VK Logger Ham Radio Forum Archive

Hi All,
Was just wondering if anyone else has expreience this problem with a T-Box. Whenever I transmit the pitcure freezes. This does not affect any other TV in the house. I have earthed both radio & antenna, as well as placing ferrite cores on the power cord and antenna input to the T-Box, all to no avail. Any sugestions as to how to fix this interfence with giving up transmitting.

Eddie - VK2ZEJ

At what transmission frequency is this occurring, Eddie?

73,
Barry
VK3BJM

Hi Barry,

Happening on all HF bands, haven't tried higher ones, and with as little as 5w when running WSPR mode.

Eddie - VK2ZEJ

Hi Eddie.

OK - obviously you're running your TV antenna into the T-Box. What about the connection to your broadband service? Ethernet cables could look really attractive to HF, especially if it happened to be a really sexy multiple of our HF wavelengths. I have no idea what level - if any - filtering or immunity to HF the Ethernet input might have. Though I may be able to track down a suitable colleague at work to ask...

As for the TV antenna input - if it is the entrance point, I'd suggest using a High Pass Filter inline rather than a ferrite. If HF is coming down the inner of the coax straight into the T-Box, a ferrite won't achieve anything from outside the shield.

Incidentally, what frequencies are you local FTA channels on? Actually, when you say the picture freezes, could you clarify if it is the FTA channels freezing, or the channels via the broadband connection, or both?

I doubt that the connection to your screen - via the HDMI, component or composite video out would be a likely point of entry.

73,
Barry
VK3BJM

I have the same problem here with our TBox.
Happens on all HF bands and 2 meters down as far as 10w output.
Disconnect TBox TV is good even at 100w
Notices that every time I tx the wifi between router and TBox drops out as well

Adrian

VK4EDD wrote:Hi All,
Was just wondering if anyone else has expreience this problem with a T-Box. Whenever I transmit the pitcure freezes. This does not affect any other TV in the house. I have earthed both radio & antenna, as well as placing ferrite cores on the power cord and antenna input to the T-Box, all to no avail. Any suggestions as to how to fix this interference with out giving up transmitting.

Eddie - VK2ZEJ

More information would help . analogue or digital channels ( I assume digital) with sufficient signal , direct antenna connection (might need a suitable high pass), are cat5/6 cables shielded or acting as receivers .
If you have access to suitable monitoring equipment perhaps some checking and establish just what is actually happening or maybe a local Ham who can offer an opinion ?

Sometimes the addition of a metal shield box with feed throughs may be required
Your antenna may be down on signal or perhaps you have a preamp fitted which will often exacerbate the situation , if you have a scope take a look at things whilst on tx and let us know
Barry

Hi All,
Follow up on this post. Apart from place ferrite cores every where I also brought n "AMECO" high pass filter "HP-75T" from Milestone Technologies for $18 + postage. This eliminated any interference I had http://www.mtechnologies.com/ameco/othel.htm#hpass. Hope this may be of some assistance.

Eddie - VK4EDD (ex VK2ZEJ)

Excellent!

73,
Barry
VK3BJM

Hi Guys,

Thanks for the help in solving the same TBox TVI problem I was experiencing here from HF transmitting.
The two TV's in the house and a Topfield set top box exhibited no interference connected to the same antenna.
We are close to the TV translator, (1km line of sight) so TV signals are strong.

The TBox antenna here is fed from 75 ohm coax, so the 300 ohm HP filter mentioned was more difficult to utilise.

I found and built an excellently designed HP filter by G4WPW, available from his web site. It is a 75 ohm
Input and output circuit and isolates the shield of the coax as well. ("Braid Breaker")

Did the job well here, so this thread was much appreciated!

Ian