Order / Gain Structure of RX Front End? - Page 1
Forum section: electronics / rf-microwave

author: elmood
author_rank: Regular Contributor
timestamp: January 06, 2022, 09:15:05 pm
content: Hey folks,I'm working on a homebrew design for an HF transceiver and there seem to be just as many approaches to receiver design as there are radios out there.Are there any best-practice rules on the order of blocks / gain settings for receiver front ends? What is the normal thought process that goes into deciding how much gain to put right after the antenna, after filters and attenuators, after the IF mixer, etc.?I'm working on a basic block diagram for my project and feel funny just trying to arbitrarily stick things together.73 VE2EOT

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 07, 2022, 10:11:59 am
content: Doesn't have to be any; the downside is mixer noise/loss is in full view. Usually a preamp is added to deal with that, and that's about it. So, if typical mixer loss is say 6dB, adding a preamp somewhat over 6dB, and with better than 6dB noise figure, will improve sensitivity. Note it should have high IP3 to avoid mixing/clipping from strong (local) signals. Or can be looped in to AGC if that helps to a similar end.Preamp also affords isolation, in case the mixer is prone to spurious outputs from the RF port. So, a good idea for a single diode mixer (but, you'd probably only use one of those at frequencies where you can't amplify in the first place, i.e. vintage microwave hardware?).Isolation can also improve filtering, as antennas are a mess of reactances.Tim

author: A.Z.
author_rank: Super Contributor
timestamp: January 08, 2022, 01:24:07 pm
content: I agree with teslacoil, a simple yet quite effective design is to place a wideband and low gain stage at the antenna input, a simple JFET common gate stage will work well there and give both impedance adaptation and I/O isolation, following such stage you'll have a bandpass filter cutting out the undesired frequencies and, at the output of the bandpass, a preamp wich will offer the desired gain and that may be AGC controlled, after that ... well it depends from the design you'll use for your receivermy 2 cents

author: radiolistener
author_rank: Super Contributor
timestamp: January 08, 2022, 05:21:52 pm
content: There is a book which explains what you're looking for:Joy Laskar, Babak Matinpour, Sudipto ChakrabortyModern Receiver Front-Ends: Systems, Circuits, and Integration

author: rfdave#gmail.com
author_rank: Contributor
timestamp: January 11, 2022, 03:36:31 am
content: Generally, all this is worked out in a spreadsheet that calculates all of this. I haven't done this at HF yet, just VHF and higher, so the noise/linearity tradeoff is significantly different. ICOM published a "IC-7850/IC7851 Technical Reference Book" that goes into the details of this radio, including a nie detailed block diagram.Also, "Modern Communications Receiver Design" by Drentea might be a more relevant reference.

author: UR5FFR
author_rank: Contributor
timestamp: January 11, 2022, 03:29:07 pm
content: The structure of the receiver very much depends on what requirements we place on it in terms of parameters and power consumption. In any case, before the quartz filter, the gain should be small, and the dynamic range of the stages should be maximum. For example, a + 10dB common gate amplifier with 4*J310 can be used between switch mixer (FST/FSA series IC) and the filter. The total current through the transistors will be about 80-100mA. Too much for your portable transceiver? Then you have to sacrifice something - sensitivity or dynamic range.An interesting option when a quadrature hybrid and two quartz filters are used after the switch mixer. This circuit is slightly inferior in sensitivity, but has a maximum dynamic range. By example see HGCR2010http://www.oe3hbw.eu/Projects/HGCR2010/HGCR2010.htmFor design, I use the program "Cascade" W7ZOI - this is an appendix to the book Experimental Methods in RF Design. VU2ESE has made the implementation of these calculations available onlinehttps://www.vu2ese.com/index.php/2021/05/17/cascade-calculator

author: radiolistener
author_rank: Super Contributor
timestamp: January 12, 2022, 01:00:09 am
content: The book "Modern Receiver Front-Ends: Systems, Circuits, and Integration" expains receiver design, include frequency planning, noise, linearity and gain analysis. It also explains different receiver architectures, include the following:- Heterodyne receivers,- Image reject receivers (Hartley and Weaver architecture),- Zero IF receiver,- Low IF receiver,- Direct Conversion receiver- Subharmonic IF receiverIt also explains possible issues, such as spurs, LO leakage, images, linearity, noise, phase and amplitude imbalance, DC offset, intermodulations and other.And also it explains design and integration of passive components and silicon components for receivers up to 60 GHz