...And the reason I know the choke is lowering the impedance rather than increasing it is because when it rained the vswr went up from 1.3:1 to 1.7:1 @ 50mhz. But it then tuned at 1.3:1 @ 47mhz which is an increase in electrical length. The upper radiator cannot change because its aluminum so the electrical lengthening had to have come from the lower leg. If the impedance went up then the antenna would have been resonant at an higher frequency not a lower one. For it to be resonant when wet then the new electrical length has to terminate somewhere in the choke itself probably two inches or so into the first winding of the choke after the rain dropped the choke impedance probably from one mega ohm to maybe 0.75 mega ohms. That's just a rough guess. Why is it doing it? probably because air has a different dielectric property than water.
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Modified Vector 4000
- Thread starter bob85
- Start date
I would but its raining really bad, the swr has gone to hell again so the tape didn't work. My 11m dipole worked fine even in rain but had two aluminum radiators, this has a coaxial lower element and its shockingly poor in the rain.
Eddie
That's about the same gain as your 27mhz model which it should be imho,
I would be happy with it working like the 27mhz version, I want to change the radials & calibrate the analyzer before I get back to tuning,
it looks like the upper 1/2wave is a little over 1/2wave electrically, I expected it to be a little long @178"
what tube diameters are you using ?
My monopole is using the lower 5 sections of vector 4000,
I can't do anything about the radials until I make smaller spreaders,
I must be getting old, bad weather never stopped me in my youth,
not sure if I lost enthusiasm for antennas or just got soft sitting too close to the fire.
That's about the same gain as your 27mhz model which it should be imho,
I would be happy with it working like the 27mhz version, I want to change the radials & calibrate the analyzer before I get back to tuning,
it looks like the upper 1/2wave is a little over 1/2wave electrically, I expected it to be a little long @178"
what tube diameters are you using ?
My monopole is using the lower 5 sections of vector 4000,
I can't do anything about the radials until I make smaller spreaders,
I must be getting old, bad weather never stopped me in my youth,
not sure if I lost enthusiasm for antennas or just got soft sitting too close to the fire.
Bob I didn't have all your dimensions, so I scaled my NV4K model at 27.205 to 50 MHz. That changed the radial bracket dimensions at the bottom too, and in the model above it is set at 1.36" inches. That too will change my tuning of the model.
The model also has a simulated gamma also, and with a physical gamma added to the model...it may have shown a bit more gain.
The FS model shows the Average Gain results, and that shows us the gain for the model above is understated...needing an error correction of 0.02 dbi. This error needs to be added to the reported gain to be correct.
I posted 2 images of the antenna, so you could see the dimensions I used for the radiator and radials, noted at the bottom left of the images.
The radials are a bit short too, but again that is due to a little geometry error in scaling the model to 50 MHz.
When I have a model set in inches or feet and I scale...the scaling changes the dimensions. I can change all the dimensions to wire gauge values and those values will remain the same when using the scaling feature. I didn't bother figuring all that out.
So, I just guessed at some dimensions I was missing.
If I had the gamma dimension I noted in my post above, I would have done the model using a physical gamma match.
Bob, you're not old yet. Wait until you get to 83 and have to watch all the details when making an Eznec model. To bad you didn't follow me on this journey back in the days when I started modeling.
With your understanding, you'd have be good at it.
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I got a bit more done on the 6mtr vector,
drilled a spare vector hub to take sirio 827 radials, i will find out if 4x 1/4wave radials help or hurt the vector,
just need to change the old rusty bolts & modify some spreaders so i can move them & adjust the cone length,
it will be isolated from the mast on one of my fiberglass isolators.
drilled a spare vector hub to take sirio 827 radials, i will find out if 4x 1/4wave radials help or hurt the vector,
just need to change the old rusty bolts & modify some spreaders so i can move them & adjust the cone length,
it will be isolated from the mast on one of my fiberglass isolators.
Homer we have conflicting models of what effect radials have on the vector,
Eddies model shows radials cause a drop in gain & radiation wasted at high angles,
Donald claims radials spoil the cake too,
Henry's model shows radials give an increase in signal strength that becomes less of an advantage the higher the antenna is above ground,
w8ji also says this type of antenna needs radials,
Best way to find out is put 1/4wave radials on a vector & make them quick/easy to add & remove,
My buddy 6 miles away has chopped a sirio tornado for 50mhz so i will have somebody for signal checks,
rx will be the RSP1a, its the only calibrated s-meter i have.
Eddies model shows radials cause a drop in gain & radiation wasted at high angles,
Donald claims radials spoil the cake too,
Henry's model shows radials give an increase in signal strength that becomes less of an advantage the higher the antenna is above ground,
w8ji also says this type of antenna needs radials,
Best way to find out is put 1/4wave radials on a vector & make them quick/easy to add & remove,
My buddy 6 miles away has chopped a sirio tornado for 50mhz so i will have somebody for signal checks,
rx will be the RSP1a, its the only calibrated s-meter i have.
Homer, I have a better model that has a physical gamma match. The model you posted as an example above uses a simulated gamma which is OK, but I don't think it is as technically correct as my models with a real gamma match included in the model.
Bob, maybe you could give me the exact dimensions for your new 6 meter antenna, and I'll scale my NV4K with a gamma match and I can check how close Eznec scale feature is to your 6m dimensions.
Then I can fix the model dimensions to exactly what your 6 meter uses and we can address these ideas about different radial length head on.
If I missed the point of your test Bob or my idea here is screwballed, let me know.
Bob, maybe you could give me the exact dimensions for your new 6 meter antenna, and I'll scale my NV4K with a gamma match and I can check how close Eznec scale feature is to your 6m dimensions.
Then I can fix the model dimensions to exactly what your 6 meter uses and we can address these ideas about different radial length head on.
If I missed the point of your test Bob or my idea here is screwballed, let me know.
