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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