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Thursday, 8 December 2016

Counting all the way to 13cm


You may have realised that I had something in mind when I made the Signal Generator up to 4.4GHz recently? Well, the idea is to use that to test a new transverter I have for 13cm:

This is another most excellent piece of kit from SG Labs. You may remember that the transverter used in this 23cm project came from the same place.

So, this transverter has a number of options for the LO, but with that set to be 1870 MHz, and my new Signal Generator set at 2301 MHz:

Lo, and indeed behold, on 431MHz we see a strong carrier:

Now, this transverter even came with a PCB antenna for 13cm:

So, the next thing is to try and test the TX side; not too sure how I am going to manage that yet, but I am sure I will find a way!

I have an ultra low noise amplifier from G4DDK ready to construct also for this band, plus a surplus telecoms PA block that should give some power. I also seem to have a 13cm Wimo antenna sat on my desk:

So, lots more to follow on this topic!

Local conditions.

Wednesday, 7 December 2016

Boxing Time


You may remember the 35MHz to 4.4GHz signal generator made from cheap eBay components I was fiddling with last time.

I've stuck it in a box now:

I've removed L1 from the board:

so that there is no power to the on-board 25MHz XO. I'm running mine using the shack 10MHz frequency standard I made back here. This external oscillator input simply connects to the SMA socket on the back of the board.

I've recently made a distribution amplifier for the frequency reference so  I have 8 50R outputs at 10MHz to lock a recently acquired Microwave frequency counter and also my HPO signal generator.

Good egh?

Thursday, 1 December 2016

JT4F - Really?


A bit more Wednesday night activity on 23cm digital modes; last night I worked Neil, G4BRK on JT4F, here's how it looked from his end:

And this is from my end:

Now, two main observations:
  1. There is simply loads of Doppler or other effects - probably due to Aircraft Scatter / Reflections
  2. The report I sent was received with an additional "000" on the end - I wonder why
But the decodes of this mode seem extremely reliable in the presence of  multiple reflections - which makes it ideal for this kind of frequency.

Good, egh?

Monday, 28 November 2016

4.4GHz Signal Generator - Really?


I attended the GMRT event this year, one of the highlights was seeing this in the flesh:

I also spotted a great project by GM8BJF which was a great signal generator covering 35MHz up to 4.4GHz using very cheap Chinese and eBay sourced components.

Here are the bits, firstly a ADF4351 evaluation board:


Secondly, a CY7C68013A development board:

And finally a broadband amp module:

Total cost of these three modules delivered was less than 45 GBP.

Now, I've tried two ways to drive the ADF4351, firstly using some excellent software from F1CJN - this worked very well and would make an excellent stand alone sig gen.

However, I have decided to replicate the project by GM8BJF exactly and use the three boards above together.

I followed the instructions on his website and have programmed the EEPROM on the CY7C68013A board and am now using the software from Analogue Devices from my PC to set the output frequency:

This software controls the ADF4351 from a PC using a USB connection and allows you to see all the register values and fiddle with all the device config - most excellent!

Here's a quick shot of the spectrum analyser connected to the output with the device set to 1.2GHz:

This is an appalling picture of the boards under test:

And here, Miss Florrie Cat assisting:

Neat, egh?

Sunday, 30 October 2016

The SWR tripping issue


You may recall that back here I was starting to construct the SWR trip mechanism for the 23cm linear I built back here.  I've finished this and tested it today; as soon as the RF level on the reflected port reaches 10.8dBW my amplifier trips.

It looks like this in reality:

The return loss bridge is connected to the ANT socket of the linear and the forward and reflected ports are connected back to the amp box with SMA leads. Inside the box is the RF detector board that converts the RF into a -ve voltage and that has been adjusted in accordance with the calculations I did back here. So assuming the maths was correct I the linear will now trip if the SWR exceeds 1.8:1.

I also note there is good propagation on 2M today; looking out the window I see slightly misty but very still weather, often a sign on tropo:

The situation with Chopsey (AKA Git Bastard Cat from Hell) using my desk as his bed is now completely out of hand:

Florrie the ham cat has also taken to sleeping terribly close to my nixie clock which I am very fearful for:

Local conditions.

Sunday, 23 October 2016

Microwaves - now that's really nuts!


Following the build of my amplifier for 23cm here. I've been involved in some on-air tests of the JT modes on 23cm.

Here's a screen shot of my signels on JT65C as received by Tony, G4NBS in JO02af (Cambridge).

You will see multiple signals at times and we are sure this is due to Aircraft Scatter - I was seeing very much the same kind of thing on RX also. Anyhow, I am pleased to have logged 23cm JT65C QSOs with G4BAO. G4DDK and G4NBS.

I've been back up to Alport Heights in Derbyshire today with my 10GHz equipment from back here.

And have been listening to GB3FNY on 10,368.752 MHz:

I can find no trace of GB3LEX on 10,386.955 and can only assume it's off air.

Bonkers, egh?

Saturday, 22 October 2016

Tripping over SWR


I've been thinking some more about the linear for 23cm I started back here, and more importantly how I can generate a high SWR trip signal for the control board.

I have one of these directional couplers:

It has a forward and reflected port at -30dB. Then I remembered I had one of these kits, which built looks like this:

This will turn the sampled RF into a -ve DC voltage for the SWR trip on the control board.

Now, fortunately or unfortunately we now need to do some maths to determine the attenuation needed. The RF detector board contains two samplers, I have configured one for the forward power and one for the reflected.

So, starting with the forward port:

Assuming a maximum output from the linear of 150W, we can convert that to dBW using:

So my 150W RF becomes 21.8 dBW. Therefore the maximum power at the forward port of the directional coupler is 21.8 - 30 = -8.24 dBW.

Given that the maximum input power to the detector part of the board needs to be 3mW or 0.003 W we can also calculate that 3mW = -19 dBW.

Therefore I need an attenuation of the difference which is roughly 16dB.

Then assuming a trip level of 1.8:1 (or about 10dB return loss) the reflected levels need to be 10dB down from the forward so an attenuator of 6dB is needed on the reflected port.

Using my signal generator at 1,000 MHz (1 GHz) and adjusting the output we find this is the response of the board:

So it all looks pretty good.

I now need to do some reading up on how I can drive the trip alarms on the control board, but this should do the trick nicely.

Here's the dogs doing what dogs do:

Local conditions.