PL259 radio connectors

[tsh]

Re the Q&A on extending DSC radio cables in the October issue.

To an ex RF engineer, the pl259 connector which is typically used for consumer VHF applications is an abomination. It's only saving grace is it's cost, bit I've never found it possible to archive a satisfactory connection to a cable with one.

True, the insertion loss in the VHF range when properly installed may well be less than 1dB (or a 12% increase in range), and maybe the loss in not significant in many applications. Not something to gamble on if reliability over a long period of time is of concern.

The most obvious connector to recommend if you have a choice, and want to reduce signal loss is the N-connector. Not only are these connectors good for use up to microwave frequencies, you will have a good chance of achieving an air-tight (and so corrosion resistant) connection between plug and socket. The connectors cost about £5 each, and must be chosen to fit the cable size (diameter). There should be plenty of radio amateur sites online with detailed instructions on achieving a high quality termination.

Most importantly, the inside of the coax cable must be protected against corrosion from moisture (or acid from curing sealant!)

sean

 

[Refueler]

I find it strange that you join in 2005 .... and only 1 post in 4 years.

When you post you are using subject that many already know about !

But it's become the industry standard ( boat VHF I'm talking about ! ) and many wouldn't go against that.

Me ? I've used BNC on one boat as I had a PC Network box handy - I used to set up co-ax Networks in the old days ... BNC worked fine. Well so it appeared ..

 

[Salty John]

The PL259 is a big rugged connector of great mechanical integrity.
All VHF sets and most good antennae have SO239 sockets to take the PL259 connector, so each end of your system has one, so why not use tham to make intermediate connections as well? The only downside is their physical size; two PL259's and a PL258 barrel connector make a hefty joint, difficult to hide under the headlining. But you can't deny it's ruggedness.
I've never found the PL259 difficult to attach to coax - the soldering is simple and testing the joint is simple with a multimeter.
The insertion loss is considerably less than 1db.

 

[shmoo]

What I would like is something like a 258 barrel connector big enough (and with a flange) to use to take a connection though the coach roof, so you could have a plug on the outside and another one on the inside. A few dBs loss doesn't really worry me since I get reasonable range from my VHF and AIS.

<edit> I have always found it reassuring to use a connector hefty enough to tow the boat with and if you use tinned wire and smear petroleum jelly over everything corrorsion isn't a problem</edit>

 

[jason -and the arguenauts]

The real purist answer is, of course, not to have a connector but just to cut and replace the cable every time you need to take the mast down. Between that extreme and a bodge, the PL connector seems a quite effective compromise to me. And the range argument is theoretically correct but practically irrelevant.

That said, it's a free world so everybody can do what takes their fancy.

 

[Refueler]

Having recently changed my VHF from old Seafarer to new Cobra ... I was concerned about losses in the cable / antena set-up. I'd heard of new radios being intolerant of significant losses and basically blowing the output when keyed.

So I did the job I was dreading ... I pulled the cable out from behind lining etc. UGH !
The cable had been extended using screw choc block terminals .... and then just pushed out of sight. Rest of cable had good deck socket and I renewed the antena with Saltyjohns Metz - one of the few that allow you to fit own cable, (old had a splice in cable just outside it's base and not able to reconnect as the Metz does).
Luckily the choc block joint co-incided with the new position I wanted for the radio.

Point I make here - is that the Choc block worked for 10 yrs ! A totally wrong connector.

 

[DavidNB]

I often make antennas and balums with choc blocks, I have a dipole thats been up for nearly 20 years, made from house wiring and choc blocks, why buy new fancy stuff when this works??

 

[goboatingnow]

PL connectors that are crimped with a proper tool are mechanically very good, in 17 years never had a probloem with them. I agree with OP though PL types with "screw in" type braid connectors are junk. And hes right re N series. however its PL's that are on the back of the radios.....

 

[Refueler]

I have Saltyjohns PL connector with the correct sleeve for the co-ax. I compared it to PL connectors over counter out here - completely different quality. Thanks SJ ... I followed your fitting guide, connected your Metz antena ... I have no complaints at all.

 

[st599]

I often make antennas and balums with choc blocks, I have a dipole thats been up for nearly 20 years, made from house wiring and choc blocks, why buy new fancy stuff when this works??

But if you're using the chock block to connect a dipole to a balanced-unbalanced transformer, then it's not in the middle of a transmission line, is it?

 

[DavidNB]

But if you're using the chock block to connect a dipole to a balanced-unbalanced transformer, then it's not in the middle of a transmission line, is it?

OK so how else do you join 75 ohm twin to coax?

 

[st599]

OK so how else do you join 75 ohm twin to coax?

Seeing as co-ax is unbalanced and twin is balanced, the correct way is to use a balanced-unbalanced (balun) transformer of the correct impedance.

A choc block would just place an impedance mismatch in circuit leading to lots of reflections and a poor VSWR.