Author Topic: Alternative PCB Dipole Designs (433, 868, and 915MHz)  (Read 354675 times)

CarlyAzuma

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #60 on: August 28, 2020, 02:00:50 PM »
Hello...the input impedance of a short dipole will be capacitive in series with a small radiation resistance. There's no basic difference between printed and discrete wire design. In a printed dipole design, you may want to integrate a matching network on the PCB. Because the room is apparently limited, this should be imagined as a lumped network.

Slople

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #61 on: October 15, 2020, 07:27:23 AM »
I am not able to order from pcbs.io - I wanted to order the 433mhz-version and tune it to 868, but no luck. There's always a payment-error on the page, no matter if I use PayPal or CC.
I need to connect the antenna using a u.fl to my transceiver, but my friends antenna analyzer has an SMA-connector I suppose. Is the right way to do this to solder the coax-cable with u.fl to then antenna and connect it via an adapter to the analyzer? Do we need to compensate for the extra length of the adapter to be precise?

john k2ox

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Re: Alternative PCB Dipole Designs (433, 868, and 915MHz)
« Reply #62 on: May 06, 2021, 12:21:13 AM »
Glad to see all the thoughtful discussion here. 

I would like to say a few things about transmission lines.  If you have an infinitely long transmission line (feed line) any energy you put into it will propagate down the line never to return, zero reflected.  That is because the line just ahead of the wave has the same impedance as the impedance where the wave is. It is 'matched'. It has Z0 impedance, typically 50 ohms. 

Another solution that mimics the infinitely long line is to terminate the line with a Z0 impedance (50 ohms). That termination can consist of a resistor or more useful a resonant antenna.  Notice that a transmission line with a Z0 termination results in no reflected power irrespective of the line length!   

As it turns out there are three cases that describe transmission line behavior without messy complex math.  A shorted termination, an open, and the Z0 termination just described.  The short and open are useless for moving power as it yields 100% reflection. No power exits the far end.  The main goal here is to move the power from one end of the cable to the other end with minimal loss and that results with a Z0 load.

Transmission lines with non Z0 terminations will result in a range of impedances at the input simply by changing its length!  This is an advanced topic.  When the line is terminated with Z0 the impedance at the input is, once again, is Z0 independent of the length!  That is good news indeed and simplifies our lives.

If you want long range put your antenna as high as you can, ideally in the open.  There is loss in the cable and the longer it is the more loss.  This is usually offset by the signal gain due to height.  Just look at cellular towers.