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Picture of Yaesu FT-450D RF Tap Modification for SDR

Hello anyone that may be interested,

I think I had better first explain what this instructable is all about. There are thee main components involved in this project as follows:

The Yaesu FT-450D is a modern compact HF/50MHz transceiver capable of covering the 160-6 meter amateur bands with a power output of 100W. Too many features to list, so just Google the radio if you want to know more.

The SDRPlay is a superb wideband Software Defined Radio covering a frequency range of 1KHz to 2GHz and allowing the spectrum to be viewed with a bandwidth of up 10MHz.

SDRPlay : https://www.sdrplay.com/

(I have no connection with the company other than to have purchased their excellent product)

Both these pieces of equipment are superb in their own right. However, the purpose of this instructable is to bring the two pieces of equipment together and to be able to exploit the best of both worlds. By that, I mean being able to use the FT-450D radio as it was intended (as a narrow band radio transceiver) but at the same time being able to use the SDRPlay receiver to visualise the wide band channel.

This inherently poses a problem as both the FT-450D and the SDRPlay need to see an antenna. One approach is to simply use two antennas. A second approach might be to use a single antenna but split the RF path and transmit/receive using in-line switching. A third and preferable approach is to tap off the receive RF path from within the FT-450D using a suitable low noise circuit and present the tapped signal to the SDRPlay. This latter approach results in both the FT-450D and SDRPlay essentially seeing the same antenna. The low noise circuit is only powered while receiving and so during transmit provides substantial isolation protecting the input to the SDRPlay receiver. The low noise circuit has a high impedance input thus presenting a minimum load to the tap point within the FT-450D. This last point is important as suitable tap points within the FT-450D are located either side of passive 50 ohm band pass filters. Any loading or change of impedance introduced by an additional circuit will change the transfer function of the filters and also reduce the power in the wanted signal path.

Most of the off the shelf low noise amplifiers (LNA) available use feedback to generate gain and also have a 50 ohm input impedance - neither of these features are desirable.

A simple high impedance tap circuit has been designed by Dave G4HUP and was available to buy. Very unfortunately, it is my understanding that Dave has passed away. I have taken a part of the design and with modification, produced my own printed circuit board, tested and fitted to my own FT-450D. It is this process which forms the subject matter of this instructable.

Step 1: Creation of LNA Schematic and PCB Layout

Overview

Over the years I have generated a few Printed Circuit Boards (PCB) for products and for home use. In the early days this involved using copper clad board, transfers and special pens to draw the design onto the copper. The board would then be etched in Ferric Chloride to remove exposed copper and leave the wanted tracks. It was also possible to buy light sensitive copper clad board and use a mask to produce a resist before etching. Having a one-off board made commercially was very expensive and required tools that were just not available to hobbyists.

Nowadays, computer tools are free and widely available to design boards in a matter of hours not days. Also fabrication costs have plummeted with many cheap fabricators being available in China and elsewhere outside the UK. However, that said having a single board made is still not that cheap once you include shipping.

Another approach, and the method I have used in this project, is to mill the board using a CNC milling machine. Obviously, you would not buy a CNC machine to make one board but I already had a machine which has been used for lots of other projects involving milling wood, metal and glass.

To mill a PCB using a CNC machine involves using a very fine cutting tool to mill out isolation around the wanted tracks but not to mill away all the copper. This approach is particularly useful when building RF circuits as the remaining copper islands are desirable acting as a ground plane improving stability and performance. I have used a doubled sided copper clad board in this project and have drilled through linking the top and bottom copper surfaces.

PCB design using EasyEDA

I have tried various PCB design packages and had really settled on a package called DipTrace. However, it is ever more popular for design packages to be web-based rather than use a stand alone application. Having not used DipTrace in some time I was a little rusty so looked around on-line and found a web-based design tool called EasyEDA. I found this tool excellent, very intuitive and simple to use. Very easy to generate a schematic in a matter of minutes and then convert to a PCB, the entire process took less than an hour including a few modifications and refinements. The tool designers are obviously hoping you will use the provided fabrication facilities but it is still possible to export a design in industry standard gerber format for use by a subsequent tool chain.

MarkP127 months ago
Hi Dave,

Would you mind sharing your files? I too have a tabletop CNC mill and an FT450D. I also own the SDRplay RSP2Pro which I'd like to add to the 450.

Thank

Mark
G7LTT
dtrewren (author)  MarkP127 months ago
Hi Mark,
Further - that SDR-Kit price is for a fully assembled tested board not a kit !
Dave
dtrewren (author)  MarkP127 months ago
Hi Mark,
Sure I can share the design details. However, before you spend time making a board ... SDR-kits are now selling the entire range of boards at very reasonable prices. They have the complete kit of the board I made PAT-V for £14.40 or the PAT-70M for the 450D IF tap for the same price. I think you would struggle to make the boards for that price. At the time I made my board these kits were not available - all I had was a schematic.

Here is the link:
https://www.sdr-kits.net/index.php?route=product/category&path=66_73_84

Or Google SDR-Kits.

Cheers,

Dave (G7IYK)
df9910 months ago
Nice! I bought the G4HUP board from SDR-Kits in the UK. I opted to install the tap after the 1st IF mixer, before the roofing filter. It works up to 2MHz wide, but favors the center 40KHz by a few dB due to the parallel tank circuit at that point. I get a bit of 24KHz bleed through from the second 24KHz IF on the FT-450D, visible as a fixed signal offset +24KHz from the tuned spot. It must be mixing with the first IF and getting through the low pass filter of the board.It is always offset, and is low level so does not affect the operation of the panadapter.

I use a NOOELEC "NESDR Smart" dongle for my SDR.. It has a metal case, TCXO, and SMA connector plus other upgraded components. It still only has 8 bits of dynamic range, but works very well with HDSDR. I found my two cheaper dongles drifted a few PPM with room temperature, creating annoying sync issues between the SDR and radio. The TXCO is rock solid with the new dongle.

Thanks
AdelE171 year ago

Hi Dave,

I have the same radio and I'm interested with this project. could you please send me the schematic/ PCB layout? my email is adelkeid@gmail.com.

73

Adel A92FF

could you please send me the schmatic and PCB layout of the LNA as well. My email is cheungderek@hotmail.com.

dtrewren (author)  cheungderek1 year ago

Hello,

I have emailed you all the required information.

Cheers,

Dave

Starsekr1 year ago
Dave, Nice instructable. Can I get a schematic/PCB layout? Have you thought about a write-up for RSGB or ARRL? PCB isn't a problem, there is a company in Ohio, USA, that does small board protyping at a reasonable cost
Thanks,

Jim McEwen, KA6TPR
Laughlin, Nevada, USA

dtrewren (author)  Starsekr1 year ago

Hello Jim,

Sorry for the slow reply. Sure I can send you schematics and PCB layout. Please can you send me your email address and I will send you a link to the information.

Cheers,

Dave (G7IYK)

JamesA411 year ago

Hi dtrewren, Excellent detail and thank you very much for sharing. I was working on modification of a PRO-2006 Scanner and KTR-1661 and planning on performing a similar SDR interface though found that the CPU/Logic board on the PRO-2006 has issues being able to tune where I am not able to input individual frequencies, I'm only able to tune with the scanner process starting from the top or bottom of the frequency range.


I didn't get into the feedback circuitry yet to see how the SDR software can tune the scanner (I didn't think the radio is feasible) and will read more into the Omni-Rig Remote Control Software. That looks really neat.

Are you aware of any open source remote control software? I am guessing the remote control tuning software process will be something that will require comprehension of the hardware software, command line or firmware code relating to the hardware controls and some sort of process to translate/pass the commands from the SDR software tuning process events to the hardware software/firmware.

I haven't yet de-soldered the modifications on the pro-2006 to see if miraculously the scanner will work. Hoping will work then and the current draw goes into specification. Figure some higher power is calling me to learn how to input the individual frequencies and settings on the scanner either way.

Again, really awesome detail and excellent instruction! Thanks again for sharing as there isn't much on the internet regarding this interesting way to upgrade older equipment.

dtrewren (author)  JamesA411 year ago

Hello James,

Thank you for the feedback, very pleased you liked the project. I have had a look at the PRO-2006 scanner - looks like a nice bit of gear. It is a shame it doesn't have a control input port fitted. Obviously it is quite an old scanner and back then they didn't think too much about computer control.

However, you can fit a Optoscan 456 control board to the PRO-2006 which allows you to control the rig via a serial interface. There is (was) control software for this board called Probe from a company called Datafile. If you can find the software the problem will be that is was DOS based and command line driven. I have put few link below that might help you work out what can be done. One of the links details the command interface so the other option, assuming you can find a serial board to fit, is to write your own control interface software. As the control board is a serial interface you can talk to it using Visual Studio for example and write a control program in Basic, C or Python. Hope you have success or at least fun trying :)

Cheers,

Dave

http://www.monitoringpost.com/pro2006/comment2.html

http://www.monitoringpost.com/pro2006/os456.html

http://www.monitoringpost.com/

Thanks for the reminder Dave and additional information. I had printed some information from online research when I first received the scanner that I didn't even read into and do have a folder for CS232 and OPT456 that I forgot about. I even have a specification I found somewhere for a OPT535 for a later model.

There is a DB-25 port on the unit I have and I had assessed that there is additional memory storage added as another mod, where two switches were added to the back for the different storage banks selection, a tone squelch mod and I forget off the top of my head what the IC socket is on the case.

I do recall the IC9 had too high current and last left off there pretty much.

I still have to read into some more and assess the device as I think I contracted Valley Fever from it and had other issues I had to attend to that now with the snow on the ground... I am able to get back inside and get back to work on some electronics projects.

Here is the details for those that may be interested:https://forums.radioreference.com/radio-shack-scan....

Thanks again Dave, Cheers!

snoop9111 year ago

Do you have any thoughts on how an SDR that's capable of transmitting at very low power (ex. LimeSDR or HackRF) can be used in conjunction with a traditional radio (like the Yaesu) to achieve a high power output?

dtrewren (author)  snoop9111 year ago

Hello snoop911,

Interesting idea ... looking at the schematic for the Yaesu it might be possible to inject a signal into the transmit path but it would take quite a bit of work and modification. I think a better approach would be to use a stand alone PA block to increase output power. Two units cannot transmit at the same time so you might as well use a separate power amplifier. Hope that helps ?