Thank you guys for all this discussion. This is my first 80m fullsize, so,
some questions might have been childish.
I learned a lot. What is easily achievable and what is not, what precision
should I expect.
73
--------------------
Vytenis
2017-09-13 23:22 GMT+03:00 StellarCAT <rxdesign@ssvecnet.com>:
> One should be able to get within say 3% .... 5% tops to start with –
> right?!
>
> Measuring the actual frequency of the actual antenna and changing it this
> much will work ... if done properly – in one go. I’ve done it many times
> with tapered elements. Again – you’re not changing or impacting the antenna
> enough for a simple ratio correction to be off by much. I’m not saying that
> if you measure it to be 3468 Khz and you want it to be 3584 Khz that it
> WILL be at 3584 ... but it will be close and in the right direction. For
> most purposes good enough. That is all that one needs – right? We’re not
> looking for perfection here. Or at least I am not/was not.
>
> I totally agree with you Chuck that IF the antenna were widely tapered –
> if you change it substantially either in length or diameter it is going to
> be off – and if that is indeed the case then fine – “maybe” he does it
> twice.
>
> As for modeling – yes – you can obviously do that and should do that. But
> my experience has been that modeling generally gets you in the ball park –
> you might still need a small tweak to that. So I’d start with a model ...
> but testing the ACTUAL antenna in situ can’t be beat. It is THE info you
> needed – precise for that antenna in that location.
>
> What I would do and have done is I would model the antenna as it is to be
> built or is built ... test it ... but here’s where people start to get
> confused re using a model, if they’re not totally familiar with changes
> like this. So you model for a resonance of 3600Khz. You build it precisely
> to the model and test it – its actually at 3540Khz. If you have to have the
> original design frequency now what? Well you go back to the model – you
> change the tip length to effect the DIFFERENCE in frequencies – i.e. you
> need it to be 60Khz higher – so you go back to the model, shorten it to get
> a new frequency of 3660Khz! This change in length is what you would do to
> the antenna. The same DIFFERENCE that you need/saw in the actual antenna.
> Again: this is not precise – but it will work just fine.
>
> g.
>
> looked at another way: (didn’t know this was going to be controversial :>)
> )
> -tapering effectively gives you an average diameter.
> -so his antenna starts at 4” and tapers to 1”. Lets say the average is
> 2.5”. That is more than likely not what the model would come up with but
> its probably close ...
> -a 67’ vertical that is 2.5” in diameter has a resonance of 3.517Mhz
> roughly give or take a couple Khz.
> -if I change the effective diameter by 10% – MUCH more than I believe
> we’re talking change here which is my whole premise, to 2.75” the resonant
> frequency in the model changes – whoops... about 3 Khz!
> -even changing it to 3”, a pretty substantial effective diameter change –
> moves it only ~6Khz.
>
> ok?
>
>
>
> *From:* w5prchuck@gmail.com
> *Sent:* Wednesday, September 13, 2017 3:39 PM
> *To:* StellarCAT <rxdesign@ssvecnet.com> ; V. Sciucka
> <vytenis.sciucka@gmail.com>
> *Cc:* Charles Morrison <junkcmp@gmail.com> ; towertalk@contesting.com
> *Subject:* RE: [TowerTalk] 80m vertical size calculation
>
>
> I agree. But, what was wanted is a formula where only one adjustment was
> needed. I think that will only work when the entire element is one diameter
> such as a wire. The ratio will get close, but will probably need at least
> one more “tweak.”
>
>
>
> Chuck W5PR
>
>
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows 10
>
>
>
> *From: *StellarCAT <rxdesign@ssvecnet.com>
> *Sent: *Wednesday, September 13, 2017 2:24 PM
> *To: *V. Sciucka <vytenis.sciucka@gmail.com>; Chuck Dietz
> <w5prchuck@gmail.com>
> *Cc: *Charles Morrison <junkcmp@gmail.com>; towertalk@contesting.com
> *Subject: *Re: [TowerTalk] 80m vertical size calculation
>
>
>
> these are only starting points! Local conditions - the antenna itself, the
>
> surroundings, the ground, etc etc will all conspire to move that value up
> or
>
> down slightly. KNOWING what your particular antenna is in place - that is
>
> the perfect starting point.
>
>
>
> g.
>
>
>
>
>
>
>
> -----Original Message-----
>
> From: V. Sciucka
>
> Sent: Wednesday, September 13, 2017 2:46 PM
>
> To: Chuck Dietz
>
> Cc: Charles Morrison ; towertalk@contesting.com
>
> Subject: Re: [TowerTalk] 80m vertical size calculation
>
>
>
> I just thought that it might explain why different formulas are used.
>
> Charlie gave me formula which is widely available: 246/f(mhz) = element
>
> (feet), but I also found https://www.dxengineering.com/
>
> techarticles/verticalantennainfo/dx-engineering-comtek-verti
>
> cals-for-phased-arrays (see p.5) where 234/f(mhz) is used.
>
>
>
>
>
> --------------------
>
> Vytenis
>
>
>
>
>
> 2017-09-13 21:33 GMT+03:00 Chuck Dietz <w5prchuck@gmail.com>:
>
>
>
> > Maybe I don't understand, but I would think that if you had a tower with
>
> > an aluminum tube "stinger" on top, this might not work because of the
>
> > change in percentage of the various diameters.
>
> >
>
> > Chuck W5PR
>
> >
>
> > On Wed, Sep 13, 2017 at 1:00 PM Charles Morrison <junkcmp@gmail.com>
>
> > wrote:
>
> >
>
> >> Not length to diameter, It is independent of diameter.
>
> >>
>
> >> It is a simple method to determine a difference of length as a ratio
>
> >> based
>
> >> on frequency.
>
> >>
>
> >>
>
> >> On Wed, Sep 13, 2017 at 11:41 AM, V. Sciucka <vytenis.sciucka@gmail.com
> >
>
> >> wrote:
>
> >>
>
> >> > Thanks Gary K9RX and Charlie N1RR, 2nd question is clear now.
>
> >> > Charlie also gave formula for length 246/f(mhz) = element (feet)
> which
>
> >> I
>
> >> > assume includes length to diameter ratio or this ratio is not so much
>
> >> > important.
>
> >> >
>
> >> > --------------------
>
> >> > Vytenis
>
> >> > _______________________________________________
>
> >> >
>
> >> >
>
> >> >
>
> >> > _______________________________________________
>
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>
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>
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>
> >> >
>
> >> _______________________________________________
>
> >>
>
> >>
>
> >>
>
> >> _______________________________________________
>
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>
> >> TowerTalk@contesting.com
>
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>
> >>
>
> >
>
>
>
>
>
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