most of all have fun.

 

[BJ radionut]

FX: I made mention of the radials being cut to length for this reason....
Using the cut to this length radials(33ft.) for a 40/15m vertical will get the antenna working by giving you a starting point.
This for me gave me a starting point to tune the vertical radiator.
Knowing from just my own experience of getting a working model this will produce results. These radials for now would just be stretched out at ground level in 4 generally equal distances around the base of the antenna.
The suggestion of using tubing versus wire has a couple advantanges....
Greater bandwidth and for me easier tuning. The tubing length can be increased or decreased by simply loosening a hose clamp or two near the base, without needing to drop the entire vertical element for tuning.
CK and others make some good points in that, you can never have enough radials....More is always better....And length is not always critical
I however look at it this way, once you have a "working model", each increase or change you make to reduce the ground absorption and increase the overall efficiency requires only minor changes to the length of the vertical radiator...(normally it gets shorter...normally!)
I hope this helps!
Drop me a PM and give me your call again (I knew it once) I may be able to help with a few parts, so you can assemble a tuner once I can find somethings again...
This remodeling of the my shack has got all my "Stuff" in piles in the garage while I paint and redo the shack and work bench....
GL
All the Best
Gary

 

[mr_fx]

I could build with 1/2" galvanized EMT... with that 160m vertical would only be about $20-$25, 80m would be about $10-$14, 40m would be around $6-$7