Electronics > RF, Microwave, Ham Radio

High isolation LNA for the HF band direct conversion receiver

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szszjdb:
Hi, A.Z., dk4xp and UR5FFR,
Many Thanks!

The existing 30-20m bandpass have a 3dB bandwidth from 9.5 to 16.9Mhz and -40dB at 30Mhz and -60dB at 42Mhz. I will fine tune the filter and there might have some trade off as I am designing a portable QRP unit.  As running by the battery, the current drain is critical.
Then how about the P1dB or OIP3 requirement for the following preamp? Does a P1dB +5 dBm with 15-20dB gain preamp fulfill to the QSD with -5dBm saturation point?

Best Regards & 73,
James

A.Z.:
forgive me, but I can't see how a rx bandpass filter would have an impact on battery drain

[edit]

a set of bandpass filters, one for each ham band won't require too much components (L/C) and will help avoiding out of band issues

szszjdb:
Hi, A.Z.,

Sorry, I mean the preamp. The higher OIP3 the higher current drain and the Vcc. I just want to make sure the bias point of the preamp is just fulfill to the system requirement. What should be the banlance point?
I am considring refining the bandpass filter in the very front end.

Best Regards,
James

Gerhard_dk4xp:
Some pointers:

Really about noise blankers, but that's the same area in the receiver:
<    https://dk4sx.darc.de/eigenbau_rx.htm     >
<    http://www.oe3hkl.com/rx-homemade/rx-mit-h-mode-mixer-ip3-45dbm/stoeraustaster.html    >
<    https://worldradiohistory.com/Archive-DX/Ham%20Radio/80s/Ham-Radio-198006.pdf    >


<    https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1994/05/page29/index.html  >
<    https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1994/06/page27/index.html    >
<    https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1994/07/page42/index.html   >

There is a lot more on Rob's web IIRC.

S9 is defined as 50uV in the 1/3 Rohde articles.  0 dBm is 635 mV
S9 = 50 uV is -73 dBm for comparison.

73, Gerhard

szszjdb:
Hi, dk4xp,

Many Thanks!
Your information help much!

It seems the preamp  P1dB should have 3 dB higher than the QSD and following . As the saturation point of QSD is about -5 dBm, the 0 dBm P1dB  of preamp should be enough for my system. Is that right?

Best Regards & 73,
James

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