Dr. Slack wrote ...

You could buy five of these things for £75

or five of these for £15

I'd imagine you could take the crystals off the first ones, which have the advantage to you of having manual front panel controls. I know you could take them off the second ones, but these would need a bit of software to control, but not a lot, they are SPI, and at least you know what the device is and can get data sheets, which might be difficult for the first ones.

It's fairly straightforward to move clock signals around at 10s of MHz. It needs a bit of care, you don't want long wires and haphazard paralleling of loads. A single hex HC buffer from the master clock source, each output driving a single source terminated transmission line to each driven device should be pretty bomb-proof.

Dr. Slack wrote ...

Both of those products are a bit light on details in the listings, you will have to download their operation manuals and read carefully.

In the first one, you have 'sync out' and 'sync in' sockets. You might hope that if you have two generators, and connect one to the other, and maybe daisy-chain onto a third, that they would be synchronised in some fashion. Unfortunately, and perhaps this reflects why they don't go into much detail in the listings, there's several things synchronisation could mean. I note that so far in this thread, you've not stated exactly what *you* hope to achieve by connecting several together, other than implicitly by talking about disconecting crystals, which would result in a common frequency standard between all units.

The 'level 1' of synchronisation would be that they all use the same frequency standard. 'Sync' might mean that on the first one, or may not. 'Level 2' would assume same frequency, but would add that two generators making the same frequency waveform would have settable mutual phase. Is this required? Sync may be a timing pulse, to establish a common timing reference. Or it might be programmable in some way.

One the second unit you link to 'ext in' would very likely be an external frequency reference, but whether 1, 2, 5 or 10MHz, or selectable between those, will be in the furnished manual.

The TTL I/O only tells you one thing, it's a digital signal at TTL levels. Whether it's a timing reference, or a square wave version of the sinewave from panel output, or pulse amplitude modulation in, or programmable between all of those and more, will be in the fine manual. It's probably not however a frequency reference.