[OZAPRS] Newb HF questions ;)

Tue May 19 16:40:14 EST 2009

Howdy Folks,

So I've *finally* unpacked all my gear from their boxes, fixed a few  
faults (seems a dry joint on the output DIN socket was why the old MFJ  
running the vk1 igate went silent), and thought I was ready to play  
APRS on HF..  But it seems not..  After doing a lot of playing about  
with the help of an immensely more RF-knowledgable colleague, I've  
come to realise that I live in a pretty horrid area to be trying to do  
anything RF-related in, but I'm going to try and struggle through that..

Backstory - when we shifted here from 10km down the road, we had to  
replace our 900mhz cordless phone with a 5.8ghz DECT setup, as the  
mains hum on the old one was pretty horrid..  When we got a baby  
monitor earlier this year (yep, I added to the pool of hams with girl  
children.. seriously, does ANYONE in our hobby have boys?!?), we had  
to replace that with a DECT unit, as that was absolutely horrid..  and  
then that DECT unit had to be replaced with one from a different  
manufacturer, as even IT had 50hz mains hum..  I actually spoke to the  
bloke that designed the DECT one we had problems with, and he was  
pretty concerned, as he figured the only place it'd be getting in was  
actual mains proximity to the receiver.. - but it was doing it in the  
carpark at the local shopping centre!  But stopped 10km down the  
road..  APRS on my D7 is completely deaf, even though RAG hears me  
fine, and my FT8100R with a 9db colinear on the roof of the shed can  
hear it and RAG fine - but get more than a block or two away with the  
D7, and the 8100 no longer hears it even at 5W output!?

Anyway, back to my problems, and questions. If there's a list more  
appropriate, PLEASE point me at it ;)  This is just the only ham- 
related list I'm on (apart from the APRS admin list..)

So I'm finally setup - the FT8100R with a 2/70 9/6db mobile antenna  
(used to be on my luxie) mounted above the roof of the shed (http://photos-a.ak.fbcdn.net/photos-ak-sf2p/v646/250/124/506862762/n506862762_1735424_1072471.jpg 
).  And an FT-897 with an LDG AT-897 feeding RG-58U (couldn't see any  
point running LMR-400 for an 8-meter run on HF..?) to a TEV-1 (8.5m  
aluminium vertical ) via a 4:1 balun (http://photos-f.ak.fbcdn.net/photos-ak-sf2p/v646/250/124/506862762/n506862762_1735429_1155875.jpg 
). (There's been three radials added since that shot - 120 degrees  
apart, at around 40 degrees down, grounded at the ends, and bonded to  
the 'radials' point on the antenna end)
The pole the TEV-1 is mounted on is rammed about 20cm into the ground  
at the base, and is touching the shed roof about 50cm below the base  
of the antenna - not sure on whether I should be insulating that point  
or earthing it, or leaving it as is?

The shed is thin steel sheet, and is earthed both to the AC earth, and  
via a 1m steel rod driven 90cm into the ground (seriously, have you  
seen the cost of copper clad earth rods recently?!?), with 5mm steel  
cable (I have *so* much of the clear plastic-covered 5mm steel cable  
left over from old microwave link installs, and it fits perfectly into  
5mm crimp connectors ;) ) to the frame of the shed.  There's also a  
run of cable bolted from the frame of the shed to the -ve terminal of  
the 60A 12V supply, and to the gnd connection on the back of the FT-897.

So anyway, apart from having S8-9 noise below 18Mhz, which I'm just  
going to try to work around, I'm fairly sure there's something not  
right in my setup.. - Any time I hit TX below 20Mz, my USB mouse turns  
itself off (has to unplugged and re-plugged), my two LCD monitors go  
wavey (like old crt's would when you hit tx with a handheld near  
them..), and all the serial ports into the pc in the shed start having  
random crap appear on them..  Since I'm seeing the meter movements in  
my SWR meters (neither of which are plugged into anything at the  
moment, though are powered up..) are coming up to about 1/2 a watt, I  
got to and pluged a probe into the cro, and attached a metre of wire  
to the tip.. -  I'm seeing 1V p-p of signal (tx'ing on am, a nice  
clean sinewave at the tx frequency) inside the shed, which I wouldn't  
normally expect, especially with the shed frame (and it's a completely  
steel shed..) being grounded? I would have thought that with the case  
of the 897 grounded, an the antenna tuner bolted to the 897, there  
shouldn't be any radio signal anywhere but the coax, and that  
shouldn't be radiating??  Plugging the 2m/70cm antenna's cable  
straight into the cro, I see 5v P-P, but that's outside the shed, so  
I'd kinda expect that..

SO.. After that extremely long blurb, does anyone have any thoughts?  
*should* I be seeing that much RF inside the shed?  If not, where  
should I look next?  Is it worth reaming a hole in the shed wall, and  
make up a run of LMR-400?  I wouldn't have thought that the RG58 would  
be an issue, but maybe?  Or should the majority of the coax run be  
outside the shed, rather than inside? (again though, I wouldn't have  
thought the coax would be radiating?)

Thanks!

Damien

Damien Gardner Jnr
VK2TDG. Dip EE. GradIEAust
rendrag at rendrag.net -  http://www.rendrag.net/
--
We rode on the winds of the rising storm,
  We ran to the sounds of thunder.
We danced among the lightning bolts,
  and tore the world asunder

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