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On a PCB
03/08/2016 at 07:31 • 1 commentI rebuilt the receiver onto the dot protoboard today and had a chance to listen to the same station with my FT-857D (IPO off) and the simple receiver, and, over my local S7 noise they are relatively similar in sensitivity. I do want more gain from the receive section, and I have left room on thee protoboard for that, I'm thinking a buffer section before the LM386 might solve that.
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T/R Switching
02/04/2016 at 10:17 • 0 commentsFound a great article by N5ESE on T/R switching a receiver and transmitter without the use of a relay, this is something I will try to incorporate into my design, rather than needing 2 relays for switching. I will also let the microcontroller have full control of TX & RX power, and as I have said before, sidetone; that's 4 output pins I need...
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Going forward, DSB or CW?
02/03/2016 at 05:37 • 0 commentsI've recently been learning Morse code and I came back to thinking about my project. I currently have a receiver, and adding a CW transmitter would be dead easy, for example the IRF511 circuit on Switching-FET RF Amplifiers page. DDS output at one end and an LPF at the other and I likely have a CW transmitter with about 5W output.
Now, if I give the microcontroller full access to controlling the hardware, it could take care of the T/R switching, offset frequency and side tone (PWM output). This opens up the possibility of having a full keyer in the Arduino.
The only negative here is that the receiver is DSB, which means I will hear CW signals on the opposite sideband unless I start looking at phased SSB or an IF with filtering. But there is nothing stopping me from upgrading later to do that, and a phasing SSB receiver could also be fed directly into IQ inputs for an SDR.
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Project so far
02/03/2016 at 03:55 • 0 commentsYou can have a look at my blog for a longer explanation, but the short-ish version:
It is currently only a receiver, no transmitter stages so far.
This project originally started off as a simple transceiver, meant to run from a 5V source, like a cheap USB battery. The reason here is so many cheap USB battery packs and also being able to reuse a USB pack for Amateur Radio. I soon found out I could not easily run a transmit power amplifier from 5V, but this may still happen later, with some sort of up-converter, probably to 24V. The receiver section completely runs off 5V.
I then started to change direction a little, thinking about the TenTec 507 Patriot, an Arduino based open-source transceiver, and thought that I could do something like that in this project, like adding a DDS. I want to take this further and have the microprocessor control all functions of the radio.
The DDS is just a cheap AD9850 module from eBay and it drives the circuit well. I moved to a Arduino Nano clone briefly, but had trouble driving the LCD, I later found that the SPI driver for the AD9850 uses pins 10 & 12, even if they aren't actually used, and I will move back to the Nano for size.
The display is not permanent, it's just there for debugging. Firstly, there just aren't enough IO pins to do everything, at a later date a display might be added via serial IO. Secondly I want this to be dead simple with less things to drain power, I am thinking along the lines of the TenTec Rebel, Patriot and the LNR Precision Mountain Topper.