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Got the new Sirio Tornado up

Eddie, you are correct about the mk1 & mk2 av170,
the aluminum slugs inside the Fiberglas tube that the hoop bolts to form a capacitor of about 47pf in parallel with the hoop as measured with my cap meter,

The tornado looks to work in a very similar way but i have never measured if there is parallel capacitance across the coil.
 
Thanks Bob, but what does mk1 and mk2 mean?

Did Antenna Specialists make a change in this antenna like I suggested above?
 
Last edited:
Yes Eddie,
The redesigned av-170 included the addition of a coil connected from the bottom of the hoop to ground to make DC short circuit like the av-190, the coil is hidden inside the tube rather than external to the tube as in the av-190,

They also reduced the length of the antenna by 6"
http://www.cbtricks.com/ant_manuals/avanti/av170/ad/index.htm

MC posted pics of the two versions on here years ago.

 
I looks like they simply added an RF choke of some sort between the two sides... That would give you a DC connection that would have minimal effect on the rest of the design RF wise.


The DB
 
Yes that is what makes the mk2 DC ground Eddie, I'm sure I posted the dimensions of the choke for my av-190 for somebody on here.
 
I bought my AV-170 used in '75 from an old timer who had put it up 5 years before I bought it from him - which made it no newer than late 1970 and it had the inner coil.
I later helped a High School friend install one he bought new in 1976 and it was identical to mine.
I don't see a need for capacitive matching when having an inner series inductor to ground coil to balance to ground any inductive reactance in series with the radiator made by the matching ring.
I also don't see across where the 47 picofarads would be measured on a coil-less earlier version..?
 
I bought mine in the late 70's off a neighbour who I was with when he bought it new, it had no choke nor did the European ELECTRONICA clones I have seen/owned,

The redesign according to avanti's advertising came in 1978,

The capacitance is between the two aluminium slugs that the hoop fixes to which is in parallel with the hoop,
remove hoop and the so239 & central wire, measure between the bolts that hold the hoop,

You don't balance inductive reactance of the hoop with inductance to ground,
the radiator & hoop need to be electrically short or capacitive to use inductance to ground,
The av170 with the choke is 6" shorter than the original av170,


I have seen where they snap, even repaired one and a couple of clones,
I don't see how you shoved a solid rod in there that would do anything useful to strengthen it because the hollow tube is full of aluminium and wire that you can't remove without redesigning the antenna ?
 
bob85 said:
I bought mine in the late 70's off a neighbour who I was with when he bought it new, it had no choke nor did the European ELECTRONICA clones I have seen/owned,

The redesign according to avanti's advertising came in 1978,

The capacitance is between the two aluminium slugs that the hoop fixes to which is in parallel with the hoop,
remove hoop and the so239 & central wire, measure between the bolts that hold the hoop,

You don't balance inductive reactance of the hoop with inductance to ground,
the radiator & hoop need to be electrically short or capacitive to use inductance to ground,
The av170 with the choke is 6" shorter than the original av170,


I have seen where they snap, even repaired one and a couple of clones,
I don't see how you shoved a solid rod in there that would do anything useful to strengthen it because the hollow tube is full of aluminium and wire that you can't remove without redesigning the antenna ?
Click to expand...
Hi Bob, I just found I'd missed this post.

I wonder if your neighbor hadn't incorrectly assembled it, leaving out the coil?

The first re-design that I'm aware of came in '78 as the FCC had just opened up the new 40 channel band and it required slightly shorter, re-tuned antennas to move the center SWR of the band from 27.11 to 27.185, but that was only an inch or so.
The ones I owned/installed measured 9" longer (from the top connection of the ring to the radiator) than did my Penetrator from the radials up, NOT including the top hat.
This is what convinced me to try making a top hat radial from R/S aluminum ground wire so I wouldn't ruin an original by bending it straight up to approximate the vertical radiator length/height of the Sigma II.

As I stated in my earlier post, my early ~1970 Avanti Sigma 5/8 (AV-170) had the inner coil, as did the new one my friend bought in 1976. Perhaps they were different in the UK, though I don't know what advantage that would produce, except for slightly lower production cost.

In the one I beefed up I used a short piece of fiberglass rod above the top aluminum insert to strengthen the hollow tube between the match bolts and up into the base of the radiator because it had been previously bent and was several inches shorter having cut off the bottom foot or so of the radiator, losing the aluminum insert in it's base (he added some to the top).
I drilled a hole in the fiberglass about the diam of the bolt so it would have fiberglass for extra strength in the bottom of the radiator and hopefully not bend again.

Remember, this was just a couple years ago ;), when I was 16, and am having Brain-strain in just trying to recall these infinite details.

I also helped a local older guy erect his AV-170 about 5 years ago and recall measuring the radiator from the top ring conn to the tip, which was 22' 4".

- I have never seen a 21.5' version, but I wonder if it hadn't been shortened to slightly below a 20' radiator to comply with even newer FCC regs, then had the length of the mounting base added into the overall measurement of 21.5' to still appear to be a full 5/8, like the assembly measurement of the MacoV5/8 includes mounting base tubing in the overall length?
 
I have a Avanti Sigma 5/8 (AV-170) that I picked up from a guy for taking it down. It has the coil like the one on the left above. When I took it apart to rebuild it the two slugs were destroyed and i had a friend make some for me. I still haven't finished putting it back together but i did pick up a piece of acrylic tube to replace the fiberglass, but I didn't remember the size and got one size too big lol. But during a kitchen rebuild came across a piece of plastic pipe that is the exact size which i plan to use but with the acrylic over the top to double it up for strength. If and when I ever finish it i will try to post up the results. My plan is to set it for 10 meter band and hope to get 11m also. I also have the tornado up and it's a great antenna but is no waybill as well as the Avanti outside of maybe the fiberglass part. 73's all.
 
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NB
The antenna came with the base assembled,
afaik i was the first person to take it apart, he certainly did not when we assembled & installed it, if he had taken it down before i bought it i would have been there helping him,
i also had the euro copy which had no choke, they both looked like the right hand pic above,

fire runner,
which slugs did your friend make for you?
does your av170 have two slugs that the hoop bolts to plus the one at the base with the so239?.
 
Thanks fire runner,

NB,
You cut off the lower section of radiator and the slug that plugs the radiator & gives the upper hoop bolt something to screw into,

That explains why i could not see how you could have shoved a solid rod up there,

If my measurement on the av190 is anywhere close to correct you must have removed some parallel capacitance from the hoop.
 
bob85 said:
Thanks fire runner,

NB,
You cut off the lower section of radiator and the slug that plugs the radiator & gives the upper hoop bolt something to screw into,

That explains why i could not see how you could have shoved a solid rod up there,

If my measurement on the av190 is anywhere close to correct you must have removed some parallel capacitance from the hoop.
Click to expand...
This was the AV-170, and if I remember correctly, I added a few inches of the next size up (or down) to the top of the radiator to extend it back up to a full 5/8 of 22' 4" or thereabouts, but I didn't change the ring dimensions.
 

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