MC3361 Mixer IC

What can I say, I like to trawl through parts catalogues and find somewhat obscure parts or ultra cheep parts to play with. So, when i found the MC3361, which is an FM Cordless phone IC, I thought why not. It costs 25 cents in one offs, and has some conversion gain and I assume its a gilbert cell in there, so its way cheaper than an SA612 and others.

LO in is on pin one, you can also add an xtal here for the LO. RF in is on pin 16 and the IF out is on pin 3. Now i did not try and match the impedance’s which are around 1800 ohms, i just fed in 50 ohms from my function generator into the LO and RF ports and then attached the spectrum analyzer to the IF port.

Other than some DC blocking caps and a 50 ohm termination resistor on the input there is not much to add to this. And as you can see from the plot below from the spectrum analyzer its working doubley balanced. RF in is suppressed and the sum and difference are the dominate signals. RF in was 7Mhz and the LO was 1Mhz for the sum and difference of 6 and 8mhz IF frequencies.

Is it as good as other mixers? I don’t know, but it works and its cheap, so i think its worth a go. Oh and it also has an FM de-modulator, AF amp and a op-amp for filtering in there also. I am yet to play with the other bits, i just setup the board for mixing only and well, mixing works.

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RF In The Ham Shack

I have had this intermittent problem with RF in the shack. Mainly this was on 20m where when transmitting some digital mode like FT8, the software would crash and the computer would send random serial commands to the radio and just mess things up. Mostly this was on 20m, but also on 15m the wireless mouse would stop working while in transmit. So i had some RF issue happening and by chance I worked out what it was.

Now, for work i spend a good part of my time on a motorcycle out delivering and I like to listen to the radio, podcasts and even ebooks using software that reads the text to me, while i work. I use these cheep arse bluetooth headsets to pipe the audio into my ears from my phone.

It turns out, when i have these plugged in and charging, they are acting as antenna and RF is then being fed into the mouse and keyboard dongle and computer VIA USB and then out the USB to serial cable for the radio’s cat control. Who would have thought that something as simple as USB charging would be the cause of all my problems.

Solution was simple, unplug the bluetooth headsets and everything is tickety boo. Oh and the reason why I have 2 of these, the battery only last 4 hours and 2 means I can work all day and keep the sounds coming. 🙂

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Pi Pi Pi Piledriver

The boards I designed and ordered have arrived today, so i hastily threw together the Pi board to make sure I did not screw anything up. Everything is legit and I no longer have the stupid low power symbol coming on all the time. Everything is now powered off a 5A psu and even with the LCD, wireless keyboard and mouse and hard drive hanging off it, its happy as. No more losses in crappy USB cables. The other thing on the board is a bandpass filter. So i can play with some of the rf generation techniques that you can do with the pi. More on that later.

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15m FT8

Well, from what all the talk is currently, we are no longer in solar minimum and the new solar cycles has started with vengeance. As of writing this post there are currently 21 sunspots and 15m has been open during the daytime for the last couple of days. Not that there is lots off activity, but there is enough to warrant showing some interest in the band. Anyway, I am a 15m fan boy as it is, so i need no coaxing to get on 15m and see what is going on.

The above image shows 24 hours worth of data. Not that i have been spending great amounts of time here, every hour or so i put out a few calls or enough calls for the watchdog timer to kick in and then check the map. I am not making much in the way of contacts, but I am being heard and I am hearing stations and I have had 2 incomplete contacts.

Well, I have now managed 1 contact in 2 days HAHA. Not that it matters all that much, but its good to see my favorite band open and doing something. Its been a while since there has been much action here. I know the 10m fan boys must be foaming at the mouth for some action up there. Bring on more sunspots.

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A Typical Day In Australia

Just a typical day in Australia where there is something trying to kill you. I am pretty sure this big bastard was an eastern brown snake, probably the most deadly snake in Australia, which is a land of deadly snakes. Brown snakes are aggressive and will stand up and attack anything that pisses them off including cars. I was far enough away from this guy to not be a threat, I took my photo, the snake crossed the road and I rode away. Lucky i was riding on the footpath, if i did not see him and rode to close, it might have struck me.

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HackRF and SdrAngel PTT

One of the annoying things about the HackRF is that its only 1/2 duplex. It could be a receiver or a transmitter but never both at the same time as a transceiver. Not anymore. SDRangel now has a new feature, the PTT button that automatically switches from RX to TX and back again. To use it is very easy. Setup your source device, then setup your sink device, click the play button and then when you hit the PTT button you will switch from RX to TX like a pro,

I have been playing with this new feature this morning using a 2m handheld and the HackRF and having QSO’s with myself at the milliwatt level LOL. The received audio in SDRangel sounds rather rubbish, i am sure I have some setting wrong somewhere, but it sounds thin and at times distorted. The transmitted audio does sound a little better.

As far as software goes, its good to see the developers of this continue to improve and expand it. There are also a lot of new demodulation types as well since I last updated it.

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