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Base Have a look at this Antenna

Bob, after i posted my model that I started with above...I got to thinking that the gain seemed inflated, even though it agreed with what Avanti reported years earlier.

I didn't remember the source of the model I started with, and I didn't recall ever talking with DB about my results. However, I dated the model to 07/25/17, and added DB's handle to the title. I'm dangerous when I get to thinking. Now I vaguely remember, at the time, I likely used a model of an A/P I had on file, and modified it using the feed point location that DB had been talking about.

I just looked back at some of my models with the feed point location where I thought it should be...and those models, showed gains closer to 2.25 - 2.50 dbi, instead of 4.58 dbi like I reported in my post #14 above. Next, I will use another old A/P model showing a match with values closer to R=74.85, X= -0.6668 ohms, SWR = 1.497. I would think this is much closer to what a vertical CFHW antenna should indicate.

(Edit): I will tune the model here and get a better match if I can. It may also effect the gain and/or the TOA...just not sure yet.

Sorry, IMO this results from bias, and shows what bias can do to one's thinking...if they get locked-into some dubious ideas.

Do you think Avanti was probably puffing their antenna performance back then?

So, discount the models I posted earlier. I will wait and see if Tagra answers my email.

Sorry I jumped the gun! (n)
 
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Hello eddie,

Tagra did gold anodise & cast monkey metal copies of avanti antennas, much better made than the cte/sirio salut, performance was the same,

i hate cast or sintered monkey metal antenna parts(n) and bling don't mean a thing,

avanti puffing yes but no more than other cb antenna manufacturers past & present,

i think avanti used some artistic licence with the advertising, especially the image showing the astroplane beaming over obstructions,

they told us most radiation from prior art antennas comes from down around the radials but show typical 5/8 of the era that the astroplane was competing with for best signals under the fcc height restrictions,

that been said there is some advantage to raising current maxima higher above ground & obstructions compared to other antennas,

i think raising current maxima will give more of an advantage than will fiddling around with less resistive losses in your end-fed matching transformer /coil / hoop / trombone, especially when an extra 4ft puts current maxima above near bye obstructions,

the only disadvantage i see for the astroplane is for a given tip height the astroplane will always have a higher wind load on the support structure than a conventional antenna, and they look less easy on the eye,

i came to the conclusion that most of the differences people see with reasonably constructed antennas come not from the antenna design but from currents flowing on mast & feed-line skewing the pattern and local obstructions,

once you get rid of those with isolation & radials and height,
your left with matching efficiency and most important which antenna puts current maxima highest above ground,

i don't at this time believe ANY cb antenna maker builds a groundplane vertical that will out perform a 1/2wave dipole correctly isolated and installed at the same tip height as their super antennas, not that we would notice on the air.
 
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Thanks Bob. Very good description of this stuff.

Are you getting plenty of Apple pie these days?
 
bob85 said:
i don't at this time believe ANY cb antenna maker builds a groundplane vertical that will out perform a 1/2wave dipole correctly isolated and installed at the same tip height as their super antennas, not that we would notice on the air.
Click to expand...

BTW, My typical A/P model uses a radiator inside the bottom cone that is 197" inches long. I think DB has told us he has improved this length somewhere over 200" inches. I use 4" inches for the exposed insulator on my models, but I do that so the space clearly shows up in my antenna view images.

What length and diameter mast do you use, down from the mounting bracket at the feed point to your insulator?

How long is your exposed part of the insulator?

Just curious!
 
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I don't remember the exact length Eddie, its a two piece diy tellescopic mast,

top piece is 1.5" & extends about 2ft below the hoop,
bottom piece is 1 29/32" (48.3mm) x 7ft aluminum scaffold pole,
plus 4" of clamp extending below the tube,

at the time i figured it would be close to 1/2wave allowing for the fat tube and some detuning from been inside the other two conductors,

no idea how close i got to minimising mast & feedline currents but it works surprisingly well.
 
Well guys, it's been a few days and no response to my email. I'll give this more time.

I checked for a date in case this was an old ad. They said, at the bottom of their ad, they have been providing service for 79 years since 1941. So, it is up to date.
ES EN FR







+34 937 512 752 sales@tagra.net
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TERRESTRIAL
OMNI ANTENNA BASE CB 27 MHz
OMNIDIRECTIONAL BASE
BT-101
CB
BT-101 OMNI ANTENNA BASE CB 27 MHz
Type 5/8
Power 2000W
Gain 2 dBd (4,15 dBi)
Impedance 50 ohm
Material Aluminum
R.O.E - S.W.R - T.O.S 1,2:1
Type mounting Mast 0,025-0,060 m
Connector type UHF connector
Polarization Vertical
Wind load 180 km/h
Temperature from -40º to 55º
Adjust type Adjusted
Mastil diameter 0,030-0,045 m
Support Included
Length 6,68 m
Weight 1,60 kg

ES EN FR
Antenna made of high strength aluminum with anti-corrosive treatment.

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I thought tagra had gone out of business in the 80's Eddie,
not seen their cb antennas sold here since back then,

Their 2020 catalogue lists the bt101 @180 euro,
that is a crazy price, more expensive than any european vertical i can think of & it uses the least aluminium, you need a 1.5" mast adding more cost over alternative antennas,


old tagras did use thick wall tube better than sirio use & i guess anodising costs a few bucks extra but its just bling,
the joints are naked and do corrode like any other antenna.
 
I believe you, but the Adv that Jeff posted looks to be dated as current showing 2020 in the details I posted above.
 
The link won't work but i saw the tagra bracket on their website, it reminded me of the cte bracket you sent me, i don't remember what the old tagra bracket was like but the other parts were much better than cte used.
 
I doubt it Eddie, we voted for brexit ,

The latest advertising says nothing about a new larger version & the images look the same size antenna as the old one,

maybe Tagra advertsising folk just swapped height for length,

5/8 is the distance from the feedpoint down one leg, across the hoop and back up to the tip of the antenna, that would be a more likely source of the new measurement than my other idea including a 1/2wave mast,

i don't think a 5/8 wave tall version would give a good match to coax or perform well.
 

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