G5JIM / W5JIM – Ham Radio Journey – Page 6 – G5JIM / W5JIM

Testing my Direct Conversion Receiver

By m7jdj-admin on Saturday, November 6, 2021

After completing all the parts to my receiver I took it to the club this week for some more help testing. I knew that the receiver worked when I injected a signal from my NanoVNA, but testing in the real world didn’t yield any results. The club has a signal generator which I used with much assistance to test the product detector.

It turns out that although the product detector works it has horrendous sensitivity, of the level that would require something like a 1KW station across the street to ‘hear’ anything, so more work ahead to diagnose that fault.

In addition to this something went pop in my audio amp yet again. The amp was working, I turned to focus on the product detector then I heard a spark, saw some smoke and the chip was very hot. There is definitely some kind of fault in that audio amp, I think as it’s has so much desoldering, resoldering and adjustment there is probably an intermittent short, or something along those lines…more work to diagnose this fault too.

RSGB

RSGB 2021 Convention Online

By m7jdj-admin on Sunday, October 24, 2021

The RSGB 2021 Convention was held online two weeks ago, I wasn’t able to “attend” however I’ve been catching up on the talks and there are some real crackers. There were two streams, An introduction to… and Learn more about… which shared the keynote talk but then diverged. So far I’ve listened to the An introduction to… talks and I’ve just started Learn more about….

For me the highlights have been Michael Sansom G0POT on Portable skills and approaches and Sean Kutzko KX9X on Intro to ham radio satellites both in the An introduction to… stream. Neither of those subjects would have been my first choice looking at the programme, but seeing a different way of operating and not using high power and tonnes of equipment is quite appealing.

From a technical perspective Andrew Barron ZL3DW on Software Defined Radio on the Learn more about... stream was fascinating, Andrew is the writer of The Radio Today guide to the Icom IC-7300 and a bunch of other radio amateur related books. One thing that was interesting about this talk were some of the comments going on in the chat alongside, and I like some of the other viewers disagreed with his opinion that a modular approach for GNU radio stifles innovation.

From the perspective of a Software Engineer it’s always tempting to start everything from scratch and do it yourself, however doing that you can just find yourself reinventing the wheel, and often not as well as it has been done by others. Having the modular/open source base to build upon can allow you to focus on new features improvements etc. There is of course the other side of the argument that having these pre-built modules means that people don’t necessarily think about other ways of doing things, it’s already done, if it aint broke don’t fix it.

I don’t have any experience with GNU Radio (or SDR development) and by his own admission Andrew Barron also doesn’t have any experience of GNU Radio, but I found it interesting to consider.

I’d definitely recommend that anyone who hasn’t watched the convention get along to YouTube and watch it, it’s free, even if you aren’t a member of the RSGB, so what have you got to lose!

Homebrew M0NTV Projects

More Audio Amp “Fun”

By m7jdj-admin on Saturday, October 23, 2021

After chatting through the noise issues with my audio amp with a club member I’ve made a couple of changes, firstly I’ve replaced the AF input cable with a jack socket (and using a shielded jack to jack cable for the input audio) and secondly I’ve grounded the cases of the potentiometers.

After adding the audio in socket I was having issues, the noise was much reduced and I was getting output when playing audio through my laptop but I wasn’t hearing anything when testing the output of the product detector, eventually I realised that my issues and confusion was because I was using a stereo cable and stereo jack socket in the audio amp but a mono jack socket in the product detector. For the audio amp of the laptop out it was fine, the ring output from the laptop socket went through the stereo TRS cable to the ring of the socket in the audio amp and then out mono through the (correctly) wired AF out socket. In the case of the product detector the audio went through the tip which was connected at the audio amp end and the ring was grounded, so no sound unless I pulled it out a little, once I rewired it the issue resolved.

For the grounding of the potentiometers I connected the three together using some old desoldering braid, perhaps a bit odd and used a lot of solder but pretty effective, I then connected the end one to the ground on the voltage regulator. This all worked fine, but then when trying to track down some remaining noise I unplugged the AF in cable and it went silent, I then replugged it and the same and no sound… after a bit of checking over the board I replaced the LM386 chip and it worked, so once again I’ve somehow fried a LM386!

Regarding the remaining noise I’ve realised that it is only present when my KSGER T12 is switched on, so I’m guessing that the noise is from the switched mode power supply and is coming in via the power in on the amp, so I’ll need to do some decoupling there, to be continued…!

NanoVNA

NanoVNA as a Signal Generator

By m7jdj-admin on Thursday, October 21, 2021

The NanoVNA is a fantastic tool for radio amateurs and those interested in RF electronics, I’ve found it invaluable for testing antennas, filters, coax etc… but I’ve now discovered another use for it. When I was trying to test my product detector I was thinking about how best to inject a signal and was considering adding a second output to my oscillator but a friend from our radio club Dave G8KBB suggested I use the NanoVNA as a signal generator, it’s sort of obvious given how a VNA works, but I hadn’t even considered it. I did a little google and it really is as simple as reducing the sweep down to the required frequency to get a square wave signal (and I believe that this only works up to 300MHz due to how the NanoVNA uses harmonics for the higher bands). Clearly this is only suitable for simple applications, but very helpful nonetheless.

Homebrew Projects

Product Detector

By m7jdj-admin on Friday, October 15, 2021

The final part of the M0NTV ‘Building with Blocks’ talk direct conversion receiver. I’ve built it in a different order from the ‘building backwards’ order suggested, partly based on what I had available. I’m waiting for some DC plugs and sockets I’ve ordered to complete it, but I’ve attempted powering it up connecting power with croc clips and not managed to receive anything. I don’t have an ideal 80m antenna here, but I’d expect to hear something, particularly on the FT8 frequencies. The audio amp is very noisy and receiving signals on its own so I’ll need to sort that and then try again, watch this space…

Homebrew Projects

80m Filter

By m7jdj-admin on Wednesday, September 15, 2021

I’ve been working on a direct conversion receiver, on and off (mainly off with a couple of spurts) for a few months now based on a talk by ‘Nick the Vic’ M0NTV, and I recently put together the 80m filter. It’s designed to be modular which is quite nice because it does mean that I can dip in and out. I’m going to put together a writeup of what I’ve done, but for now a couple of pictures.

You can see in the first picture that I’m using a ‘mint tin solder pads’ PCB which I purchased from Kanga UK, very convenient for using with my mint tin, I’ve found it great and on the reverse side it has the same but with split pads.

Not pretty, I’m going to try to get some bulkhead SMA sockets for next time.

Projects

Project Tins

By m7jdj-admin on Monday, September 13, 2021

Looking for project tins recently I found some for sale on Etsy, however they were a bit expensive and on searching a bit further I came across a cheaper and more tasty solution…

Projects

Auto ATU back home

By m7jdj-admin on Wednesday, August 4, 2021

After my latest adventures with my Auto ATU and adding a jumper wire I was having some odd behaviour so a club member Dave G8KBB offered to take a look and give me a second (and far more experienced) opinion.

It turns out I somehow jumpered the wrong trace and there was also a soldered end of wire which wasn’t cut short enough and was therefore prone to short out, silly things as usual! Dave has jumpered the other trace, cut short the wire and advised that I box it up ASAP and add a fuse to the power cable.

Many thanks to Dave for the assistance and advice!

CW QSO with Russia

By m7jdj-admin on Saturday, July 10, 2021

It’s been somewhat slow with the QSOs with life getting in the way, but I recently managed my first CW QSO on 20m around 14055 (the QRS frequency) and managed a QSO with Russia, much clearer than the UK and Netherlands QSOs I’ve had recently, banging through with no QSB! I also got an email from a UK based ham who heard the QSO and tried to join in afterwards but I didn’t hear him, really nice to get feedback from people who’ve heard my QSOs, hoping for a few more to follow.

Two more CW QSOs

By m7jdj-admin on Thursday, June 10, 2021

I’ve now managed another 2 CW QSOs, this time both with G4 stations in the UK, both stations were very helpful and understanding and responded to my CQ calls at the speed I’d called.

One thing I have struggled with is QSB, on both occasions I had booming signals one minute and pretty much silence the next which made it super tricky to copy at times, I’m not sure if that’s an issue with the 40m band or just recent propagation.

It has definitely already got much easier since the first QSO, I think getting past the shock of hearing a response to the CQ and being prepared for that and knowing what I’m going to respond helps.