New Sirio Tornado 27

[Galaxy 959]

Oh 5H!T, You have a metal roof! I'd get the antenna at least 1/2 wave above it. Might be why the antenna is acting too long by a couple inches.

Yea its about 15' above it now. I'm not sure what a half wave is. I had the same problem with my antron when I put it up. I had to put the tuning rings almost all the way to the top to get flat SWR. My coax may be mismatched not 50 Ohms. I really dont know how to check it. I put on new amphenol ends today also.

 

[543_Dallas]

Looks good. What do you mean by mismatched coax? As long as it's 50 ohm coax in good condition with the ends installed properly you're good to go.

Some kind of common mode choke at the feed point and tune for the lowest SWR is the best you can do without an analyzer. I tune my antennas with an MFJ and electrical half wavelength of coax, but that's not a must. Then I use whatever length I need to reach the transmitter. My neighbors love my ferrite choke and non conductive guys BTW.

 

[Galaxy 959]

Looks good. What do you mean by mismatched coax? As long as it's 50 ohm coax in good condition with the ends installed properly you're good to go.

Some kind of common mode choke at the feed point and tune for the lowest SWR is the best you can do without an analyzer. I tune my antennas with an MFJ and electrical half wavelength of coax, but that's not a must. Then I use whatever length I need to reach the transmitter. My neighbors love my ferrite choke and non conductive guys BTW.

Yea its 50 ohm coax. I was meaning the half wave length stuff by the mismatch. Rg8u 2yrs old with new amphenol ends today. I would like to tune it with a analyzer. Drives me crazy to see it go to 1.5 swr when on upper channels. Just OCD I guess.

 

[222DBFL]

It's the roof!! Get that antenna up another 10-20ft or move it away from the roof entirely if possible. It's going to interact with the metal roof for sure and any other obstructions as well like trees and such. Is it real close to the tree behind it in the 2nd pic as well? Looks to be pretty close there. Could just be the pic. But like said, that roof is most likely going to be your main issue. Hope you get it resolved. Look for another spot to move it if you have the space, preferably away from the roof entirely. If not then at least get that antenna another 10ft higher or more. Good luck and hope you get it resolved.

 

[Galaxy 959]

Yea I figure it probably is. Someone gave me a nice 50' Stand alone tower. A guy said he would charge $100 only to take it down and put it up at my place. I need to get it done. Then I will need new coax and all. And yes them trees are close. I could take a couple limbs off the one but dunno if it would help or not.

 

[222DBFL]

Any and all obstructions should be as far away from the antenna as possible. If that tree limbs are close to the antenna, cut as much of them off as possible. Getting the antenna up above that roof is going to be the main thing to worry about. And yes for $100 a 50ft stand alone tower being taken down and put up would be priority number 1 on my list. JMHO. That will definitely get the antenna up and out of the way!! Any way you look at it, you need to get the antenna up and away from your roof and also the trees. Again, hope you get it sorted out!!

 

[Galaxy 959]

I will do some tree pruning tomorrow and see if it helps any. I'm also gonna try and get that tower. The wife is the main problem on the tower HAHA. She hates my antennas.

 

[Marconi]

The wife is the main problem on the tower HAHA. She hates my antennas.

959, check out this model of a simulated metal roof 17' feet high at the peak. I will put a vertical center fed dipole 30' feet high and 1' foot from the end of this roof...and we will see what ill-effects an Eznec model suggests for your setup. I'm just guessing the antenna is close to one end of the building.

Oh 5H!T, You have a metal roof! I'd get the antenna at least 1/2 wave above it. Might be why the antenna is acting too long by a couple inches.

NB, earlier you told me your NV4K idea in another thread was to check an antenna on a roof. Your idea was not to use a conductive metal roof, but when I read your comments to 959, I realized he had a metal roof, so I decided to build a large conductive roof line model. I will place a center fed dipole on top of a 30' foot mast 1' foot out from the end. Maybe this will show us what could happen. I will also make a model of this dipole by itself in order to compare the effects of being close to this building.

I've used a lot of segments to make this roof, so I'm limited as to the antenna I can add to the roof model. As a result I will use a vertical center fed dipole, because it is a simple model with few segments, and produces a well understood match...so we can check the effects on the match and see if such a setup might be a problem. The roof has to have an effect, but does it cause the problems we might expect.

Here is the metal roof line model.

 

[Needle Bender]

959, check out this model of a simulated metal roof 17' feet high at the peak. I will put a vertical center fed dipole 30' feet high and 1' foot from the end of this roof...and we will see what ill-effects an Eznec model suggests for your setup. I'm just guessing the antenna is close to one end of the building.



NB, earlier you told me your NV4K idea in another thread was to check an antenna on a roof. Your idea was not to use a conductive metal roof, but when I read your comments to 959, I realized he had a metal roof, so I decided to build a large conductive roof line model. I will place a center fed dipole on top of a 30' foot mast 1' foot out from the end. Maybe this will show us what could happen. I will also make a model of this dipole by itself in order to compare the effects of being close to this building.

I've used a lot of segments to make this roof, so I'm limited as to the antenna I can add to the roof model. As a result I will use a vertical center fed dipole, because it is a simple model with few segments, and produces a well understood match...so we can check the effects on the match and see if such a setup might be a problem. The roof has to have an effect, but does it cause the problems we might expect.

Here is the metal roof line model.

Ah oh, looks like your model came out inside out & wackbirds

What I really want to see is a 45' high NV4K with an extension on the base of the antenna of;
1/4, 1/2, 5/8, 3/4 & 1 wavelength
to see how it loads any metal connected to the base of the NV4K, using 45' as the reference standard height.

 

[Marconi]

Ah oh, looks like your model came out inside out & wackbirds

That is meant to simulate a (edit) conductive roof. This was done to check the effects of this roof on an antenna nearby or on a metal roof. I have not added the antenna yet.

What I really want to see is a 45' high NV4K with an extension on the base of the antenna of;
1/4, 1/2, 5/8, 3/4 & 1 wavelength
to see how it loads any metal connected to the base of the NV4K, using 45' as the reference standard height.

Go check this link out...I posted these models earlier today. If that is not what you expected then let me know.
To 7/8 or NOT to 7/8, that is the equastion

 

[Galaxy 959]

959, check out this model of a simulated metal roof 17' feet high at the peak. I will put a vertical center fed dipole 30' feet high and 1' foot from the end of this roof...and we will see what ill-effects an Eznec model suggests for your setup. I'm just guessing the antenna is close to one end of the building.



NB, earlier you told me your NV4K idea in another thread was to check an antenna on a roof. Your idea was not to use a conductive metal roof, but when I read your comments to 959, I realized he had a metal roof, so I decided to build a large conductive roof line model. I will place a center fed dipole on top of a 30' foot mast 1' foot out from the end. Maybe this will show us what could happen. I will also make a model of this dipole by itself in order to compare the effects of being close to this building.

I've used a lot of segments to make this roof, so I'm limited as to the antenna I can add to the roof model. As a result I will use a vertical center fed dipole, because it is a simple model with few segments, and produces a well understood match...so we can check the effects on the match and see if such a setup might be a problem. The roof has to have an effect, but does it cause the problems we might expect.

Here is the metal roof line model.

Yes my antenna is about center on the east end of the house. House is 28x40 plus a front and back deck. All the roof is metal.

 

[222DBFL]

Do your radials stick over the actual roof? If so this is most likely your main issue. I would venture to say if you were to move the antenna away from the metal roof your VSWR would go down like it should. JMHO.
But I still would like to see what Marconi's plots show as far as the pattern and any ill effects the roof might have.

 

[543_Dallas]

The roof isn't ideal but I wouldn't call it an issue. The SWR can be tuned flat if he doesn't mind pulling it down another time or 2.

He tuned the thing on the ground next to a house with a metal roof and what looks like aluminum siding. It's no surprise the swr is no longer equal on 1 and 40. This is why I said to push it up as it was and see what happened. Odds are it would need to come down again for some tweaking anyway but no time would be wasted fine tuning it on the front porch.

I didn't notice the roof or the siding but there's still a house there. If you tune it perfectly next to a house you can bet it will be wrong in the air. The best place to fine tune it is where it will be used. That takes more work though.

Man this is crazy. I just checked it with my Workman HP201S and it shows 1.7 on ch1 and 2.7 on ch40 but with the radio meter it shows 1.3 on both 1 and 40. Whats really weird is that on 11 meter band on ch1 and 40 the calibration on my Workman needs no adjustment when checking. Don't make any since from past experience.

Asuming your coax and connectors are in good shape and your meters are ok. I'd be willing to bet a common mode choke below the feed point will bring your readings closer together. If your SWR changes as a result it means you needed it.

 

[Galaxy 959]

Do your radials stick over the actual roof? If so this is most likely your main issue. I would venture to say if you were to move the antenna away from the metal roof your VSWR would go down like it should. JMHO.
But I still would like to see what Marconi's plots show as far as the pattern and any ill effects the roof might have.

Yes 2 of them do. The pole is mounted to the side of the house almost right in the peak.

 

[Galaxy 959]

The roof isn't ideal but I wouldn't call it an issue. The SWR can be tuned flat if he doesn't mind pulling it down another time or 2.

He tuned the thing on the ground next to a house with a metal roof and what looks like aluminum siding. It's no surprise the swr is no longer equal on 1 and 40. This is why I said to push it up as it was and see what happened. Odds are it would need to come down again for some tweaking anyway but no time would be wasted fine tuning it on the front porch.

I didn't notice the roof or the siding but there's still a house there. If you tune it perfectly next to a house you can bet it will be wrong in the air. The best place to fine tune it is where it will be used. That takes more work though.



Asuming your coax and connectors are in good shape and your meters are ok. I'd be willing to bet a common mode choke below the feed point will bring your readings closer together. If your SWR changes as a result it means you needed it.

Dallas you mean roll up some coax below the antenna? Like how many laps? I probably only have about 6' of coax to spare without lowering the antenna some.