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Saturday, 7 December 2019

More ADF4351 - really?


You may recal my dissapointment back here with the Practical Electronics GPS-synced Frequency Reference.

It turned out to be a load of Dingo's Kidneys.

You may also recal the most excellent work of Brian, GM8BJF back here using the ADF4351.

Well, I have been playing with the Micromite that was used in the Practical Electronics project, and have created a touch screen signal generator using the ADF4351.

It's very much stolen from a project here.

I've modified the code a bit to have an additional digital output to show the PLL locked state, and also changed the code to use a 10MHz clock rather than the default 25MHz clock.

It's quite neat!

Albeit upside down:

I'm 3D printing a case for the front, then we can decide what to do with it:

The output is as I expected:

I've uploaded my bodged version of the code here.

Good, isn't it?

Monday, 2 December 2019

Practical Electronics - Really?


I recently built myself a project that had featured in the Oct/Nov 2019 issues of Practical Electronics (previously Everyday Practical Electronics). It is a new fangeld GPS-synced Frequency Reference.

It uses a CDCE906PWG4 from Texas Instruments as its core component which allows three independent outputs to be set over a wide frequency range.

It also uses a thingamabob called the Micromite Backpack - which is basically a microprocessor with a nice colour touch screen integrated that is designed to use MMBasic as its programming language.

The theory of operation is very simple, there is a 40MHz ovened variable oscillator and also an external GPS 1pps signal. The microprocessor counts the 40MHz signal between 1 second pulses from the GPS and adjusts the voltage control on the oscillator appropriately. Once we have an accurate 40MHz signal, this is then used by the PLL to create the reference outputs at the user selected frequency.

Unfortunately I can't get this thing to work (properly) and I **think** my fundamental problem is one of power filtering/decoupling.

Here are the basic components, the green board is the frequency reference and the red one the Micromite.

The white wires on the board you can see are a suggestion from the author "the stability of the reference may be improved by reducing the impedance of ground tracks on the PCB" which smells rather fishy to me.

Anyhow, the output of the oscillator from the PLL looks like this:

and the output, when set to 10MHz looks like this:

All looking rather nasty - wouldn't you agree? The bursts of apparent crap on the signal are when the GPS is sending data to the processor.

I've tried to get some support for this project; but failed rather dismally. There used to be a chat room for EPE projects, but that has been closed. There is a dedicated forum now, here:

but I posted there over a week ago, was notified that my post is subject to moderation, but it still hasn't appeared. I also note the last post there is over a month ago.

All of the self tests in the software appear to pass; that suggests all is well, but I can assure you that all is not well at all! The output frequency is a mile from being accurate, the "approx freq" in the screen above swings wildly around the 40MHz target suggesting the processor is having issues counting the clock, and generally it's all a bit pants.

Not sure what to try next.

This makes me sad.

I even ended up digging out a CD4046 to remind myself how PLLs work,

In the image above, we have the source oscillator from my desk function generator in yellow, the light blue is the output from the on-chip VCO, the purple is the basic comparator (type 1) output and the darker blue the type 2 comparator output. When I change the frequency of the bench generator the on-chip VCO follows in frequency and locks - just as it should - I remember now!

Alan Wolke, W2AEW, has a superb video explaining this stuff on YouTube here.

This, however, makes me very happy as it is our very beautiful Pepper Cat enjoying a bit of late winter sun:

Local conditions.

Saturday, 19 October 2019

JARTS - doesn't time fly


It's the JARTS RTTY test once again and the bands are full of RTTY signals.

Propagation contitions are very poor, but there are plenty of signals about.

I've been using the IC-7610 today and it's a superb RTTY radio:

The internal decoding capability is also excellent:

Here is the 40M band early on the Saturday evening - CW and RTTY everywhere!

Here's a map of my log:

Local conditions.

Saturday, 24 August 2019

DVB-S2 - really?

A very quick special message broadcast on the QO-100 Digital Amateur Television:

Local conditions.

Saturday, 17 August 2019

Radio Analog PTRX-7300 - Really?


You may well have seen adverts for the PTRX-7300 from Radio Analog. This is some kind of new fangled adaptormabob for the Icom IC-7300 that gives you an RF output that you can hook up to an external SDR for a panadapter display.

Well, I ordered one.

Here are the bits that you get (but not the screwdriver):

You start by taking the radio top cover off:

Then we disconnect the cable that attaches to the rear external tuner connector and remove it:

Then the new gubbins clips into the space where the external tuner connector was:

Hook up the cable into the now vacated socket for the external tuner connector:

and then pull a plug out of the radio PCB and insert into the new gubbins:

Then we have a supplied cable from the new gubbins to the PCB socket we just disconnected:

And thats it! Now externally the tuner connector is re-connected and also a flying lead with an SMA connector to feed to the SDR. This is extremely neat!

So once we have all that done, I have set up SDR Console:

and it just works.


Tuesday, 13 August 2019

Up-converting - you what?


Further to the PA I made last time, today I have been finishing off the up-converter to accompany it.

The theory goes something like this:

  • The Portsdown will output DATV on 439 MHz through the transverter output
  • This will be sent down the garden in Ecoflex-15
  • The co-ax losses will be compensated for using the 70cm amp I made back here
  • This will feed the SG Labs transverter we played with back here
  • The output of the transverter is then boosted by the Wi-Fi amp from here 
  • Finally the output is fed to the PA
Here's the up-converter in its finished form, there's a simple sequencer in there to handle the PTT switching and send a PTT signal to the PA:

Tomorrow I hope to install this and the PA in the small shed I have near the dish - then for some on-air testing.

This is the output of the up-converter DVB-S, SR250, FEC 1/2 - received with an antenna across the bench:


I've not yet installed the equipment in the garden, so I have about 4-5dB minimum of cable loss between the PA and the dish feed. However, here's my first RX of my own TV signal through Es-Hail'2:

** UPDATE 2 **

I've moved the gubbins to the small shed near the dish:

And am now sending 439MHz (ish) down the garden from the Portsdown.

This is a 333KS transmission via QO-100, you can see my signal on the left of the Mini Tioune software at 10,497.750 MHz:

And here is a testcard:

Local conditions.

Sunday, 11 August 2019

Even More Power!


I've been messing about and finishing off my 13cm linear. The idea is to make something that will work on the 2.3GHz amateur band frequencies as well as 2.4GHz for DATV on Es'hail-2.

This has been quite a challenge, but eventually we have something working ready for on air testing.

This is the final build, which even though I say so myself, is a masterpiece:

The PA module itself is something from my travels made by PowerWave:

There are five MOSFETS in total - each one is a SRF7068H5HS.

This is controlled by a W6PQL Amplifier Control Board which in turn uses an external FET switch to turn on and off the 12V bias lines to the PA, provide the sequencing necessary, generate an ALC voltage (just in case I need it later), generate an external PTT out for switching VLNAs or other external gubbins.

There's also a chassis mounted directional coupler (a NARDA model 31152) which provides a -30dB forward and reflected port output which is attenuated and rectified to produce a DC voltage. There's a forward voltage for a future power meter and also a reflected power voltage to activate a trip if the SWR should exceed 2:1.

I've even included a thermistor on the main heatsync and a trip in the amp control to switch on the fans or even shutdown the amp when over temperature.

I'm seeing about 26dB of gain from the amplifier and it will generate about 250W of CW on 2.407 GHz so should easily generate the 30-40W I might need for some DATV experiments.

Here is the unit under test, I'm using the Portsdown to generate a signal at 432.75 MHz, then using the mixer from the UK Microwave Group forum to mix in 1975 MHz to generate an output on 2004.75 MHz. This is then amplified up and fed to the linear. The forward port of the directional coupler (-30dB) is coupled via another 20dB attenuator to my XL Microwave meter. A short piece of coathanger shoved into the front of the Spectrum Analyser allows me to measure the harmonics and also look at the TX waveform.

A thing of beauty is a joy to behold! I'm delighted with this.