Need expertise on choosing & deciding Coax Cables

[prcguy]

Looking at a lab table measurement of a 50 ohm source into a 75 ohm resistive thingee, there will be less than .2dB loss due to the mismatch. However, when there is coax involved different lengths and type of coax will alter the VSWR and resulting loss. In one online conversation someone stated there can be up to a 2.25:1 VSWR using 75 ohm coax of random length on a 50 ohm antenna. That would equate to a .695dB loss.

So the question of using 75 ohm cable on a 50 ohm antenna is complicated and cannot be answered without a complete analysis of the antenna and cable used. In my book do some research on cable loss and use 50 ohm cable on a 50 ohm antenna and you have one less thing to worry about.

Only one concern with going with the RG-6 or the RG-11 Coax Cable is the (mismatch) being that my Discone Antenna is 50 Ohm & those 2 types of Coax Cable are 75 Ohm? But then again, I am only going to be (receiving) from my antenna to my receiver & not transmitting out at all ever.

 

[CorwinScansNM]

If you are using a Uniden BCD536HP, and it will be generally the same with any scanner, you have 40 ohm impedance in the scanner at 750MHz and 115 ohm at 800MHz and 20 ohm at 850MHz. You don't have to bother with impedance matching in antenna, coax and connectors when dealing with scanner equipment.

/Ubbe

OK, good to know. You taught me something technical about Coax Cable & the Uniden BCD536HP. That helps.

 

[CorwinScansNM]

Looking at a lab table measurement of a 50 ohm source into a 75 ohm resistive thingee, there will be less than .2dB loss due to the mismatch. However, when there is coax involved different lengths and type of coax will alter the VSWR and resulting loss. In one online conversation someone stated there can be up to a 2.25:1 VSWR using 75 ohm coax of random length on a 50 ohm antenna. That would equate to a .695dB loss.

So the question of using 75 ohm cable on a 50 ohm antenna is complicated and cannot be answered without a complete analysis of the antenna and cable used. In my book do some research on cable loss and use 50 ohm cable on a 50 ohm antenna and you have one less thing to worry about.

Cool, thanks prcguy for the additional information regarding my concern. Appreciated.

 

[CorwinScansNM]

It is final. With many mixed talks, suggestions & ideas from everybody here who has put in & provided their efforts & feedback in helping me to pick & choose a good type of Coax Cable for good to excellent receiving from my outdoor Discone Antenna to my receiver; I have my choice narrowed down to just 2 now thank goodness & eliminated the others that I was considering.

One still being the 75 Ohm Tri-Shielded RG-11 Coax Cable which I can order in a 20 or 25 foot length & then add the N-Type Male to F-Type Female Antenna RF Adapter to make it compatible with my antenna.
https://www.amazon.com/CIMPLE-CO-De...pID=41aztpQAf5L&preST=_SX300_QL70_&dpSrc=srch

The last one is a bit higher cost & is 50 Ohm rated. (LMR-240) Andrew Commscope CNT240 Coax Cable custom built to my choice/needs from https://usacoax.com

 

[mmckenna]

Since the difference between the two at 25' long will not be noticeable to your ears, go with the LMR-240.
You won't need to use adapters, which is a bonus, especially outdoors, and if you ver decide to start transmitting with anything, you have the right cable.

Get the LMR-240 built with the correct connectors to match the antenna and to match your radio.
If you are buying from The Antenna Farm or one of the others, spring for the heat shrink tubing on the connectors. That helps with strain relief.
And don't forget to properly weather seal the outdoor connections.

 

[Ubbe]

https://www.robertponge.com/telechargements/ebooks/antenne-bicone-discone.pdf
UHF Discone Antenna

/Ubbe

 

[Ryangn]

The last one is a bit higher cost & is 50 Ohm rated. (LMR-240) Andrew Commscope CNT240 Coax Cable custom built to my choice/needs from https://usacoax.com

While I can't speak for all the technical aspects of coax I do use TimesMicrowave LMR-240 for all my radios and it works great for me. I get the ultraflex cable as it's easier to work with since it's not as stiff. I have used MPD Digital (usacoax.com) via their Ebay store in the past and while they aren't the cheapest I have never had a problem with them and they were fast in processing my orders.

 

[CorwinScansNM]

75 ohm is always superior for receive.
.....
50 ohm coax only exists for transmitters.

Um, No. Not so true as I just found out from MPD Digital.

Both transmitters and receivers are manufactured with the requirements for specific cable resistance. While it is true that the impedance mismatches are most recognized when transmitting as current is sent down the wire and lost as heat, the mismatch also applies on the receiving end, just not as much.

 

[prcguy]

Generally speaking and not taking radio or antenna impedance into account, 75 ohm cable actually is better for receive purposes compared to an otherwise identical constructed 50 ohm cable. There is less capacitance per foot and a tiny bit less loss in a 75 ohm cable compared to 50 ohm and the larger center conductor in 50 ohm cable is slightly better suited for higher power where higher currents and less resistance per foot comes into play.

Um, No. Not so true as I just found out from MPD Digital.

Both transmitters and receivers are manufactured with the requirements for specific cable resistance. While it is true that the impedance mismatches are most recognized when transmitting as current is sent down the wire and lost as heat, the mismatch also applies on the receiving end, just not as much.

 

[Frankhappyg]

FYI:
Another good coax is;
Altelix Low Loss 400 Series.
About $60 50 feet with connections on Amazon.
Made in the USA.


Sent from my iPhone using Tapatalk

 

[iMONITOR]

Bob Grove of Grove Enterprise always claimed RG6 is all you need for any scanner radio. The same holds true today. It's readily available, inexpensive, easy to work with, connectors are weather proof and inexpensive.