VHF Antenna and Coaxial Continuity Testing

[Deleted member 36384]

Hello,

I have just replaced the mast end of my VHF cable. The Pl239 plug was soldered onto the mast coaxial cable with the copper centre wire soldered onto the PL239 pin and the braided shield bent back over the external flex and PL239 screwed over it. The copper centre insulation was left in place and measured so that the insulation would be just be inside top 1/4 of the centre pin. The soldering was performed with the pin down to stop any solder running back and bridging the pin to the PL239 outer housing and thus connecting pin and coaxial together.

I tested this connection with a multiple meter, tested the multimeter which showed 1 when leads are not touching and 0 when leads are touching. With the red on the Pl239 pin and the black on the PL239 body, I got 0; so good to go. The old cable was pulled and the new cable was run from the mast head and connected to the antenna (a Metze Manta about 5 years old).

I did the continuity test again at the deck end of the cable (no connector just on the centre and shield) and found that it was 0, a circuit. It was late by this time last night so I came home. I have a new Metze Manta Antenna at home as a spare and today tested the continuity on the antenna's SO239 connector between the pin receptor and outside body that the PL239 screws onto at it measured 0 resistance, a circuit.

Having searched the forum, I am now understand that when the VHF cable is disconnected from antenna there should be no circuit between the pin and the shield, when the VHF antenna is connected to the cable, there is a circuit between the centre wire connected to the pin and the shield. The reason for this is due to the antenna construction. Hence, my tests show all is okay.

The reason I am asking is that I get someone to do this for me, but with lockdown everything is taking an age so I did this myself. Just looking for validation that my tests are correct. The reason for the validation is that everyone starts arguing on the threads about nuances and while one or two forumites are clear, the rest muddy the waters, no criticism intended, it's just the way it is.

Is this what you would expect with a Pl239 and SO239 when conducting these tests as described?

As always, thanks in advance,

BlowingOldBoots

 

[black mercury]

Tried mine. It reads 9800 ohms resistance through the antenna.

 

[starfire]

Hello,

I have just replaced the mast end of my VHF cable. The Pl239 plug was soldered onto the mast coaxial cable with the copper centre wire soldered onto the PL239 pin and the braided shield bent back over the external flex and PL239 screwed over it. The copper centre insulation was left in place and measured so that the insulation would be just be inside top 1/4 of the centre pin. The soldering was performed with the pin down to stop any solder running back and bridging the pin to the PL239 outer housing and thus connecting pin and coaxial together.

I tested this connection with a multiple meter, tested the multimeter which showed 1 when leads are not touching and 0 when leads are touching. With the red on the Pl239 pin and the black on the PL239 body, I got 0; so good to go. The old cable was pulled and the new cable was run from the mast head and connected to the antenna (a Metze Manta about 5 years old).

I did the continuity test again at the deck end of the cable (no connector just on the centre and shield) and found that it was 0, a circuit. It was late by this time last night so I came home. I have a new Metze Manta Antenna at home as a spare and today tested the continuity on the antenna's SO239 connector between the pin receptor and outside body that the PL239 screws onto at it measured 0 resistance, a circuit.

Having searched the forum, I am now understand that when the VHF cable is disconnected from antenna there should be no circuit between the pin and the shield, when the VHF antenna is connected to the cable, there is a circuit between the centre wire connected to the pin and the shield. The reason for this is due to the antenna construction. Hence, my tests show all is okay.

The reason I am asking is that I get someone to do this for me, but with lockdown everything is taking an age so I did this myself. Just looking for validation that my tests are correct. The reason for the validation is that everyone starts arguing on the threads about nuances and while one or two forumites are clear, the rest muddy the waters, no criticism intended, it's just the way it is.

Is this what you would expect with a Pl239 and SO239 when conducting these tests as described?

As always, thanks in advance,

BlowingOldBoots

You are quite right, some anntenas, read a short between centre & shield, some open circuit, yet others which would normally be open circuit but have a high value resistor attached inside the antenna so you can measure it with a multimeter.

The coax should read open circuit when disconnected from the antenna & radio.

Any resistance reading would show a whisker of braid bridging the connector (low reading) or corrosion, water etc (higher reading).

That resistor would account for the 9800 ohm reading, in spec for a 10,000 resistor

 

[andsarkit]

Just checked my new Metz Manta 6 which I have yet fit. Resistance = 0.0 ohms.
The instructions that came with it say to' expect a dead short when testing with a multimeter'.
A quick check of RG8 coax resistance gives 0.76 ohms/100ft (centre + shield in series) so I would expect to see less than 1 ohm at the radio end.

 

[Deleted member 36384]

Thanks everyone. Now I understand why various threads discuss the nuances as it depends on the antenna type. Good, that saves me taking the cable out and redoing the PL239.

Thanks again, BlowingOldBoots

 

[GTom]

Hello,

I have just replaced the mast end of my VHF cable. The Pl239 plug was soldered onto the mast coaxial cable with the copper centre wire soldered onto the PL239 pin and the braided shield bent back over the external flex and PL239 screwed over it. The copper centre insulation was left in place and measured so that the insulation would be just be inside top 1/4 of the centre pin. The soldering was performed with the pin down to stop any solder running back and bridging the pin to the PL239 outer housing and thus connecting pin and coaxial together.

I tested this connection with a multiple meter, tested the multimeter which showed 1 when leads are not touching and 0 when leads are touching. With the red on the Pl239 pin and the black on the PL239 body, I got 0; so good to go. The old cable was pulled and the new cable was run from the mast head and connected to the antenna (a Metze Manta about 5 years old).

I did the continuity test again at the deck end of the cable (no connector just on the centre and shield) and found that it was 0, a circuit. It was late by this time last night so I came home. I have a new Metze Manta Antenna at home as a spare and today tested the continuity on the antenna's SO239 connector between the pin receptor and outside body that the PL239 screws onto at it measured 0 resistance, a circuit.

Having searched the forum, I am now understand that when the VHF cable is disconnected from antenna there should be no circuit between the pin and the shield, when the VHF antenna is connected to the cable, there is a circuit between the centre wire connected to the pin and the shield. The reason for this is due to the antenna construction. Hence, my tests show all is okay.

The reason I am asking is that I get someone to do this for me, but with lockdown everything is taking an age so I did this myself. Just looking for validation that my tests are correct. The reason for the validation is that everyone starts arguing on the threads about nuances and while one or two forumites are clear, the rest muddy the waters, no criticism intended, it's just the way it is.

Is this what you would expect with a Pl239 and SO239 when conducting these tests as described?

As always, thanks in advance,

BlowingOldBoots

Twisting the thread a bit: are you sure that your connector is PL239, not PL-259?

For antenna testing (I intend to keep the old one as AIS antenna), I am thinking on this SWR-meter: TEAM - SWR-PRO-UHF/VHF - 120-500 MHz SWR meter (googling reveals other sources too, around €20+shipping)

 

[MM5AHO]

The problem with using a multimeter (which uses DC from a battery and tests things with this low voltage DC) on antenna circuits is that an antenna is designed to handle radio frequency, not DC. (like AC, but much higher frequency that mains AC.
Such things as resistance mean something different at Radio Frequency (RF) than they do at DC.
And then to complicate the matter, there are many designs of antenna. Some antennas show a short at DC (0 ohms), some show open circuit, (v high ohms) some show a resistance (some ohms).
But with no antenna and no radio connected a multimeter can test coax cable for shorts or not.

 

[black mercury]

The problem with using a multimeter (which uses DC from a battery and tests things with this low voltage DC) on antenna circuits is that an antenna is designed to handle radio frequency, not DC. (like AC, but much higher frequency that mains AC.
Such things as resistance mean something different at Radio Frequency (RF) than they do at DC.
And then to complicate the matter, there are many designs of antenna. Some antennas show a short at DC (0 ohms), some show open circuit, (v high ohms) some show a resistance (some ohms).
But with no antenna and no radio connected a multimeter can test coax cable for shorts or not.

That explains why my emergency vhf antenna reads 9800 ohm but the main vhf antenna is open circuit. Interesting, thank you for explaining why.

 

[trbt]

Hello,

I have just replaced the mast end of my VHF cable. The Pl239 plug was soldered onto the mast coaxial cable with the copper centre wire soldered onto the PL239 pin and the braided shield bent back over the external flex and PL239 screwed over it. The copper centre insulation was left in place and measured so that the insulation would be just be inside top 1/4 of the centre pin. The soldering was performed with the pin down to stop any solder running back and bridging the pin to the PL239 outer housing and thus connecting pin and coaxial together.

I tested this connection with a multiple meter, tested the multimeter which showed 1 when leads are not touching and 0 when leads are touching. With the red on the Pl239 pin and the black on the PL239 body, I got 0; so good to go.

Maybe I misunderstood, did you test the resistance between the pin and the body of a PL-239 (or PL-259?) connector that was just installed on a new cable and that cable had the other end not yet connected to anything? If so, then '0' is definitely not 'good to go'

 

[MikeCC]

The number confusion arises because it's a PL-259 plug but SO-239 socket.

 

[Deleted member 36384]

Maybe I misunderstood, did you test the resistance between the pin and the body of a PL-239 (or PL-259?) connector that was just installed on a new cable and that cable had the other end not yet connected to anything? If so, then '0' is definitely not 'good to go'

PL259 is what I have so thanks GTom for and others for the correction. With the cable made up to the PL259 only (not connected to the VHF or antenna) I tested the connection between the pin (with the cable core soldered into the pin) and the body of the PL259 (with braided sheath clamped to the body. The resistance read 1 on my multimeter,

Edit, PL259, checked package on boat.

 

[bobhy]

BTW, Shakespeare 1515 (inexpensive, and therefore, very common) sailboat VHF antenna is documented to be an *open* circuit at DC. Mine actually measures 10's of mega-ohms, declining gradually over many seconds. Here's the install sheet: https://shakespeare-marine.com/wp-content/uploads/2021/09/5215_5215-C-X.pdf

 

[Bilgediver]

Is this what you would expect with a Pl239 and SO239 when conducting these tests as described?

As always, thanks in advance,

BlowingOldBoots

Y E S !! On your particular installation with the Metz . Others may vary as some antenna can show open circuit.

 

[niallw70]

The problem with using a multimeter (which uses DC from a battery and tests things with this low voltage DC) on antenna circuits is that an antenna is designed to handle radio frequency, not DC. (like AC, but much higher frequency that mains AC.
Such things as resistance mean something different at Radio Frequency (RF) than they do at DC.
And then to complicate the matter, there are many designs of antenna. Some antennas show a short at DC (0 ohms), some show open circuit, (v high ohms) some show a resistance (some ohms).
But with no antenna and no radio connected a multimeter can test coax cable for shorts or not.

Hi id appreciate comments from you MM5AHO, on my issue. I'm trying to fit a new PL259 connector to my antenna cable. This is at the radio end of cable. After fitting i tested for short with multimeter, i thought I'd done ok job of not burning out the insulation, but there is still a short. I cut plug off to start again. This time i measured resistance on cable before soldering, 0.5ohms! So cable must be shorted at antenna end. So in theory it shouldn't matter if the cable is also shorted at radio end, correct. . or not. The antenna is glomex, hasent been touched or inspected in over 12 years, do i also need to get up mast to check for corrosion?

 

[PaulRainbow]

Hi id appreciate comments from you MM5AHO, on my issue. I'm trying to fit a new PL259 connector to my antenna cable. This is at the radio end of cable. After fitting i tested for short with multimeter, i thought I'd done ok job of not burning out the insulation, but there is still a short. I cut plug off to start again. This time i measured resistance on cable before soldering, 0.5ohms! So cable must be shorted at antenna end. So in theory it shouldn't matter if the cable is also shorted at radio end, correct. . or not. The antenna is glomex, hasent been touched or inspected in over 12 years, do i also need to get up mast to check for corrosion?

Some antennas will measure short circuit. Best check is with a VSWR meter.

 

[andsarkit]

So in theory it shouldn't matter if the cable is also shorted at radio end, correct. . or not. The antenna is glomex, hasent been touched or inspected in over 12 years, do i also need to get up mast to check for corrosion?

The cable must not be shorted at the radio end. The short at the antenna end will be some impedance matching components within the antenna. It is difficult to measure such low resistance with a standard multimeter so just take great care when assembling and soldering the connector.
Depending on the type of antenna there might be a connector at the masthead or the cable might be moulded into the antenna.
As Paul said, if you can borrow a VSWR meter this will be the best way to check the complete antenna system as it gives a measure of how much power is actually transmitted and how much is reflected back down the coax.