Is it common to have a CB antenna work well between 26.000.0 to 29.4900.0

[W5LZ]

You know, it's precisely because it's a 1/4 wave groundplane with no matching system (other than the positioning of those radial) that I find a 3 or 4 Mhz usable bandwidth as exceptional. The pictured graph of those SWR sweeps is also confusing (intentionally I think). Either information was left out or it's to confuse the results. Those graphs are not typical at all. And why would lengthening those radials produce an exact reverse result than the shorter radials? I'd love to hear the reasoning behind it!
- 'Doc

...and those frequencies at the top of the graph have no relation to what's displayed on that graph.

 

[wavrider]

Doc look at that chart again.

Freq is at bottom for the VSWR curve.

Longer element is in brown, it is lower in frequency.

I had to look at it twice before I got it figured out.

 

[W5LZ]

Yep, I saw that. It doesn't change what I said though.
- 'Doc

 

[hammer0630]

" Is it common to have a CB antenna work well between 26.000.0 to 29.4900.0"
No it isn't. The key work in that question is 'well'. You can certainly make one antenna -work- betweren those two frequencies, but it will not work -well-. And then that depends on how you define 'well' and how you measure it. Lot's of 'lee-way' in that, meaning if you are only going by SWR then you are using a characteristic that just isn't very definitive for defining 'well'. SWR can't tell you anything about how 'well' an antenna is working, only how well it's impedance match is, which is also a way of measuring the transference of power. It can't tell you anything about how the antenna deploys that power, what it does with it, where it goes. A 50 ohm resistor has a fantastically nice SWR. But it's a terrible antenna.
- 'Doc[/ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^This is true I was basing that my antenna was doing exceptionally well by observing low swr's and the RF output. It was a long time ago when I had a radio capable of these freq's and the receive and output was terribly off balance from channel to channel. Since this is a ten meter radio instead of a cb stretched out I guess I was impressed by how the transmit and receive seem to stay the same around the band/bands.

 

[W5LZ]

"Since this is a ten meter radio instead of a cb stretched out..."
What's the difference?
- 'Doc

 

[AL567]

But it doesn't show "great SWRs"(whatever that means) in the same range or anything approaching it. The Sirio is at best 2Mhz and that is 2:1 and below. Hammer0630 is getting 1.1:1 or less over 3MHz and less than 1.4:1 over more than 4MHz.

The only way to do that is with a lot of loss.

Guess I should have written "a decent SWR" not great swr's

 

[hammer0630]

"Since this is a ten meter radio instead of a cb stretched out..."
What's the difference?
- 'Doc

I would say that it is like comparing a 4X4 truck to a 2X4 truck even though they are the same make color and year.

 

[AL567]

I would say that it is like comparing a 4X4 truck to a 2X4 truck even though they are the same make color and year.

Or you could say those two trucks are on the same road. One is at mile post 10 and the other is at mile post 11. same road but ones just a little further away.

 

[Marconi]

42, my main reason for my trying to duplicate this work was because the two bandwidth patterns looked so different in shape and the resulting frequencies with the best SWR were so close together. There also was a big difference between the bandwidths in the image you posted, and I wondered why that showed up as it did.

I did the two Eznec antenna models below with both 100" and 106" radials and radiator elements, just like the Sirio Manual suggest in the "Tuning Instructions" section...and I got notably different results than your graph shows.

Both of my bandwidth curves were very similar in shape and the best SWR for each was also very close at 1.40:1 for the 106" antenna and 1.37:1 for the 100" model. Way different than your bandwidth image shows.

The difference noted between the two antennas in your graph link with the lowest SWR at 2.71 mhz - 2.68 mhz = .30 mhz difference in frequency, which is very close together, and not much of a difference due to a 6" tuning difference in antenna length.

My Eznec models on the other hand show this difference for the lowest SWR at 27.7 mhz - 26.4 mhz = 1.30 mhz difference in frequency due to the 6" added length for the elements and this make my resonant points (lowest SWR) 4> times farther apart in frequency than your graph indicates, and that is a big difference.

Did Sirio produce this graph? I don't see it listed on the Sirio Website or in the manual for their M400 Starduster antenna.

Can you give us the source of the graph you posted here?

Here are my Eznec models:

View attachment Sirio M400.pdf

 

[Mudfoot]

http://www.ar15.com/archive/topic.html?b=10&f=22&t=635881

 

[Marconi]

M-400 "Starduster" Review - AR15.Com Archive

Thanks for the source. I didn't think it was from Sirio.

Nothing wrong with the effort and the report, but this guy apparently made the graph from measurements he got from using an inline meter and a feed line, and then he produced the result using a spread sheet to include in his comments.

If Sirio did produce a bandwidth curve for their M400, they would likely use modeling, and that would yield results at the feed point, thus I would expect things to be notably different.

So, we can forget about the modeling results and comparing of results I posted.

Below is your link compared to a real world bandwidth curve I took when I last put my A/S version of an original Starduster up late in 2011. My report shows my results from using an analyzer and a inline meter, but both were done using a working feed line and that too will make some differences.

You will note that the patterns it makes is very similar to the pattern you posted for the 100" antenna. My pattern even has a little hump going up in frequency close to 28.000 mhz if you notice. The points of the lowest SWR are also very close to the same too. So IMO your report for the 100" antenna looks good to go for me, and that is what one might expect to see using a feed line at some modest height.

Thanks for the follow up.

View attachment Starduster bandwidth.pdf

42, it always gives me a good feeling when I see modeling results come out close to some arbitrary real world results.

 

[hammer0630]

I just want to thank Marconi for the results I have with my Star Duster even though my technical understanding of what has been said and represented has exceeded what I can fully understand. When I was setting up my SD and mast I followed Marconi's directions completely and have a antenna that has exceeded anything I could have hoped for.

 

[Marconi]

I just want to thank Marconi for the results I have with my Star Duster even though my technical understanding of what has been said and represented has exceeded what I can fully understand. When I was setting up my SD and mast I followed Marconi's directions completely and have a antenna that has exceeded anything I could have hoped for.

Thanks 0630, but I just gave you some simple tips I've learned over the years using my Starduster antenna. The credit has to go to Sirio that decided to resurrect this old antenna that works so well and did a good job of it.