Topband: Topband Digest, Vol 169, Issue 22

[Jim Jim]

Bob,

>From what you have said I would suspect you have changed the pattern of the antenna but that is just a guess. The other thing is that the last few years has seen a marked change in 160M propagation and use it seems.  On occasion I have seen WSPR stations have propagation to EU but there are no EU stations on the band operating CW.  I would think if a low power WSPR station could get through a 1500w CW station could certainly make it but then I am just a little gun and don't know much about such things.


As far as the pattern you will only know about that if you model and even possibly measure the field in the far field of the antenna. Might I suggest however you put a halyard up and then you can run the antenna up and down much like you would a flag.


I will say that I have noticed many people not being able to break through what few pileups there have been... many that I have seen getting reports in past years.  I would have thought prop would have been better seeing how we are supposed to be on the down side of the solar cycle.... but again what do I know.... I just keep plugging away in hopes of adding another new one, which I guess is all any of us can do EVEN the big guns.


Good luck with your efforts and let us know what you find out


Jim WA3MEJ


> 
>     ----------------------------------------------------------------------
> 
>     Message: 1
>     Date: Sun, 29 Jan 2017 21:23:15 -0500
>     From: "Bob Garrett" <rgarrett5 at comcast.net>
>     To: <topband at contesting.com>
>     Subject: Topband: My Shunt Fed Tower
>     Message-ID: <00d001d27a9f$d0a552d0$71eff870$@comcast.net>
>     Content-Type: text/plain; charset="us-ascii"
> 
>     Greetings Listers,
> 
>     I'm looking to this group for some input on my shunt fed tower loaded down
>     with antennas HI.
> 
>     I have 85 feet of Rohn 25G with three sets of broken up guy wires that was
>     installed in 1999. Probably 200 to 300 short radials that have been put in
>     since 1988 for the previous tower and added to over the years, all bonded to
>     the base of the tower.
> 
>     On top, from bottom up I have - Optibeam 9-5 9 EL yagi, 5 EL M2 6 meter yagi
>     and at 100 feet, an Optibeam 30 - 40 rotary dipole. All cables run inside
>     the tower and are grounded at the base. I use an omega match made up of two
>     vacuum variables.
> 
>     Now, this season, I wanted to have a few more options for contesting. I
>     installed a 3 foot metal support from KF7P and put up a 80 meter inverted
>     VEE at 70 feet and a 60 meter inverted vee at 60 feet using the same
>     arrangement. I did have to adjust the omega match after adding the two
>     additional antennas.
> 
>     Regarding the shunt, I use a piece of RG8X with the attachment point at
>     about 48 feet and a spacing of 24 inches, a 1KPF variable in series and a
>     probably 400PF cap for the omega match. No problem getting a perfect match.
> 
>     Over the years, this arrangement prior to adding the two inverted vee
>     antennas this year performed very well. Now I know about TB conditions so,
>     I am not making sweeping statements but, seems like I just don't get through
>     those pileups as quickly as before.
> 
>     My questions - Is there any fact to the statement that an 80 meter antenna
>     on a 160 meter shunt fed tower will degrade the performance? Is it just one
>     happy amount of loading? Anything else I should be considering? The
>     problem is I live on a small lot and only have so many options to cover all
>     bands. Any input appreciated. 73, Bob K3UL
> 
>     ****************************
>