Masthead VHF Antenna - The devil is in the details...

[Wotname]

I'm with Dockhead on the UHF / N type connector debate.

Apart from any other considerations, IME it is hard to buy a poor quality N type and it is easy to buy a poor quality UHF connector.

While I normally use a crimp style, one of advantage of the solder / clamp style is that they are totally reusable.

[transmitterdan]

Originally Posted by TranceNT

Always brings myths, beliefs, and facts, this VSWR/SWR topic.

Try reading this before taking too much of the first two into your memory:

https://www.arrl.org/files/file/Tech...f/q1106037.pdf

To whet your appetite, here is an extract (credit K5DVW) :

Does Higher SWR Lead to Lower
Power Being Transmitted?
Not always so dramatically. Believe it or
not, 100 percent of the power is actually trans-
mitted in both of the previous examples. In the
first case, with a 50
Ω
antenna, it’s easy to see
how all the power is transferred to the antenna
to be radiated since there are no reflections.
In the second case, the 33 percent voltage
reflection travels back down to the transmitter
where it doesn’t stop but is re-reflected from
the transmitter back toward the antenna along
with the forward wave. The energy bounces
back and forth inside the cable until it’s all
radiated by the antenna for a lossless trans-
mission line. An important point to realize
is that with extremely low loss transmission
line, no matter what the SWR, most of the
power can get delivered to the antenna.

Cheers, Terry (VK4JC)

Terry,

Your theory is correct as regards power. But it ignores the insidious problem of frequency response error.

Re reflection from the transmitter can cause big problems. Because we are talking about wavelengths on the order of 2 meters the re reflected signal creates significant amounts of ripple in the transmitted frequency response. There will be deep nulls all across the transmitted bandwidth causing lots of AM modulation and the FM receiver will not be happy. This is almost certainly why the OP could not be received only 1/2 mile away.

High VSWR is a bad thing for VHF FM.

I agree that UHF connectors are lower loss than type N. The center pin is bigger as is the outer area. Keep it dry and it is the lowest loss connector for marine radio.

A type N is exactly the same as a BNC except for the outer threaded part. Don't believe me? Try putting a type N male onto a BNC female. It will fit just fine except it has no mechanical locking feature. Electrically they are identical.

[Dockhead]

Originally Posted by Pyxis156

Dockhead, thanks for taking the time to provide the detailed description of your installation. It is hugely helpful as I will be pulling the mast probably next year and will likely mimic your installation. A few more questions below if I could trouble you further:



By saying "...and (separate!)..." I believe you are advocating that the masthead antenna not be shared by the AIS, am I interpreting this correctly?

You should get more opinions on this -- I don't claim to possess complete information. But the whole idea of using a splitter seems to me to be just fraught with problems. I just never liked the idea of it. Separate antennas avoids all of those problems and risks, and in addition, adds redundancy. It just seems to me like the correct systems architecture approach. I would even add a third, backup antenna if you have a radar pole, mizzen mast, etc., but then my paranoia is showing . . . .

I would add that spreader height, and probably pushpit height, is perfectly adequate for AIS. You want to communicate with ships at 15 miles or so. Ships have high antennas so you'll have line of sight even from the pushpit. Comms with other pleasure boats need not have such range.

Good luck with your installation!

[Auspicious]

Originally Posted by TranceNT

Always brings myths, beliefs, and facts, this VSWR/SWR topic.

What the article you cite fails to address is the foldback circuitry in solid state transmitters that reduce power in the face of high SWR to protect the equipment.

Originally Posted by Dockhead

Well, thousands of hams and sailors use UHF connectors successfully -- certainly nothing fatally wrong with them.

Challenging John on this was knocking over a hornets nest. *grin* He's published test results.

I use the best solder/solder silver-teflon UHF connectors I can get. I can avoid soldering at the masthead by good planning. I avoid barrels at all costs. Good coax - either RG-213 or RG-214.

[ka4wja]

Dockhead, et al,
Not going to ramble on about this....

Just to clear there are MANY inferior "UHF" connectors made and sold worldwide, as there is no real "Mil-spec" standard, as long as the threads match, many manufactures sell 'em by the 1000's!! (I've even seen some at hamfests that the threads aren't cut correctly!! and people are buying 'em, in pairs / groups!)
This is opposite the case, in regards to "N" connectors, where stringent standards do exist....and those needing them will pay for mil-spec'd connectors.
And, most of my Australian friends that cannot find Amphenol's, use generic far east manufactured connectors....(and while no mention was made of the manufacture/source of connectors in that article, I'm assuming it's they used the typical "generic far east manufactured connectors")
So, for two PL-259's and one PL-258, all connected together, I accept their findings of 0.2db thru loss...

BUT..

But, if you are looking at Amphenol (or Kings) PL-259's (and PL-258's), the "impedance bump" at VHF (~ 150mhz) is minimal and the insertion loss is negligible...
I know Amphenol specs their 83-1SP (the PL-259's that I use and have used for ~ 40+ years, now) thru 300mhz...
PL-259, UHF Straight Solder Plug for RG-8 | 083-1SP | Amphenol RF

I'm sorry I don't have the plots to show....but I've used the same 0.1db (or less) spec for a pair of PL-259's and a PL-258 barrel (at 150mhz) for more than 30 years....and I think Amphenol actually published something like < 0.05db per connector, return loss > 20db, at 150mhz...years ago...but cannot find it...
Fact is the at return loss of 20db, the VSWR is 1.2:1 and max insertion loss is 0.05db...
And, a pair comes to 0.1db, at 150mhz...
And, in my opinion, for VHF-FM, that's insignificant...especially since various cable manufacturing tolerances, etc. as well as an extra couple feet of cable, etc., can add up to more than that...

But, even if we take twice that number (as the referenced Australian article specs), that's still only 0.2db!!
Quite a small amount!

And, in my opinion, this isn't worth worrying about for a VHF-FM system, mainly used in line-of-sight comms...
[now understand that I WILL squeeze out every last 1/10 of a db, out of my 2m EME (moonbounce) system, as that's just that much more transmitter power....but, for VHF-FM, worrying about a 1/10 of a db is, in my opinion, not worth it...]
Yes, I know the adage that "everything adds up"...(like back in the days racing, where you didn't remove one thing from the car that weighed 100lbs, but removed 100 things that each weighed one lb!!)...but we're talking VHF Marine, where 95% of our comms have huge margins (20nm, line-of-sight, from sailboat to sailboat, has about a 50db margin!), so worrying about the difference between 0.1db total connector loss versus 0.2db total connector loss, in my opinion, is insignificant!!

Originally Posted by Auspicious

Challenging John on this was knocking over a hornets nest. *grin* He's published test results.

I use the best solder/solder silver-teflon UHF connectors I can get. I can avoid soldering at the masthead by good planning. I avoid barrels at all costs. Good coax - either RG-213 or RG-214.

So, Dockhead and I have differing opinions....not a big deal...


Fair winds...

John

[Dockhead]

Originally Posted by ka4wja

Dockhead, et al,
Not going to ramble on about this....

Just to clear there are MANY inferior "UHF" connectors made and sold worldwide, as there is no real "Mil-spec" standard, as long as the threads match, many manufactures sell 'em by the 1000's!! (I've even seen some at hamfests that the threads aren't cut correctly!! and people are buying 'em, in pairs / groups!)
This is opposite the case, in regards to "N" connectors, where stringent standards do exist....and those needing them will pay for mil-spec'd connectors.
And, most of my Australian friends that cannot find Amphenol's, use generic far east manufactured connectors....(and while no mention was made of the manufacture/source of connectors in that article, I'm assuming it's they used the typical "generic far east manufactured connectors")
So, for two PL-259's and one PL-258, all connected together, I accept their findings of 0.2db thru loss...

BUT..

But, if you are looking at Amphenol (or Kings) PL-259's (and PL-258's), the "impedance bump" at VHF (~ 150mhz) is minimal and the insertion loss is negligible...
I know Amphenol specs their 83-1SP (the PL-259's that I use and have used for ~ 40+ years, now) thru 300mhz...
PL-259, UHF Straight Solder Plug for RG-8 | 083-1SP | Amphenol RF

I'm sorry I don't have the plots to show....but I've used the same 0.1db (or less) spec for a pair of PL-259's and a PL-258 barrel (at 150mhz) for more than 30 years....and I think Amphenol actually published something like < 0.05db per connector, return loss > 20db, at 150mhz...years ago...but cannot find it...
Fact is the at return loss of 20db, the VSWR is 1.2:1 and max insertion loss is 0.05db...
And, a pair comes to 0.1db, at 150mhz...
And, in my opinion, for VHF-FM, that's insignificant...especially since various cable manufacturing tolerances, etc. as well as an extra couple feet of cable, etc., can add up to more than that...

But, even if we take twice that number (as the referenced Australian article specs), that's still only 0.2db!!
Quite a small amount!

And, in my opinion, this isn't worth worrying about for a VHF-FM system, mainly used in line-of-sight comms...
[now understand that I WILL squeeze out every last 1/10 of a db, out of my 2m EME (moonbounce) system, as that's just that much more transmitter power....but, for VHF-FM, worrying about a 1/10 of a db is, in my opinion, not worth it...]
Yes, I know the adage that "everything adds up"...(like back in the days racing, where you didn't remove one thing from the car that weighed 100lbs, but removed 100 things that each weighed one lb!!)...but we're talking VHF Marine, where 95% of our comms have huge margins (20nm, line-of-sight, from sailboat to sailboat, has about a 50db margin!), so worrying about the difference between 0.1db total connector loss versus 0.2db total connector loss, in my opinion, is insignificant!!



So, Dockhead and I have differing opinions....not a big deal...


Fair winds...

John

That all sounds quite logical and reasonable, as we may expect from John.

I do use UHF connectors - you have no choice in many cases. And I have a supply of Amphenol ones on board, both crimp and solder types.

I use them mostly to help other cruisers with radio problems, 80% of which can be solved with new connectors, in my experience. My fee is one connector, one beer. Or two beers, if I have to go up the mast.

[hellosailor]

Pyxis-
A lot of folks would say to replace coax every 5-10 years in any case, because the plasticizers may be breaking down, and the vertical run in the mast usually is not supported correctly, so it either stretches out or is pinched, and either one eventually changes the cable properties.
If it is just zip-tied every six feet, those are pinch points, compressing the layer that separates the center from the outer shield. If it just hangs, like silly putty it deforms. There are "chinese finger trap" type fittings that are professionally used, which grip a slightly longer (i.e. 6"long) stretch of cable, which then allow it to be secured without a pinch point. You won't find them at a chandlery, but if you search online for how to properly install vertical coax runs...You can find out where to get them and how to use them, or alternatives.
I'd also mention that these antenna problems are a good reason for a handheld radio. Yes, it is weaker than a good ship's station, but it is an awful handy alternative when the fixed installation has gone south.

[Cadence]

Originally Posted by hellosailor

Pyxis-
A lot of folks would say to replace coax every 5-10 years in any case, because the plasticizers may be breaking down, and the vertical run in the mast usually is not supported correctly, so it either stretches out or is pinched, and either one eventually changes the cable properties.
If it is just zip-tied every six feet, those are pinch points, compressing the layer that separates the center from the outer shield. If it just hangs, like silly putty it deforms. There are "chinese finger trap" type fittings that are professionally used, which grip a slightly longer (i.e. 6"long) stretch of cable, which then allow it to be secured without a pinch point. You won't find them at a chandlery, but if you search online for how to properly install vertical coax runs...You can find out where to get them and how to use them, or alternatives.
I'd also mention that these antenna problems are a good reason for a handheld radio. Yes, it is weaker than a good ship's station, but it is an awful handy alternative when the fixed installation has gone south.

That or possibly an emergency antenna that screws right up to the 25W job.
Probably limited range but blowing 25W has to be better than 5.

[hellosailor]

"an emergency antenna that screws right up"
At that point I get out an alligator clip that's ~18" long. They jamfit pretty nicely in the center of a UHF socket. Or, a wire coat hanger. Each just as effective and way cheaper.(G)
Actually I've got an emergency antenna, stored along with an ancient (crystals!) small VHF. It's about 20' of free salvaged coax with the end turned back on itself, inside out, and a small loop to tie it aloft to something. The business end sometimes get called a "bazooka" or "sleeve dipole" antenna. Which isn't perfect but works very nicely and stows, well, in a loop next to that spare radio.

[Pete7]

Originally Posted by Dockhead

Almost five years later, this installation is still going strong. I once got a "weak but readable" signal report from Solent Coast Guard from 60 miles away across the Channel in Cherbourg -- USING 1 WATT TRANSMISSION POWER. I normally use 1 watt transmission power and LO receive attenuation settings on my Icom M604. As any radiohead will tell you -- the antenna and transmission line account for at least 80% of the performance of your radio.

I seem to remember listening to you make that call and I quietly said to myself "no chance". 15 seconds later I was eating my words and thankful I didn't bet a good bottle of Port on them hearing us

[Dockhead]

Originally Posted by Pete7

I seem to remember listening to you make that call and I quietly said to myself "no chance". 15 seconds later I was eating my words and thankful I didn't bet a good bottle of Port on them hearing us

Yes, Pete, that's the call I was thinking of! You were there!

[Auspicious]

Originally Posted by Cadence

That or possibly an emergency antenna that screws right up to the 25W job.
Probably limited range but blowing 25W has to be better than 5.

Reading this the first thing I thought of was:

Originally Posted by hellosailor

"an emergency antenna that screws right up"
At that point I get out an alligator clip that's ~18" long. They jamfit pretty nicely in the center of a UHF socket. Or, a wire coat hanger. Each just as effective and way cheaper.(G)

Hellosailor got there first.

[Pyxis156]

Originally Posted by ka4wja

1) First off, this discussion will probably be long and controversial...
But, as long as you don't mind the long discussion and give some benefit of the doubt, we should be fine..
Also, hope you don't mind if I digress a bit and clarify some points that should be understood by all, before moving forward??

EDIT:
Just saw the other posts here...I spent over 3 hours (on and off) typing all of this...

John, again thanks for taking the time to respond in such detail... hugely appreciated! I will try to answer your questions below and then I have some more questions at the end:

Originally Posted by ka4wja

Second, the use of LMR cabling is one of the more frustrating things in our lives these days...

[I understand that the initial moisture intrusion in your installation may have come from the antenna / connector itself, and the main issue you started with was probably a bad connection (actually likely no antenna connected at all!)....I think you'll see that if there wasn't LMR cabling being used, this issue would probably have been less severe...and possibly not occurred at all..]

I am quite certain that the antenna losing its watertight integrity was the problem. I know for a fact that the cable was installed and the connectors put on the same day when the boat was being built. However, that was in 2008, and when we bought the boat in 2013 the VHF was tested and both the send and receive appeared to work, but photos I took of the masthead when we had the boat surveyed do indicate some discoloration on the antenna base so the leaking may have already started.

Performance appeared to deteriorate rapidly after we sailed the boat from San Francisco to Seattle and the very rough conditions the first five days may have contributed to that. The first real indication I had that things were not working well was on the 4th day of our trip, a USCG helicopter hovered about a quarter mile behind us and maybe 500' up and we had a conversation but they did indicate that our transmission quality was poor.

Originally Posted by ka4wja

So, please just know that using LMR cabling is NOT recommended by anyone that knows their stuff in the marine electronics business, unless for some specific purpose and then only if full-disclosures are given!!

Point taken and lesson learned... we plan to pull our mast in about two years before we head for the South Pacific and I intend to replace all the mast wiring at that time. RG-213 will be replacing the LMR-400!

Originally Posted by ka4wja

Also, do you have any splices / disconnects in the bilge or at the mast base (most of us do) to allow disconnecting of the mast wiring when unstepping the mast?? As, these are many times the cause of the problems described here!!

The masthead VHF antenna has LMR-400 to the base of the mast, and then there is an LMR-400 run from the VHF at the Nav Station to the base of the mast, and the two are connected with a barrel connector.

The dedicated AIS antenna on the first spreader has LMR-400 run directly to the AIS unit mounted next to the base of the mast, so no connectors or other breaks in that antenna to AIS run. Note when we bought the boat, the dedicated AIS antenna was showing a fairly low VSWR but it now has a 4:1 VSWR (according to the AIS unit) so the VSWR has deteriorated significantly over the past three years since we bought the boat.

Originally Posted by ka4wja

Whether my preferred Shakespeare 3' SS Whip or your Digital Antenna 3' SS Whip, what you refer to as the "loading coil" is not a loading coil....
These are end-fed 1/2-wave antennas and are not "loaded" antennas...
What is in the base mount is the feedline matching, which is a parallel tuned circuit that allows feeding a very high-imp (1500-2000 ohms) end-fed 1/2-wave antenna with 50-ohm coax...

Thanks for clarifying that, I am still learning and have a long way to go...

Originally Posted by ka4wja

As to why / how your antenna's base got water into it...I don't know, I'm not there, I can't see it...
But, if the instructions talk specifically about how not to mount the antenna and it was installed/mounted that way (the improper way), that is a big tip-off to me...(perhaps they know that their antennas need a particular mounting inorder to not break/crack??)

I am reasonably certain that the leak was not caused by the mount. The old (Metz) antenna that leaked was mounted the same way as the masthead VHF antenna in the pictures you posted in the recent Multiple Masthead Antennas thread. That is, the L-bracket was mounted with the "L" right side up and the vertical portion of the L parallel with the base of the VHF antenna. The instructions from Digital Antenna indicate the "L" should be mounted upside down, so the metal of the bracket is not right next to the base of the antenna but below it.

Originally Posted by ka4wja

Also, the fact that Digital has some sort-of "twist-off" mechanism for their antenna, that may in fact impart more stress / force on this base section?? And/or may allow some pathway for moisture to get in???

Again, the antenna that leaked has been removed and replaced with the Digital Antenna, it was not the Digital Antenna 222 that leaked. And in looking at the design of the twist-off mechanism, it appears robust and not likely to leak. It is hard to describe, but the twist-off design looks to be even more leak resistant than a more typical antenna.

Originally Posted by ka4wja

You notice I didn't mention VSWR yet??

That's because I wanted to get some of the above basics out-of-the-way first....AND...

And, because while I think Vesper makes excellent AIS units (and are really nice guys!), I'm not a fan of "software VSWR measurements"....mainly because if they're shown out a decimal point or two, or three, everyone thinks that they are accurate, but they are NOT....in actual practice, even "lab grade" power/VSWR readings are +/- 10%, and at VHF many consumer grade devices have twice the variances, or more....
Not saying that you cannot believe the readings you took, to the contrary I'm going to assume they are pretty good readings, but just understand that when measuring small amounts of power at VHF frequencies, absolute accuracy is tough, so let's just say that these readings are +/- 10%...okay??

I hear what you are saying and completely agree. However, I do wonder if there is not some utility in the measurements from a relative standpoint. That is, three years ago the VSWR was 2.66:1, and now it is 4:1 (as measured by the same unit). While the absolute accuracy may not be there, would it not still be a fairly strong indication that the VSWR has indeed gotten relatively worse over time? And if so, what does that mean?

Originally Posted by ka4wja

Also, please note that when measuring VSWR at the radio end, rather than at the antenna itself, means the "loss" in the cable actually improves the VSWR you see....meaning that the VSWR is worse at the antenna than you are seeing on the meter (unless there is a bad connection at the radio end, in the bilge, etc..), see below for details...

Please see my questions at the end...

Originally Posted by ka4wja

Further, you've made no mention of the type / brand / quality / length, etc. of the coaxial jumper cables that you used to connect these devices together...(such as those connecting your radio - Vesper SP-160 - Vesper XB-8000 - antenna)

Sorry for that oversight, and as I stated above, all cabling is LMR-400, the AIS is connected directly to the AIS antenna on the spreader, and the VHF connected to the masthead antenna with a single barrel connection at the base of the mast.

Originally Posted by ka4wja

And, even further, we have no idea if these connections were tight and secure?? Which can also cause intermittents and VSWR issues...

Checked and double checked, all are tight...

Originally Posted by ka4wja

Looking at the Digital 222-VW SWR plot in their spec sheet shows it to be a bad choice for AIS (or VHF/AIS) use...it shows 2:1 at 153.8mhz and 159.8mhz, dipping to 1:1 (?) at 156.8mhz...
This is not what you'd want for AIS (at 162mhz)...as I suspect that it is as high as 3:1 at 162mhz (but this is masked by the losses in the cable)...

Might that explain why the VSWR was 2.66:1 when things were "working OK" when we bought the boat?

Originally Posted by ka4wja

Looking at the numbers that you write, it seems likely that originally you had connection to the antenna, but since I don't know if your system actually worked or not, I cannot be sure! (understand that a dummy load has a perfect VSWR, but does not work as an antenna...and an antenna that is up in the clear with a bad VSWR will still work okay....)

Prior to buying the boat we had it surveyed and they did a radio test, and the surveyor was able to reach a friend at a marina in Alameda from where our boat was located in Sausalito, a distance of approximately 10 miles with some land in between blocking direct line of sight. They seemed happy with that performance.

Originally Posted by ka4wja

And, at some point water got into the antenna base (and connector), and either corroded things beyond ability to maintain contact and/or the water froze in the winter and just broke the connection altogether??

I did a close inspection of the connection when I replaced the antenna, and while there was some green corrosion in the connector, I saw no signs of freeze / expansion damage.

Originally Posted by ka4wja

You mention that you don't use the VHF often??
You wrote that it "seemed to receive OK", and that you "do not use the VHF often", so you just assumed things were not optimal but OK??

I would estimate I use it to transmit probably fewer than 10 times in a typical year, but it is on and receiving all the time when we are underway.

Originally Posted by ka4wja

Please note that our VHF Marine Radio systems have incredible margins built-into the system design...and as most of our comms are within 15-20 miles (which is line-of-sight distance between 2 sailboats' masthead antennas), this margin is typically 40+ db!!
So, even mediocre installations can still work "OK"...
So, without any real indication from you whether your VHF radio system ever worked well at all, it's difficult to troubleshoot from 1000+ miles away!!
But, I am trying...

And again, your assistance and efforts are most certainly appreciated!!! I mentioned the radio test during the survey just above, so hopefully that gives you a better idea of whether or not our "VHF radio system ever worked well at all".

Originally Posted by ka4wja

Since your masthead antenna and "dedicated AIS antenna" are fed with different cables, I'm assuming you (and Vesper) discounted the cabling as proximate cause of these issues???

Vesper concluded there was a problem with the installation, but did not conjecture on what the actual problem was. Once we established that the AIS and splitter were functioning OK, efforts to further troubleshoot tapered off (understandably).

Originally Posted by ka4wja

Of course we do know you need to replace the antennas, but I suspect the cables will also need to be replaced as well...(unless you have enough slack to cut-back a few feet and inspect the cable interior, and if it's good, you could just install new connectors, but I'd NOT recommend this....just replace the whole darn run of cable!!)

The antennas are replaced, and I fortunately have about 3' of slack at the bottom of the mast so I can try pulling that up and cutting back to "clean" cable at the top as a short-term fix. I would like to get things working well enough to limp along until we pull the mast in a few years and will then replace all the coax.

And now my questions (I have searched through the archives and not seen anything specific on this so I hope you might be able to provide some guidance).

1) You stated that measuring VSWR at the radio (or at the mast base as I did) is not really helpful, and that it should be measured at the antenna.
Could you please elaborate on exactly how VSWR should be measured in an ideal world? Should I take my Shakespeare VSWR meter up to the masthead with me and test up there? Do I connect the antenna to the antenna end of the VSWR meter using a short pigtail connection?

2) If I read what you said correctly, then measuring power at the antenna is a more useful diagnostic tool. Could you please elaborate on how one would correctly do this?

3) Are there any other diagnostic tests or tricks of the trade you could suggest that will not only help me identify and fix my problem, but also be useful to test that my overall VHF and AIS systems are functioning correctly?

Thanks again John, I cannot thank you enough for taking the time to share your experience!