No GPS on AP side of a link


On the AP side of a B5 link, the radio has no GPS reception. It comes and goes (due to interference) but is mostly gone. The client side has good reception.

Can the client side act as timing for this link? What effect will no GPS signal have on the AP? We don’t have to use a synchronized link but we would like to…


Ran some tests on this link. AP side has no GPS (due to FM tower interference). Client side has great reception.

Using 2x20 channels with an MCS 8 on each stream. MAC is 208x208. If I run an internal bandwidth test using the radio test, it gives me 200 x 200 each time. Great looking link from an RF perspective.

However, if I run an internal iPerf test or a TCP bandwidth test, they both show 15 x 200 (at the client end).

Is this GPS related? Should I expect to see terrible download from an AP with no GPS sync? If so, can I simply swap which radio is the AP and which is the client (not physically but in the radio setting) and will the radio with good GPS send the sync data over the link to the radio without it and bandwidth improves?


You should better take a look at ethernet negotiation speed and flow control. Most of the times it is related to such problems.


Both sides are negotiating at 1G on the switch. While flow control is enabled on the radios and switch port, it is not active on either end.


I have ran into this multiple times on some of our sites. The simple fix is this. Turn the B5C around so that the metal is facing the interference. I then wrap Copper Tape from the top of radio to the bottom front and back. Make a point not to cover the very top of the Radio as that is w

here the GPS antenna is. This simple fix gave me full GPS on the B5C that I have at my site. Special note. use the copper take with 3 layers.


We are using the B5 so I’m not sure I can do that here. We reversed the ends (made the client with the good GPS become the AP and vice versa). That did not improve throughput at all. Same issue. It looks like both ends need to have a good GPS signal in order for the link to work properly. It won’t transmit timing information from the AP side to the client side I guess.


Buena idea, Nice Idea


You can cover the back of the B5 with the same tape. But use 5 layers. It acts as a barrier. again on the B5 the GPS is at the top of the radio so if you cover the back and sides it should help.


Let’s hope this does the trick… Really need this link to work and it won’t transmit more than 25 Mbps without GPS. I only had enough tape for 4 layers on the back and sides so I hope one less layer is not the deal killer.


looks good. i hope it works. we have maintained GPS on ours.

just a note. give it some time to acquire the gps signal dont expect it immediately on boot up.


Well, the 4 layers of copper tape helped - alot - but did not solve the issue. Before the tape, no GPS lock ever. After the tape, I have GPS lock 90% of the time. However, during those 10% outages, transmit speeds from the AP drop way down and latency issue appear.

I wish I could turn this into a large B5-lite and not use GPS but I don’t see a way to do that. This link is a little far (2 km) for B5 lites to be used.

Mimosa: any chance you have some private firmware that can turn off the GPS in the B5 and let me run without?


Sorry, no private firmware that turns off GPS. If GPS signals are lost, the disciplined oscillator and TSF algorithm take over to limit the performance impact. Please ping Support with the device names so that we can take a look. It sounds like there may be another interference source.


OK, So we are halfway their. The problem on this is very simple. The GPS shielding in the B5 and B5C are not as good as those on the A5 and A5C. So what you need to do is block the interference on the radio. The only next logical step is to create something that will cover the back of the Radio. Maybe a small Dish or a metal plat mounted behind it. I am glad to hear the tape helped. But you may need to add something little thicker. Sorry it did not work 100% right off the bat.



I think I may have to punt on this and move to a different vendors radio. We had the B5’s and I really wanted to use a pair here but I don’t have much physical space at the top of this tower to build shielding and the client is needing the link working soon. While these radios work great at the lower half of the tower (and our other locations), this is just not going to be an ideal place to use them. I hate to be chasing GPS issues for a while. We had a few Cambium PtMP radios we had to upgrade due to GPS issues as well on this same tower - so it’s not just the B5’s having trouble.

I do wish a B5 link could get timing from either end, not both ends. We have great GPS at the client side. Or use an external timing signal over Ethernet I could send up from the bottom.


I hear ya. I wish they would put on an optional external antenna so we could put on a higher gain receiver. I have discussed this with them a couple of times. I do think however, they are looking at fixing the shielding problem with the radios.