Avanti Sigma 4

Back in the late 70's early 80's i used to run a Sigma 4 mounted about 3mtrs above the top of my roof. Probably 15 to 20mtrs above ground level. 

Great for shooting Dx but poor for local work or maybe it was just me

Did anyone else have one of these or does anyone have one now?

Hi Wade,

I think everyone that was ever involved in CB has heard of, seen or even had an Avanti Sigma IV

This antenna was copied by loads of different manufacturers and I think the modern day equivalent is the "Sirio Vector 4000", (god knows where they get these names from).

There's a lengthy paper published if you want to go into depth here :-

Avanti Sigma IV analysis

Warning......this paper does start blurbing on about antenna modelling difficulties, etc. but does have some good insight into said antenna. Including some clever thoughts on "shiny-big-new-expensive-antenna-syndrome"


I think what you've said about this antenna can be pretty much said about any antenna for CB. "Great for DX, poor for local"
I've had many antennas over the years for CB, some purchased, many homemade and I can say the same thing for everyone of them. When the "skip" is in, you can make contacts hundreds if not thousands of miles away on 27MHz, (what makes CB great!), but in 'normal' conditions you're lucky to push 20 odd miles away unless you live high up, go high up or stick your antenna as high up as you can.
It's where the old CB adage of "height is might" comes into play
(Of course there are variables, two CBers pointing beams at each other and running many watts are obviously going to do better!)


The problem with antennas is we remember fondly, with rose tinted glasses, that antenna we had when we were "shooting the skip" like there was no tomorrow. Whether that was sat in Dad's car with a mag mount on top of the local hill, or that expensive monstrosity the missus hated bolted onto the house precariously hanging off discarded scaffold poles!

Honestly, when the "skip" is in, you can DX with the proverbial piece of wet string as an antenna on CB.

When it's not, we can be left feeling a bit "meh" about it all or start pushing our local DX capabilities.
(More scaffold poles, different antenna, linears, different rig or even better coax?!?)


.......but for me, that's the fun of CB!


All the best,
Victor

Oh so true Victor.

I went from the Sigma to a GPA half wave which seemed to work better locally.

Happy day's

No worries Wade.

It's great to chat CB, radio in general, antennas and all that fun stuff!

Weirdly I'm looking at swapping out my 'Inverted V' bit of wire in the loft for an end fed half wave. From all the antennas I've ever put up it's the kind that was the best all-rounder.

Take it easy,
Victor

Even more weird i put up a vertical 5mtr long Sigma SE HF 60 multi and have nothing but complaints especially the plonker opposite who is local councillor. So was thinking of putting a inverted V in the loft. How much space do you need?

I used to own a Siggy 4 back in the 80s and now use its younger bro the 33ft Vector 4000,great for dx and local and has withstood some very strong winds...

The neighbours have got used to a beam and the vector and often ask isnt it about time i got something bigger..

Hi Wade,

My apologies for not getting back to you sooner mate, grandkids round and with a hot day we've been splashing around a blow up pool! (Damn near killed me blowing the flipping thing up!)

What a shame with your Sigma.....are you sure the councillor in question can't be ousted for dodgy deeds? That'd sort them out
(Sodding "Civil Servants".....never met a civil one or any that practice servitude )

Joking aside......


An Inverted V doesn't take up much space at all and can be made with pretty much any wire you have laying around.

Here is an online calculator that'd give you the dimensions you'd need :-

M0UKD Inverted V calculator


Mine is made out of some solid core copper electrical wire, simply hung from the roof rafters. I calculated it for 27.5MHz and it was well into a good SWR range for mid block/euro, freeband and UK. Don't expect a 5/8ths performance from it, but it does do rather well. The best thing is, no-one else will ever know it's there! (I regularly run 100 watts through my bugger as well )

If you have problems getting it in SWR range, (shouldn't do), you can bend the end tips back on themselves rather than cut them....saves the "Oh flip I've cut too much off!" scenario. Just make sure you bend equal lengths both sides.
You shouldn't need a choke at the antenna feed point but it doesn't affect it if you do.

Simple stuff really. (Apparently you can pay sums of money for someone to pre-cut the wire for you....but where's the fun in that?!)

Honestly, if you've never made an antenna before you'll be super stoked when you do and get a contact with it

Much simpler than many DIY wire antennas and I haven't found anything yet that can be hidden so well.


Anyway, hope that helps.

All the best to ya,
Victor

Hey Sam,

I knew I'd seen a Sigma 4 looking antenna somewhere on Charlie Tango.....and there it is, on your profile pic
Ain't it weird that one of the complaints about that antenna was wind resistance yet everyone who had one never did have problems even in the fiercest of winds(!)

My old Sigma 4 survived some fierce storms. You could lie in bex so.e times.andisten to the wind howling and wonder what you would find in  the morning . It survived though.

Here's a photo of my Mk.1 Sigma IV with the tip up at 83ft. I bought it back in 1980 for £64 which would be over £200 in todays money.Te old saying "height is might" definitely rings true. I took it down a couple of years ago and replaced it with an Imax 2000 which certainly helps me sleep better on windy nights. The difference is less than an S-point on the meter.

Blimey. That is a serious installation.

Victor wrote:

No worries Wade.

It's great to chat CB, radio in general, antennas and all that fun stuff!

Weirdly I'm looking at swapping out my 'Inverted V' bit of wire in the loft for an end fed half wave. From all the antennas I've ever put up it's the kind that was the best all-rounder.

Take it easy,
Victor

The dipole is better than an end-fed. If you put up an end-fed half wave you'll need to also put up a ground plane unless you want to have all kinds of common mode issues. Contrary to belief yes half wave antennas DO need a RF ground. All end fed antennas do because physics. Any end feds that claim to work without one use your coax - put a good RF choke at the antenna feedpoint of said antenna and you'll see performance drop off a cliff. The only exception are antennas like the Sirio Gainmaster which are actually a centre fed dipole with the feedpoint placed at one end.

Swadeyboy wrote:

Even more weird i put up a vertical 5mtr long Sigma SE HF 60 multi and have nothing but complaints especially the plonker opposite who is local councillor. So was thinking of putting a inverted V in the loft. How much space do you need?

Using bare wire 9ft long per leg as a starting point although you'll find you'll need to shorten it, reduce the starting point by 4% if using insulated wire. You can however bend the legs in any direction you want with a dipole to fit the space, as long as there isn't a bend tighter than 90 degrees. Some examples...

Hi Conor,

How are you keeping? Well I hope.

I don't think anyone who's been on Charlie Tango for any length of time could ever miss your advice and proclamations on RF grounds

We get it, or some do and I'm sure we appreciate the advice


All the best,
Victor

Yeah I do kind of feel like I bang on about it all the time lol.

Avanti  sigma4  one of the best 11mtr vertical  dx antennas ever made , unless you had a massive beam with a rotator .I had no issues with mine for local stuff either  it is just too big for most folks to put up .
Now i have a 5/8 Gainmaster and for dx i would say its nearly as good  concidering it sat on the ground leaning against my garage for a few years and no issues getting dx around Europe . I have since  hoisted up in the air.
For the Hams everything is a compromise as all the different bands that they have  unless you can afford and have the space for a Step IR antenna .