> From: Garry Shapiro <garry@ni6t.com>
> Subject: Re: Topband: T-antenna dimensions?
> To: "Mike Waters W0BTU" <mrscience65704@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
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