HEMT as power JFET replacement?

There are some nice cheap SSRs around. Or real relays.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Too slow. It needs to switch quickly (say a few microseconds) to catch the RX signal, and needs low distortion for the TX. Really, the JFETs work very well, they're just very big and space is at a premium.

What's the signal level? Do you need gate isolation?

We use some USB bus switches as analog mux'es. Wideband and very low ON resistance.

We just discovered the TMUX4052. Take a look.

Mosfets?

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Would paralleling smaller package JFETs work to replace the larger one?

"Simon Simple" snipped-for-privacy@nottoday.co.uk> wrote in message news:112l443$3fcfu$ snipped-for-privacy@dont-email.me...

I did something similar more than 30 years ago with mosfets but it probably isn't adaptable to your needs.

Assuming I've remembered it correctly. The TF048 transformer is the only component which is definitely the same.

Version 4.1 SHEET 1 880 680 WIRE -336 -576 -432 -576 WIRE -304 -576 -336 -576 WIRE -432 -560 -432 -576 WIRE -304 -512 -304 -576 WIRE -432 -464 -432 -480 WIRE -368 -464 -432 -464 WIRE -432 -448 -432 -464 WIRE -720 -400 -832 -400 WIRE -672 -400 -720 -400 WIRE -832 -336 -832 -400 WIRE -432 -320 -432 -368 WIRE -672 -272 -672 -400 WIRE -624 -272 -672 -272 WIRE -496 -272 -544 -272 WIRE -128 -256 -128 -272 WIRE -832 -224 -832 -256 WIRE -432 -208 -432 -224 WIRE -1088 -128 -1392 -128 WIRE -848 -128 -1024 -128 WIRE -720 -128 -768 -128 WIRE -624 -128 -720 -128 WIRE -464 -128 -544 -128 WIRE -128 -128 -128 -176 WIRE -1392 -16 -1392 -128 WIRE -640 -16 -640 -32 WIRE -720 0 -720 -128 WIRE -672 0 -720 0 WIRE -464 16 -464 -128 WIRE -464 16 -608 16 WIRE -448 16 -464 16 WIRE -416 16 -448 16 WIRE -256 16 -336 16 WIRE -240 16 -256 16 WIRE -80 16 -144 16 WIRE 0 16 -80 16 WIRE 32 16 0 16 WIRE 128 16 112 16 WIRE 320 16 304 16 WIRE 432 16 400 16 WIRE 720 16 432 16 WIRE 784 16 720 16 WIRE -672 32 -928 32 WIRE -1008 64 -1008 48 WIRE 0 64 0 16 WIRE -640 80 -640 48 WIRE -224 80 -224 64 WIRE 432 96 432 16 WIRE -1392 112 -1392 64 WIRE -448 112 -448 16 WIRE -448 112 -880 112 WIRE 128 112 128 16 WIRE 192 112 128 112 WIRE 304 112 304 16 WIRE 304 112 240 112 WIRE 784 112 784 16 WIRE -304 160 -304 -416 WIRE -272 160 -304 160 WIRE -224 160 -272 160 WIRE -1008 176 -1008 144 WIRE -928 176 -928 32 WIRE -928 176 -1008 176 WIRE -880 176 -880 112 WIRE -848 176 -880 176 WIRE -720 176 -768 176 WIRE -624 176 -720 176 WIRE -464 176 -544 176 WIRE -224 176 -224 160 WIRE -1008 192 -1008 176 WIRE -1008 192 -1120 192 WIRE 0 192 0 144 WIRE 192 192 0 192 WIRE 304 192 240 192 WIRE -1120 208 -1120 192 WIRE -1008 208 -1008 192 WIRE 304 256 304 192 WIRE 432 256 432 160 WIRE 432 256 304 256 WIRE 464 256 432 256 WIRE 784 256 784 192 WIRE 784 256 464 256 WIRE -224 272 -224 256 WIRE -640 288 -640 272 WIRE 464 288 464 256 WIRE -720 304 -720 176 WIRE -672 304 -720 304 WIRE -1120 320 -1120 272 WIRE -1008 320 -1008 288 WIRE -1008 320 -1120 320 WIRE -464 320 -464 176 WIRE -464 320 -608 320 WIRE -416 320 -464 320 WIRE -256 320 -336 320 WIRE -240 320 -256 320 WIRE 0 320 0 192 WIRE 0 320 -144 320 WIRE -928 336 -928 176 WIRE -672 336 -928 336 WIRE -1120 352 -1120 320 WIRE -640 384 -640 352 WIRE -80 416 -80 16 WIRE 0 416 0 320 WIRE -80 544 -80 480 WIRE 0 544 0 480 FLAG -80 544 0 FLAG 0 544 0 FLAG 464 288 0 FLAG -640 80 0 FLAG -640 -32 +12v FLAG -640 384 0 FLAG -640 272 +12v FLAG -1120 352 0 FLAG -1008 48 +12v FLAG -128 -128 0 FLAG -128 -272 +12v FLAG -1392 112 0 FLAG -256 320 sm1 FLAG -256 16 sm2 FLAG -336 -576 +12v FLAG 720 16 output FLAG -432 -208 0 FLAG -720 -400 logic FLAG -832 -224 0 FLAG -272 160 gate SYMBOL ind 176 96 R0 WINDOW 0 -34 37 Left 2 WINDOW 3 -41 63 Left 2 SYMATTR InstName L1 SYMATTR Value 2.6 SYMATTR Type ind SYMATTR SpiceLine Rser=50 SYMBOL ind 256 208 R180 WINDOW 0 -33 75 Left 2 WINDOW 3 -40 49 Left 2 SYMATTR InstName L2 SYMATTR Value 2.6 SYMATTR Type ind SYMATTR SpiceLine Rser=72 SYMBOL ind 16 32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L3 SYMATTR Value 4m SYMATTR SpiceLine Rser=1m SYMBOL ind 304 32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L4 SYMATTR Value 4m SYMATTR SpiceLine Rser=1m SYMBOL nmos -144 272 R90 WINDOW 0 -19 23 VRight 2 WINDOW 3 71 79 VLeft 2 SYMATTR InstName M1 SYMATTR Value 2N7002 SYMBOL nmos -144 64 M270 WINDOW 0 -16 60 VLeft 2 WINDOW 3 72 82 VLeft 2 SYMATTR InstName M2 SYMATTR Value 2N7002 SYMBOL TVSdiode -16 416 R0 SYMATTR InstName D1 SYMATTR Value SMBJ24CA SYMBOL res -16 48 R0 SYMATTR InstName R1 SYMATTR Value 470k SYMBOL TVSdiode -96 416 R0 WINDOW 3 -121 69 Left 2 SYMATTR Value SMBJ24CA SYMATTR InstName D2 SYMBOL TVSdiode 416 96 R0 WINDOW 0 41 17 Left 2 WINDOW 3 41 42 Left 2 SYMATTR InstName D3 SYMATTR Value SMBJ24CA SYMBOL res -320 0 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 270 SYMBOL res -752 -144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL res -528 -144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 10k SYMBOL res -320 304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 270 SYMBOL res -752 160 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL res -528 160 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 10k SYMBOL res 768 96 R0 SYMATTR InstName R12 SYMATTR Value 600 SYMBOL res -992 48 M0 SYMATTR InstName R13 SYMATTR Value 10k SYMBOL res -992 192 M0 SYMATTR InstName R14 SYMATTR Value 10k SYMBOL cap -1104 208 M0 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL voltage -128 -272 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL cap -1024 -144 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100n SYMBOL voltage -1392 -32 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value SINE(0 1.2 4000) SYMBOL pnp -368 -416 M180 WINDOW 0 58 64 Left 2 WINDOW 3 59 32 Left 2 SYMATTR InstName Q1 SYMATTR Value BC857B SYMBOL res -416 -464 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res -208 64 M0 WINDOW 0 37 54 Left 2 WINDOW 3 -47 54 Left 2 SYMATTR InstName R5 SYMATTR Value 100 SYMBOL res -208 160 M0 WINDOW 0 38 53 Left 2 WINDOW 3 -51 49 Left 2 SYMATTR InstName R6 SYMATTR Value 100 SYMBOL res -416 -352 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R7 SYMATTR Value 10k SYMBOL npn -496 -320 R0 SYMATTR InstName Q2 SYMATTR Value BC846B SYMBOL res -528 -288 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 10k SYMBOL voltage -832 -352 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 5 SYMBOL OpAmps\\LT1678 -640 16 R0 SYMATTR InstName U1 SYMBOL OpAmps\\LT1678 -640 320 R0 SYMATTR InstName U2 TEXT 176 216 Left 2 ;TF048 TEXT 160 88 Left 2 !K1 L1 L2 1 TEXT 488 280 Left 2 ;Ground for sim only TEXT 712 152 Left 2 ;Line TEXT -1112 456 Left 2 !.tran 0 500m 0 100n startup TEXT -1112 512 Left 2 !.options plotwinsize=0 numdgt=15