VK Logger Ham Radio Forum Archive

I am thinking of using a single heliax feed line with triplexers at each end to feed my 6m, 2, and 70cm antennas, (or maybe the 2m, 70cm and 23cm antennas) to save weight and reduce clutter on my lightweight antenna mast.

I would be very interested to know if others are using such a system and whether the saving in weight would be cancelled out by increased losses.

I would also be interested min what brand of triplexer you are using, especially at the antenna end because of weather proofing issues. I have used such a system before using Comet triplexers which are not designed for outdoor use.

73

Wayne VK4WDM

Hi Wayne,
I have a similar project underway here, I have a pair of Omni loops (Par Omni Angles) for 50MHz and another pair for 144MHz that are nested on the same pole off the side of my tower and a limited number of coax runs that all go underground to the shack. I have a commercial Diplexer (Diamond brand) that is also not rated for outdoor use but have bought an old saucepan from the local second hand store to use as a cover for the Diplexer, with a 90 degree elbow on the fixed line so it will sit under the saucepan without a nasty kink in the coax.

My logic is that it only needs to keep direct moisture off of the case so the old ali saucepan will be mounted inverted with the Diplexer Velcro'd to its underside, this should keep it dry and provide free drainage for any condensation.

At the shack end I will have the opposite to split to the radio's for each band. It may sound complex but easier than digging a new trench for more coax runs (existing conduits are full)

Good luck with yours..

Regards,

I just checked the cost of triplexers - about $150 each in VK so I might have to look at running three separate lines after all.

73

Wayne VK4WDM

Hello Wayne
In a previous life, I had one run of Heliax on my tower, with a triplexer at each end for 10, 6, and 2M. I made my own triplexers from designs on the web (there are many).
You need good quality ceramic trimmers, capable of handling your output power (and more... the "fudge" factor). I found my trimmers in old 'valve' type VHF transceivers (STC I think).
With a reasonable sig gen, quite good results are achievable, after all, they are only 3 band tuned filters.

73 Bruce VK2EM

Hi Bruce (and Barry VK4TI)

Thank you for the suggestion but I not in the situation to do much in the way of home brewing atm due to trouble with my hands. Have to go commercially built. I am getting some prices from triplexers from the USA. If still to expensive I will go with separate lines lines.

73

Wayne VK4WDM

Wayne,

The commercial triplexers you are after are:

(1) Comet CFX 514 models
(2) Diamond MX2000 models

Both brands have a Low Band (which includes 6Mx), a mid band (which includes 2mx) and a high band (which includes 70 cm)

Prices are around the US$70 to US$80 mark.

HRO and DX Engineering will export to Australia - Universal Radio won't (but you can use a US forwarding agent)

Locally, you'll pay about A$150 for them.

BUT DON"T UNDERESTIMATE THE BUYING POWER OF EBAY - I have picked up a number of various diplexers and triplexers on Ebay for around the US$40 mark - the secret is in knowing exactly what you want!

Good luck

Cheers

Peter VK3QI

Hi Peter

Thanks for the info. I am having a good look around.

73

Wayne VK4WDM

Hi Wayne,

I used a commercially made triplexer a number of years ago with good results however the unit as supplied had RG58 flyleads with PL259 plugs which added somewhat to the overall cabling losses. Much later I fitted BNC sockets for the output and an N connector for the input and in the process was able to have a good look at the construction. Although rated at 800watts PEP the small ceramic caps. used would have struggled under a high SWR situation which can occur by accident at the most inconvenient of times. Waterproofing with a small plastic box was all that was needed.

The unit is now used for portable work where power levels never exceed 50 watts PEP.

The homebrew route using robust components might be the better way to go if you are planning QRO operation.

Cheers,
Rob
VK3MQ

I just looked up the insertion losses of some of these Triplexors and Diplexors and the figures look much lower than I would expect. Has anyone actually measured the losses x 2 (If there is one at either end) I am sure the additional connector loss alone would exceed the rated losses I googled? Maybe its a bit like antenna gain, the figures are purposely misleading. Seperate feedlines has to be much better although possibly more expensive, especially if quality feedlines (Mandatory on VHF/UHF) such as Heliax is utilised.

Hi Tony

In my case it is not so much the cost of the heliax, its the weight of the feed lines I am trying to save on. My system consists of a light weight tilt-over mast that a semi-geriatric like me can easily raise and lower in a very short time. This not going to be a world-beating station so I am happy to put up with a bit of connector loss for the sake of convenience

73

Wayne VK4WDM