I am looking at DGM, I never heard of them before.
Am I right with the math here? The transistor has specs
admittance : 0.7 millimillihos, 1.4Megaohms
conductance : 0.5 millimillihos, 2Megaohms
Antenna impedance ~ 36.8 ohms (1/4 wave dipole)
VSWR : 114906
Mismatch Attenuation : 44.583 dB
I just used ~33MHz as a test point.
https://chemandy.com/calculators/return-loss-and-mismatch-calculator.htmSo I have attenuation of 141x at this frequency
If I do it 10MHz less, at ~23MHz,
Admittance: 0.45 mmHos, 2222222 Ohms
Conductance: 0.3 mmHos, 3333333 Ohms,
Antenna impedance ~ 36.8 ohms (1/4 wave dipole)
VSWR : 196256
Mismatch Attenuation : 46.908
So over a 10MHz range the impedance of the op-amp causes a mismatch error of ~2.4dB, and it appears to be linear
is my understanding that the V/M on the antenna basically has a ripple/slope error (if you trust the graph being so strait) of 2.4dB on the 22-32 MHz band, which needs to be corrected with a lookup table thats sloped with a coefficent correction of times ~140 to negate the loss? Is any kind of impedance matching network between the antenna and the buffer possible to try to make the losses less? 40dB is alot of gain at these frequency ranges, the GBW of the amplifier would need to be in the GHz, if you wanted 40dB with 30MHz you would need a gain bandwidth of 4.2GHz, so you likely need to use multiple stages which would increase the noise by a fair bit, I think 4GHz GBW is basically the fastest amplifier that LT/AD makes, and I am worried about using it, a more reasonable current mode amplifier with 1.2GHz bandwidth means you would need to use 5 of them, I figure the quiescent current would be high if you want to make it battery powered like those devices. I guess its not mandatory to bring it up to 40dB because instruments can handle alot less, but I am curious as how these devices are used.
Where do I go from here to find out what volts/meter on the antenna (this is the unit they seem to use) translates to output of the amplifier, so I can set the gain stages? Some kind of impedance match would make it less noisy because there would be less amplified gain required right?