VHF - can hear but not be heard at a distance

[MathiasW]

Originally Posted by 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.

Sure, you are of course right and I an aware of this. My point was more that the initial very high reflection on the AIS line meant that something was most definitely wrong there. And I could fix it. Now the sister vessel is seeing AIS signals some 640 nm away, same as I do.

Cheers, Mathias

[team karst]

640 miles. Time for u to teach us a few things

[MathiasW]

Originally Posted by team karst

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

Yes, water is a potential problem. I have a rather dry technical room and I have used heat shrink making sure it closes tightly...

[MathiasW]

Originally Posted by team karst

640 miles. Time for u to teach us a few things

I do not think I can claim the credit for this. It is reflected signals that I am picking up, I am sure. My record is a sea buoy in France which I saw whilst in the Caribbean... more than 2500 nm away...

[team karst]

My ais antenna is a crappy short helical, 7 ft off the waterline. Lucky to get 4 miles. Its on the list…

[MathiasW]

hmm, ok, that is not a good performance. My ais is the same type of 1.5 metres antenna as the vhf and is sitting in some 25 metres at the top of the mast, next to the vhf antenna. My sister vessel has an rg58 cable from the ais unit to the foot of the mast and from there up some better cable of unknown marking. I had replaced my rg58 part with eco flex 10, but that was surely overkill and only done to train my skills of pulling thick cables through tight hoses...

I have seen other sailing vessels in 65 nm distance with this, but only a very few. I guess their ais also needs to be working well for me to pick them up. I suppose I won't see you either in that kind of distance.

Given that ais is all digital it should really have an excellent reach. At least line of sight between the two antennas, plus a few %.

[team karst]

I might have a tendency to drop the ais aerial to the upper spreader.

[MathiasW]

Originally Posted by team karst

I might have a tendency to drop the ais aerial to the upper spreader.

That seems a wise choice, given the problems I am having with the ais antenna being so close to the vhf...

[team karst]

The COM antenna will thank you with a very nice horizontal pattern.
Of course now the ais antenna will have the mast as a reflective element. But better AIS takes the hit than com. IMO.

[MathiasW]

Originally Posted by team karst

The COM antenna will thank you with a very nice horizontal pattern.
Of course now the ais antenna will have the mast as a reflective element. But better AIS takes the hit than com. IMO.

That makes perfect sense!

[Cynara]

I don't have much to say, but we never had any VHF or HAM radio antennas issues. I installed mine in qwqqqqqqq1 977. Of course there was no AIS and very few people had radars. I am no where near an expert and it is not that hard or complicated