Bob,
While determining that your rig can match a non-resonant antenna and thus
transfer some power to it, this discussion fails to address the question of
antenna efficiency and relative field strength of the radiated signal. Coaxial
cable is extremely lossy when the SWR on the coax line (which does not change
regardless of what your internal antenna tuner is doing) is above 3:1. Thus, it
will not be delivering significant power to the antenna on non-resonant
frequencies.
Thus, the best advice we should be providing is to recommend the use of
resonant antennas when coax is the feed line of choice. If the installation can
accommodate the use of either ladder line or open wire feed line, then a
non-resonant multi-band dipole can be used with a wide range tuner located at
the rig with minimal feed line loss in spite of the high SWR seen on the
non-resonant frequencies.
73
Dave,K2DP
Sent from my iPad
On Feb 7, 2013, at 2:38 PM, "Bob McGraw - K4TAX" <RMcGraw@Blomand.net> wrote:
> At risk of stirring the proverbial pot on this subject, I launched into a
> morning project of seeing what the internal ATU would handle and investigate
> if anything could be done to explain why some get better results than others.
>
> The antenna used for this test is a center fed 75M dipole some 50 ft high and
> having a natural resonance at 3.8 MHz. Center feedpoint has a 1:1 current
> balun and the feedline is some 75 ft of RG-213. The output of the radio is
> connected to a to a suitable cross needle SWR/Power meter via a 1 ft RG-8x
> jumper. The antenna side of the SWR/Power meter is connected to a Current
> Isolator or UNUN being a product from The Wireman item # 8232. This is
> basically a coax jumper of some 3 ft in length fitted with a series of #73
> and #43 beads. This jumper is connected via a barrel connector to the RG-213
> feeding the antenna.
>
> It is noted after the initial test and repeating same for reliability, I
> found the removal of the Current Isolator between the SWR/Power meter and the
> coax to the antenna did cause some noticeable to very large errors in the
> value displayed on the external SWR/Power meter. Thus the value indicated on
> this meter were affected by circulating current on the coax feed line. This
> is not surprising. I have had some suspicion that these circulating currents
> may have some effect on the performance of the internal ATU as well. A
> point not of concern was the time required to attain a match as I only check
> one frequency on each band.
>
> The values shown below are:
> Band.......Frequency........SWR as shown on the radio.........SWR value as
> shown on the external bridge with the Current Isolator in place
>
> These values are using the Eagle with its internal tuner:
> 160M..........1942.......No Match......>10:1
> 75M............3900.......1:1...................4:1
> 60M............5357.......1.5:1................8:1
> 40M............7100.......No Match......>10:1
> 30M...........10114.......1:1.................10:1
> 20M...........14325......No Match......>10:1
> 17M...........18135.......1:1................ 10:1
> 15M...........21290.......1.2:1................5:1
> 12M...........24995.......1.5:1................5:1
> 10M...........28402.......1:1...................4:1
>
> These values are using the Omni VII with its internal tuner:
> 160M..........1942........No Match........>10:1
> 75M............3900........1.1:1..................4:1
> 60M............5357........1.5:1..................8:1
> 40M............7100........No match.......>10:1
> 30M...........10114........1.1:1...............10:1
> 20M...........14325........2.5:1.............>10:1
> 17M...........18135........1.1:1...............10:1
> 15M...........21290........1.2:1.................5:1
> 12M...........24995........1.4:1.................5:1
> 10M...........28402........1.5:1.................4:1
>
> So what am I to conclude? The Eagle ATU matched 7 out of 10 bands and the
> Omni VII ATU matched 8 out of 10 bands. And the use of the Current Choke or
> line isolator does make a difference. I did go back and re-test on 20M and
> have no explaination for the difference observed between the two radios using
> the same procedure and equipment for measurements.
>
> {I hope these tables stay in alignment}
>
>
> 73
> Bob, K4TAX
>
>
> DISCLOSURE:
> This is to inform all persons, I am a Tentec Ambassador and I receive
> compensation according to the Tentec Ambassador program. In addition, I
> serve as a volunteer beta test person to Tentec for the Omni VII, Eagle and
> Argonaut VI radios. I hold no employment relationship, no financial
> interests nor do I conduct any commercial business, direct or indirect, with
> Tentec.
>
>
>
>
>
>
>
>
>
>
> .
>
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