Working on a Multiband Portable Antenna

[HomerBB]

Here is something I've been working on in spare time for a few days. It's not complete as I want to refine it and do more testing.
I gave it a test run for a while this afternoon and managed 3 contacts, 2 on 20m, 1 on 40m today. My QTH is NW Arkansas. I was running my uBitx 5.1 at 3 watts out. I was able to tune both 40m and 20m to less than 1.3:1 SWR across the bands, and with an antenna change I tuned 11m under 1.2:1 SWR. The antenna above the matching coil is a 102" SS whip extended to 126" using a 24" copper/brass homebrew extender.
I can remove the extender for matching higher than 20m. I used three radials 24' long laying on the ground.
My tuning was done using an MFJ-259B.
As I proceed I want to test 80m, too.
I was frustrated with my progress using a 25' RG8X cable I'd purchased just for this project until I realized it had a break in it somewhere. I did the actual tuning and testing today with a 50' RG58 coax. I want to repair the shorter cable for the go box.

 

[Riverman]

Here is something I've been working on in spare time for a few days.

Wolf River Coils’ long lost cousin from Arkansas.
Good job!

 

[AudioShockwav]

Nice I like it!
How did you do the contact inside the coupling on the coil?
Very cool.

73
Jeff

 

[HomerBB]

Nice I like it!
How did you do the contact inside the coupling on the coil?
Very cool.

73
Jeff

Bought the small metal cable clamps.

 

[binrat]

Great stuff.

 

[Riverman]

Homer,
Pardon me for going off-thread momentarily. But have you ever given thought to a homebrew Isotron? Perhaps a 10, 11 or 20 meter version? Doesn't look too involved and would love to see the results as all of your other creations are fabulous.


Isotron 10

Size (H x W x D} - 16" x 1.5" x 4"
Bandwidth - 1.0 Mhz.*
Impedance - 50-75 ohms
Freq. Range - 28-30 Mhz.
Power Input - 1000 watts PEP**
Wind Load (sq. feet) - .16
Wind Rating - 85
Pattern - Omni

* Bandwidth is within 2:1 SWR. May vary with environment.
** 300 watt, CW (AM, FM, RTTY, etc.)

 

[HomerBB]

Homer,
Pardon me for going off-thread momentarily. But have you ever given thought to a homebrew Isotron? Perhaps a 10, 11 or 20 meter version? Doesn't look too involved and would love to see the results as all of your other creations are fabulous.


Isotron 10
View attachment 44205
Size (H x W x D} - 16" x 1.5" x 4"
Bandwidth - 1.0 Mhz.*
Impedance - 50-75 ohms
Freq. Range - 28-30 Mhz.
Power Input - 1000 watts PEP**
Wind Load (sq. feet) - .16
Wind Rating - 85
Pattern - Omni

* Bandwidth is within 2:1 SWR. May vary with environment.
** 300 watt, CW (AM, FM, RTTY, etc.)

Riverman, I haven't.
I've naturally noticed them, but because of the huge size to wavelength ratio I've passed them by. Perhaps my skepticism has caused me to overlook them, but they smelled of dummy load to me. Now, you may have poisoned my thinking by tickling my curiosity.
I suppose I can look closer and make (another) decision.
Homer

 

[HomerBB]

Because of the wire spacer material not being as rigid as the one pictured above the first coil is less pretty. Now, because of the bad coax discovery I am going to have to revisit the original. It is bigger, 1-1/2" core vs 1" core, and may have broader bandwith potential.
I'll be checking them both out some more.

 

[Riverman]

Riverman, I haven't.
I've naturally noticed them, but because of the huge size to wavelength ratio I've passed them by. Perhaps my skepticism has caused me to overlook them, but they smelled of dummy load to me. Now, you may have poisoned my thinking by tickling my curiosity.
I suppose I can look closer and make (another) decision.
Homer

Cool!
I bet several members would be interested in the results and your honest reporting of them.

 

[Riverman]

View attachment 44206

I might have missed it earlier in the thread, but how did you determine the length of wire and/or number of turns to use on the coil?

 

[Riverman]

Another question.
Have you tried elevating the radials 2-3 feet off the ground? Would be interested in knowing what difference it makes.

 

[Slowmover]

A random crackle or spark here & there, boy, ain’t nobody gonna dare cross that backyard. Grackles and opportunistic thieves move right along.

I do miss having a yard. Antenna experiments are one more reason.

 

[Riverman]

I do miss having a yard. Antenna experiments are one more reason.

I like Homer’s diving platform but don’t see a pool.

 

[HomerBB]

I might have missed it earlier in the thread, but how did you determine the length of wire and/or number of turns to use on the coil?

I screenshot the wolf river coil and then zoomed it in . I tried to count the turns. The wolf river site gives the length over all of their coils.
The length of wire is determined by wrapping one turn around the coil then measuring it. Multiply that length times the number of wraps.
In the case of the original post coil the length of the grommet edging I purchased determined the wraps.
I think the wolf river coil has ~80 wraps.
As you can see I measured my wire a little short and left off 2 wraps.
I needed ~27' of wire for that one. The bigger coil required more, but I didn't count it, just kept wrapping it until done.
The big coil has 18 ga wire on it.
The smaller coil 14 ga wire.

 

[HomerBB]

Another question.
Have you tried elevating the radials 2-3 feet off the ground? Would be interested in knowing what difference it makes.

Yes. I had to make the radials tuned to band lengths to get the SWR down.