Dummy loads for RF dummies

Its been well over 30yr since I messed with RF stuff, but now I find myself starting on the panel and buying used gear. So I'd like to bench the stuff as I build. If someone with the smarts could help me with the following questions....

1) 50ohm dummy loads for all comm radios (75ohm is only for flat wire TV ants right? Do we do that anymore?)
2) What freqs are we talking for com, nav, xpdr, gps etal?
3) Would something like this get the job done for the comm radios? https://www.rfparts.com/dummy-loads/dummy-load-25/50t-054-bncf.html
4) GPS and Nav antennas receive only/dont transmit so no need to hook up them up to test the box functions....unless I want to get a signal (?)
5) Transponders need a monster load.....but how much? 300W? Cost=ouch!
5a) Can I get away with a xpdr ant bolted thru a sheet of AL for the gnd plane, and if so, how big is good enough? 1ftsq?
5b) Do I gnd the gnd plane to the xpdr chassis or just let it float electrically if I go the 5a way?

Thanks for any help.

Responses in line...

1) 50ohm dummy loads for all comm radios (75ohm is only for flat wire TV ants right? Do we do that anymore?) 75 ohm is TV coax, 300 ohm is the old flat wire transmission line. All avionics commonly encountered in GA are 50 ohm characteristic impedance, RG58 and RG400 are typical coax cables used for this purpose.

2) What freqs are we talking for com 118-137MHz, nav 108-118MHz, xpdr 1030/1090MHz, gps 1575.42Mhz or thereabouts etal?
3) Would something like this get the job done for the comm radios? https://www.rfparts.com/dummy-loads/dummy-load-25/50t-054-bncf.html That should work.
4) GPS and Nav antennas receive only/dont transmit so no need to hook up them up to test the box functions....unless I want to get a signal (?) You might want to hook up your GPS antenna and get it pointed out a window - avionics are much prettier when the GPS is feeding in much-needed position so your moving maps etc work!
5) Transponders need a monster load.....but how much? 300W? Cost=ouch! Transponders have a low duty cycle - the dummy load you mentioned above is probably adequate.
5a) Can I get away with a xpdr ant bolted thru a sheet of AL for the gnd plane, and if so, how big is good enough? 1ftsq? 8" square is enough, but bigger is better - just get some physical isolation between you and the antenna (distance). Keep in mind the xpdr normally doesn't transmit unless interrogated by the ground radar station, however some transponders, particularly Mode S transponders, transmit immediately upon power-up without the need for ground interrogation.
5b) Do I gnd the gnd plane to the xpdr chassis or just let it float electrically if I go the 5a way? Ground connection is via the shield of the coax.

Thanks for any help.

Canadian_JOY said:

Responses in line...

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Thanks a bunch. Didnt forget everything, but enough that I'm glad I asked. Now if I could just remember where I put my old pack of Smith charts!