More 5/8 hombrew questions about tuning

[bob85]

if you look at the avanti sigma2 it does not use a tapped coil like most 5/8waves or a tapped hoop like the maco v5/8 and similar antennas,

your coax center conductor connects to the bottom of the hoop, top of hoop connects to bottom of radiator,
inside the fiberglass where the hoop attaches are two aluminum slugs which if i recall correctly form a capacitor of about 47pf in parallel with the hoop, that's about 125ohms Xc @27mhz,

when nav built a sigma2 copy using the same size/style hoop as my avanti with no capacitor it would not give a low vswr with any radiator length close to 5/8wave,
he ended up using a tapped coil to get the low vswr,


later version sigma2 and the avanti saturn have a dc grounding coil from bottom of hoop and about 6" shorter radiator.

 

[Marconi]

sounds good,,

That's great. Are you going to start this new thread? I think that one will be something to discuss plus Camaro you can post pictures that help show us what you're describing.

 

[camaro1]

yes I did,, sorry for the confusion to the original post

 

[Marconi]

No problem bud.

 

[bob85]

eddie, i have had conflicting claims from people i asked to measure their tornado for dc grounding, some say theirs is shorted and some say its open circuit,
there are two versions short radial and long radial with revised hub,
id be surprised if one was open and the other style shorted.

 

[Marconi]

eddie, i have had conflicting claims from people i asked to measure their tornado for dc grounding, some say theirs is shorted and some say its open circuit,
there are two versions short radial and long radial with revised hub,
id be surprised if one was open and the other style shorted.

I understand when you talk about how you sometimes get conflicting claims from folks, with good intentions hopefully, when you simply ask for measurements on their antennas. IMO, most probably don't do it on purpose...they just tend not to give too much details.

I don't know about matching circuits, but sometimes I'm surprised when I check the feed point, and the condition of continuity turns out different from what I figured.