Wednesday, October 28, 2009

UV916 tuner receiver based (part 1) - Power supply


For the UV916 tuner one needs an 33v power supply. That's a small problem, my bench power supply only has 12v (more or less). Digging for an easy step up converter (read: search for what components were available locally) I found the MC34063 IC that my local electronic shop stocks as KA34063. After reading the datasheet I came up with a schematic.

Now it's a question of start dismantling some computer power supplies to find the 170 microH inductor since I don't feel like't to make one. I still don't have the IC so for the first time the schematic come first!
The local store doesn't stock the BYV10-40 diode but stocks the 1N5822, they look similar (10-20% values) in the datasheet so I will give it a try.
This is my first "switched" power supply so anything could hapen!!!

Adendum:
Replaced the 47K resistor by an of 33K and the 1850 ohm for an 1K2 in series with an 220ohm variable pot.
Diode was replaced by an 1N5819.
I did wind, after all, the toroid, it was salvaged (along with the output 200V!!! capacitor) from an old computer power supply and has 82 turns of 24swg wire on a yellow core... probably less turns would work also.
The 0.22 Ohm resistor was made winding around 40cm of wire.....It works.
Placed an 56k "bleed" resistor in parallel with the output to discharge the capacitor.
After following the data sheet on the MC34063 and making the schematic I found an online development aid for the IC at: http://www.nomad.ee/micros/mc34063a/index.shtml

Tuesday, October 27, 2009

UV916 tuner receiver based (part 0)

I was given some obsolete electronic equipment, namely some VHS video recorders.... I accepted thinking in using the boxes for some project.... but there's more than the box, a big collection of components including an UV916 tv tuner. Some time ago I came across some spectrun analizers and receivers using this tv tuners, now it's my time to test.

First thing to do is desoldering the most important components, I will not mind for now with resistors and capacitors, just the ones I could use on "rf", like the tuner some filters, cristals and inductors.

Now I have to look how things are connected:















And the TDA9813 match's in the datasheet from what I draw from the PCB circuit...VIF and CIF inputs I thing has something to do with bandwith beeing one of it mpeg4...














Here's another IC's used in other type of VCR's... looks like they are all almost the same...and the technology matches the components I removed....there's also two exits on the saw filter bellow...





























Now I am having the idea on how to connect everything.... The front end will be the tuner next the saw filter then an MC3361 based FM receiver from 30 to 40Mhz so I can fine tune since the PPL in the UV916 has step's of only 62.5Khz. The UV916 will be computer controled...


Ther's is a nice site with one completed receiver based on this tuner at:

http://hem.passagen.se/communication/uv916rec.html


....this will not be an easy job to do but I will give it a try.... but will take long for sure.

VHF FM receiver with Si570 VFO


Now I have two receivers working in sync with the same VFO, the airband receiver and a VHF FM receiver based on the NE602/MC3361 combination, they have separate antennas but a common audio amplifier.
The MC3361 circuit is based on the one at: http://f6feo.homebuilder.free.fr/RX_LA1185.html
I just replaced the TA7358 front end for an NE602 front end similar to the one on his datasheet. The 10.7 filter is a salvage unit from a chinese store radio.
Unfortunately the squelch is not fully operational and I will have to check again the schematic against the datasheet.

Here working simultaneously with the AM part of the circuit:

video

As soon as I build the other Si570 kit that arrived probably will place it in another box and not in the airband receiver box. Initialy my idea was to make an coil vfo for the NE602 but since I have the Si570 it will stay more acurate and frequency stable. Tried to replace the discriminator coil for an 455Khz ceramic cristal but didn't worked good, will try one of this days a combination of an commercial inductor and a capacitor since discriminator coils are not the easy thing to get around town. Probably an 360 microH with an 340 Pf capacitor will ressonate at 455Khz.

Friday, October 23, 2009

New IF for the airband receiver


I changed the IF of the airband receiver, now is 10.7Mhz for the first conversion and 455Khz for the last one, that way I can now add an FM 10.7 IF to the circuit, being double conversion on AM an single on FM in order to optimize the Si570 kit (AM airband and FM 144Mhz), probably will make also an front end and IF for 50Mhz ssb.
The circuit is a simple NE602 with an 10.245Mhz cristal and the filter is an 10.7Mhz cristal front the first mixer to the secound mixer, case connected to ground and a paralel capacitor in the secound mixer input (pin 1 on the ne602).

Sunday, October 18, 2009

What's next

Now that the airband receiver is done (closed inside a box) I am a little bit out of ideas on what the next project should be....

Ok, I have some boards left during the development of the airband receiver, am thinking in the one that has the TDA1072, it gives a nice SW receiver.... one of the audio amps probably will also be used and as soon as the new Si570 kit arrives will be used for an VHF FM receiver with the MC3361 but them what... there are some boards almost ready for an HF transceiver and the "Speaky" ssb transceiver is waiting for the final touch.

I am opened to suggestions...

Friday, October 16, 2009

The Airband receiver....at last!

...Not quite but enough!

Yes the Si570 kit returned from the "repair" (thank you Kees)... well it was more an operator issue than a repair, anyhow the thing works and I can finish now the airband receiver and move on to another project. After finishing the new squelch circuit (I changed from the TDA1072 to an TCA440 if) and put the boards in a box, I will consider this project done.
The receiver is not perfect but works to the minimum level I wanted, in the future probably will rebuild the input filter making it simpler.

The final circuit is similar to the ones I allready posted on previous articles so will not put again heres since I didn't draw it completly. Main features are:

Neosid coil rf filters.
BF981 rf preamplifier
NE602 mixer
Si570 VFO - kit from Kees, K5BCQ (can't get anything beter for the price)
TCA440 AM demodulator on 455Khz
LM386 (what else?) audio amplifier
CA3130 comparator for squelch circuit (shorting audio input via pnp transistor on act).

Sensitivity: enough
Audio power: enough


Here's the "beast" working, sory for the audio quality.


video


...there's a new Si570 VFO kit crossing the Atlantic.... but that is for another day...

Sunday, October 11, 2009

Multiple receivers on one antenna, some tests

Recently I came up with an interesting problem, I have more receivers (note: transceivers working as receivers) than antennas so I have sometimes to interchange antennas between them, wouldn't it be nice to split an antenna to several receivers.

Saw some interesting circuits in the internet but didn't tested any of them but I have some cable tv splitter's that would be nice for the job, here's the testing circuit:



Splitter is an "Teka" brand model 4302S/P-15 2-way tap 5-2400Mhz

Some problems with my testing:
1 - My signal source is not 75 Ohm
2- I didn't terminated all ports
3 - I don't have an rf voltmeter I can trust, only a simple rectifier probe connected to an DVM.
4 - I only tested at VHF

Anyhow I still didn't tested connecting to an receiver, probably some acceptable results could be found but I am sure only for high level signals.
One interesting part is that when connecting directly in the "power pass" output I have more output (on 145Mhz) than the signal generator directly connected to an dummy load....oh well that's the problem of not having accurate meters....

Some circuits that probably will work (for HF):

http://www.qrp.pops.net/swl-ant-split.asp
http://www.geocities.com/n2uhc_2/hfsplitter.html

will test them one of this days....

Saturday, October 03, 2009

Goodie's from the UK

My good friend Per from Sweden, working in the UK, came for a visit to Portugal... ain't we in a global world?
He asked before if I needed something from the UK.... hum....no....hum...yes! A quick look in the website of an UK electronic shop and I remembered my enameled cooper wire was on the short side and that I can't get locally nice buttons, so here is what I got. Next time he fly's here I will ask for an lousy t-shirt!



Now I just have to get some free time to give this some nice use.