[DX] FS: Brand New Tennadyne T3.20M 20m Monobander

[Bill Tippett]

 > N0JR wrote:
 > > 3 driven elements optimally spaced at 9' on an 18' boom, gain in
 > excess of
 > 8dbd.

I wrote:
 >         Caveat emptor.  I don't believe Tennadyne's claim below of
 > 8.5 dBd (or 10.6 dBi) for an 18' boom on 20 meters.  Like most
 > things in life there are no free lunches (or magic) in antennas.
 > Gain is a direct function of boom length.  According to NEC
 > models, you need boom length of about 40' to achieve >8 dBd (or
 > 10.1 dBi) on 20m.  Claims like this are why ARRL doesn't accept
 > antenna advertising without specific reference to NEC modeling.
 > If Tennadyne is touting this sort of performance, I would be
 > highly suspicious of anything else they claim.  Remember the
 > Gotham vertical ads years ago?  Caveat emptor!
 >
 > http://www.tennadyne.com/specs&prices.htm


N0JR wrote:
 > There are no free lunches.  There are a lot of empty heads who know
 > othing of driven arrays, however.

         Jan, some empty heads believe anything they read.  I
suggest you read a little farther down to Tennadyne's own
fine print at the bottom of their webpage above:

"*These gain figures are fictitious, but since other antenna manufacturers tend
  to use them to manipulate things in their favor by enhancing their 
specifications
  with phony data, we've added them so that you can get accurate comparisons."

I just love the logic..."fictitious...so you can get accurate
comparisons".  Makes perfect sense to empty heads I suppose!
Of course Tennadyne ("Aluminum with a PhD") does not provide
NEC models for support since that actually WOULD provide an
accurate basis for comparison.

         Cal-AV is another driven array company whose specs I do
believe since they provide NEC models publicly:

2D-20A FULL-SIZE 20M BEAM - Two driven elements for 20 meters provide 
maximum bandwidth, and a front-to-rear ratio an S-unit better than 
2-element parasitic antennas. Pattern advantage over shortened (e.g. 
linear-loaded) parasitics is even greater. Heavy-duty construction provides 
years of reliable service. Patented integral balun-hairpin feed and 
hardware rated at 3KW. Gain, 6.5 dBi min; Front to rear, 20 dB min; VSWR, 
1.5:1 max; each over the entire band. Boom: 8.5 Ft. Turn radius: 18.5 ft. 
Weight: 38.5 lbs. Wind survival: 100 MPH no ice. Projected area: 4.7 SqFt.; 
Effective area (RS-222-C): 3.1 SqFt. Price $693 UPS shippable. 
<http://www.cal-av.com/2d-20.html>Specifications / 
<http://www.cal-av.com/2d-20-models.html>EZNEC Models / 
<http://www.cal-av.com/yagi-stress.html>Yagi-Stress Model

http://www.cal-av.com/antennas.html

         Based on Cal-AV's 6.5 dBi on a 8.5' boom, I estimate
Tennadyne's actual gain for a 18' boom is in the ballpark
of 8.6 dBi, not the 10.6 claimed in their self-admitted
"fictitious" advertising.  The Gotham Vertical Company's
advertising writers are alive and well.  Caveat Emptor.

                                                 73,  Bill  W4ZV