VHF - can hear but not be heard at a distance

[ka4wja]

WOW!
I've been away, and still a bit tied up...

I'm actually not sure what to say....there is so much here, and to be honest it's gonna' take me a while to sort out the actual good info from the BS / argument.

Give me a day or so...

'Til then, Mathias be aware that:
--- the coaxial cable you used is a very bad choice (and whatever connections to this are suspect).....
---Also, understand that making communications range / distance evaluations to/from DIFFERENT targets or the SAME targets in DIFFERENT locales / positions, is highly suspect (meaning, many of the subjective results are too subjective to be useful)...
---And, with multiple antennas on the masthead (multiple VHF antennas within inches / centimeters of each other) is NOT good, and just that CAN very well be the only cause of these issues / discrepancies...

Before I even read any of these additional posts and try to get some info from them, I suspect your "issue" is proximately caused my all three of these above!

Fair winds.

John

[MathiasW]

Originally Posted by ka4wja

WOW!
I've been away, and still a bit tied up...

I'm actually not sure what to say....there is so much here, and to be honest it's gonna' take me a while to sort out the actual good info from the BS / argument.

Give me a day or so...

'Til then, Mathias be aware that:
--- the coaxial cable you used is a very bad choice (and whatever connections to this are suspect).....
---Also, understand that making communications range / distance evaluations to/from DIFFERENT targets or the SAME targets in DIFFERENT locales / positions, is highly suspect (meaning, many of the subjective results are too subjective to be useful)...
---And, with multiple antennas on the masthead (multiple VHF antennas within inches / centimeters of each other) is NOT good, and just that CAN very well be the only cause of these issues / discrepancies...

Before I even read any of these additional posts and try to get some info from them, I suspect your "issue" is proximately caused my all three of these above!

Fair winds.

John

Thank you John!

I am very curious what your assessment will bring.

Please bear in mind that I noticed the effect already BEFORE I had changed the antenna cable. So, it does not seem to be the culprit, however bad that choice might have been.

I will also be interested to hear why this was a bad choice, given that the specialist that installed my ssb system used this very cable for the ssb installation. Naively, I would not see a big difference between the two, ssb and VHF. If anything, the ssb requirements are higher.

Cheers

Mathias

[Bycrick]

John. — I, too, am curious why you think this Ecoflex 10 cable is so awful. While I’ll admit that it’s certainly "exotic" and has a data sheet full of puffery, it looks like it would work just fine. It’s certainly overkill for the HF SSB radio, but in many respects is similar to LMR400UF, but with lower loss. The copper foil/PE shield might be marginally less corrosive than the aluminum/PE, but in the real world ….? The fancy center conductor again seems over-engineered for VHF, but …? I’d expect that the real difference in the loss figures are based on more air in the dielectric foam. That theoretically might lead to more moisture absorption and therefore a shorter life span. But LMR is speced at 15-20 years, so that doesn’t seem like an insurmountable problem. As long as the supplied connectors are designed for the cable, and properly installed, I can’t see why they’d be any worse than any other UHF connector. Please explain.

[Bycrick]

Further, the antenna "too close together" ideas. From what I remember of antenna theory, if the two "elements" are "too close," energy will be coupled from the driven element to the parasitic element. So what? If they’re really close together, then they’ll just act as a single element, sort of like the GAM antenna. I could see coupling too much energy from the driven to the parasitic element, but that would only produce desensitization of any receiver attached to the parasitic element or perhaps damage to that receiver if you had enough power coupled. But to have an effect on the radiation pattern of the combined elements, the parasitic element has to be far enough away that it’s energy is somewhat out-of-phase with the driven element. And if I remember my AM station antenna design stuff from the late 50s, using only two elements results mostly in an "oval" pattern, not one with any sharp nulls. Again, please explain.

[team karst]

I"m new to the ecoflex 10. looks like a lower loss RG8 variant, using the same connectors.

It does this with foamed insulation, good news/bad news. It must be kept dry at the ends, so water doesn't wick up the insulation. UHF connectors are not water sealed, so exposed marine installs will need special end treatments. I like the fact it does NOT use aluminum. So, its a largerRG8x in my mind.

[team karst]

Originally Posted by Bycrick

Further, the antenna "too close together" ideas. From what I remember of antenna theory, if the two "elements" are "too close," energy will be coupled from the driven element to the parasitic element. So what? If they’re really close together, then they’ll just act as a single element, sort of like the GAM antenna. I could see coupling too much energy from the driven to the parasitic element, but that would only produce desensitization of any receiver attached to the parasitic element or perhaps damage to that receiver if you had enough power coupled. But to have an effect on the radiation pattern of the combined elements, the parasitic element has to be far enough away that it’s energy is somewhat out-of-phase with the driven element. And if I remember my AM station antenna design stuff from the late 50s, using only two elements results mostly in an "oval" pattern, not one with any sharp nulls. Again, please explain.

very much a function of the spacing. Look at this pattern with 2x 1/4Wave verticals: it is almost entirely one direction pattern. https://hamsignal.com/blog/2-element...-first-attempt

[Bycrick]

As I read the ecoflex specs, the center conductor is a copper-sleeved, stranded aluminum core where the shield is copper-flashed plastic. The equivalent Times Microwave cables are either a center conductor of solid aluminum with a copper coat, or stranded copper. So both of them use aluminum someplace in the construction. I’d expect that the aluminum core would make the cable lighter weight.

So, my preferences would be a stranded core for flexibility, whether aluminum or copper isn’t very important. Nor is whether the plastic shield foil is copper or aluminum; all the power is carried by the braided shield, which is copper in both cases.

The lowest loss cables use air (or dry gas) as the dielectric. So the more gas in the foam, the lower the loss. The trade off is when moisture replaces the gas over time. A solid dielectric has a longer potential life, but higher loss.

There’s no such thing as the "best" cable.

Your other post makes my point. Two 1/4 wave length verticals space 1/4 wavelength apart, with BOTH of them driven. But make one of them driven and the other one parasitic while at the same time placing them closer together reduces the null. If I remember from years ago, once the two elements are closer than 1/10 wavelength, it doesn’t make much difference.

[MathiasW]

So, two additional data points:

My sister vessel and me had a successful communication at 19.5 nm apart. Rather noisy, on both ends, but it worked. Our mutual orientation was slightly different compared to the initial attempt that triggered this thread - she was perhaps at a bearing of 30 degree port side now.

Secondly, I chased the gremlins on the AIS front on our sister vessel yesterday and could isolate the issue down to a faulty connector, which I replaced. In the process of doing this I measured the output power of her VHF and the amount of reflections: 25 W and almost no reflections. I thus conclude that her VHF output is not at fault.

It all seems to me now to point at the multiple antenna setup that we both unfortunately have. It will make for an uneven 360 degree radiation pattern. Sometimes it will be good for me and bad for my sister vessel, sometimes it is the other way round.

Cheers, Mathias

PS: Still interested to learn why my choice of antenna cable was a bad choice...

[Bycrick]

25 watts output is fine. But the reflected power tells you nothing (hence neither does the SWR) unless you already know the real loss in the cable. In fact, one can compute the cable loss leaving the far end completely disconnected and measuring the return power. The open end theoretically reflects all the power that gets there. So you measure the returned power and the result is twice the cable loss. Glad to hear you found the problem.

[Jim Cate]

Mathias, thanks for the update.

I refer you to post #4 in the thread where someone said:

"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."

Just sayin'...

Jim

[team karst]

Originally Posted by MathiasW

.,,


PS: Still interested to learn why my choice of antenna cable was a bad choice...

Ecoflex 10 is not a bad choice. Better than 90% of the boats out there. All copper conductors. But keep water out of it.

[team karst]

Originally Posted by Bycrick

25 watts output is fine. But the reflected power tells you nothing (hence neither does the SWR) unless you already know the real loss in the cable. In fact, one can compute the cable loss leaving the far end completely disconnected and measuring the return power. The open end theoretically reflects all the power that gets there. So you measure the returned power and the result is twice the cable loss. Glad to hear you found the problem.

All true. But dont get the idea that transmitting into a severe mismatch is a good idea; it is not. Best done with a sig gen, network analyzer, or at least a 10 dB pad at the transmitter with a dual directional coupler[emoji106]

I do have an antenna analyzer that is bosuns chair friendly.

[Bycrick]

I wasn’t recommending transmitting into a disconnected cable. I was pointing out that measuring the reflected power and then assuming that because it’s "low" (ie, a low VSWR), that everything is OK simply isn’t true. For a horrible, contrived example, if a bird tried to land on the antenna and literally broke it off. With 100’ of RG58, the cable loses can result in an "acceptable" VSWR at the radio. That’s eyeball math.

You’re right that you shouldn’t be doing antenna tests using you VHF radio as a signal generator.

[thomm225]

Originally Posted by MathiasW

PS: Still interested to learn why my choice of antenna cable was a bad choice...

Probably wasn't the cable itself unless it was damaged in shipment etc. more likely though it was the installation/installer (or the way it was installed including the connectors/connections)........

That is unless the cable has failed with most antenna uses...which would be sort of odd for antenna cabling.

There's a similar thread about certain outboards being unreliable........in this case replace outboard with cable.

Post #104!

[MathiasW]

Originally Posted by Jim Cate

Mathias, thanks for the update.

I refer you to post #4 in the thread where someone said:

"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."

Just sayin'...

Jim

Jim, yes indeed, that was my point of reference and I now believe it is the main culprit in this matter.

Cheers, Mathias