masts, coax,CMC or anything

[Marconi]

Marconi what I have tried thus far is running coax through the mast pipe with an rf choke AKA ugly balun at the bottom of the mast. I have no TVI, RFI, CMC issues SWR look as to be expected using the mfj259b analyzer.

Hey wavrider! IMO, it's a good idea to check and compare the possible effects of any modifications to our antenna system.

Based on reports that a coaxial choke, not made correctly, can make matters worse...sounds to me like a good reason to check.

Another install I did not put the rf choke at bottom of mast pipe, same results no RFI , TVI, CMC issues, swr same as one with choke.

A good idea to double check too.

I seem to think, and as is suggested in several articles online,
running the coax through the mast pipe presents an easy method to isolate/shield the coax within the 1st 1/4wl of the antenna effectively decoupling the coax from the antenna where the bottom radials of the starduster type antenna is radiating.

I use to think running the coax thru the supporting mast, like the Starduster does, was done for convenience in the design. Then I saw were Avanti was suggesting a similar installation idea for their Sigma 4, and that made me wonder.

I like my Imax for the multiband coverage but I will never homebrew any more 5/8 wl gp, the 1/4wl does just as well if not better performance IMO.

Some years ago I bought an I-10K. I did it planning to compare it to my Starduster. I found if I just raised my SD'r up and got it within a couple of feet of the 5/8 wave tip...there was little to no difference, and my SD'r was much quieter when conditions were on the quiet side of good.

 

[wavrider]

Have been comparing the two different installs.
One at my QTH another 65 miles away at friends QTH.

Both are working as good as can be expected, one with rf choke and one without.

I agree if the antennas can be installed "AT THE SAME TIP HEIGHT" very little difference can be determined between any type of GP.
There just is not enough gain between a 1/4 wl and a .64wl to notice any difference in RX or TR "IF" the antennas are installed correctly.

Many will say they notice 1 or 2 S unit difference between antennas.
then if that is the case something was not correct with the install of previous antenna.
Just my opinion.

 

[davev8]

but don't folk put antennas up as high as they can....or at the top of thier mast ...so if a 5/8 wave is taller than a 1/4 wave and gets out better will that not make it typically a better antenna?

 

[wavrider]

Which is less expensive?? Mast pipe or antenna?

Why spend more for an antenna that does not perform any better than a less expensive antenna installed at same tip height?

It all depends on personal preference and what the operator/owner thinks is performing best for him.

Also consider any losses in a matching network for any type antenna except a direct fed resonant 1/4 wl vertical?

if you can only mount your antenna on a 10 foot pipe, then a I2K would be great as current maxima is around 10' above feed point, so it will get your signal out better than a 1/4 wl mounted at 10 feet, in theory.

Once the antenna is over 1 wl agl then the 1/4 wl just might outperform the 5/8 wl due to no loss in a matching network.

Whatever gain ever so slight that might be seen in a .625 or .64 wl vertical may be loss in the matching network.

Modeling only shows gain, it do not think it can show what percentage of your transmitted power(watts) is being radiated as heat (loss) in the matching network.

 

[The DB]

Like wavrider essentially said, the higher the antennas are mounted, the less of a difference you will see between a 1/4 and a 5/8. Their is still a bit of a difference at 1 wavelength, but as you move past that point and continue to raise the antennas you will get to height that the difference is so small that you will never notice it. Also, as has been said, raising a shorter antenna to the same tip height will also cause the antennas to perform the same, and if they don't its because you have a problem with one of them.

A model that includes a matching network will factor in said matching network losses. However, such a model is not always easy to create, depending on the matching network of the antenna in question. In the cases I have been able to model, matching networks made an insignificant difference to overall gain. This is especially true with 5/8 length (and near) antennas, which makes sense as the main correction needed is reactance (X), and reactance is much more efficient to tune than impedance (R).


The DB