Sunday, September 30, 2012

RockMite 30 Arrives and the Build Begins

The 30 meter RockMite kit finally arrived in the post and this weekend I will begin the build and then complete my RockMite trilogy!
The intention is to incorporate all the mods I have used on the 40 and 20 RMs, adding the more powerful 2N3053 transistor, reducing the resistor R18 to a lower value and altering the zener diode D5. I will also soften the sidetone with Dave Benson's recommendation of a "10 10" filter (10 ohm resistor and 10uf capacitor)
Then on top of that I will add the bifilar PA mod (toroid) and include the CW audio filter I built earlier. Add sockets to the components I may want to change, which will include the crystals as the frequency I will be using is 10.116 instead of 10.106, (I’ve done some research here and 116 looks a little friendlier for my slower CW)! I managed to pick these up from the same company who sold me the audio filter, the Hamshop. It's a good shop for buying those sort of parts that are sometimes hard to come by.
Finally I’m changing the enclosure to an aluminium case which will be slightly bigger to take the audio filter and also so should I wish add extra components in and outside the case such as LEDs switches etc. So, in all I should have a nice little RM transceiver complete with all the mods and an output of around 700 milliwatts.
I’m also very tempted since 30 meters is my favourite band, to purchase the small amplifier from QRP project a German company that has some very good reviews. Getting the power up to approx 10 watts just for the one transceiver might prove fun especially on 30 meters.  
The other project I’d like to go ahead with is to buy the OHR 100A 5 watt CW transceiver from Oak Hills Research. I’ve been eying this little kit up for some time and believe it will be ideal for me to progress in my QRP kit building quest but we’ll wait and see how I am after the completion of the final RockMite build. 

So on with the build:
The first procedure for the RM30 mods is to cut some of the traces between various components, I thought I would do this first while the PCB is free spaced giving me more room to work.

So my first trace cut was for the sidetone filter which was between pin 5 on U3 and C8 which you can see top right. The next cut was for the PA toroid mod which again on the bottom of the PCB is a cut between L1 and C14 (middle left of the PCB) a bit tricky as it's fairly close together.

Turning over to the top of the PCB and continuing the trace cuts for the PA mod I cut a gap at both ends of the trace between L1 and C1 (middle right, a bit small but the picture will enlarge).

With all trace cuts completed I will now start fitting some components and sockets. I will also fit the PA mod toroid by inserting the jumper lead between C1 to the junction of C14 C15 and L2 and solder up the centre tap of the toroid (ab) in to L1 and then a and b taps in to the holes either side. Below is the details of the toroid fairly simple but a first for me!

Two hours later and the majority of the PCB build is complete with the toroid in place, which was a little fiddly to fit but I finally got there in the end. All I have to do now is insert the sockets and add the 2N3053 transistor together with the lower value R18 and the 10.116 crystals. Finally to finish off before the smoke test add the "10 10" filter on to the bottom of the PCB.

I'm pretty pleased so far, my soldering has certainly improved since first starting a few months back on the old RM40, just proves practice makes perfect! 

 The "10 10" filter for the sidetone mod and the jumper to complete the PA toroid mod.

Nearly there, the completed RM slotted in to the enclosure case, you'll note there is plenty of space left as I want to add the CW filter and internal batteries. I've also added an LED and an off on switch just to make things easier.

 The internals look fairly neat for even to me! I've fitted sockets to the transistor (which is not in the picture), and for the crystals, hence the copper ring which acts as ground and can be opened up when I want to replace each crystal.

And finally all sealed up in the lovely new enclosure! I will add some small black decals so that I remember what everything does. So far no successful QSO but to be honest I haven't really given it a proper try, although my Brother-in-Law down the road, (about 4 miles away) could hear me testing when he was listening out on his FT1000D, so I am getting out at approx 700Mw, I will attempt a proper try later this week, so hopefully the next post will bring some good news!

Thursday, September 20, 2012

Audio Filter SMD Update

I’ll take it all back re Surface Mounts Devices; They are fiddly little things and I was cursing and swearing away as I attempted to solder the individual parts on my audio filter! I had no problems with the SMD on the RockMites but when doing something as small as the audio filter it is a different game.
Everything within the audio filter is so small it takes a lot of getting used to and lessons have  been quickly learnt. Perhaps I shouldn't have started with such small resistors and capacitors, but hey, you have to start somewhere......... Here's a few tips I learn't along the way:
1. Get my eyesight sorted; wearing two pairs of glasses over each other does not work, go out and buy a headband magnifying tool or a large magnifying glass on a stand!
2. Have a clamp which will hold the small circuit board, otherwise the thing moves all over the place as you attempt to solder tiny fiddly resistors and capacitors. (Re resistors and capacitors it's a good idea to work out the value beforehand hence the magnifying gear......he he)!
3. Don’t use the XYL’s old pair of tweezers, believe me, they don’t work and she wont appreciate it either; get yourself a good pair from the local hardware shop.
4. Have the correctly tipped soldering Iron and the right solder specifically for SMD work; Try soldering with a chisel end? (It doesn't work, I know), you will find that soldering SMD’s is much easier with the right tools.
5. Give yourself plenty of patience especially if you are new to this lark; believe me it took me a while to actually get something soldered on to the board. After numerous attempts I finally got something in the right place but at one stage I was doing more un-soldering than soldering. 

 The circuit board although small looks like it's been in a war, (R5 looks a bit off!) whether it will work is another matter, I will at some point put the multi meter on it but at the moment I reckon I still need to calm down!  
Other news; I'm still waiting for the RM 30 which is sadly still stuck at Wonderlabs awaiting spare parts. No matter, like soldering SMD's, patience is the order of the day.

Monday, September 17, 2012

Building a 2 Meter Yagi

I managed to purchase a Kenwood TH-215 2 meter handheld off EBay for the princely sum of £11.50. 
The radio works ok off the mains but the two batteries are not holding their charge, no real surprise as the handheld is an old bit of kit. So I'm on the lookout now for a spare battery, whether I find one could prove interesting. I rarely use 2 meters but to be honest there is a good morning net that I'm missing out on, plus I can keep in touch with all the local operators.

Anyway now that I have the rig I needed an antenna and although somewhere in my shed I have an old 2m vertical I quite fancied the idea of building a Yagi. Nothing too elaborate just a small 3 element to boost things up. So I had a search on the web and found details of a fairly simple yagi build  which seemed to promote a good db gain.
According to the details the maximum forward gain was around 8db (6 dbd) on 145 Mhz. So doing the math, with 6 db (6 dbd = 8,15 dbi) gain, this antenna offering an “effective radiation power” 4 times greater of the transceiver output (without Coaxial-Loss), i.e with my little handheld with an output power of 5 watts, my ERP will be multiplied 4 times = 20 Watts (in the forward gain). 
Reading further it went on to say this antenna was compact enough (78 cm boom between Reflector-director) with excellent F/B ratio (20 db). The Impedance on center frequency (145,000 MHZ) is 65 Ohms, so in practice the antenna needs a "matching system" for a 50 Ohms coax and to get the SWR down to 1:1, the website recommended a "Hairpin" system which is very simple and effective "matching method"

So I gave it ago and had a prototype antenna built within a day, but without the hairpin method and some slight alterations in measurements which proved costly as my SWR was totally out. 

Build number two I followed the plans regarding the measurements and managed to find some thick copper wire for the hairpin. After checking everything was tight and correct I did a check with the MFJ 259 and Bingo I had an SWR of 1:1 at 145 Mhz. Just goes to show, follow the plans and you can’t go wrong!

Build Number two, it's pretty basic, held together with pressure clips and tape. The elements are made from the old aluminium tubes I had on the Moxon and the boom is an old TV boom I found in a skip.

The Hairpin fitted in place and taped up to make it weather proof, luckily I had some reasonably sized copper wire which I had originally used when constructing the Cobweb. Again fairly basic but as long as it does the job.

The final product slotted in to the rotator and mounted on a 20 ft scaffold pole. Its just enough height to clear the nearby tree and first impressions look good with a 1:1 swr at 145.00. I have already heard some chatter from pointing north up the Severn valley towards Birmingham and this morning before going to work heard the local Cheltenham net having a chat. Certainly when rotating the signal fades in and out so all seems to be working ok. Just got to do a transmit to make sure I'm getting out!

Monday, September 10, 2012

CW Audio Filter and Audio Amplifier

The CW filter from Hamshops arrived in the post today and as I have this week off I hope to get it built and set up with the 30 meter RockMite as soon as I can, although the RM 30 is still to arrive. The first thing you notice with the filter is just how small it is, believe me it's tiny and of course its surface mount! After watching a few demonstrations on You Tube I'm pretty certain I shouldn't have an issue when it come to SMD assembly.

I added the 5 pence coin so you get a rough idea of the size, apologies for the quality of the picture but the camera has literally just come to us and I'm still getting the hang of using it!

Good news on the Audio Amplifier front, I completed the build and it's working nicely. I'm especially pleased because it's my first home brew PCB build and although a very simple circuit it took some time to work out the layout, but once you have that sorted and know the basics like where ground and live are going to end up it all falls in to place! Its just a simple circuit using an LM386 amp, I added a few extras like the switch and LED, all good practice.

Fingers crossed the RM 30 will arrive in the next day or two and I can then get on to complete the collection of RockMites. Already thinking what an earth am I going to do when it's all completed, but I have joined the GQRP club and hope to gain some ideas about some more projects.

Tuesday, September 4, 2012

Good Conditions and More Projects

The bands were wide open over the weekend and I managed to take advantage and get some good qso’s, the highlight being on 28 MHz with Carlos in Sau Paulo who gave me a 579 not bad for a distance of 5816 miles. Admittedly I was using 250 watts but for me 28 Mhz is not brilliant on the old Cobweb.

When I had the Moxon up I could contact stations with ease on 10 meters but for some reason the Cobweb doesn’t like it too much. I constantly check the swr which is good at 1:2:1 but it just seems foggy if you know what I mean.
I’m still awaiting the arrival of the 30 meter RockMite which hopefully will turn up sometime this week. I now have all the extras I require, the 2N3053 transistor, the reduced value R18 and I have wound the toroid choke so it's all ready for the kit. Also I 've ordered a small audio filter kit from Ham Shop CZ which should be arriving any day. Together with the RM 30 the PCBs should both fit snugly in to a nice metal enclosure I've bought from the local Maplins store.
In the meantime I’ve decided to redesign my audio amplifier project, before it was literally an LM 386 with a 5v regulator with no resistors or capacitors, hard to believe I know, but I did some more research and have found some better schematics which I am going to have a play with because I'm sure I can do a lot better.
I’ve bought various capacitors and resistors as well as a 10k potentiometer, also some stripboard but after examining it I suddenly realised how on earth do you use it?
Normally with all kits the circuit board is printed, I have no experience of how you solder components on to a stripboard, so I went back to the net and had a read on how to place components and use a track board cutter.
It looks like fun but I can see it isn’t going to be easy to start, but there are plenty of examples of audio amps with schematics and stripboards designs. So as soon as I get the chance I will have some experimentation.