Can you connect different types of coax?

[KJ4ZFJ]

Are there any issues in joining two different types of coax (RG-8X and RG-213) to complete a feedline from antenna to radio?  I would assume that the losses would be impacted to somewhere between the characteristics of the two, but this is just my 'logic'.  Thanks!

[K3MRI]

Hi Tim.

Great question.

Impedance is always the name of the game. Any two feed lines, no matter their type, can be connected in series if their impedance matches. In your case, both are 50 ohms so you're absolutely fine. Where you will have a problem, not really a problem but a slight impact, is in loss. If we use 10 Mhz, RG-8X will have 1 db loss per 100-feet. Your 213 will only have 0.6 db loss (obviously, the higher the frequency, the greater the loss). Another issue is always the connector. Connectors are weak points in so many ways. Make sure that if you connection is intended to be permanent, you choose the best possible connectors and properly grease them and protect them from water/humidity. Of course, try to keep the number of connectors to a minimum. An approximate loss for most barrel-type connectors is approximately 0.5 db, so if you introduce two connectors, for example, you're losing an additional 1.0 db. Depending on the frequency, that can hurt.

Because you asked, let me give you a slightly more in-depth answer as regards any type of connection, including two coax cables. There is something called PIM - Passive Intermodulation. You really do not need to worry about it in HF frequencies. It only becomes an issue in very very high frequencies such as EHF/SHF or LTE, HSPA and CDMA cellular networks. Again, not your concern, but the reality is that any connection introduces a slight signal distortion. The higher the frequency, the greater the consequence.

Finally, make sure you choose a 'good' connector. Remember, if it's a permanent installation, it does not have to be the same as your other connectors. If you tend to use the 259/239 combo, you can still use N-connectors for this particular junction. Also, you have metals options to think about. But connectors were not your question so we'll stick to coax for now 😁

I hope this was helpful and maybe another Elmer will weigh in with their better answer 😇

Jim

 

[KJ4ZFJ]

Jim, Thanks for the in-depth response!