> Last night, just before dark, I put a TV balun, one of those cheapy,
> 6:1, 300 ohm balanced to 50 ohms unbalanced baluns at the end of my
> 700' balun...
Hi Doug,
I've been winterizing my Beverages lately--making them longer,
improving their feed and putting up new ones. I have gotten tired
of replacing balun matching components destroyed by lightning.
Because of that I recently made tests similar to what you're trying...
I connected a service monitor generator sending 1.8 MHz to the 75 ohm
side of TV baluns (note that they're 4:1 300/75 ohm) and connected a RF
voltmeter to the 300 ohm side. I tested 3 baluns and one Palomar unun
(UU-9). The two of the three baluns were cheaper similar looking
tubular baluns made by different manufacturers. Via ohmmeter tests
they appeared to be of an autotransformer design (low resistance from
primary to secondary leads). They had identical voltage readings
across their secondaries. A third balun (one made by RadioShack) had
no primary to secondary DC continuity. In fact it had no continuity
between the two secondary leads! It had about a 1/2 dB higher output
level at 1.8 MHz. [I admit to a pro-RadioShack bias being the owner
of a RadioShack franchise store and from having compared components
hidden inside of those and other baluns]. The UU-9 had a signifi-
cantly higher level on the high impedance side. However, it was
almost precisely in agreement with the difference in turns ratio
compared to the TV baluns. NOTE: These tests were flawed! I did
not take the extra minute to properly load the high impedance side
of these matching components. After the tests that followed I wish
that I would have...
I use 75 ohm Beverage feedline and figured that the 300 ohms from
a TV balun might be close enough (remember that the 4 times your 50
ohm coax = 200 ohms). So this weekend battling 50+ MPH winds I tried
one on a new 30 degree Beverage to northern Europe that has much
better isolation from my transmit verticals then my past ones to EU.
It was horribly insensitive with the RadioShack balun. I tried one
of the cheaper baluns. It probably had the same change as had
previously shown on the meter--I couldn't hear any on the receiver.
I tried some custom matching circuits that worked in the past--it
was better but still wasn't acceptable to me. I only had one option
left with what I had on hand--the Palomar unun. Its turn ratio was
more than I wanted for 75 ohm coax (x 9 = 675 ohms) but felt that it
was worth a try.
Happy days are here again! I then had an acceptable signal level!
I tested directivity with daytime high frequency AM broadcast stations
and it looked promising. The real test was on 160--reception of
Europe was good as well as its directivity (a W7 called me and he was
at the noise level--switching to another Beverage brought him well
above the noise level).
Monday I ordered four UU-6 ununs (1:6, 75:450 ohms)...
When my work is done my Beverages should be as follows:
Azimuth Length (ft)
8 885'
30 584'
43 380' (This zero ohm termination "Beverage" has helped
too often to change)
86 544'
140 584'
264 584+' (?)
323 885+' (?)
> ... that's sort of what mother nature did after the three foot snow
> storm of 10 days ago...
The same storm hit here and knocked out power for some people
in the area for up to a week and took down three of my four 80/40
meter directors towards Europe...
Good luck on 160, Doug! Hope that this helps...
73, Bill K0HA
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