The TVI filter page and photo's
|As I live in a rural
area far away from
my local VHF and UHF TV services, we are what is generally called a
"Fringe area" viewer. To get a reasonable picture on the
TV system we had a Hills CA16 phased array for VHF and a long yagi for
UHF with a Hills masthead amp (did not use F connectors). While that all worked well we
still had many days each year where we would experience fade outs of
the VHF and UHF signals and end up watching DX stations from Victoria
After moving to a digital set top box (Bush Brand), then a Panasonic digital recorder (SD) we still experienced the fade outs on Digital but it is much more frustrating than the analouge system where you would get a snowy picture, digital just stops decoding :-(
During this entire time I have had to endure the "get off the radio as the TV is dropping out" especialy after a higher gain modern masthead amp was fitted recently, so the quest for a HAM proof TV system started. I had thought of going to a satelite service but you then loose the ability to record multiple programs from the free to air, something we like to do as we can then fast FWD through the adverts.
Aug 2011, time to bite the bullet, we have decomissioned the old Hills CA16 and yagi in favour of newer dedicated VHF and UHF digital optimised antennas, which is great as the VHF antenna has no real gain at lower frequencies creating a natural High Pass filter (I hoped) trouble is the mast head amp still gets swamped by the RF from my HF, 50 & 144 MHz signals so I need to stop that seeping into the VHF section of the mast head amp.
Okay, time for some filters, now do I build or can I find something that is already out there. I thought I would look for a commercial solution that might be already water proof and have the right connectors on it, also if I found a commercial product I could tell my neighbors to buy one and have it fitted by a trades person or handyman if they had problems. Then I did not have to become a production line for filter production.
My search turned up a few offerings from KingRay (GME) and not much from Hills (shame on you Hills) so I bought two different model from Kingray via an ebay supplier (cheaper and faster than the local stores it turns out).
The first one I tested turned out to be the best: KINGRAY FL3BPMH INTEFERENCE FILTER & COMBINER DIPLEXER, which is shown below and the subject of my tests.
The second one, a KINGRAY DPOLUHF DIPLEXER FILTER & ANTENNA COMBINER, did not offer much attenuation for 144Mhz signals which was of major interest to me, so I have not compiled any results for it. I will add some photos at a later date for completeness.
|Under test with its
die cast cover off. from left to
right are: "VHF-Low" - "VHF-Mid" - "VHF-UHF Combined" &
The small POT in the central region of the PCB sets the low frequency roll off and then adjusted provides an extra 15 - 20 dB of attenuation below 100 MHz and made be even happier when I followed the instructions and adjusted it fully anti-clockwise.
The slide switches define which of the input ports are active and how they are combined to create the output signal. The jumpers at the top set whether the FM trap is in or out. I have elected to leave it in so it can kill any 100MHz harmonics from my 50MHz transmitter.
|KingRay FL3BPHM, is what the nox says and so far I am all smiles with the tests I have made. At this point it is NOT in service but if it lives up to the plots shown below then I will be impressed.|
|Here is how
the filter attenuates for at 50MHz signal:
-45dBC now thats not to be sneezed at.
Scan start is 30 MHz, stop is 800 MHz on the tracking generator, insertion loss is quite good, come to think of it I did not actually measure it as I was so gob smacked with its resonse that attenuated all my frequencies of interest.
Later: I ran some further tests all the way down to 1.5 MHz and it just kept improving (higher attenuation) as I went lower in frequency, so yes its good for HF too.
|Here is how the filter attenuates for a 144MHz signal: -30.3dBC|
|Here is how the filter
attenuates for at 432MHz signal: -29.7 dBC|
That sharp dip above the marker poing is 477 MHz so if you have a UHF CB, it does extremely well there.
|Real life result: A few days after taking these measurements the filter was placed into operation with startling positive results, I now have not TVI problems when on any band from the shack. A big thumbs up from me for this one.|
|This web page was last edited on Monday, 5th Spetember 2011 by vk5pj|