Connecting bare wire to SMA?

[SpaceForceCmdr]

Right now, I have a random wire connected to my SMA feed line via gator clips. The wire is actually clipped to a whip, which has an SMA out, and that goes to the feed line. I'm wondering if it'd make any difference if I connected the wire directly to the SMA feed cable? Is there some kind of adapter that would allow me to connect a bare wire (I think it's 14 gauge or so) to a male SMA?

 

[PDXh0b0]

i remember that day...I cut 8in off the end of a short coaxial cable soldered 6in of wire to the center conductor and one to the shield, soldered alligator clips to the end of the wires, the used an f type female to sma female on the other end.

20220507 135054 — Postimages

postimg.cc

then I bought a couple nooelec 9:1's

Amazon.com

https://www.amazon.com/Balun-One-Nine-v2-Barebones/dp/B07XJRTF94

article on uses

The NooElec Balun 1:9 v2

Many thanks to SWLing Post contributor, Grayhat, who writes: Hi Thomas, was about to write you about some infos related to the NooElec balun when found that they now offer a v2 model: The new balun…

swling.com

and, get lots of various sma adapters

 

[SpaceForceCmdr]

Thanks! The nooelec 9:1 looks like it could work. Do I really need a balun when using a random wire antenna, though? I'm new to all this stuff.

 

[Dirk_SDR]

Yes, the long wire is better adapted to your receiver input with a 9:1 balun/unun.
But if I want to solder wires directly to SMA I use th like this:

10pcs SMA Female Jack Lötanschluss, Durable Messing SMA Female Basen Mehrzweck-PCB Mount-Stecker für drahtlose Geräte : Amazon.de: Gewerbe, Industrie & Wissenschaft

Amazon.de: 10pcs SMA Female Jack Lötanschluss, Durable Messing SMA Female Basen Mehrzweck-PCB Mount-Stecker für drahtlose Geräte - Schneller & kostenloser Versand ab 29€. Jetzt bestellen!

www.amazon.de

... or like this:

AERZETIX - Anschluss-Stecker SMA weiblich für Chassis Panel: Amazon.de: Elektronik & Foto

AERZETIX - Anschluss-Stecker SMA weiblich für Chassis Panel: Amazon.de: Elektronik & Foto

www.amazon.de

 

[SpaceForceCmdr]

Cool, I just got the one PDX mentioned above (nooelec). Is anyone familiar with this one? Some of the reviews says it's actually a BALUN and I'd need an UNUN. I guess one of the parts of the circuit can be cut to make it into an UNUN?

 

[Dirk_SDR]

The "Nooelec Balun 9:1 v2" really is an Unun, that transforms the high impedance (several 100 Ohm) of an end fed long wire antenna down to a low impedance input (50 Ohm coaxial SMA) of a receiver.
Both, antenna and receiver input, are UNbalanced, therefore the name UnUn for that HF transfomer.
If you cut R1 on the PCB, then the middle of the primary winding of the transformer is not grounded any more. Then you get a BalUn (= transformer Balanced to Unbalanced).

 

[SpaceForceCmdr]

Hey, thanks. I just realized I got the v1. Someone over on reddit was saying I should cut the trace to it works with my long wire setup. As it is, I hooked it up, but it doesn't seem to to much, if anything.

 

[Dirk_SDR]

Hey, thanks. I just realized I got the v1. Someone over on reddit was saying I should cut the trace to it works with my long wire setup. As it is, I hooked it up, but it doesn't seem to to much, if anything.

Perhaps you'll get better results with a "counterpoise" connected to the other contact of the balun.
A simple wire 2-4m lying on the floor of your shack is a good counterpoise.

 

[SpaceForceCmdr]

Thanks, this actually does seem to help a little. So it doesn't have to be grounded? It can just lay on my wooden floor up there? What helps a lot is me holding the wire coming out of ground on the BALUN, but as soon as I let it go, there's goes the nice signal boost, too.

 

[Dirk_SDR]

You can try:
Let the wire lie on the floor, hang it out of a window, ...
It can be grounded as well, so try it. But in modern houses nearly each "ground" (heating pipe, cable TV installation ground, ...) is noisy and pulls the noise into your SDR.
If you are on the 1st floor or have a garden, you are lucky. You can make your own RF ground.

 

[SpaceForceCmdr]

OK, thanks. I'll play with it a bit and see It does seem like I get a slightly stronger signal with a wire coming out of the unun and going to a metal pipe, but like you said, it could also be introducing more noise. When I was setting this up earlier, I originally tried grounding it to a copper water pipe, and there was a lot of extra noise. Maybe just hanging the wire out as a counterpoise would be a better solution. We'll see.

What's the easiest way to test this? Should I have a station tuned in, and then connect to ground vs counterpoise, or just tune to static, and see if I hear a difference with the two options?

 

[Dirk_SDR]

I would use a quite stable station with low fading in your favorite frequency range, write down and compare the values Peak, Floor and SNR with different antennas, antenna positions, RF grounds, counterpoises ...
Peak: the peak signal level is important, but with also much noise it's possibly not usable.
Floor: the base/floor (noise) level. The higher the more real signals are buried in it.
SNR: signal to noise ratio. SNR = Peak - Floor. Two antennas might have the same SNR, but the better one also receives less noise, has a low Floor value.

 

[SpaceForceCmdr]

One other quick thing: should the counterpoise be the same gauge as the long wire, or does it not matter? The long, random wire is 14 gauge, but I also have some copper wire lying around, and it's very thin (and not not insulated).

 

[Dirk_SDR]

I would give the counterpoise "some copper", so I wouldn't use a very thin wire.
As far as I understood there are 2 ways the counterpoise can be seen:
1. As an artificial ground
2. As 2nd part of a dipole (the long wire antenna is the other part)

If you see it as 1., you can use larger gauge wires, you could even use steel plates and other big metal structures below your shack.
If you see it as 2., the wire can be thinner, should be aligned straight, the length matters and is depending on the frequency used.

 

[SpaceForceCmdr]

Cool, I'm thinking option 1 at this point. I've also been wondering if my RG58 cable is acting as part of the antenna or not. I think with the unun connected, it shouldn't? I have the long wire in the attic, then that connects to one input of the unun (also up there), then I have an RG58 cable connected to the unun which runs down through the wall to my computer (I'm running an SDR at the moment).

One other possible issue I considered is that there are some electrical lines running down that same hole. I'm hoping the shielding in the RG58 is enough to stop interference. Unfortunately, there's not really another good way to run the line down to my radio without busting holes in things.

 

[SpaceForceCmdr]

I think I'm pretty good for now. I ended up attaching some wire to the ground input and using it as a counterpoise. It didn't seem to make a ton of difference vs having it connected to a water pipe, but I figure why take the chance of introducing RF from other things connected to the pipe?

The noise floor was lower without any counterpoise, but so was the signal. I seemed to be getting the best SNR with it connected, so I'll roll with that for a while and see how it goes. I was listening to a guy from Italy earlier, so this setup works way better than the rinky dink telescopic antenna that came with my SDR. Thanks again for the info!