[TenTec] swr

[Dr. Gerald N. Johnson]

On 8/16/2010 11:14 PM, Richards wrote:
>
>
> On 8/16/2010 10:22 PM, Dr. Gerald N. Johnson wrote:
>
>>
>> Likely the loss in most tuners feeding the 43' vertical through a short
>> coax is a lot more than 50% (3 dB) probably more like 90% (10 dB).
>>
>
> Yes, this comports with conclusions stated in
> the much of the literature on the matter.
>
> Oddly enough, this big stick vertical monopole has
> proven itself a very quiet, solid RECEIVING antenna
> for both ham and general SWL purposes. I am lucky
> in that I do not suffer from excessive or increased
> QRM-EMI-RFI type noise as is usually associated with
> vertical antennas. Also, it seems to work quite
> well on 80 meters (especially for AM mode) and
> on 40 and 20 meters quite well, indeed.

On HF the atmospheric noise is so high that 99% loss in the tuner with 
most receivers (other than a very simple direct conversion radio or a 
crystal set) are limited by atmospheric noise, not receiver noise. The 
Beverage is one of those very low efficiency antennas but its 
directivity makes up for the few percent efficiency. You wouldn't 
transmit with a Beverege though.
>
> My take, is that asking this to do fully service on ALL
> the major HF bands is asking too much of it. I am
> happy just getting a reasonable signal out on 160
> and on bands higher than 20. It does a lot in a little
> space and without a large footprint and without
> a big visual impact. The wife has no objection and
> I am sure an 80 foot tower, with a big yagi beam,
> and several low band dipoles would be way less
> accepted. Not the best antenna, but not an
> altogether bad one, either. It certainly is cost-
> effective.

Well, its cost effective IF you make it yourself, the commercial ones 
are not so cost effective.

It requires a robust tuner, or adding proper loading coils for 80 and 
160. For some 20 or 25 years I had an 80 meter double extended Zepp up 
at the house I'm moving from. A mere 326 feet long with various 
feedlines over the years, but its two x 5/8 wave on 80 meters. Not 
resonant on any band, but my 160 to 20 meter tuner is made of a coil 
from a 5KW BC matching box, made of 1/4" wide edgewound copper and 
adequately spaced air variable capacitors that will carry all the 
current I've ever been able to produce, even with a 200 watt amp key 
down on a shorted sample of transmission line. When I switched it to 
parallel tuned to check the high voltage capability of that particular 
transmission line, I had to add corona knobs to the open end of the 
transmission line to hold the discharge. Its a ROBUST tuner twice as big 
and more versatile than the KW Johnson Matchbox, though I called this 
one my Johnson Matchbox being that it was built by A Johnson and can be 
used either series or parallel tuned with any number of turns on the 
antenna side in the link coupled scheme.

I built separate (and mostly compact) tuners for 15, 10, 6, and 2m. It 
worked well as a 6m and 2m SSB/CW contest antenna though not as good on 
2m as a yagi 33 feet long that I had up most recently.

Were I to build a tuner for the 43 foot vertical, I would use different 
circuits for 160 and 80 than for the higher bands. On 160 and 80 its 
known to need a loading coil, so I would likely use an L network, with 
the L towards the antenna (and like working the 8' whip on my little 
Airstream) mounted very close to the antenna. The auto tuner does that 
in its wisdom but the coil and switches are not robust enough to handle 
the PA and the obnoxious load of the unloaded vertical. The tapped 
loading coil that goes to ground is a valid almost tuner, though it 
would be more versatile if it had some variable tuning to resonate the 
loaded vertical at any desired frequency IN the 160 and 80 meter bands. 
The 43 foot vertical has decent enough impedances though nearly always 
reactive at the higher bands that a typical tuner can handle it. Once it 
gets more than 5/8 wave tall the radiation angle is high and its not all 
that great for getting out, warming the sky on 10m doesn't work DX.

At the commercial prices its not a good replacement for a trap vertical, 
and its upper HF performance is poorer than the trap vertical.

On my Airstream (with that 8' whip in the middle of the roof, but 
removed for travel) my present L match works on 40 through 15, has too 
much strays for 10 and 6 but not enough C for 80. I've worked DX with it 
on 20m, FD with it on 10 through 40 (several times alone and as part of 
a club setup) and made contacts on CW about as fast as I could keep a 
paper log while running 25 watts to save the battery.

If the subject vertical was 33 feet instead of 43 feet tall, it would 
present nice impedances on 40 and 15 meters (though it would have that 
high radiation angle on 15 and shorter wavelength bands), a bit more 
obnoxious impedances (lower R, higher reactance than the 43 foot) on 80 
and 160, and obscenely high resistive on 20 and 10 meters. Fed through 
the right length of 300 or 400 ohm feedline (an odd multiple of a 
quarter wave on each of those bands) the impedance would tune OK, or a 
robust manual tuner at the base in parallel connection would tune on 
those two bands. The 43 foot length keeps away from the high impedances 
on most all bands at the cost of being reactive everywhere.
>
>
>> You do have to adjust that coax transformer's length depending on the
>> velocity factor of the coax that depends on the insulation density if
>> foamed.
>
> Agreed.
>
>
> THANK YOU FOR THE ADDITIONAL GLOSS IN ANSWER TO MY QUESTIONS.
>
> ================================ JHR =========================
>
The 43 foot vertical is like half the 80 foot centerfed I used a few 
years, beginning in a location where that reached from the front edge of 
the roof over a mast and then to the back yard back fence. With the 
robust tuner it worked multiple bands and at three subsequent locations 
where I didn't take the time to lengthen it to a half wave for 80 and it 
still fit within the yard. Then I put up the double extended zepp.

Now I'm at a more permanent location (having paid rent 40 years where 
the double extended zepp fit) that has more room and I'm figuring on a 
160 meter half wave with tuned feeders as my first antenna expecting to 
use it up through 2meters and maybe 432 where I did build a tuner in the 
past but never got around to using it having some sort of yagi on hand I 
could sort of toss up for band openings. In this county there are no 
rules so I can put up whatever I want and I will, in time.

73, Jerry, K0CQ