SMA connections on SDR Dongles

[whirled-traveller]

Greetings:

First of all, I do not know if I should have placed this thread either in the "Antennas" thread or in the "SDR" thread. If I placed this in the wrong thread, I apologize. My logic was that I am specifically wanting to discuss those micro small SMA antenna connection points on the SDR USB dongles.

Two weeks ago, I purchased the RTL-SDR USB dongle with the dipole antenna kit from Amazon. I have set the unit up and working and am exploring. I am learning new things everyday and enjoying the hobby. I learned using the dipole to the point where I ended up buying some adapters to adapt the ends of my home-made antennas to SMA. However, I am wanting to make my own cables with the ends I am in need of. Here is where I have questions.

1. It appears that the common cables used is either a "RG316" or an "RG174". I have never heard nor seen these cables before. I even looked at the cable in the dipole kit and did not see any markings for these two numbers printed nor embossed on the cable. Therefore, my questions are
   • Which is the better wire to use? The RG316 or the RG174?
   • What is the advantages / disadvantages of the two cables to each other?
2. On Amazon (or any other online merchant), is there any particular crimp connector brand you found superior to others?
3. From reading, I am seeing where some people are recommending shrink tubing the ferrule to the connector after the crimp. What diameter shrink tubing do I need?
4. What is the strip length measured from the end of the wire for exposing the bare wire only (to the white insulator and braid)?
5. What is the total strip length measured from the end of the wire for exposing the bare wire plus the white insulator and braid (to the outside jacket)? I haven't been able to yet find a recommended strip diagram for inserting / crimping a connector to the wire.
6. Do you have recommendations for a crimping tool and wire stripper? I am looking at this particular crimp kit as there is a die for the RG316 and RG174. Anything better on a hobbyist level?

Thank you in advance for your questions.

 

[Dirk_SDR]

Wow, many points ...
A good overview of coax strip lengths is here:

https://hamwaves.com/connectors/doc/crimp.wimo.pdf

You can buy shrink tubing with the diameter of the cable plus 0.5 ... 1mm.
The difference between RG316 and RG174:

RG174 vs RG316 compare – Koax24.de

blog.koax24.de

 

[mmckenna]

I find it easier to work with RG-58. It'll have significantly less loss, it's less expensive, easier to work with, and the connectors are easier to install.
Unless you have a specific need to use the really small diameter cable, you'll make life easier with the RG-58

You could even do RG-6 and just use an adapter from F to SMA. Super easy to install F or even BNC connectors on RG-6.

 

[jeepsandradios]

I run a pile of SDR on a USB hub. I run 12" RG316 jumpers with SMA M and NF on the other end. I got them all premade so i didn't have to mess with connectors. All terminate to LMR400 with NM so works well. For a 12" cable the loss is not the end of the world and it keeps a bit of stress off the cable. As mmckenna pointed out rg58 will work fine also, I just liked the flexibility of the jumpers on the unit.

 

[ems55]

I find it easier to work with RG-58. It'll have significantly less loss, it's less expensive, easier to work with, and the connectors are easier to install.
Unless you have a specific need to use the really small diameter cable, you'll make life easier with the RG-58

You could even do RG-6 and just use an adapter from F to SMA. Super easy to install F or even BNC connectors on RG-6.

What about LMR-200 or is that overkill ???

 

[mmckenna]

What about LMR-200 or is that overkill ???

I don't think that would be overkill.
The only concern I'd have is that a solid center conductor cable may put some additional strain on the antenna connector on the SDR. Just be aware of that and mitigate the risk of it stressing that connection.

If you have the tools to crimp LMR-200, then go for it.

 

[whirled-traveller]

After researching what everyone said, I may just go buy a high quality pre-made SMA cable, and the SMA to F adapter kits and work RG-6 from there. As I already have RG-6 cable, compression ends, wire stripper, and compression crimp tool. That way, I won't stress the DONGLE and not stress the USB receptacle on my laptop which seems to be a little loose with this module plugged into my laptop.

Hopefully, there would be no significant loss going from the 50 ohm SMA cable to the 75 ohm RG-6 cable. There is mention of the old dongles with the F series 75 ohm impedance connector on the RTL-SDR page that "using 50 Ohm cabling on a 75 Ohm input will be very minimal at less than 0.177 dB" loss. I have the v3 dongle with the webpage states has the 50 ohms impedance. Hopefully that 0.177 dB loss is the same.

Thanks for the advice and help so far.

 

[Spleen]

I've been down this road...invest in a handful of these to further reduce stress on that laptop USB receptacle, especially if you're mobile or are planning on going mobile with that setup (the link is just an example, there are myriad varieties and lengths, including full-length extenders if you really just don't want the laptop anywhere near the antenna connection).

https://www.amazon.com/C2G-52119-USB-Extension-Cable/dp/B00CJG2ZYM/ref=asc_df_B00CJG2ZYM/?tag=hyprod-20&linkCode=df0&hvadid=309743296044&hvpos=&hvnetw=g&hvrand=10409223470286502398&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007894&hvtargid=pla-365069363213&psc=1

That way, I won't stress the DONGLE and not stress the USB receptacle on my laptop which seems to be a little loose with this module plugged into my laptop.

 

[PACNWDude]

I went through this issue as well when I started using SDR# and USB dongles. I ended up buying some pre-made jumpers that had BNC connections on one end to make it easier to add different antennas to my USB stick dongles. Has worked pretty well for VHF to 896 MHz public safety radio network monitoring. Heavy duty Velcro to mount the USB to the back of the laptop computer and my mobile kit is set.

My only issue now is that people have taken these thinking they are normal USB sticks, and I end up replacing them with even smaller versions in metal cases and metal heat sinks (Nooelec) which makes changing out cables even harder (trying to swap cables on the small connector without torqueing it too much). The USB extender cable is also a good thing to have, as mentioned above.....saves that USB port. Good luck on your solution, it is fun to have a mobile kit to look at the spectrum.

 

[spongella]

Good question and lots of good responses.

I use R174 jumpers that I bought on line. They take the strain off the dongle when it's plugged into the computer. I also have an assortment of SMA adapters that allow me to attach the SMA pigtail (aka jumper) to my antenna feedlines which are RG58 and RG8.

Nooelec is a good company to deal with, bought many components from them in the past. Check them out. Have fun.

 

[ems55]

I don't think that would be overkill.
The only concern I'd have is that a solid center conductor cable may put some additional strain on the antenna connector on the SDR. Just be aware of that and mitigate the risk of it stressing that connection.

If you have the tools to crimp LMR-200, then go for it.

Thanks !!!

 

[whirled-traveller]

Greetings:

I finally got back around to play with the SDR and decided to place my order with Amazon. Everyone had some great ideas. From the 1 foot USB cable to placing velcro to the dongle and to the back of the laptop to the small length SMA cables. I ordered these things, along with some adapters to get me to "F' cable and some other stuff to start back on an old hobby of rebuilding antennas. I lost some of that stuff in a move years ago. I have been wanting to get back into this for years now.

Thanks for your help.