Author Archives: Colin Shaw

QRPp on an IC-705

I have been wanting to work QRPp for while after reading about contacts CW ops were making on 80mW. The idea was to make a simple crystal controlled transmitter and use the 705 as the receiver. Than I read about the MFJ-813  which is advertised as a 5W QRP watt meter. Yesterday one arrived and has just been tested.

The 813 is reasonably accurate for such a low-cost meter. Starting with the 705 I set the power to 5W the meter showed 5W. Then I turned down the power to 5% and the 813 meter reading was remarkably close to 500mW. Turning down to 1% output on the 705 the meter read 100mW.

Next are some on air tests with 100mW – 1W power levels.

 

 

 

20m End fed half wave

I used a 20M EFHW and few years back with varying degrees of success. It was about the time when ‘squid poles’ became a popular antenna supports. The single core wire element was wrapped round the pole but the problem was that most poles then were made of a carbon fibre material which made them conductive. The antenna did not work so well.

This week I tried out a new, 10M fibreglass pole and, like before, wrapped the wire round to the pole. First indications are good with low SWR using a commercial 49:1 balun. This was much better than using the small EFHW tuner I made some years back.

Another idea is to use an off centre loading coil to make it a multiband antenna. More to come, watch this space.

 

New antenna analyser

I have been trying to setup the Buddistick outside but it’s been so bright I could not see the screens of the cheapo analysers I have. So, decided to upgrade to a more professional version, the Rig Expert AA-55 Zoom.  The first impressions are good.

Not used it outside yet, waiting for enough energy to do the job bit it does look better than the mini VNA,

Instant nostalgia

It reminded me of the first solo trip to London I was allowed to make around 1964. I asked a typical London policeman the way to Lisle street as London Central radios Stores was there. I was grilled for several minutes about my real motives until he eventually believed my story and gave directions.

Auto antenna tuner kit

There are many different versions of an automatic antenna tuner on ebay and other sites. Some come with a case while others are supplied as a PCB and a bag of parts. There are few instructions around but there are circuits diagrams, or schematics, on some sites.

The board as received

The insulated rear panel

I ordered what I thought was a complete PCB with case but what arrived was a populated board without a case. I complained that it was different to the photo for the item and accepted a partial refund which amounted  nearly what I paid. I then ordered the case for under £13 post-paid.

The board came with SMA sockets already attached which meant it would not fit in the case, so they were removed. Assembly was a bit fiddley, but all seemed to go well. The first power up showed the screen was working. Next came an RF test which did not work. Some quick tests showed that the rear panel had no earth connections to the PL259 sockets!

I decided to make a new panel from aluminium. After reassembling the case and testing with a TX connected to my long wire antenna  everything worked as it should.

I now have an fully automatic ATU that senses when there is a band change and retunes.

The new aluminium panel ready for testing

Transceiver new build 1

The workshop clean up was delayed, I just had to get the VFO working. When I built the kit a few months back I did not solder one of the headers! Found that this afternoon, soldered it and all was well.

First job was to setup the IF at signal frequency + 9Mhz. Then a quick run through to see if all the functions were working as they should.

I like the minimal display. It would be even better to be able to go back to using one the old Eddystone slow motion drives like this one on a G2DAF RX from 1963. No water falls, flashing lights, bleeps, tones or warning messages on screen. Don’t get me wrong there is a place for all of that but sometimes I just want a radio that is simple and easy to operate without the need for an A4 ring binder full of instructions.

G2DAF RX at the national radio museum

At the end of the afternoon this is what I had; a VFO covering all bands from 160M – 10M with the IF set to 9Mhz and giving about 80mV P-P of sine wave ready to go straight into the mixer.

Building an HF Transciever

Over the years I have built a lot of gear from simple test equipment to an eight band CW transceiver using reclaimed parts. Technology moves on and I now have three commercial SDR rigs. The performance of modern transceivers is amazing but I feel something has been lost; it’s all done in software which feels a bit cold, clinical even.

A few years back I followed a series of articles in RadCom written by Eamon Skelton, EI9GQ, where he described how he built a transceiver mainly from discrete components. I bought the book a couple of years ago and now feel I want to make my version of his project.

Why now? It is mainly the availability of cheap test equipment like spectrum analysers, VNAs, GPS locked frequency meters and wide band noise sources which work well with SDR receivers like the RSP1A.

Not long ago all we had were grid dip oscillators, drifting sig gens and frequency counters with dubious accuracy.

I have made a start and almost fallen at the first hurdle! Instead of making a 9Mhz, 2.4Khz wide SSB filter I have bought one from Spectrum Communications. That will save buying lots of 9Mhz crystals and spending hours matching them to get a good shape.

I have already built a VFO based on a synthesiser chip. There are some things it is not worth trying to replicate and a drifting VFO is top of the list. I did build a free running 8 Mhz VFO in the early 1970s that was multiplied by 18 to drive an old Pye valve TX on 2M. It took hours to sort out the drift but eventually it was rock solid. The key was an Oxley Tempatrimmer. The fixed vanes of the capacitor were fixed to a bimetalic strip so as as the temperature varied the capacitance changed. They are impossible to find these days.

Watch this space as I will post progress reports as each stage is completed. The first thing to do is tidy up the workshop, I may be some time…

IC-705 and a new portable antenna

Although I still make stuff it is getting harder especially with small components. Last year I was told that I have rare form of cataracts. That makes working on circuits boards difficult. When the current pandemic is over maybe they will be able to replace to duff components and restore the circuit to its original condition.

This is all leading up the to be the excuse for buying an IC-705! It’s an exceptional radio with amazing performance which is hard to believe for an old timer brought up on HF receivers that occupied a full 19 inch rack.

 

Above left – Marconi HR11 telegraphy receivers with the boss pretending to tune one and above right, Plessey PVR800s telephony receivers. The first transistorised professional RX for the HF point-to-point service. Pics from around 1968 at PO radio station Bearley.

The IC-705 which I can hold in one hand!

So now the work is on perfecting the HF /P antenna. I have gone back to an end fed half wave made from a homebrew system that breaks down into 1m long sections. The aim is to cover 40m-10m with different lengths of wire wound on a reel, after removing the washing line. See Steve Nichols, G0KYA,  post on his blog here.

I also have a couple of light weight fibreglass poles and a drive over support just to make everything more flexible. That will allow me to operate from the car/micro camper.