Topband: T-antenna dimensions?

[Mike Waters W0BTU]

> From: Garry Shapiro <garry at ni6t.com>
> Subject: Re: Topband: T-antenna dimensions?
> To: "Mike Waters W0BTU" <mrscience65704 at yahoo.com>
> Date: Tuesday, January 19, 2010, 11:50 PM
>  
> All I hear on  topband this  season is noise--powerline hardware, plasma TV's, heaters, thermostats, dimmers, switching power supplies. I am slowly drifting away.

Hello Garry,

I'm sorry to hear that. I know what that's like. 

I just looked at the satellite view of your QTH at http://www.qrz.com/db/, and it appears you might have room for Beverages or some other kind of receive antenna. Regardless, have you considered using an MFJ-1025 or -1026 to help reduce that noise?

 
> One thing about modeling is to have enough segments. A 
> simple dipole
> does not require many, but complex shapes, corners, and
> close-spaced
> wires do--at least where they are complex. EZNec will often
> tell you
> when you have an insufficient number of segments, but for
> best results,
> increase segments until the results don't change--kind
> of like adding
> radials until the bandwidth does not change.

Thanks for that advice!

> Don't trust results where wires are very close to ground unless you
> have NEC4 (you don't). And if you get results that seem illogical, they
> are.

> EZNec has limitations, like all software. If you fold the Tee wires back with small spacing, it may not model right.

I was wondering about that. That statement makes sense. Herb Schoenbohm, KV4FZ, helpfully suggested that a 10' spreader at the ends of the T might work. This agrees with your thoughts, I believe.

I'll have time to model this after the contest. For now, it looks like I'll have to make do with something simpler (if I want to play in the contest next weekend), since I haven't even started putting up any wire yet.


I received so many helpful tips from many hams on the Topband list. Wow.


73 Mike



> Really? I appreciate that tip. I was wondering about that.
> 
>   
>     FIrst, model an "ideal" vertical
> for reference--quarter wave, lots of radials. The try
> modeling
> with the height you have and the tee you have room for, and
> find a
> coil that brings you to resonance. Assign a reasonable Q to
> the coil;
> bear in mind that the coil carries a lot of current and you
> want
> maximum Q.
> Then compare the resultant pattern to the reference
> vertical. That should ballpark you.
>     
>   
>   
> 
> That makes sense.
> 
> Thanks for taking the time to help. I appreciate it! Hope
> to CU on 160 soon.
> 
> HB9LCW is S9+ on my NE Beverage right now. Sure wish I
> could transmit. 
> 
> 73 Mike