link over water ptp 600


We have a link across sea, its on ptp600 connectorized. The link had been getting bad in short times, upon graphing i discoverd that this happens most of the time during afternoon hrs, could this be ducting or reflection ? as the signal goes from -58 to -70 the modulation starts to play and we loose the throughput.

any help ?

Many thanks,

Can be. Could also be multipathing.

Is it a diversity configuration ie 2 dishes 1 end? Length of link?
Is it high enough above the water that your frenzel zone is not touching at high tide?

What firmware, its only the latest version that iDFS was enabled for certain regions. Without this the PTP600 wont change channels if there is a better one as it fades out.
They still change if interference detected, just not low signal. iDFS is enabled in spectrum management?


post your status and spectrum management pages preflably when the link is good and again when it fading. Use print screen and save as JPEG

what antennas are you using and what is desired link throughput?

Thanks Privatteer for the reply.

Its using single dish, 4ft, dual pole. Link length is about 60kms, of which just 3-4 kms is over land, rest over water.

I have the new Firmware running, 58600-08-03, iDFS is enabled on Spectrum management, i have alsoenebled different channel use, TX and RX. Attached screen shots when the signal is good and bad.

I cannot attach anything here. Is tehre a way to attach these images

Wow 60 kms over water that’s a big ask if you want to maintain high modulation modes also post kmz placemarks when you work out how.

60Kms… I have had links at 2Km have multipathing issues. One in particular dies totally at a certain tide point.

The other issue you could be having is related to refraction causing the signal to “bend”.

At that distance I can only suggest you try a diversity configuration. ie install 2 dishes at one end, one connected to H, one to V. No need to replace the dual pole I’ve used them at both ends and it makes it easy to try switching V and H without rotating the dishes.
Link planner will give you a start for the spacing but if you can be onsite and move one dish during a fade out period you can sometimes find a better spot.

Have to host images on a site such as imagehost and then link to it.

Privatteer wrote:
60Kms... I have had links at 2Km have multipathing issues. One in particular dies totally at a certain tide point.

I think Tides are a key question here, is this a tidal body of water? If so is their a time of day correlation between the path acting up and the point in the tidal swing?

Are the problems unidirectional ? I.E. does one direction start taking hits and the other side remain relatively clean?

If so you have a real problem that may be tough to resolve. Worst case is typically a high to low shot which will have a close in reflection point causing total blockage in the direction of the low end during certain periods of the tidal swing.

You can sometimes fix a tidal problem by adjusting antenna heights at one or both ends. What you want to do (if it is tidal) is figure out the path geometry, including where the bounce is taking place. Then adjust antenna height to move the bounce point further out towards the center of the path.


I will try diversity first and see if that helps, but then do i need same size dish ? on each location ? or can i add a 2 ft tot he 4ft i have on one side ? I have not done diversity installs, and how do you align ? one dish at a time ?

And this just happens random times, but i have noticed much during day, at night its stable. and i can go to near max modulation.

Thanks for all the helps.

abdock wrote:
And this just happens random times, but i have noticed much during day, at night its stable. and i can go to near max modulation.

Before spending money I would put a Dude or other monitor on the link and try to determine more about when the events are happening.

If it is not a tidal body, or there is no correlation to the tidal swing you can probably eliminate the over the water concern.

The next thing I would be looking for is a correlation with day to night and night to day, IE are you taking most of your hits at dawn and dusk? This is when propagation is generally changing due to a change in stratification. Almost surely a prop problem and diversity may well help you out.

A final thing I would be looking for is any other kinda time of day correlation, for example are you taking more hits between 9 am - 11 am and 1 pm to 5 pm Monday to Friday? This would almost certainly point at something man made and probably a diversity solution is not going to do you much good.

I am far more familiar with how a diversity combiner worked in the old analog days than today's implementations, but I think the concept is about the same.

In diversity you have two isolated paths between the two locations, in general you want to have your diversity antenna at least one wavelength separated from the primary. You also do not want to have it an even number of wavelengths of separation so go for something like 1.25 as a start. edit Vertical spacing much better than horizontal, if you have to use horizontal separation go for as much distance between antennas as you can afford loss in cable.

In an analog system you have two separate receivers, each of which has a measurement of some characteristic of path goodness, for example the C/N ratio.

The received signal, and the measure of goodness, from each is sent to a diversity combiner. Combiners in analog systems can either be switching, IE selecting the signal from the best path and disabling the signal from the less good path. Or they can be proportional where the output signal from the combiner module is proportional to the Goodness of each source, if both paths are equally good the output would be a signal that came 50% from one path and 50% from the other.

Alignment of these things used to be a lot of fun.

Modern digital units are a bit more complex, some do the combining at the input stage where the signals are first converted from RF to a bit stream, another difference you run into is that some systems use FEC (forward error correction) over the RF path, not to mention all the complications that ODFM can introduce.

Fortunately dish alignment does not depend on diversity implementation. Simply disable one dish and peak the other for best signal. Disable that dish and peak out the other dish.

There should be a screen someplace that tells you how well diversity is operating for your system. Check out the before and after and set up dude to monitor it as well, then run it for a couple of weeks and see if you have any measurable improvement.


I have been graphing signal levels and i don’t think its related to tidal, all i could say is that the ducting effect is making the link go bad.

On diversify, is it ok to install 2 dish on one side and 1 on the other side ? or do i need to have 2 at both sides ?

Thanks for all the help.

On diversify, is it ok to install 2 dish on one side and 1 on the other side ? or do i need to have 2 at both sides ?

Yes you can equip for diversity in only one direction. If you are only taking hits in one direction it might be that you have a high/low configuration with some near end situation that would cause it to hit up during the shift from day to night or night to day.

Can you tell me what model of equipment you are using ? I will take a look and see if Motorola has any recommendations about diversity operations.


I have PTP58600 and PTP54600, there are no interference on channels, but the fading happens, i have attached the db plotting with vector errors, this might help in seeing what could be problem.