Sunday, 14 September 2014

Some results from using the Anglian with K3

One of the things I dislike about the internal K3 144MHz transverter is the number of birdies that appear in the DX part of the 2m band. This has always tended to put me off using the K3 on 144MHz.

I spent some time testing yesterday with the antenna replaced by a 50R load.
Rather that use an objective set of measurements such as an analyser at the IF output, I used the simpler technique of just listening. After all this is what most operators really notice!
Incidentally, not all the birdies seen on the P3 or other SDR attached to the IF output are audible at the receiver output and are possibly due to shortcomings of the SDR in the P3 or other SDR (SDR-IQ in my case).

Tuning from 144.00 to 144.500MHz, with the internal transverter, I recorded about 10 significant birdies. Some weak and some medium strength. There were no strong birdies.

With the Anglian selected as an external 144 to 28MHz transverter the number of birdies dropped to under half those with the internal transverter and many of those that remained dropped in level to barely noticeable. I have therefore decided that the Anglian is a better choice for Dxing. Well, I would, wouldn't I?

I suspect that the problem with the internal transverter is more down to lack of screening than anything else, although the extra IF output filtering incorporated in the Anglian also probably helps.

I plan to do some objective testing in due course.

Sunday, 7 September 2014

Red in beak and talon

Just been watched a Goshawk kill and devour a starling in the garden.
Fierce looking bird!

Saturday, 6 September 2014

144Mhz results

I took the opportunity to listen and operate during the 144MHz Trophy contest.
100mW is not a lot to use during such a contest and indeed I worked one ON using the 100mW and he told me he was using 1kW! There was a slight difference in the reports with 40dB power difference......
What was interesting was the difference in ability of some stations to hear me and others to not even notice that anyone was calling them. How much was down to receiver blocking at their end and how much to shear QRM will never be known. 
An interesting evening.

144MHz antenna

After my recent changes to the YU7EF 9 element 144MHz long yagi feed point I changed over the 6/4m yagi for the 144MHz one.
I wanted to check out the new preamp on the 2m antenna.
The first thing I noticed was how quiet the YU7EF yagi is. As long as I don't beam towards the house ( approx 10 to 20T) the back ground noise is extremely low, although punctuated by the usual pulse noise from a nearby electric fence and some computer/data equipment carriers.

The plot above shows the return loss ( match of the yagi directly at the feed point. This was achieved by the usual calibration procedure at the yagi, using short,open, term.
A across the range 144 to 145MHz the return loss is around 20dB. I'm not so happy about the way the match starts to deteriorate rapidly above 145MHz.
The original 6/4m feeder is Ecoflex 10. There is now a short length of RG213 beteen the EF10 and the yagi feed point. This will be replaced with something of lower loss once the masthead preamp is installed.

The feed line loss is 1.9dB. Measured as half the two way loss from the shack to the yagi with a cal short circuit replacing the yagi. This is a great way to check installed cable.


Friday, 5 September 2014

Preamp plot

The yellow plot is preamp input match ( Return loss) and the blue plot is the insertion gain.
Both plots are from 50MHz to 500Mhz
Marker 1=98MHz
Marker 2=144MHz
Marker 3=220MHz
Marker 4=432MHz
The red line is 0dB

A 144MHz preamplifier

As mentioned earlier on my twitter account (@dxing) I have spent much of the day 'fettling' with a PGA103+ preamplifier, getting one ready to use with my Anglian transverter.


The basic PGA Amp I have been selling has no RF filtering and is subject to overload from nearby strong out of band signals. This is not ideal.

The third order input intercept (IIP3) measured previously seems to have been overly optimistic when compared to recent results. The latest measurements have been done more carefully and at slightly lower levels than previously. Even so, the IIP3 still measures better than +1dBm and is currently beyond the range of my test gear.

By adding a different configuration LPF to the input it has been possible to better noise match the PGA103+input; place a big notch in the middle of the band 2 FM ( possibly still the worst interferer for 144MHz systems in the UK) and yet keep the noise figure low. The LP filter is a variant on a design suggested by G4SWX

A simple 150MHz LPF at the output rolls the gain off above this frequency with minimal impact on gain and reducing 432MHz and 220MHz( DAB) response.
My preamp measures 0.6dB noise figure, 25.4dB gain and >+1dBm IIP3
Stability is excellent. 
An attenuator may be required at the output, in some circumstances, as the gain is rather high for most applications.

I am not planning to produce kits at this stage.

I will produce a full construction article in due course for anyone wanting to build the preamp. First, I want to do some more testing in conjunction with the Anglian transverter.