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Interesting, did not know that. Any way of distinguishing via description, like with 50 ohm vs 75 ohm?

Picture showing the similarity between 50 Ω (bottom) and 75 Ω (top) Type N connectors
From wikipedia N connector - Wikipedia

The SMA connector employs a 1/4-inch diameter, 36-thread-per-inch threaded barrel. The male is equipped with a hex nut measuring 5/16 inch (0.3125 inch / 7.9 mm) across opposite flats, thus taking the same wrench as a #6 SAE hex nut.

Connectors mate using a ​3⁄8 in-32 unified extra fine (UNEF) thread.

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The characteristic impedance depends on the dimensions of the cable and the connector.

The impedance is usually displayed on a Bode plot and some RF parts will include one. This chart will plot characteristic impedance vs frequency.

There is a lot of things in RF are strange since any wires will pick up RF signals. The dimensions, length, and orientation of wires matter a lot.

Hey, thanks for the instructive reply. :grinning:

Now lets see if I got that right. The SMA F connector is the one eg the Flightaware ProStick, and the other F is the one from SAT cables? I feel they differ quite a lot in size, and I would not confuse the two at all, even if they are the same “type” of connector.

Combination of a 50 ohm cable with 75 ohm connector OR 75 ohm cable with 50 ohm connector is a case of stepped transmission line, cable forming one section, connector forming the other setion. The combined impedance of stepped transmission line depends on the ratio of lengths of the two sections. Since connector length is a fraction of length of the cable, resultant impedance is nearly same as that of the cable. Please see the calculation below which I have prepared in 2016, showing resultant impedance of a 75 ohm RG6 cable connecting 50 ohm mcx connector of generic DVB-T is 74.13 ohms, almost that of the RG6 cable alone.


So what im taking from this is that if i use a 75ohm connector with RG6 it shouldn’t make too much of a difference?

RG6 is 75Ω, so a 75Ω connector is ideal.

It should not be an issue, especially in receive only mode. If using a long coax run, make sure the coax is good quality. If you don’t plan on re-terminating the coax, go with quad shield.

I use all that (RG-6 75 Ohms coax, F connectors, adapters) in transmit, and do not see a difference.

There will be negligible difference as far as impedance matching is concerned.

There will be BIG difference as far as electrical continuity is concerned. The pin of 75 ohm N-male connector is thinner than the hole of 50 ohm N-female connector of antenna. It will result in no connection or loose connection.

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Put aluminum foil inside the N female plug to ensure contact. :grinning:

In my case, the N to SMA adaptor is likely 75 Ohms (I have not checked it, as it’s going gangbusters now, and I don’t want to touch it). Since the FA antenna is 50 Ohms, loosening up the connector should not have ‘fixed’ the problem.

Any guesses?

When I got the FA Antenna, I did not have a proper adaptor N-male to F-female.
I did not want to wait for a week for delivery of the connector I ordered on Amazon, and tested antenna by connecting RG6 to FA antenna like this :rofl:

. . . .


When there is a will, there is a way.:grin:

So the FA Antenna is 50 ohms but the tuner inside Pro Plus is 75 ohms?

ProStick is generic DVB-T + RF Amplifier
ProStick Plus is generic DVB-T + RF Amplifier + SAW Filter

Below is the schematic diagram of a Generic DVB-T
The input impedance 75 ohm is written in green color (the left arrow points to it).


So 75 ohm cable should be used… ?

Mixing 75 ohm and 50 ohm results in mismatch loss of 0.177 dB. This is so small that making effort to eliminate it by “all 75 ohm system” or “all 50 ohm system” is not worth.

Mix 75 ohm with 50 ohm wherever it is convenient to you, dont worry, be happy, and smile.

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Quote from an old thread :rofl:

I just received my FA Antenna from Amazon, i just bought a N type to F connector from Jaycar so i have no idea if it is 75 or 50 ohm. I did however order a N type connector from GPIO Aus for the FA Antenna but it has sma cable and as such didn’t think to use it. Should i just go and get a sma 5 meter cable for direct connection to the FA pro plus dongle or just go with the Jaycar N type and RG6?

As you already have N-male to F-female adaptor, you can connect RG6 to FA antenna.

How will you connect RG6 to FA Pro Plus dongle which has SMA-female connector? You will need an F-female to SMA-male adapter to do this.

This is my setup using
(1) N-male to F-female adapter at FA Antenna
(2) RG6 coax with F-male screw-on connectors at both ends.
(3) F-female to SMA -male pigtaile at ProStick dongle end

Close-up of connections


Full view of setup

As @abcd567 and others have shown and discussed. There are the electric and mechanical parts to this ‘story’.

Do not/not worry about the impedance mismatch of the cable (electric part). The only concern is the mechanical part, as the plugs, depending on the impedance version, have different dimensions, even though they may appear the same to a quick look.

Again, use any good quality coax, 50 or 75 Ohms does not matter. Use the correct plug for the socket, that is, they must be the same. Both 50 Ohms or both 75 Ohms, no/no mix and match.

There is nothing wrong with using a 75 Ohms plug on 50 Ohms coax or vice-versa. Only the plug, and the socket, must be the same impedance version.

Good quality 75 Ohms coax (RG-6) is plentiful and cheap. This is the cable/satellite TV coax. Not the case with 50 Ohms. Try finding 50 Ohms coax at Walmart.:grin:

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