Power divider

[3M amateur]

Hi,
Is there anyone who has built a power divider and who can say what measures it should have.
Has built a rectangular aluminum tube with outer dimensions of 25mm and a copper tube 10mm and length is approximately 85cm. Will work on the lower portion of the FM band.
But I have too high SWR and if I run each dipole for so I have zero SWR as the dipoles are properly tuned and that these are broadband antennas, which are factory-made. Thanks in advance.

[3M amateur]

So here I mounted my dipoles.

[Albert H]

You can't test that antenna so close to the ground! The lower dipole needs to be at least 4½m off the ground. Your SWR will be abysmal with it that close to the ground, and if you do manage to match it, it'll be wrong when you put it at height.

[Spokes]

Like Albert says get them a lot higher off the floor for the matching at home, secondly have you measured the SWR of each aerial individually and checked they are like for like?

Next the divider...do you have an antenna analyser or just a SWR meter? If you have an analyser cut 2 pieces of 50ohm coax identical in length, put a PL259 or N depending on what suits your splitter on the end of each then on the other end of each place 2 100ohm resistors in parallel, this will give you a 50 ohm match probably around the 1/2 a watt mark to get a reading of SWR and impedance. If the SWR is high on the splitter then there will only ever be an equal reading when all connected together. For example if I make 2 identical dipoles with a reading of 1.0 SWR and 50ohm impedance and a splitter that matches at 1.3 SWR and 46 ohm impedance then once my dipoles that match 100% on the button are connected through this divider my new reading will match 1.3 - 46 ohm!
I would say to get optimum performance from your splitter you make need a wider gauge of square tube and maybe step up to 15mm on the copper pipe, it's more about the distance in space rather than length when building these kind of units.

Now the next thing that may help you out is what sort of power will you be running through the splitter? If it's not major power just go down the coax splitter route with gives minimal loss if built correctly which you will give you an easier life trying to match the feedline!

[3M amateur]

Hi,

I use a watt meter is a Bird model 43 so I see that both dipoles are properly tuned and these are broadband so you can change the frequency, both up and down within a specific area without getting any rash on the standing wave.
I've tried using 2 coaxer 75 ohm and 50 ohm which I have linked between the dipoles feeder and the 75 ohm is cut to 1/4 of the wavelength but get the same results. 10 watts and 1.5 watts out of the SWR. And at 100 watts so there will be 15 watts in the standing wave.

Have a rectangular aluminum tubes 40x40x2 mm and has a copper pipe of 12 mm and 15 mm, figured 15mm tube could work out or what do you say about that?

[Spokes]

In short...if the dipoles are performing correctly the splitter is drastically wrong, the impedance is probably way off and the SWR measurement sounds like a terrible match I would try use a wider gauge of square tube maybe a inch and half. 15mm normally works fine I've never tried with something different so can't fully comment on the 10mm stuff but you need to open up the distance...trust me mate these are fucking headache to get right

[Albert H]

You need an absolute minimum of ¼-wavelength between the dipole tips. Don't ever believe that the dipoles are "broadband". They will have a specific resonant frequency at which they work best. Loop dipoles will work OK over about 3 MHz, but simple dipoles are usually more specific than that.

[s2000]

Wow looks like a load of hassle all that! Why not build a slim jim instead?, I can usually build a fairly good one in a few hours with 3dB gain. No complicated setting up either.

[3M amateur]

Updating this thread. I have now tried to raise the dipoles in a tree and had more than 5 meters from the ground and there was no change. Even tried to make a new power splitter / divider with a rectangular pipes on 40x40x2mm bearings, inner tube of 15mm copper pipe and standing wave was still too high. Returned to the former which was 25x25x2 and a 10mm copper pipe and standing wave dropped to 1.5-2 Watt and I tried to connect a 75 Ohm coaxial cable, and then it dropped slightly to 1 Watt.
Then took a RG62 is at 93 ohms and cut it to a 1/4 wavelength and is now standing wave down to 0.5 watts and the output power is about 25 watts.
I have also tried to increase the distance between the dipoles so it is now 1/4 the wavelength between antennas solid noticed no difference if I increase or decrease the distance.
93 Ohm cable seems to make all the difference and I think it makes some sort of phase shift of antenna signal if I have interpreted this right, correct me if I'm wrong.

[3M amateur]

Like Albert says get them a lot higher off the floor for the matching at home, secondly have you measured the SWR of each aerial individually and checked they are like for like?

Next the divider...do you have an antenna analyser or just a SWR meter? If you have an analyser cut 2 pieces of 50ohm coax identical in length, put a PL259 or N depending on what suits your splitter on the end of each then on the other end of each place 2 100ohm resistors in parallel, this will give you a 50 ohm match probably around the 1/2 a watt mark to get a reading of SWR and impedance. If the SWR is high on the splitter then there will only ever be an equal reading when all connected together. For example if I make 2 identical dipoles with a reading of 1.0 SWR and 50ohm impedance and a splitter that matches at 1.3 SWR and 46 ohm impedance then once my dipoles that match 100% on the button are connected through this divider my new reading will match 1.3 - 46 ohm!
I would say to get optimum performance from your splitter you make need a wider gauge of square tube and maybe step up to 15mm on the copper pipe, it's more about the distance in space rather than length when building these kind of units.

Now the next thing that may help you out is what sort of power will you be running through the splitter? If it's not major power just go down the coax splitter route with gives minimal loss if built correctly which you will give you an easier life trying to match the feedline!

I'll run with 100 Watt that I have built before, with two stacked dipoles, I will have an ERP of more than 200 watts.

[pjeva]

No, two antennas will not give you doubled power. It would be too easy that way



Sent from my iPhone using Tapatalk

[Albert H]

A twin stack - correctly matched - will give you close to double the ERP that you'd get from a single dipole. It also puts more of the energy where you want it - less is radiated in useless directions.

[Spokes]

A twin stack - correctly matched - will give you close to double the ERP that you'd get from a single dipole. It also puts more of the energy where you want it - less is radiated in useless directions.

But not with a match like this one, this is sounding like you'd be better off putting up a single dipole!

[Undercover Neckz]

It might help to put it at the top of the tree and not the bottom.