AussieScanners.com.au

Hi Guys..

I am back to pick your brains again..

This weekend I have been setting up a 20' mast topped with a discone antenna (purchased from DSE 10 years ago) to erect from the highest point on my tile roof.

I plan on using RG213 and taking it through the roof space down into a wall socket.

What I want to know is...

1, Do I need to run a ground wire to the mast?

2, Can I also mount my TV antenna on this mast, or will they interfere with each other?

3, If I have to have the discone on it own mast, then how far away should it be from the TV mast to avoid interference?

4, I also want to set up an antenna for a uhf cb radio. Can the antenna for this be attached on the mast with the discone, or is it better to run a separate mast for that too, and if so, how far away from the others?

As always, I am very grateful for any advice you can give.

Hope your all having a good weekend (" ,)

With your discone, the same mast will be fine as typically you are receiving (I assume?)

If you are TXing, the proximity could be an issue however as you are only putting out 5W on UHF CBRS, again, this should be ok.

Only becomes a problem when you start getting into higher power or when the output freq is a multiple of the signal being received.

As for grounding, again u should be fine as only RX, however my suggestion is to always ground things when possible.

yeh agree mostly with phantom,but overall your setup should be ok.

All 3 services described above will co-exist happily on the one mast. Basically you can place your tv antenna at a low point (say 3-6foot from the top of the saddle/base) then just keep your discone on a stand-off around 3feet under the UHF vertical which would obviously be at the top. As UHF verticals radiate out (not down) it should not interfere with the scanner or TV reception, even at high power and the reduction of 4 foot will not make a noticeable difference to your scanner reception.

However as for the scanner coax, 213 is a waste of money. I have had EXCEPTIONAL results using quad-shield RG6 (like used for Austar/Foxtel) from my scanner antenna to my scanner. This is much cheaper and with the extra shielding is more functional imo.

tsunami wrote:
However as for the scanner coax, 213 is a waste of money. I have had EXCEPTIONAL results using quad-shield RG6 (like used for Austar/Foxtel) from my scanner antenna to my scanner. This is much cheaper and with the extra shielding is more functional imo.

I was told years ago to just use the RG6 by an ABC TV tech/ ham friend. He said even though it is 75 ohm it won't make a difference to the scanner receiving. Thats all I have ever used for my scanner and always received well.

tsunami wrote:All 3 services described above will co-exist happily on the one mast. Basically you can place your tv antenna at a low point (say 3-6foot from the top of the saddle/base) then just keep your discone on a stand-off around 3feet under the UHF vertical which would obviously be at the top. As UHF verticals radiate out (not down) it should not interfere with the scanner or TV reception, even at high power and the reduction of 4 foot will not make a noticeable difference to your scanner reception.

However as for the scanner coax, 213 is a waste of money. I have had EXCEPTIONAL results using quad-shield RG6 (like used for Austar/Foxtel) from my scanner antenna to my scanner. This is much cheaper and with the extra shielding is more functional imo.

Thanks Tsunami..

Your input I find very helpful. As for the 213, I already have 20 meters or so at my disposal, so I may as well use it up. Now I am just waiting on some guy wire to arrive before I can take this project any further.

Warm Regards!

Sounds good, use what you have already . As for guy wire, I use plain clothes line wire from Bunnings etc as I've found the coax is knackered well before the clothes line wire so every 5-10 years when fully setup I replace the coax and guys at the same time whilst the pole is down.

I have to actually get a roll of 213 here to setup my harness (3x verticals - 27ssb, vhf-h and uhf) which sit side by side about 3 foot from each other on top of the mast each feed with 213 and each about 25-30m in run length). I also need to pull my finger out and get a discone instead of using the tv antenna for the scanner (had a bandspanner at the last house but somehow lost it in the move ((( /cry as I've lost the other 2 bandspanners at the olds somewhere /cry some more). Of late I spend most of my time on VHF 150mhz with friends and UHF on ch5 due to the ID 10 T factor on cb now and the size of our areas VKG radio net.

I believe that 700mm is the min recommended separation by Benelec.

Using something like RG6 is ok on receive, mind you probably could get away with a piece of fence wire on receive, remember the original post said he wanted to tx UHF CB on it . I would not recommend using RG6 for any transmit purposes. Just use the 213 that you already have.

Actually if tuned right, 75ohm can be better for cb stuff. Co-phase harness' regularly use 75/79ohm and centre-fed wire dipoles often do.

It depends entirely on the antenna's resistance, most CB antenna are rated at 50 Ω and using 75 Ω cable creates a slight mismatch and ultimately a degree of loss, supporting this I once knew a fellow back in the late 80's who ran TV coax to his Station master base antenna while the SWR was manageable the TX/RX performance was significantly reduced, the poor attenuation/loss rating of the cable compared to the equivalent 50 Ω cable would have also contributed negatively.

Quality 75 Ω cable usage would have a barely negligible effect in an RX only application I guess however dissect some regular 75 Ω cable and you'll notice significantly fewer outer braid strands compared to what you'd see in an equivalent 50 Ω coaxial cable.