[OZAPRS] Newb HF questions ;)

[Terry Neumann]

G'day Damien,

Some random observations on your installation:

1)  You are seeing much more RF in the wrong places than you need to.   
Take heart, things can be better.
2)  The TEV-1 antenna is really intended to be fed with an ATU at the 
base of the antenna and by implication reasonably remote from the 
transceiver; this is essential if you want to use it as a multiband 
radiator.
3)  Such an ATU should ideally be designed to feed its output directly 
to the base (feed point) of the antenna, and a significant counterpoise 
or earth, without the confusion which coax cable of any length  can 
introduce.   The SGC 237 ATU which I use here manages this well .    The 
Icom AH-4 is a similar device intended  primarily for Icom transceivers 
(which somewhat limits the circumstances under which it can be used).   
4)  The AT - 897 is (I suggest) really not intended for the role you 
have asked of it.  It is intended to "fine tune" a match to an antenna 
which is substantially resonant at the desired frequency and is fed with 
a length of coaxial cable.   In this situation the location of the 
AT-897 is fine.   All of this suggests mono band antennas or a trapped 
antenna which provides a match somewhere in the 50 ohm area already at 
the desired frequency.   Wider mismatches are tolerable - provided your 
ATU has the range to match and the coax losses in such a "mismatch" are 
acceptable.    The  fixed length of the TEV-1 really stretches the 
friendship here if you want to use it on all bands.
5) The balun may actually make things worse in some bands rather than 
better - especially with an ATU which is already somewhat limited in its 
scope because it's intended for coaxial operation.

What to do ..................?

Essentially I think the problem is that the antenna and the ATU are not 
compatible.  The TEV-1 really has to be fed with an ATU at the base.  
There are some frequencies at which you may get a match with the present 
setup, but it's very hit and miss.  You really need a dedicate long wire 
tuner for this installation, unless you are prepared to experiment with 
the length of the TEV-1 to bring  it back to (ideally) a quarter 
wavelength in the band you are interested in.  In this situation the 
AT-897 should make a relatively easy match and I think your problems 
will largely disappear.   If you want to go all band, then a dedicated 
longwire ATU feeding the bottom of the TEV-1 - and the 
ground/earth/counterpoise system at the same point will probably have to 
be considered. 

I once used a 9 foot SS whip on the steel roof of one of my tractors for 
many years using and Icom AH-3 "long wire" ATU in the roof cavity.   
This was all done at 100 watts and I used to work all bands from 80 
metres to 10 metres without any RF problems affecting any other 
electronics in the installation.  The base of the antenna was only about 
1.5 metres from the transceiver and the ground plane for the antenna was 
primarily to roof of the tractor cab - about 1.2 metres x 1.6 metres in 
size.   Less than ideal, but it worked - astonishingly well at times.

My present home HF station is a 22 foot vertical - similar to the TEV-1 
but shorter and mounted against the colorbond fence as a 
ground/counterpoise.   I feed it with an SGC 237 ATU at the base of the 
antenna and the ground side of the atu is strapped to the fence.  The 
radio installation it the other end of about 25 metres of RG-213, but 
the antenna is about 7-8 metres in front of our TV antenna.   We get no 
TVI from operations on any of the bands used so far, nor any 
interference to any other equipment in the house apart from these 
blasted Altec Lansing computer speakers which are wide open RF 
collectors and especially offended on 40 metres, but also to GSM phone 
operation and our WDECT uniden phone system.  They (the Altec Lansing 
boxes) will be dealt with in time - with an axe if no better solution is 
found.

I've mentioned my own operations because they hopefully show that HF 
operations with antennas of the type you are using can be relatively 
free from hassles.   However Ray had it right when he mentioned early in 
his answer that you need to get all the RF to the antenna system.   
Anything which restricts this or impedes it puts RF energy where you 
don't want it, and that's what seems to happening in your installation 
at present.  I imagine that the transceiver is probably not enjoying the 
present situation either.

Take heart, it can be fixed. HF is not seriously different from VHF in 
the theory and practical aspects of antenna feed issues.   Have a good 
look around the WWW for antenna HF sites - Google is your friend here.   
Look through as much as you can, and you will get a picture of what 
needs to be done.  

Power line noise and other crud - ah well, that's a different situation 
and I too look for answers here too (sigh).

Best 73
Terry
VK5ATN

BTW I have three daughters - all arrived before radio experiments 
started.   I had been gliding for many years before the family arrived, 
and there are similar theories - probably all false - about pilots 
producing daughters.   My observations would say they there is no 
evidence to support either theory, but it makes for good bar discussion. 
              


 



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