So right now:

modem-->r6400 (with static IP from provider) --x--> CPE510(1) --x--> CPE510(2) --x--> CPE510(3)

Just to be sure: you connect the CPE1 to the r6400 using repeater mode and the following CPEs to CPE1 also using repeater mode, right?

This not only creates big issues with alignment of the CPEs to each other (did you align them at all?), but with bandwidth/throughput, too: using 3 repeaters in a row will reduce bandwidth to 1/8 (yes, that's 12.5%) of what you could get with a straight setup between two CPEs with one radio link. Not to speak of the hidden node problem you almost certainly are running into with such an adventurous topology.

So some of the first questions are: why don't you use cable to connect the CPE1 to the r6400, what sites would you like to connect and why do you need repeating mode for what purpose? How many directional links there are to cover from the source network to the remote place?

Leftboot wrote

May I ask how you would do this?

The CPE has directional antennas with a beamwidth of 45° on the H plane and 30° on the V plane, thus a pair of them need to be aligned front-face to front-face.

Especially in the 5 GHz band you need an (almost) free line of sight (LoS). Although it does not interpenetrate foliage as good as 2.4 GHz, it will even go through some kind of trees (e.g. willow trees), but never ever it will pass through an area with metal structures. No chance at all. Only way is to go "around" the metal structures, in a way to go at angles/over corner.

You could do that with 3 CPE's only if the first CPE (#1, home), which faces a second one in direct LoS to a "middle" positioned CPE (#2) at the corner, is in the same angle (inside 45°) as is the third CPE (#3, studio) facing to the one in the middle. A picture explains this better:





Instead of repeater mode, I personally would use AP mode for CPE #2 and client mode for CPEs #1 and #3, so that I could take advantage of using MAXtream/TDMA to avoid the so-called hidden node problem (see wikipedia for an explanation of the HNP).

The best place of CPE #2 depends on the angle of the antenna's beamwidth in respect to CPEs #1 and #3. Both should be inside the 45° range for best results, even on short distances.

If you can't set up CPE 2 in the middle of such a "above corner" link, four CPEs would be needed, so you have two independent radio links with almost straight alignment to each other, such as this:





In this case, one of the CPEs #1 or #3 are in AP mode, while #2 and #4 are in client mode or vice versa, doesn't matter for the flow of data. But avoid repeater mode. Not only there is no need to use this mode for the kind of setup you want to use, but it also will almost certainly cause problems (see HNP).

As for your question re directional link: it describes the characteristics of the radio link with aligned antennas so you will get the strongest signal, independent of TX power. If you look at the CPE 510's antenna beam patterns, you see that it is a very bad idea to point the back of a CPE to its counterpart, the remote CPE:





Outside the 45° plane you will have a 10 times weaker radio signal. Facing one CPE back to the other one or even leaving the 70° plane you will experience a 1,000 times weaker signal due to attenuation.

As for the wireless setup, Johnsontp already answered. I just would add: use fixed 802.11n mode and be sure to set the distance correctly (or set to auto).

Antenna patterns are from the CPE data sheet. It is always useful to read the fine manual (RTFM). :D

Leftboot wrote

As I understand it AP mode creates a new network does it not? Would bridge mode be better?

No, AP mode does not create a new subnetwork, it just creates a new virtual WiFi interface, that is (internally) bridged to the LAN network.

No, bridging mode over wireless (rather than internal bridging of the virtual interfaces) would be even worser.

Anyway, depending on the old folk's home (reinforced concrete, number of walls etc.) you can't build a stable directional link in the 5 GHz band.

Mount the CPEs locally in your home. Set them up as you wish, test connectivity. Then mount them on the final places. If it doesn't work, don't waste your time trying to fiddle with it. The chances that it works if a big building is in between the radio link and you're using 3 repeater links are very low, since this is not, what the CPEs have been designed for.