View Single Post
Old 21st Dec 2022, 3:12 pm   #394
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: 6-gang FM stereo tuner heads

Quote:
Originally Posted by regenfreak View Post
Quote:
G0HZU_JMR
I can get a slightly better response with the revised network below but the centre capacitor value value reduces to about 0.35pF.

I can't show a six element network with this smith chart program, but I can draw in the sixth element by hand on the chart. See the diagram below. I think this is the kind of thing David was referring to.
I have tried your 5-element approach and got similar component values. But it shows a horrible lopsided sweep response.
My first attempt with the 6-element networks had a much better symmetric sweep response.
.
OK but the circuit I gave was based on real world experience in terms of what could actually be transferred to a PCB using real lumped SMD components. The smallest inductance was 8nH and the smallest capacitance was 0.5pF and the network topology was chosen to make the design as realisable as possible. The network I provided also gave a bias feed connection for the amplifier, a dc blocking cap and an L match at the output that could all be absorbed into a real PCB layout such that the PCB interconnection pads would not upset the frequency response. A real PCB will have interconnection pads that have distributed properties. I chose a circuit topology that could be absorbed into a real PCB with minimal impact caused by the small interconnection pads on the PCB.

You need to think about those little connection pads on the PCB that connect those lumped parts together. The network I provided takes all this into account.

Try building the 2GHz networks on a real PCB and you will find that my original network will perform well. The inductances will have to be tweaked slightly and the 0.5pF cap might become 0.35pF but the network will still end up looking like the original network. The final L match could be flipped to a shunt C series L to give a better lowpass response if that was desired? It would also increase the bandwidth slightly but it would still give a fairly lopsided response.
__________________
Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 21st Dec 2022 at 3:37 pm.
G0HZU_JMR is offline