Steve,
1) Your question comes up from time-to-time....and, while Zak, W1VT has give you a wonderful answer....if you're not interested in a full-on SO2R set-up?
The short answer (for a non SO2R set-up):
Then all you really need is a decent coax switch (to switch between your two radios), or if you have multiple antennas as well, then you'll probably want a second coax switch (to switch between your antennas)
Of course, if you've got the time/money and do want a full-on SO2R set-up, then look more at Zak's link.
I'm not clear on how many antennas you have, and what antennas they are...for what bands, etc...
Also, which radio are you using as primary (I assume the '890!!!)
The more info you can give, the better and more detailed the answers you'll get.

Hi Elmers. A question for you, if I may?
I got my licence only last year. Like most, I love to see shack photos with multi radios.
I’m lucky to own both a Yaesu FT-2000 and a new Kenwood TS-890s.
How do you transmit on one radio, without damaging the other? I do not have both switched on at the same time, when transmitting. I’ve got antennas for both radios.
I’ve heard that one has to be ‘switched to earth’… I’m not entirely sure how to do this (or even, what it means).
Can you tell me what I need to do, in a kind of ‘big dummies guide’ explanation?
Thank you.
Steve.
2) Before getting to the long answer...
Ironically, we just got through discussing how much signal one radio's receiver can handle from another radio's transmitter, when they are both connected to antennas that are separated by a certain distance....
And, fyi...most radios have their receiver connected to the antenna jack when powered off, so turning one radio off is not solving the issue...
The good news is that you can leave both radios on, while transmitting with one....you just need to either "isolate" the second radio (by using a coax switch, etc.)...or have it connected to an antenna a significant distance away from your transmitting antenna...
Have a look here at our recent discussion:
https://www.eham.net/community/smf/index.php/topic,138012.msg1283234.html#msg1283234Okay, now the long answer...
3) If you just want a cheap, simple, and "easy-peasy" way to switch between your two radios (and antennas?), then I suggest a Daiwa CS-201a coax switch. (and, a second one...to switch between two antennas if needed....or if you have 3 or 4 antennas, look for a Daiwa CS-401a)
You can find 'em here:
https://www.radioworld.co.uk/daiwa-cs-201a-2-way-1kw-coaxial-antenna-switch-with-so239-connectorshttps://www.hamradiostore.co.uk/product/daiwa-cs-201a-2-way-1kw-co-axial-antenna-switch/https://stecker-shop.net/CS-201a-DAIWA-Coax-switchhttps://radioarena.co.uk/product/daiwa-cs-201a-2-way-coax-switch/https://www.nevadaradio.co.uk/product/daiwa-cs-201a/OR...if you want a Alpha Delta 2B switch (it's good...just that I personally prefer the Daiwa)
https://moonrakeronline.com/eu/alpha-delta-2b-coaxial-switchhttps://www.radioworld.co.uk/second-hand-alpha-delta-2-way-coax-switch-500-mhz4) If you want to read about how others have gone about this...as well as isolation specs / tests of some of these...
Have a look here:
https://www.eham.net/community/smf/index.php/topic,132761.msg1217881.html#msg1217881https://www.eham.net/community/smf/index.php/topic,132604.msg1217846.html#msg1217846https://www.eham.net/community/smf/index.php/topic,136487.msg1265363.html#msg1265363https://www.eham.net/community/smf/index.php/topic,136421.msg1264701.html#msg1264701https://www.eham.net/community/smf/index.php/topic,135560.msg1254317.html#msg1254317Here is a quote of mine, from one of those linked threads:
I've used this isolation to listen to / monitor my transmit signal on another radio...
Since I'd rather not subject the Daiwa switches to the Alpha 77Sx, I've generally just used them at 150 watts or less....but that still allows me to listen to my transmit signal to evaluate mic gains, etc. as well as key clicks, etc....
If you're interested in doing so....
Let's assume you have a typical HF rig with 100 watts out = +50dbm
Subtract the switch isolation (~ 80db) +50dbm - 80 = -30dbm
-30dbm is a strong receive signal, approx S-9 +43db, but should not "overload" any decent HF ham radio, so it is a great way to be able to "see"/"hear" all your spurious signals, whether IMD, key clicks, harmonics, etc....
(most HF ham rigs have a sensitivity in the -130dbm range, depending on rec bandwidth and what rec S/N is being used as the basis.....so, this allows you to hear and see any transmit spurs, and transmit noise radiated down to -100db from your carrier / PEP signal)
To be honest, I've never understood why all hams with two or more radios (that operate on the same bands), don't have 'em run thru an excellent switch....I know, I know, some swear by a "patch panel", and I won't argue these points here....but....
But, using a switch with a known isolation gives you another tool to use in maintaining your transmit signal as clean as possible, without spending much $$$.
(no, of course, this isn't a lab-grade test....and of course it won't "track you" as you move around the band, nor will you get a visual display as you do from a monitor scope, and no, this isn't a substitute for a spec analyzer.....but, if you have two rigs, my opinion is: do yourself the favor of using a good switch, and listen to your transmit signal on your other radio, especially listen off frequency / tune up and down 5 - 10khz, or even 20 - 50khz, and LISTEN to what you might be / or actually are transmitting, and make adjustments to assure your transmit signal is clean and intelligible!)
Steve, I hope this helps?
If not....look at Zak's link again.

73,
John, KA4WJA