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alenK

Coax cable for use with passive antenna?

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Hello,

 I am trying to learn about occasionally and temporarily augmenting my bag mounted Lectrosonics SRc receivers with supplementary antennas mounted up in the air on a pole. For the foreseeable future It's unlikely that I will make the leap to using an antenna distribution system and multiple receivers. I am primarily interested in being able to quickly hook up one SRc and cover an occasional long distance walk and talk shot with two radio mics and then resume a day of near proximity scenarios.

 

 I started experimenting with some home made dipole antennas and they have provided an effective improvement in range during testing.

 

 The Lectrosonics SRc receivers introduced me to SMA connectors. Previously all my receivers used BNC connectors.

 

 I bought some 5 foot SMA to BNC RG 174 cables for my dipole experiments, and I look forward to using slightly longer cables, perhaps 10 feet in length.

 

 The "low loss" RG 174 cable is specified to have much greater loss than a familiar RG 8 cable (such as the specification used in Lectrosonics RF cable products). I am second guessing the merit of combining an antenna that only adds a few dB gain with a RG174 cable that loses 1dB (5 foot length at 500MHz?) or 2dB (10 foot length at 500MHz?) of signal strength.

 

Which brings me to the question; How do other people connect the SMA connections on a Lectrosonics SRc receiver to an antenna? I realize that a lot of people use an interim buffer system such as the PSC Multi SMA, but I am not that sophisticated yet. I am reluctant to hook a SMA terminated RG-8 cable directly to my SRc radio because it seems like the relatively stiff cable could strain the radio's connector, so I am considering using a very short 6" length of SMA to BNC RG174 cable as a strain relief and then connecting a RG-8 to that.

 

I am wondering what other people have done in a circumstance such as I have described.

 

Thank you.

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What you're thinking of doing cable-wise will work fine.  However, shark fins will yield a significantly greater improvement than any concern with cables or connectors at the lengths you're working with. 

 

It's about much more than just gain.  With an antenna system, you can also have too much gain, which will overload the front end. 

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Thank you for the suggestions.

 

Here are some line loss specs (obtained from an online calculator) that prompted me to consider RG-8 for a 10 foot connection to a passive antenna system;


Belden 8216    (RG-174)   loss @500MHz  = 2.181dB

Belden 9913    (RG-8)       loss @500MHz  = 0.302dB

Belden 9258    (RG-8X)     loss @500MHz  = 0.888dB

Belden 9201    (RG-58)     loss @500MHz  = 1.054dB

 

Placing my dipoles higher in the air may improve line of sight conditions, but I don't expect them to provide much more than 1 or 2 dB of Gain so negating that positive gain with an inconsiderate choice of cabling seems counterproductive.

 

The RG-8 seems like the most effective way to address the concern, but the convenience of working with a more flexible cable certainly seems valuable.

 

Thank you.

 

 

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Hi Allen,

RG-58 or RG-8x is a reasonable cable to use in a 10 foot length. The extra loss of half a dB is negligible in the true sense of the word. The smaller, more flexible cables will work with the SMA connectors. To use RG-8, you will need adapters which will lengthen the lever arm on that small SMA connector, guaranteeing  mechanical failure of the SMA.

Best Regards,

Larry Fisher

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