Topband: High performance RX antenna at T6LG

[Arunas LY2IJ]

>>> The key component
here was the CAT 5 single twisted pair to feed the flag antenna without any
common mode noise pickup (it is necessary to strip the CAT5 and separate
each of the 4 pairs),
>>>


Hi,

Yes, T6LG hears really well.

I just wondering what is the reason to separate each of CAT5 pairs?

Why not use original outdoor CAT5(e) UV protected cable with other 3 pairs
floated
(or might be loaded with 100 ohms resistors from both ends for I don't
know what reason).


I used single ordinary CAT6 cable (200 m meters long) to feed 2 pairs of
temporary reversable

Beverages in IARU HF in 2011 (LY0HQ - 160 station)- every of 4 directions
via own pair in same not splitted cable.

Terminated near radio, transformers adjusted to 100 Ohm line.

Everything worked fine, I just forgot that cable in field after removing
temp installations - cows chewed it till I found it in
autumn.


"Worked fine" is not very scientific evalutation, but Greg ZL3IX helped to
decide with something real - Thank you Greg.
See his message with measurements below. CAT6 is better variation of CAT5,
so I had less loss and better crasstalk.

73 Arunas LY2IJ


:
>>Hi Arunas,

I have just run a test on a 200m length of cat5 cable.
I bought a 305m
reel for controlling the relays at my remote receiving site,
and only
needed 100 m of that.

I tested the cable using my N2PK VNA with the MyVNA software.
I took
the precaution of using a balun at each end of the cable, as the cat5
pairs are balanced
feeder, while the VNA is single-ended.  I checked the
transmission impedance before I started,
and found it to be 100 ohms, as
expected, so I connected two lots of two pairs in parallel,
to make two
50 ohm balanced lines.



The results are :- transmission loss 7.5 dB at 1.8 MHz, or just under 4
dB/100m.
Crosstalk -45 dB between the two lines.
For a 100m length you
could therefore expect the crosstalk to be around 50 dB down.
Thus it
seems that cat5 is a fair alternative to coax, although, as I said
before,
the difference in price is not that great, at least in ZL.
The
flooded RG6 I use, has a transmission loss of around 1.8 dB/100m.


I hope that is useful.

73,
Greg, ZL3IX