Search This Blog

Wednesday, 22 March 2017

Finally - All coming together

Well,

There have been many musings recently all building to a 13cm (2.3GHz) system:


  1. The Transverter
  2. The VLNA
  3. The masthead enclosure and switching
  4. The antennamabob
  5. The sequencer
So now I'm trying to glue it all together!


The case is a bit tall, but it's all I had. I created a very simple PSU based on a 723 voltage regulator and a 2SC5200 as a pass transistor - I have tried to over-rate the power supply (please excuse the terrible layout below):


That plus the transverter and sequencer we played with previously.



The Gubbins basically remains the same as designed:


So, there is a VLNA at the masthead next to the antenna and two co-ax feeds back to the shack - one for TX and one for RX. The TX is 15mm Web-600 and the RX line Westflex 103.

This is all driven from 423 Mhz multi-mode transceiver - I plan to use the IC9100.

Now for the linear amplifier, I picked up one of these for basically scrap metal value:



There is information on modifying the unit for our purposes here.

As ever, the first thing required is to take it to bits, once you get the bottom off this is revealed:


then that board comes out and slung to one side:


then we remove another million screws and get the screen out of the way:



and then the top of those two boards gets slung:


Now we need to lift a cap off the board and connect in where our RF feed will be:




Now for the bias for those lovely MOSFETS....  here's the board with my bodged bias circuit:

.
And throughout, Florrie the Ham cat has been assisting:


Next, a bit of testing.....

Local conditions.

Friday, 10 March 2017

13cm Antennamabob

Well,

You may recall back here I installed a 13cm antenna on the mast, and here I built the 13cm VLNA from @DXING G4DDK. The VLNA is now mounted masthead with the associated switching and a separate feed for TX and RX as I described here:


I've also recently acquired myself a much wider frequency coverage Spectrum Analyser; it's a very old HP8593A which covers up to 22GHz and came from here and has nice things like a 2 year warranty:


So, using the Signal Generator I made back here, and a cheap Chinese directional coupler being used the "wrong way" round;



like this:


I can leave the Device Under Test port open circuit and see the amplitude of the signal from the sig gen on the Spec An. If I then connect the antenna to the DUT port and calculate the difference between the open signal and the signal with the antenna connected - that should be the return loss in dB:


So apologies for the really rubbish photo, but the higher peak is with the DUT open circuit - so a really pants SWR and the lower peak is with the antenna connected. That's a difference of about 30dB. So using the maths we established back here we can deduce that the SWR is about 1.07:1 - which is bang on the money.

I was rather hoping I could hear the Leicester beacon GB3LES on 2320.955MHz - but I can't. So there may be a number of reasons for that - including my poor N-Type connector soldering, so I will have to look further.

But progress none the less!

**UPDATE**

The Leicester beacon has a fixed antenna beaming 160 degrees from its location - that's almost completely in the wrong direction for me! I've tuned to the Telford beacon on 2320.870MHz and I can hear the beacon just fine - RX working!


Local conditions.

Wednesday, 8 March 2017

6&4M Antenna and other Musings

Well,

I decided a while ago to remove the large 6/4M combined antenna I have - it's very big and heavy:


So, I decided a while ago to replace the 6/4M antenna with a 3 + 3 ele version that we originally bought for the UK ACs; this antenna had very little front to back so I wasn't happy with it for home. I've now decided to purchase the 4 + 4 ele version. All these antennas are from Innovantennas.

Now, I've bought quite a few antennas from them in my time - perhaps 10 or more. Every single one has had either no manual (sent by email normally), missing parts, the wrong parts or even one had the boom drilled incorrectly. This 4 + 4 ele is a bit better, it only had one broken pipe clamp. The instructions you receive from InnovAntennas are poor at best, but this example has to be the worst yet; take a look:


Now, there's something scribbled in the top right that looks like "ADD over Cap" - no idea what that means.

There's a box drawn on the 4M driven element and then scribbled out.

There's a box drawn on the 6M driven element with a scrawl that says "Plate oh tend Point" (I think this is plate at feed point) so we conclude that this was first scrawled on the 4M driven element and then crossed out.

Nothing to tell me which bolts to use where or anything resembling how to put it together.

Great antennas - rubbish quality control and instructions!

I've also continued the theme of 'scope obsession by making a circuit from W2AEW. This is a means of converting a composite video output (from say a camera) and displaying it on a 'scope screen by using the X, Y and Z inputs:



My build looks like this:


and it works a treat!

When Miss Luna Cat rolls on her back like this in front of Elmo Dog, this is interpreted, in human speak, as "thank God it's spring".


Local conditions.

Monday, 20 February 2017

Really? Wow!

Well,

How about this then?

I seem to be having a phase of collecting old 'scopes. I kind of love them, especially the old Tektronix devices.

There's a You Tube channel that I subscribe to by W2AEW where he does loads of fab and groovy things in general, but when I saw this, I just had to have one!

Using an Arduino Uno, a very primitive resistor based DAC and a bit of code, we end up with this, here on the scope I just repaired, a 2465:



Just fantastic!

This is the W2AEW actual video itself including the links to the code:


The Arduino and the DAC look like this on my bench:


and here running on an old 465 'scope:


Local conditions.

Wednesday, 8 February 2017

Tek 2465 Teardown

Well,

I have a Tektronics 2465 'scope that has some issues with it's timebase:


The sweep A is all out of bonk (that's a technical expression) - in the image above there's a 10MHz signal applied and at a 50ns sweep time per division we should see 5 sinewaves - we see 8 :-(

Sweep B is correct at 20ns however at 20ns we see two complete transitions of the signal.

I've started to take the 'scope to bits and will use this blog entry to document things as I go. Here are the initial shots of the 'scope in bits:




So here you can see both U700 and U900 removed, they are the main hybrid components in the Sweep A and B circuit. I'm going to try the 'scope with these two swapped round as they are the same component but for Sweep A and B:


So, swapping the two hybrid devices U700 and U900 made no difference; I now need to focus initially on this bit of the circuit:


I've also looked in more detail at the exact problem that I have. It seems all sweep speeds EXCEPT 5ns are impacted. I've annotated two points in the diagram above and have taken the voltage measurement at these points at all sweep speeds:


You will also note the consistency in the delta at all sweep speeds above 5ns - this is the same right up to 500ms but I just got bored writing the same thing over and over.

So, why is the voltage at the first test point so dramatically different at 5ns (the only sweep speed working) than all the others. Could it be that the B Sweep hybrid actually does the 5ns sweep on A? The B sweep can never be slower than the A sweep so there is no need for both to implement 5ns - I don't know if this is true or not.

I pulled R724 and in the process the end snapped clean off - but it measured 35.55K (it should be 35.3K) so I dont think that will be the problem. However, I've had to order some bits as this is a very non standard resistor value.

I also had a look at C712 which I have replaced. I also need to check that the +42V line is as it should be.

Once I have the replacement bits I'll update this post with my findings.


Some more pics while I wait for the bits:







Now the bits have arrived I have replaced R724 (made from two resistors in series) plus C712 and BINGO - the fault has gone and the sweep speeds are back on the money. The unit needs calibration now :-(

Final update: I've been through the step-by-step calibration routine. To access the routine you set a jumper on the control board and then press the delta T and V buttons together and whilst holding them down stick a chicken down your trousers (actually you press the slope button). Then you go step by step through the calibration routines and using the other test gear I have hear I seem to now have the 'scope very much on the money.

Local conditions.

Tuesday, 7 February 2017

A Lawful what?

Well,

Back in the spring of last year we removed a load of trees from our property and also had some fairly extensive works undertaken in the garden. The net result was that the antennas at the property became much more visible from the road.



Now, one of my neighbors who is particularly grumpy, decided to question the legality of the mast(s) and antenna(s) at the house with our local council.

In accordance with the planning laws, they all should be subject to planning permission. However, theory says that because they have been in place for in excess of four years the council are unable to take enforcement action. Unfortunately, the onus is on me to prove they have been in place for that time.

Thanks to this blog and my obsession with taking photographs, I was able to generate a very comprehensive document containing a load of google dated photographs stored in the cloud showing each of the antennas and masts in place with a photo upload date.

Finally, after a long bureaucratic process, my Lawful Development Certificate has been issued.



So my grumpy neighbor can go stick his complaining!

Local conditions. 

Wednesday, 18 January 2017

Fiddling with a Transistor

Well,

I found myself scratching my head the other day trying to remember the difference between Class A, B and C amplifiers and how that impacted a transistor bias.

To help me, I've drawn this quick schematic:

Now, you will see that R1 has a "*" next to it; that's because we are going to play with this value.

The transistor base will switch on when the voltage on the base is greater than 0.6V.

So, if we place a 10K resistor where R1 is, we place the base at DC voltage of about 1.6V. If we now apply a 2V peak to peak signal to the base (in my example it's a 100KHz signal), then the lowest point of the signal the base will be at 1.6V minus half the voltage peak to peak = 0.6V. Therefore the transistor will be switched on for the full input signal cycle.

The voltages on TP1 are in yellow and TP2 in blue. Here the first example with 10K as R1:


You can see that all of the input signal is above the dotted line (which is at 0.6V) and therefore the transistor is biased on throughout - this is Class A operation. Harmonically it looks like this:



Now, lets change R1 for 39K which will place the base at DC voltage 0.6V and apply the same 2V peak to peak signal. This time the transistor is only switched on for about half the cycle and the resultant voltages look like this:


Here we have 180 degrees of the input signal turning on the transistor - this is Class B operation. Harmonically it looks like this:



Finally, if we remove R1 completely, then the base of our transistor is at DC ground (being pulled low by the 4K7 resistor). If we now apply our signal we see this:


So the transistor is only on for less than 180 degrees of our input signal - this is Class C operation.

Harmonically it looks like this:



Now, you may wonder what use Class B and C are? Well, in an audio amplifier - none at all! You would hear all that distortion and harmonic content and it would sound completely awful. However, from an RF perspective, we can easily remove the harmonics from the output and retain just the target frequency - they all seem pretty much the same now - agree? And Class B and C amplifiers consume much less power (because the transistors aren't turned on the whole time) so are far more efficient. We just need a suitable low pass filter at the output and we can "reconstruct" our signal.

Interesting, egh?