Sudden Power Amplifier Board Prep

While I’m off the air I thought I’d start preparing the PCB for the next portion of the sudden transceiver which I’m (very slowly) building, the power amplifier. I’ve not really been working on this project just due to lack of spare time at the moment as I’m focusing on CW operation while the bands are good, I know that during the winter I’ll struggle with my evenings on 20 and 40 meters, although I might try to put together an 80m compromise antenna in the loft or across the garden for the winter.

Antenna Issues Part 2

So I’ve had a little investigation into my antenna issues, I brought the antenna down on the winch took a look. It looks like the tape over the crimp connectors has reacted with the Sikaflex in some way so water may well have got in there. I stripped off the Sikaflex (which I wont use again because removing it is a sticky nightmare) and put Araldite over the cracks. After winching the antenna back up I checked the SWR trace again and it had got even worse, which was similar to my experience last year.

Looking at the balun there are a fair few cracks which I’ve temporarily protected with Araldite, it’s also not potted and uses a SO-239 so I’ve chosen to replace it with a potted balun which uses an N-type connector which are what I use elsewhere in my shack and what I’ve got on the end of my coax, this allows me to remove the N-type to PL-259 adapter.

Antenna Issues

Unfortunately for the third year running at almost exactly the same time of year my antenna has stopped working. I noticed that the ATU was struggling to get the SWR down to where I would expect so I connected up my NanoVNA and noticed a bizarre trace.

Blue is the reference from last summer, yellow is the new trace.

Having had a quick look at the antenna it seems to be the same issue, corrosion of the wire that makes the legs of the antenna, I’d used significant quantities of Silkaflex sealant to try to avoid the water getting in so that’s a bit disappointing! After having a think about the issues and a chat with some of the club members it was also suggested that the issue could be water in the balun.

Given that the balun is a bit long in the tooth and already had a small crack protected by gaffa tape I may replace it.

Until I can sort things out I’m now off the air which is very frustrating. Like last year if feels as if it has happened just as I’m getting the hang of CW, last year it was around my first couple of QSOs, this year it’s as I’ve started getting in the swing of a few QSOs each week.

While I’m off the air I’m using my spare time to read Bill Meara’s book SolderSmoke ‘Global Adventures in Wireless Electronics’ it’s a really good read and I might post a bit of a review on it at a later date.

Three CW QSOs This Evening

In a somewhat unimpressive personal record I managed to rack up 3 CW QSOs this evening, in England, Italy and Austria. It was nice to have 3 very different QSOs too, the English one was G0POT who I know from LICW, a nice steady speed, the Italian one was about 5 WPM which was a real struggle, I’ve never listened to CW at that speed without Farnsworth spacing and the Austrian contact was clearly using a bug, the dits really raced!

All good practice, need to try to fit it in when I can!

Getting Back In The Swing Of CW

I recently realised that the bands I have access to (20m & 40m) have improved again in the evening giving me the opportunity to make some more CW QSOs. I have been back practicing after a bit of a hiatus in the winter and feel that my head copying in particular has really improved.

I’ve been using certain sections of the Chuck Adams K7QO course files, just listening and not copying down on paper. To start with I was using files 070 – 075 which are qth hr is…, name hr is…, rig hr is…, wx hr is, ur rst is… and ant hr is… reasonably slow, I also listened to the QSOs, 077 – 082 and the random letters, random numbers and pi 083 – 086 (I probably should have used random characters 088-089 too, but missed those). I’ve now moved on to various “essays” from 091 onwards.

One thing I’ve noticed with improved head copy is that even when I’m having a QSO and copying onto paper my hearing where spaces are has hugely improved, this was something I really struggled with, I can also sometimes skip over bits of a QSO I might not need to write down.

Over the last week (and a day) I’ve made 5 contacts which for me is a big deal, I am also feeling much more confident in the contacts I’m making, and hoping to be able to better use whatever little time I have spare to make contacts in future without it being such a “big deal”.

I am still really enjoying CW and get a kick out of this mode in a way I don’t with other modes, but that’s a personal thing at the moment. There are so many facets of radio I’m still yet to explore!

Receive BPF

Having added the trimmer caps to the BPF I still had issues, the filter was off band and I couldn’t quite work out why, I fiddled a bit, replaced one of the variable caps which wasn’t measuring correctly, and then decided to model the filter in LTSpice to reproduce my VNA findings.

First of all I reproduced the schematic (with a 50 Ohm load). C3 and C6 represent the variable capacitors, adjusting them to 35pF brings the filter on band.

Filter as designed, C3 and C6 are the variable capacitors

I managed to reproduce my problem by changing the 150pF capacitors (C2 and C5 below) to about 190pF, however I was fairly confident in those components, so I played with the inductor values and managed to reproduce my VNA findings almost exactly by adjusting the values from 0.4µ to 0.5µ.

A closer examination of my filter and it became clear that the issue was the windings on the inductors which were too closely placed, once I spaced them out further I was able to get the filter on band.