best antenna

[abcd567]

Thank you Peter for posting the crossection diagram of the coax with segmented insulation. This picture makes it very clear what is segmented cable. The white is insulation, grey is air space, and red is copper.

Thinking about the gain pattern on the coke can - that the lobes go down towards the can - might it work better inverted?

Good idea...By inverting the Cantenna, the downward lobes will become upward lobes, where the planes are....Worth trying....

.

[peterhr]

I've made up the simple half wave dipole, with amplifier and put it outside - it's a temporary rig made up of bit's I had in the hobby room and shed. I will take it down within the next two weeks.

The amplifier is powered off a 12 Netgear Router PSU, the reciever is using the extra Baspberry Pi + Dongle I have for the feeder project

coax used for the dipole has a segmented polythene tube with 6 segments as air gaps.

View the results here http://goo.gl/1D0QaL - range is 150-175nm. Pictures...

One shows the dipole + amplifier with what is required for rain protection ... fixed to a gallows on a bamboo pole.

the other shows the bamboo pole loosely fixed to the main antenna mast - I'd have like to have got it higher but didn't have the coax length required

I'll post up a virtual radar plot once I've collected a couple of hours of data (done, the range rings are at 25nm)

[ATTACH=CONFIG]4651[/ATTACH] [ATTACH=CONFIG]4652[/ATTACH] [ATTACH=CONFIG]4653[/ATTACH]

I've moved it up the mast, it's now 30 cm below the of the collinear (and is wired using lower grade TV antenna coax for the downlead) - range is now 200-225nm in the best direction.

Bearing in mind that my commercial collinear with similar amplifier gets around 240nm - I think this dipole is performance is very reasonable bearing in mind that it cost maybe $20 for all the parts including the downlead.

I'm running virtual radar now and will post a plot when it's been running a an hour or two.

Capture.PNG

There you go, the outermost ring is at 225nm - this is about an hour of capture, unfortunately not seen many flights in the SW. The land rises to SE so we don't do so well there either

[abcd567]

I've moved it up the mast, it's now 30 cm below the of the collinear (and is wired using lower grade TV antenna coax for the downlead) - range is now 200-225nm in the best direction.

Bearing in mind that my commercial collinear with similar amplifier gets around 240nm - I think this dipole is performance is very reasonable bearing in mind that it cost maybe $20 for all the parts including the downlead.

I'm running virtual radar now and will post a plot when it's been running a an hour or two.

[ATTACH=CONFIG]4655[/ATTACH]

There you go, the outermost ring is at 225nm - this is about an hour of capture, unfortunately not seen many flights in the SW. The land rises to SE so we don't do so well there either

CONGRATULATIONS!!!
Your efforts finally brought fruit.

Your experiment proves that an amplified low gain antenna gives almost the same range as an amplified high gain antenna.

This is the point I have been trying to advocate all through the time I have been member of this forum.

I have always stressed to install an amplifier as first priority, and after that go for the option of a better antenna.

[abcd567]

One thing i like to mention is that thinner the wire of which an antenna is made, narrower is its band width, and it rejects the adjuscent bands more effectively.

Hence a 1090Mhz Dipole/Franklin/Coiled Whip, made of core of RG6 coax (18AWG/1mm dia) rejects cellular signal lnterference more effectively than:

(1) A Dipole/Franklin/Coiled Whip made up of 3mm or 5mm dia tube/wire.
(2) A Coco made of RG6 coax, whose all receiving elements are 4.5mm dia braid of the coax of which the coco is made.

[peterhr]

CONGRATULATIONS!!!
Your efforts finally brought fruit.

Your experiment proves that an amplified low gain antenna gives almost the same range as an amplified high gain antenna.

This is the point I have been trying to advocate all through the time I have been member of this forum.

I have always stressed to install an amplifier as first priority, and after that go for the option of a better antenna.

I didn't make the dipole particularly carefully either, the polythene tube over the elements probably detuned it a little so the should have probably been shortened. It's worth also noting that if it had been a foam insulated coax that was used - that that is a sponge and will allow water to travel back down the wire to the amplifier.

Shall we put this in a separate thread "Working Home Brew Antennas - Amplified Dipole" with photo's how to construct and suggestions where to buy the pieces as post #1?

[abcd567]

I didn't make the dipole particularly carefully either, the polythene tube over the elements probably detuned it a little so the should have probably been shortened. It's worth also noting that if it had been a foam insulated coax that was used - that that is a sponge and will allow water to travel back down the wire to the amplifier.

If test rig is at lower level, where it is easy to access, dipole can be trimmed, a millimeter or two at a time, and tried, till the optimum length is reached. YWYY has mentioned trimming his fg whip after applying heat shrink tube. He may give some practical tips on how to do the trimming.

Shall we put this in a separate thread "Working Home Brew Antennas - Amplified Dipole" with photo's how to construct and suggestions where to buy the pieces as post #1?

Good idea. Go ahead and create a seperate thread as you have proposed.

[peterhr]

If test rig is at lower level, where it is easy to access, dipole can be trimmed, a millimeter or two at a time, and tried, till the optimum length is reached. YWYY has mentioned trimming his fg whip after applying heat shrink tube. He may give some practical tips on how to do the trimming.

Nah, it's above roof level, probably 8-9m above ground level - it's a PITA to get to.

[abcd567]

Nah, it's above roof level, probably 8-9m above ground level - it's a PITA to get to.

YWYY's fibreglass whip is also intalled at top of a pole. Maybe he can give some guidance on how he trimmed his FG whip.

[abcd567]

Nah, it's above roof level, probably 8-9m above ground level - it's a PITA to get to.

YWYY's fibreglass whip is also intalled at top of a pole. Maybe he can give some guidance on how he trimmed his FG whip.

My antenna is located 60 ft above ground. Still I can reach it without climbing, only by raising my arm. Reason: I live in an apartment which is 60ft above ground, and my antenna is inside my aprtment close to large glass window. I should do this trimming excersise. I plan to sacrifice one 1/2 wavelength dipole on this trimming excersise, possibly this weekend.

[peterhr]

My antenna is located 60 ft above ground. Still I can reach it without climbing, only by raising my arm. Reason: I live in an apartment which is 60ft above ground, and my antenna is inside my aprtment close to large glass window. I should do this trimming excersise. I plan to sacrifice one 1/2 wavelength dipole on this trimming excersise, possibly this weekend.

Only problem with yours is the steel reinforcing of the window frame and ensuring that the antenna is consistently positioned with respect to that frame. It would be excellent of the window could be opened and the antenna be fixed to a lightweight support (meccano) fixed to the glass by suckers. I doubt if the windows open. (should it come unstuck, the coax would stop it falling and save you having to reach down 60 feet to retrieve it)

[YWYY]

YWYY's fibreglass whip is also intalled at top of a pole. Maybe he can give some guidance on how he trimmed his FG whip.

Hi mate, when I was testing my whip I had it mounted on a temporary mast near the back porch, I could reach it from a stepladder. The reception distance wasn't good but I left it there for about a week, trimming 1 mm each day till it was receiving max signals.

Mike in Tasmania

[abcd567]

Only problem with yours is the steel reinforcing of the window frame and ensuring that the antenna is consistently positioned with respect to that frame. It would be excellent of the window could be opened and the antenna be fixed to a lightweight support (meccano) fixed to the glass by suckers. I doubt if the windows open. (should it come unstuck, the coax would stop it falling and save you having to reach down 60 feet to retrieve it)

My windows cannot be opened, like aircraft windows, but much larger, more like a double glass wall. So my equipment is strictly indoor.

My antennas are kept consistently at same position during comparision/adjustments. The metallic members of window frames are widly spaced & should not cause any problem.

The main problem I face is that my building is surrounded by high rise buildings, blocking signal and creating sharp spike like dip in range in their direction. My own building completely blocks signals for 180 degrees on west. My range curve, even wirh best antenna, is a semi circle with large number of sharp dips.

[abcd567]

Hi mate, when I was testing my whip I had it mounted on a temporary mast near the back porch, I could reach it from a stepladder. The reception distance wasn't good but I left it there for about a week, trimming 1 mm each day till it was receiving max signals.

Mike in Tasmania

Thanks Mike for the practical tip.

Did you download & run the .nec file (for your fiber glass double coil whip) which I have attached with my post few days ago? In that post I forgot to tell following step:

After hitting calculate button (or F7), a popup will open. It will have "Use Existing File" selected by default. Choose "Far Field Pattern" & hit "generate" button.

[YWYY]

Yes thanks for giving me that file. Its very useful, I am learning to use it - slowly. I figured that to use FAR FIELD. When I run it I get errors found - run segment check. It still works ok , but maybe my settings are different to yours.
Mike

[gregy]

75 or 50 ohm?

hello ABCD567
reference your post #1391

can you pls confirm if this design is for 50 or 75 ohm?
from the SWR plot it would suggest that its 75ohm

Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
If dimensions are different - is it possible to indicate these?

thanks

@Trigger
@HermanZA

Here is your franklin with 3mm dia wire, 6mm gap by wrapping wire around 6mm drill bit
Good news Gain=6.86 SWR=1.52

NOTE: The impedance matching stub (middle one) is slightly bigger than phasing stubs (upper & lower ones)
Reason - to meet the following two conditions:

(1) Phasing stub:
Total wire length (two horizontal parts + round part) should be 1/2 wavelength = 138mm

(2) Matching stub:
Each horizontal length should be 1/4 wavelength = 69 mm.
Hence total wire length of horizontal parts alone should be = 2 x 69 = 138 mm.
The total wire length of matching stub (including round part) should be 138 mm +length of round part.
Length of round part = pi x round part diameter/2 = 3.14 x (1.5+6+1.5)/2 =14 mm.
Hence total wire length for Matching stub = 138 mm + 14 mm = 152 mm

Do not get confused by theory above. Ignore it and simply follow the dimensions given in the sketch I have drawn below, and it is done.

[ATTACH=CONFIG]4519[/ATTACH] . [ATTACH=CONFIG]4524[/ATTACH] . [ATTACH=CONFIG]4525[/ATTACH] . [ATTACH=CONFIG]4526[/ATTACH]