VHF - can hear but not be heard at a distance

[CaptJimFrei]

Originally Posted by MathiasW

I have a question regarding VHF... ....

This Summer, I picked up a transmission on VHF from USCG Sector NC Command Center in Wilmington NC while on my vessel on Jordan Lake NC...a distance of about 180 miles. I only heard the CG's side of the convo, and I did not try to step in.

[S/V Illusion]

Originally Posted by CaptJimFrei

This Summer, I picked up a transmission on VHF from USCG Sector NC Command Center in Wilmington NC while on my vessel on Jordan Lake NC...a distance of about 180 miles. I only heard the CG's side of the convo, and I did not try to step in.

A common occurrence depending on conditions unrelated to the radio or antenna system. I know other hams who have worked all states on VHF.

[StoneCrab]

Originally Posted by Jim Cate

Mathias,
Another possibility is that the AIS antennae are distorting the radiation pattern in some directions and that during your test there was an unfavorable combination of distortions.
Antennae that are parallel and close together do influence the patterns... recommended distances are a meter or more separation.
Jim

I agree with Jim Cate on the parallel antennas. If this is a sail boat and the antennas are on the top of the mast, they will be very close to each other causing a coupling of sorts which distorts the radiation pattern.

Another possibility is that since the cable was recently installed, the co-ax connectors where poorly fitted to the cable. If the co-ax shielding isn't properly soldered to the PL259 connector you could have losses on transmission. Proper shielding is very important to the RF current flows as the co-ax is technically part of the antenna.

This is an area where workmanship is everything. It is easy to make a good looking PL259 fitting that is not doing its job due to in adequate solder or improper style of PL259 connector.... the connectors must be matched to the cable used. It affects the diameters and shielding methods. Some connectors use the crimp method where the shield is crimped in place and only the tip is soldered. Other use a compression method with the ends screwed into place and then the more common uses solder to solder the braid to the inside of the connector.

If the solder doesn't fill the cavity, or the connector is overheated during soldering, problems can arise. The quality of the connectors themselves varies. You get what you pay for generally on these. Silver plated PL259 connectors solder very easily, Nickel plated... not so much.

And then... is the braid made up of aluminum wires? Aluminum pretty much can't be soldered. An example is LMR400 cable. Very low loss. Lightweight. Waterproof for direct burial (or marine use). Large diameter inner conductor which is copper coated aluminum. The shielding consists of an aluminum foil and aluminum braid for greater than 90% fill. Sounds fantastic, right? but you can't really get a proper fitting with a solder on connector due to the braiding being aluminum. Lots of people use this cable but many have botched connector installations. The usual way of hiding and hoping for the best is to put heat shrink tubing around the connectors for that professional look... but performance will never be great.

If your shielding is copper colored, you can usually get a solid solder connection to the PL259.

Your reception is less effected by the connectors than the transmission in my opinion.

Find a local HAM operator with test equipment and have him analyze the installation. Put a dummy load at the mast top and measure your power delivery.

Best of luck to you.

[Bill_Giles]

I may have missed it within the many replies but you say the theoretical distance between you and your friend is 17M but you could not speak at about 16.5M. There is no ‘line in water’ where the signal cuts off. So 16.5 vs. 17 is not much to worry about. As long a big boats and the CG are hearing you then there is little to worry about.

Have you tried contacting via DSC?

[MathiasW]

Originally Posted by StoneCrab

I agree with Jim Cate on the parallel antennas. If this is a sail boat and the antennas are on the top of the mast, they will be very close to each other causing a coupling of sorts which distorts the radiation pattern.

Another possibility is that since the cable was recently installed, the co-ax connectors where poorly fitted to the cable. If the co-ax shielding isn't properly soldered to the PL259 connector you could have losses on transmission. Proper shielding is very important to the RF current flows as the co-ax is technically part of the antenna.

This is an area where workmanship is everything. It is easy to make a good looking PL259 fitting that is not doing its job due to in adequate solder or improper style of PL259 connector.... the connectors must be matched to the cable used. It affects the diameters and shielding methods. Some connectors use the crimp method where the shield is crimped in place and only the tip is soldered. Other use a compression method with the ends screwed into place and then the more common uses solder to solder the braid to the inside of the connector.

If the solder doesn't fill the cavity, or the connector is overheated during soldering, problems can arise. The quality of the connectors themselves varies. You get what you pay for generally on these. Silver plated PL259 connectors solder very easily, Nickel plated... not so much.

And then... is the braid made up of aluminum wires? Aluminum pretty much can't be soldered. An example is LMR400 cable. Very low loss. Lightweight. Waterproof for direct burial (or marine use). Large diameter inner conductor which is copper coated aluminum. The shielding consists of an aluminum foil and aluminum braid for greater than 90% fill. Sounds fantastic, right? but you can't really get a proper fitting with a solder on connector due to the braiding being aluminum. Lots of people use this cable but many have botched connector installations. The usual way of hiding and hoping for the best is to put heat shrink tubing around the connectors for that professional look... but performance will never be great.

If your shielding is copper colored, you can usually get a solid solder connection to the PL259.

Your reception is less effected by the connectors than the transmission in my opinion.

Find a local HAM operator with test equipment and have him analyze the installation. Put a dummy load at the mast top and measure your power delivery.

Best of luck to you.

Thank you, and I agree with all the observations with regards to quality of connectors. This is where experience and practice counts and consequently it can take me the better part of a full day to get to a point where I am happy with the result. My connectors only need soldering of the central pin.

But still, I find it hard to believe that antenna patterns or quality of connectors will affect tx different to rx. I will reach out to the specialist who installed my ssb at the time.

Cheers, Mathias

[Bycrick]

LMR400 cables DO NOT use aluminum wires in the primary shield. It is tinned copper wires and provides about 95% shield coverage. There is a secondary shield made from aluminized foil to improve the shielding. The foil is not connected mechanically to the connector. If the foil just accidentally disappeared completely, you’d end up with cable that was roughly equivalent to to any other single-shielded cable, like RG8.

Some low-loss cables use a solid aluminum center conductor. It’s usually plated with copper and solders quite nicely. If one crimps the center pin, you can’t tell the difference.

The connectors should be matched to the type of cable, especially when crimped. If you look a the Times Microwave site, you’ll see a wide assortment of available "PL259” connectors for specific cable types.

[MathiasW]

Originally Posted by Bill_Giles

I may have missed it within the many replies but you say the theoretical distance between you and your friend is 17M but you could not speak at about 16.5M. There is no ‘line in water’ where the signal cuts off. So 16.5 vs. 17 is not much to worry about. As long a big boats and the CG are hearing you then there is little to worry about.

Have you tried contacting via DSC?

The 17 nm is strict line of sight, but does not include the 6% overshooting that John referred to. And the irritation arose since I could hear him very loud and clear, but he could not hear me at all.

DSC is a good idea, I will try this once there is a larger distance again. Currently, my sister vessel is only 200 metres away...

Cheers, Mathias

[team karst]

Originally Posted by CaptJimFrei

This Summer, I picked up a transmission on VHF from USCG Sector NC Command Center in Wilmington NC while on my vessel on Jordan Lake NC...a distance of about 180 miles. I only heard the CG's side of the convo, and I did not try to step in.

Called Tropospheric Ducting. Air mass with a temporary, but effective ability to bend radiofrequencies.

[Dieseldude]

Based on your watt meter tests, it sounds like you know basic trouble shooting. But here are some ideas:


It is perplexing that you cannot be received by your sister ship, but you can be received by ships with tall antennae. Perhaps height compensates for a deficiency of your radio propagation. Perhaps your sister ship has a reception fault. How is its reception of signals from other ships? Is the problem directional? Try some radio checks with sister ship at various headings from your vessel. You might have an antenna location issue. Perhaps temporarily remove the AIS antenna.



Assuming that you have ruled out control issues such as squelch setting, and the one watt setting, some basic tests can be done. Suppose that you have visually checked all antenna cable connectors. Also power supply and ground connections should be checked. It is possible that these can allow enough power for the receiver portion to work, but resistance can be too high for enough power to reach the transmitter. Power cable needs to be checked right through to battery positive, and ground right through to vessel's ultimate ground, the negative battery terminals. Of course these should measure near zero ohms.



A load resister is another useful piece of test equipment. It can be connected to a radio in place of an antenna. This rules out antenna and cable problems for measuring pure power output. A load resister must be specified for the radio power output and frequency range. Of course short jumper coax cables for interconnecting test equipment will be needed, and coax adapters if connectors on test equipment are different from your radio and antenna connectors. Of course loads resistors are not cheap. They will have a speck for duration of applied power, or they may overheat.


Basic DC resistance checks can reveal cabling and antenna faults. Antenna and radio can be disconnected. A shorting plug can be made by soldering a shorting wire across center pin and shield of a spare connector. Alternately, a short alligator clip jumper cable can be connected between center pin and shield. Caution: Be sure that your radio is shut with any short connected, and while any connection is opened. Otherwise the radio will be destroyed if someone attempts to transmit. A person can be electrocuted if they touch a live antenna connection, so take good precautions.


With short connected at one end, ohm meter probes are connected across the open end of the cable. The loop resistance will be measured. It should be in the fractions of an ohm or in the low one's of ohms, depending on cable type and length. If uncertain of correct resistance, check cable spec chart for ohms per unit length. Keep in mind that a weak connection of perhaps one strand of a multi strand wire or braid shield can measure as a low resistance to an ohm meter, but appear as a high resistance to full power radio signal. So this test is not necessarily definitive. Low resistance can be more reliably measured with a wheat stone bridge circuit. Info can be found on a net search or in electronics texts. They are quite easy and not expensive to make. They are useful for other troubleshooting tasks.




It would be helpful to measure values for both your system, and those of your sister ship. The resistance of the antenna can be measured. In theory, this would be open circuit. But I have found in practice that it can be a fraction of an ohm, or low one's of ohms. This is because an antenna can have an internal coil connected between element and ground. It will measure as a low resistance to an ohm meter that applies DC. But to a high frequency radio signal it is a high impedance.


Sometimes just re terminating a coax cable is easier than a lot of testing. Even the pro's can make a bad termination. If unfamiliar with making coax connector terminations, a connector manufacturer should have instructions on their web site with drawings. Some connector types need a special crimp tool.


Another test that might be useful would be to check is frequency of your transmitter. It is possible that it might be out of spec. If you take your radio to your supplier's shop, they should measure it with a frequency counter at no charge if they sold you the radio. It is a quick easy test, and should be done over several frequencies: low, mid, and high. Ask then to give you the measurements in writing for future reference. Your supplier can also measure you radio's output power into a load resister. And this should also be done for low, mid, and high frequencies.


Of course all outdoor connections need to be sealed upon completing tests.

[team karst]

Originally Posted by Bycrick

LMR400 cables DO NOT use aluminum wires in the primary shield. It is tinned copper wires and provides about 95% shield coverage. There is a secondary shield made from aluminized foil to improve the shielding. The foil is not connected mechanically to the connector. If the foil just accidentally disappeared completely, you’d end up with cable that was roughly equivalent to to any other single-shielded cable, like RG8.

Some low-loss cables use a solid aluminum center conductor. It’s usually plated with copper and solders quite nicely. If one crimps the center pin, you can’t tell the difference.

The connectors should be matched to the type of cable, especially when crimped. If you look a the Times Microwave site, you’ll see a wide assortment of available "PL259” connectors for specific cable types.

LMR will not be your friend if u want durable marine coax. That thin Cu plate over Al center conductor, and the Al foil wrap will be trouble, eventually. RG214 much better choice.

[windcastle1]

The fact that you can receive well is a good indication that the issue is not at your end. Even if you were only radiating 10 watts from the antenna that is more than enough to be received. Try this test. Repeat the test you did to the commercial ship by contacting them using 25 watts then switch to 1 watt and see if they can still hear you. If they even just “barely” hear you it confirms your setup works. Assume you had an SWR meter to check your antenna efficiency as far as reflected versus forward power.

[StoneCrab]

Originally Posted by Bycrick

LMR400 cables DO NOT use aluminum wires in the primary shield. It is tinned copper wires and provides about 95% shield coverage.

OK, I stand corrected on the LMR400 shielding not being aluminum. Thanks for that.

I'll have to look up which co-ax I last had that had the aluminum braiding. I threw it out.

I'll stand by my points regarding the difficulties many have in getting the connectors properly installed.

LMR400 specs

[Bycrick]

LMR400 has a solid aluminum center conductor. I wouldn’t use it because it SOLID, not because it’s aluminum. LMR400UF uses a stranded copper center conductor. Using a foam dielectric makes the cable lighter, more flexible and generally lower loss. The trade off with a solid dielectric is that it’s heavier, less flexible and higher loss. In theory, a foam dielectric can absorb moisture over time, which will affect its losses.

In the real world, LMR400UF works just fine. A 75’ piece that I installed in 1998 was replaced in 2019 after surviving two lightning strikes which destroyed two antennas. When measured with some accurate test equipment, it’s increased loss was just barely more than the new cable.

If you want to use RG214 at 5-8 times the price, you’re certainly free to do so.

[team karst]

Tell us more about the lightning strikes. Truth be known, I took a direct strike also; with LMR400. But at the house, not boat... The coax was fine afterwards.

And, my speech about corrosion is a use case example. Times makes great stuff; just pick the correct stuff.

[MathiasW]

Originally Posted by Dieseldude

Based on your watt meter tests, it sounds like you know basic trouble shooting. But here are some ideas:


It is perplexing that you cannot be received by your sister ship, but you can be received by ships with tall antennae. Perhaps height compensates for a deficiency of your radio propagation. Perhaps your sister ship has a reception fault. How is its reception of signals from other ships? Is the problem directional? Try some radio checks with sister ship at various headings from your vessel. You might have an antenna location issue. Perhaps temporarily remove the AIS antenna.



Assuming that you have ruled out control issues such as squelch setting, and the one watt setting, some basic tests can be done. Suppose that you have visually checked all antenna cable connectors. Also power supply and ground connections should be checked. It is possible that these can allow enough power for the receiver portion to work, but resistance can be too high for enough power to reach the transmitter. Power cable needs to be checked right through to battery positive, and ground right through to vessel's ultimate ground, the negative battery terminals. Of course these should measure near zero ohms.



A load resister is another useful piece of test equipment. It can be connected to a radio in place of an antenna. This rules out antenna and cable problems for measuring pure power output. A load resister must be specified for the radio power output and frequency range. Of course short jumper coax cables for interconnecting test equipment will be needed, and coax adapters if connectors on test equipment are different from your radio and antenna connectors. Of course loads resistors are not cheap. They will have a speck for duration of applied power, or they may overheat.


Basic DC resistance checks can reveal cabling and antenna faults. Antenna and radio can be disconnected. A shorting plug can be made by soldering a shorting wire across center pin and shield of a spare connector. Alternately, a short alligator clip jumper cable can be connected between center pin and shield. Caution: Be sure that your radio is shut with any short connected, and while any connection is opened. Otherwise the radio will be destroyed if someone attempts to transmit. A person can be electrocuted if they touch a live antenna connection, so take good precautions.


With short connected at one end, ohm meter probes are connected across the open end of the cable. The loop resistance will be measured. It should be in the fractions of an ohm or in the low one's of ohms, depending on cable type and length. If uncertain of correct resistance, check cable spec chart for ohms per unit length. Keep in mind that a weak connection of perhaps one strand of a multi strand wire or braid shield can measure as a low resistance to an ohm meter, but appear as a high resistance to full power radio signal. So this test is not necessarily definitive. Low resistance can be more reliably measured with a wheat stone bridge circuit. Info can be found on a net search or in electronics texts. They are quite easy and not expensive to make. They are useful for other troubleshooting tasks.




It would be helpful to measure values for both your system, and those of your sister ship. The resistance of the antenna can be measured. In theory, this would be open circuit. But I have found in practice that it can be a fraction of an ohm, or low one's of ohms. This is because an antenna can have an internal coil connected between element and ground. It will measure as a low resistance to an ohm meter that applies DC. But to a high frequency radio signal it is a high impedance.


Sometimes just re terminating a coax cable is easier than a lot of testing. Even the pro's can make a bad termination. If unfamiliar with making coax connector terminations, a connector manufacturer should have instructions on their web site with drawings. Some connector types need a special crimp tool.


Another test that might be useful would be to check is frequency of your transmitter. It is possible that it might be out of spec. If you take your radio to your supplier's shop, they should measure it with a frequency counter at no charge if they sold you the radio. It is a quick easy test, and should be done over several frequencies: low, mid, and high. Ask then to give you the measurements in writing for future reference. Your supplier can also measure you radio's output power into a load resister. And this should also be done for low, mid, and high frequencies.


Of course all outdoor connections need to be sealed upon completing tests.

Thanks for all these thoughts!

It has been decades that I was somewhat exposed to the theory of transmission lines, but in essence, they are symmetrical - in my recollection. So, whatever bad happens on that transmission line, it will affect signals running from left to right in the same way as signals running from right to left. In other words, RX and TX should be equally affected.

For instance, if I characterise a connector by the loss it introduces as -1 db, or whatever, then this is valid for both signals. If that were not true, I would not be allowed to characterise a connector as a simple db loss.

I am still at a loss here! (Pun intended )

Cheers, Mathias