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Saturday, 20 September 2014

The Continuation of the Transverting Conundrum


I've been fiddling some more with my experimental 4M Transverter project.

I've built the RX converter:

This is fairly simple in that it takes the 70MHz signals from the antenna, amplifies them and then mixes them with the 60MHz local oscillator we developed last time:

and results in a 10MHz signal at the output. I've done some initial tests on this down converter and it seems to work as expected.

The transmit side is still work in progress:

On the right you can see part of a traditional doubly balanced mixer - I've used BAT85 diodes this time for a change.

The mixer mixes the 10MHz drive signal with the 60MHz local oscillator to make the 70MHz (plus all the harmonics and also the difference). This is fed through a band pass filter, which sweeps like this:

and then amplified and passed through another filter. The second filter is also a band pass at the moment, but I expect I will swap it for an identical low pass filter I made for the RX side - the second band pass filter is no way near as good as the first for some reason.

I then need to make a linear amplifier to increase the output to about 10W to drive my linear.

Good, egh?

Monday, 15 September 2014

To Transvert or not to Transvert


Been thinking more about my antics on 2M & 4M Meteor Scatter:

And wondering how my TS-990 would perform with transverters for 2M and 4M.

There are many designs out there for transverters, one of the best I have found are here:

Sam does a transverter for 2M and 4M; I have decided to join his waiting list....

In the meantime, you may recall we had a bash at some 4M kit a while ago, so I thought I would build on that experience and have a go at making a 4M transverter myself:

So here is what we have so far, the "traditional" approach would be to build an oscillator for 42MHz and then mix it with 28MHz IF. Well, I don't have such a crystal so I have started with a 20MHz crystal oscillator and a frequency tripler to give me a LO of 60MHz. This mixed with a 10MHz (30M) IF will get us to 70MHz.

Here's the LO:

It's output looks like this:

and its harmonics like this:

So I need to feed this through a low pass filter, which inits simplest of forms, looks like this:

The one I have made above sweeps like this:

So this is looking like a reasonable start.

I need to make the down converter next, this will be made with some dual gate mosfets - I've ordered some BS981s which should perform well at these frequencies. Hopefully they will drop through the letterbox any day soon.

Cat's not been helping much at all today:

Good egh?

Sunday, 31 August 2014

Look what I just found


Some of you may recall I had a dabble in the Mexico RTTY test early in 2013:

I just found this:

Good, egh?

Saturday, 9 August 2014

For sure, this is a bad sign!


I had rather hoped that it would never come to this:

I've started sticking pins in a map to keep track of my Meteor Scatter contacts, I'd much rather do this electronically but I can't find a way to easily edit an ADIF and then feed it into a map of some kind or other.

Here's a better shot of the new antenna atop of the others:

It's all getting rather out of hand, don't you think?

Thursday, 7 August 2014

This is even more Bonkers than before!


You may recall my recent declaration "it doesn't get more bonkers than this", well, perhaps it might.

My latest interest in bouncing RF of Meteors has expanded a little. I've decided to have a bash at this insanity at higher frequencies so I have bough myself one of these:

So, today the mast came down and the antennas came off:

A new stub mast was installed and the 2M beam constructed. I chose InnovAntennas because the beam I have for 4M and 6M seems so good I thought I would stick with what I know. The quality is excellent and the ease of assembly was superb.

There's no connector at the feedpoint of these InnovAntennas to minimise losses and mismatch, so you prepare the coax thus:

Anyhow, there's a new antenna atop of the mast:

To accompany the antenna I have also bought the matching amplifier of my 4M and 6M amplifier, the Gemini 2 from Linear Amp (DX Shop):

Initial tests show no unwanted interaction between the antennas and an excellent low SWR on the new beam.

The amplifier is delivering a good 300W on 144MHz:

So hopefully I can have a good play.

Cat's been keeping a watch on proceedings:

Fun, egh?

Monday, 4 August 2014

Even More KISS Mixer Musings


The last time I fiddled with the KISS mixer from the Minima was back here:

Now, lots of QRPers have fiddled with this since and the musings of all of us have gone into the brain of Ashhar Farhan, VU2ESE and this has popped out as an improved design:

So, here's a first bash at giving it a try.

To test this properly I need to tap into the Si570 LO inside my minima so that the LO levels are as they will be, but for now I am trying something basic using the bench signal generators I have here.

So, for this test my LO will be at 27Mhz and generated by my EMRFD Sig Gen. Here's the signal into a 50R terminated 'scope:

For the RF signal I will use my DDS Sig Gen at 7MHz. Here's that signal into a 50R terminated 'scope:

So the LO signal is connected to the LO port in the schematic above (that's the port on the far left), the RF signal is connected to the RF port (that's the one at the bottom right) and the Spectrum Analyser is connected to the IF port (that's the only one we haven't used yet). Here's a picture of the mixer:

So, this is what we see on the Spectrum Analyser sweeping 0 to 100MHz:

The 10K pot is sat in a central position and I haven't made any attempt to fiddle with it. If I do have a fiddle then I can reduce the signals at marker 1 which is the RF port input at 7Mhz quite significantly (I can also make it much bigger too):

So, in the above image we have the following:

I now need to take my minima to bits and use the Si570 as the LO signal..... i also need to go back and review the results from the last tests on the previous incarnation of this mixer....

A quick check with the IF and RF port connections swapped round suggests a good isolation between the LO and RF ports of something like 45dBm, however the harmonic at 54 MHz is stronger and needs investigation:

If I now increase the LO drive level, thus, by adding a general RF amp to the output of the sig gen:

We now see the following with the initial configuration (Spectrum Analyser connected to IF port), just to keep you on your toes the SA is now sweeping from 0 to 80MHz.:

And with the SA connected to the RF port:

In both of the last two tests the pot in the circuit has allowed me to reduce the 7MHz signal drastically.

Finally, if we swap things about a bit and put the LO at 27MHz amplitude 14dBm and a 20MHz signal amplitude -5dBm into IF Port and SA on RF port we can go from this (just to keep you on your toes the SA is now sweeping from 0 to 80MHz):

to this:

by adjusting the pot in the schematic. It looks like a multi turn pot would be a most excellent idea as the adjustment is very critical but the 27MHz LO signal can be almost nulled out completely as we could with the 7 MHz LO signal in the earlier example.

We need to test this at the LO frequency range of the Minima and with the harmonic and other content of the Si570, but it does rather look like this mixer with a single lpf at 30MHz and just one trap at 20MHz will do just nicely.

Cat's not been helping much:

He did raise an eyebrow due to the excitement when the final SA image with the nice null was saved but soon settled again, he does like an RSGB book as a pillow

Fun though, egh?

Thursday, 17 July 2014

It doesn't get more Bonkers than this!


The whole concept of bouncing RF of meteor trails is, lets face it, quite nuts:

It does, however, appeal to me for some reason. Primarily because the WSJT modes are so fantastic and secondly because it's completely insane.

I've just had a great QSO with DL4KUG, thanks Erich!

Cat wanted to play earlier, but only on the condition that he didn't have to let go of the mouse under his left paw:

Fun, egh?