Anyone tried the Sigma Venom Aluminum 5/8 from England?

[The DB]

The Imax does have a capacitor on the radiator. That being said, the capacitor was not centered on the antenna, but was more like 1/8 or 1/4 wavelengths above the matching section. I do remember that the Imax had a very similar impedance to a half wavelength antenna with the capacitor modeled in this location, which had me thinking that they used this capacitor so they could use the same matching section with both antennas.


The DB

 

[357magnum]

Marconi , the pic's I see , there is no sedan delivery ? I see a Station Wagon ? I'm sure you know deliveries had metal in place of glass in the rear . On the other note back when you were racing that's a pretty good time ! Considering Anglia's had that class covered ! But most were " Blown " & running 9.99 -10's , so for a " Carb " car you were flying !

 

[Marconi]

The Imax does have a capacitor on the radiator.

Steve, I agree. The first time I heard this idea was from the thread that Radio Daze posted.

I had seen a round cylinder like object in the middle of a broken Imax before, and it wasn't metal. Like I suggested to RD in his old thread...I figured it was to help stop the wire rattle. I also recall another situation where Copperhead565 posted he was not able to see continuity in the middle section of his Imax. Check the link below. If it doesn't work or do a forum search for "Imax 2000 Continuity Query."

<a> href="https://www.worldwidedx.com/threads/imax-2000-continuity-query.170384/">IMAX 2000 continuity query</a>

That being said, the capacitor was not centered on the antenna, but was more like 1/8 or 1/4 wavelengths above the matching section.

Steve, I don't remember your model showing the capacitor position that low on the radiator. I remember however, your pattern did look a bit different form my model and I was never able to duplicate that look. I also note that my model did not make a symmetrical current distribution in the antenna view...unless the capacitor was at or near the middle.

I do remember that the Imax had a very similar impedance to a half wavelength antenna with the capacitor modeled in this location, which had me thinking that they used this capacitor so they could use the same matching section with both antennas.

I don't see the match for my models here showing close to an EFHW either. With the capacitor added, my Imax models show a match in the SWR range of 15:1. My EFHW's are at best 40:1 or more.

You can look at the schematics noted in the two "**** Exposed" reports for these antennas on the Internet and see both match systems. I have the matcher our of an A99 and it easily has 19 or 20 coils. The Imas looks to only have 10-11 coils at best.

Thanks for the reply.

 

[Marconi]

Marconi , the pic's I see , there is no sedan delivery ? I see a Station Wagon ? I'm sure you know deliveries had metal in place of glass in the rear . On the other note back when you were racing that's a pretty good time ! Considering Anglia's had that class covered ! But most were " Blown " & running 9.99 -10's , so for a " Carb " car you were flying !

You are right 357. Back then I had 3 $100 dollar bills in my hand and this old used car guy told me about this 55 Chev and it had plywood decking and side walls in the back floor. He said nobody wanted a sedan that had no back seat. He didn't say it was a custom job, but that might have been the case.

No wonder guys use to look at the car and seem to wonder what the deal was...If they asked, I told them it was a sedan delivery.

 

[The DB]

I don't have my models from back then as they were lost, but their was a definite phase shift at the capacitor. Currents went from a near null to a positive number, and these currents were in phase with the upper part of the antenna.

I forget who it was that gave the value of the cap, and how far up the element they said it was. I do remember that it worked very differently when moved on the element itself, so positioning was important.


The DB

 

[Marconi]

The Imax does have a capacitor on the radiator. That being said, the capacitor was not centered on the antenna, but was more like 1/8 or 1/4 wavelengths above the matching section. I do remember that the Imax had a very similar impedance to a half wavelength antenna with the capacitor modeled in this location, which had me thinking that they used this capacitor so they could use the same matching section with both antennas.

Steve, I don't remember your model showing the capacitor position that low on the radiator. I remember however, your pattern did look a bit different form my model and I was never able to duplicate that look. I also note that my model did not make a symmetrical current distribution in the antenna view...unless the capacitor was at or near the middle.

Steve my original thinking was, the Imax with a capacitor needed to be in the middle. So, my previous models (radiator wire #3 with 90 segments) had it positioned as such. I was seeing better symmetry between the bottom and the top of the radiator and that looked better to me. I think you were looking for maximum gain and I was looking for better current distribution over the whole 5/8 wave element.

In that configuration the match for the FS model was not so good, but the Average Gain was = 1, the maximum gain was good, and the angle was low to the horizon...as compared to the control model without the capacitor.

So base on your earlier comments above, I made several iterations placing the capacitor lower than the middle. When I got to segment #36 of my 90 segment wire for the radiator...my model also showed the maximum gain of 4.09 dbi @ 9* degrees over Real Earth. At this position I also saw an antenna pattern similar to your pattern.

Then I changed the capacitor from 40pF to 42pF and the gain improved a little more to 4.11 dbi @ 9* degrees over Real Earth. So, you were reporting correctly back at the time of this discussion.

Thanks for the heads-up.

 

[Low_Boy]

Marconi It is Friday I am off work. We can measure today. When you do not see me on the site for a couple days that means I am being overworked. LOL

 

[Marconi]

Sounds good, you have my number, call me when you get ready.

 

[Marconi]

Thanks for the call Gary,

Keep up posted when you get it up an working.

 

[Low_Boy]

No problem. If you need anything else just call.
You are welcome

 

[Marconi]

Gary, here is another image of a coil that I think is from a Radio Shack CLR2 and may be similar to the coil in your HG Venom 5/8 wave.

 

[Low_Boy]

So that's what is in there.

 

[Marconi]

Looks like designed by idiot.
All 5/8 antennas need radials. Imax is not a 5/8. End of story.
Mike

Mike, the High Gain Silver Rod design was originally produced by Hy Gain. I don't think they were, without doubt, some idiots. However, like most antenna makers, they may have fudged a bit on the details of their products. Who doesn't?

If the Imax is not a 5/8 wave...does that suggest the A99 not a 1/2 wave?

Just for grins, how would you best describe the Imax?

 

[sp5it]

Best Imax/Antron description gave W8IJ.
If Hy gain designed and produced 5/8 antenna with short radials located ~35cm over the coil it does not mean it is correct. That design is brainlessly copied by others through the years. It can work, sure, but it does not mean it is correct.
Mike

 

[Marconi]

Best Imax/Antron description gave W8IJ.
If Hy gain designed and produced 5/8 antenna with short radials located ~35cm over the coil it does not mean it is correct. That design is brainlessly copied by others through the years. It can work, sure, but it does not mean it is correct.
Mike

Mike, when you talk about raising the radials above the coil, I assume you're referring to the mounting bracket Hy Gain designed?

W8JI has written a boat load of articles. Could you give me a clue to the article where you read W8JI talking about this issue or giving you this idea, "...regarding the radials located -35cm over the coil does not mean it is correct?"

Could you also give me a clue where he reports on the A99 and Imax?