[TowerTalk] Vertical Antenna Question

[jimlux]

On 4/9/20 4:21 AM, Máximo EA1DDO_HK1H wrote:
>> Not if you use enough radials.  I don't think I've ever seen ferrite
>> cores out on heliax at AM broadcast towers.  If you use enough
>> radials, the return current will be so divided down that the current
>> on the outside of the feedline (burying it helps but isn't necessary)
>> will be negligible.
> 
> Interesting.
> Never though on that.
> Perhaps, Some kind of "sleeve balun" ?
> Grounding the coax's sleeve at 1/4 wl from antenna base.
> 
> Thanks.
> 
> 73, Maximo
> 
> 
> 
> 
> <http://foro.ea1ddo.es/>
> 
> 
> ________________________________
> De: TowerTalk <towertalk-bounces at contesting.com> en nombre de Rob Atkinson <ranchorobbo at gmail.com>
> Enviado: jueves, 9 de abril de 2020 11:11
> Para: towertalk <towertalk at contesting.com>
> Asunto: Re: [TowerTalk] Vertical Antenna Question
> 
>> You also need to invest in some 31 mix toroids or clamp ons - choking your feedlines is going to be important.
> 
> Not if you use enough radials.  I don't think I've ever seen ferrite
> cores out on heliax at AM broadcast towers.  If you use enough
> radials, the return current will be so divided down that the current
> on the outside of the feedline (burying it helps but isn't necessary)
> will be negligible.  If you have to use ferrite cores to keep RF off
> your feedline exterior, you don't have enough radials down.
> 
>> The Cushcraft R7/R8/R9 Verticals are 1/2 wave so they do not require radials.
> 
> That's only true if they are vertical dipoles.  If they are 1/2 wave
> monopoles, they still need a ground system regardless of the
> manufacturer's snake oil sales pitch.
> 
> 73
> 
> Rob
> K5UJ
>



True, with enough radials, you create a synthetic ground that your 
feedline is under.

And for Maximo, there's tons of antennas out there using the 1/4 
wavelength choke (Ringo Ranger, etc.).  They're single band, although I 
suppose there's no reason why one couldn't do multiple choke sections.

The ferrites are just easier. And actually, you might not need them. 
Having the coax act as a radial isn't inherently bad.