Wednesday, February 29, 2012

Regen receiver audio and UHF oscillator

Here's a small video of the ARRL simple regen receiver working, for posterity...

Note the "Swiss army" tuning shaft on the trimmer cap... as we say: "those without a dog hunt with a cat.."...

I think it's not this time the regen will get a new box, I already started cannibalizing one of the boards to make some tests on UHF, maybe an UHF receive converter will come out of this...

The result:
The circuit:

..another nice photo...

The circuit came from LY3LP 70 cm rx, I just used the T3 oscillator part.

Here's what I had of drift after 1m warmup with the circuit just bellow a reading lamp:

Considering the runing frequency I think it's not bad... the idea is to feed this LO (290Mhz) to an ADE-1 mixer down-converting 440Mhz to an 156Mhz VHF FM module I have (it's in the photo bellow the frequency counter) and didn't managed to program it in another frequency. An PLL stabilizer is then also needed.

I noticed that for a frequency bigger than 490Mhz I had to short-circuit C32 for the circuit to oscillate. I used an BB105 varicap and BFR91 transistor instead of the components in the original schematic, for L6 in the "final" prototype I used an ferrite bead (around 3mm long with 1mm hole and the wire passing inside one time only) recovered from a computer motherboard (good source for beads), R17 used 56 Ohm instead of the 33 one. Not critical I guess!

Have fun, generate some signals!

Friday, February 24, 2012

Simple regen receivers

Some years ago I built the ARRL simple regen receiver, in fact it was my first working receiver. I never placed it in a box and the board as been cannibalized when components short. This time decided to rebuild the receiver again and hopefully place it in a nice box. My original construction was on a PCB but now decided to place it in wood substrate.

The schematic:

Here's the preliminary tests with the transistor amp and not the original LM386 in the design:
This method of building is nice when you don't have PCB around, not the case but gives some old style to the build.
And the link to the original article.

While building (or rebuilding) the ARRL design, found another simple regen receiver on g3xbm site and decided to give it a try....

I built the g3xbm schematic on "Hertz" day, and guess what.... it didn't oscillated! Yesterday I figure it out, probably a broken FET, I replaced the part I had by an BF244 (an MPF102 on the original design) and started working, except when my crystal headphone was connected, after all it wasn't a crystal headphone but a simple headphone in a look a like crystal phone box.
The one on the photo is a true crystal phone one and is from my dip meter accessories.

Both set's do receive but as they are simple designs so you should not expect big performance. I intend to build the following design in the next few days, looks a little more promising. You should read some considerations on regen's on the link above if you're interested in building this type of receiver....

Have fun!

Wednesday, February 22, 2012

Monday, February 20, 2012

A Simple Audio Amplifier

I've built this one some some time ago and his now my bench test audio amplifier, it works nice and if it has to much gain for the part I am testing I just connect the input to the second preamp stage as stated in the original article by ke3ij.
I built it because my test LM386 amplifier was behaving incorrectly and I could not trust him anymore, I guess that there were some problems in the solder, it was open air soldered into a baby milk box, didn't bothered to find out what was the issue...decommissioned!

The schematic:

And the lousy photo:

Here working as the audio output stage for the BITX FM demodulator tests.
There's a 9V1 zener for power supply regulating (on the left top of the board) but is not connected normally, I just connect to 12 or 9V whichever is available.

Have fun!

Saturday, February 18, 2012


Today was repair day...

Good news is everything is fixed...or half fixed:

* The FL-110: OK it was not a fix, it was operator problem, the FL-110 RF switch doesn't work on badly matched aerials.

* The FT-7: Works but was not completely fixed, I have to get to a difficult access plug and didn't fell like it today although the FT-7 is of easy maintenance.

After losing half an hour searching for a pdf of the schematic I remembered that it came on paper with the radio...
(Schematic with the possible culprits)

(audio board)

Initialy I thought that it must be some issue with a power line capacitor or one in the audio path, I inspected the audio board and found nothing suspicious, then I thought on the audio output cap, tested with a brand new cap connected to the amplifier output and audio popped up! Cool it's the audio cap, but let me test with an external speaker to make sure it is that the problem (it's always nice to double check). Placed an external speaker and audio was OK, so the problem moved along the output audio line to the external speaker plug, Something to test/clean on the next days.

The video, testing to eliminate any possible problem coming from the audio amp. You ear the completely different audio from my test speaker (series with an output cap, "the probe") and the internal speaker when I disconnected the probe.

* A heater from a friend: it was easy but not so to spot, there was a hidden thermal fuse inside a cable and that fuse was broken (fused), I did bypassed it for later replacement of a new element. Not elegant but works for this cold days!
(thermal fuse)

The heater

Good, now I have to get some courage to fix my oscilloscope....

Airband BITX AM demodulator

It's all in one.... the airband RF front-end with BITX components (2SC2570) and the AM demodulator from a 10Mhz IF, also using BITX components.

I used a mix of 2n2222 and 2n3904... whatever came first out of the transistors box...

It's a first test, I'm thinking in swapping the Ge detector diodes by 1N4148 as used on other parts of the original schematic and removing the 2 crystal filter after the first mixer by just one main filter with 6Khz bandwidth. In this schematic topology the VFO needs to be very accurate since the signal get's rapidly outside the filters pass-band. That's why I'm using the Si570 VFO. The 2 crystal in the first filter were not matched, they were some spare crystals from the batch used in the BITX crystal filter.
Of course this is the first working version so use at your own risk, I just plubished it for future reference or case someone needs ideas... It took some testing to get to this although other versions I built in the process still worked but for bigger input signals and not the small ones I was getting in the front-end. In fact one of the detectors I build and with just one RF amplifier was getting the local FM station quite well......

Here's the front-end:
Another future idea is to get a crystal hundred kiloherts near the 10Mhz IF, add another mixing an then detect AM on the kiloherts range. But this adds the difficulty of finding crystals around 9.8, 9.9Mhz, at least for the BITX intended audience.

Have a nice weekend.

Tuesday, February 14, 2012


DOSI (Department Of Stupid Ideas)

As I mentioned before, sometimes I do think a little and when that happens strange ideas do pop up!

Here's one:

This idea came to life when in one of my work travels. I was at the hotel room thinking that would be nice to operate an ham equipment at HF, problem is that I end up always on northern parts of the hemisphere well know for a not warm climate (for not saying bloody cold for a Mediterranean climate inhabitant!), so opening the window was not an option to place an antenna or I would became an ice cube....the other option was to place the cable and closing the window...but I think the normal 50 Ohm round cable would not like the idea...

So two ideas pop up:

1 - A windows pass-thru cable made of thin wire

I did some quick tests and the design works till 10Mhz (using 50 Ohm system), of course I believe a smaller distance between the wires could extend to higher frequencies, this was just a quick test, the distance between wires I made has an impedance more near 300 Ohm than 50 Ohm.
There are some commercial window pass-truth used for satellite installations (75 Ohm) that could be used in 50 Ohm system but I didn't tested any of those, maybe someone can test them, this was just an idea not for production, at least not right now.

2 - A coupling link working from the inside (antenna tuner) to the outside (antenna) like on the Z match tuner.

I made a small coupling coil about 10cm diameter connected to the antenna analyzer and another similar coil connected to a 50 Ohm load, then placed them at a small distance similar to the glass depth (about 5mm). Measuring up I end up to the conclusion that the ideal distance is the coupling link inside the transmitting link (like on the Z match, be it open air or with a toroid).
Unfortunately I didn't take photos of the rest fixture. This system might work on lower performance but further testing is necessary.

There's still another method I came up....the coupling cap method but didn't test it, a small aluminum plate inside the window connecting the transceiver cable and another one outside the glass connecting the antenna, being the ground wire radials in the inside.

Conclusion: Further and more precise tests must be done. I just left here the ideas, it might help someone. I haven't traveled that much in past times that justify making something.

Monday, February 13, 2012

World Radio Day

Today it's "World Radio Day" by UNESCO.

It's more Broadcast than Ham related but never the less both mix at some point!

More info here:

Here's a list of some important dates for radio from the Unesco site:

".....22 February 1857 : Birthday of Heinrich Rudolf Hertz, a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell. He was the first to satisfactorily demonstrate the existence of electromagnetic waves by building an apparatus to produce and detect radio waves. His achievements triggered the invention of the wireless telegraph and radio.
30 November 1858 : Birthday of Jagdish Chandra Bose, a pioneer of wireless broadcasting. Indian physicist, biologist, and early writer of science fiction, he pioneered the investigation of radio and microwave optics and laid the foundations of experimental science in the Indian subcontinent.
6 October 1866 : Birthday of Reginald Fessenden, inventor of audio broadcasting and radio pioneer.
25 April 1874 : Marconi’s date of birth.
7 May 1895 : Russian inventor Alexander Popov’s first demonstration of his radio receiver to the Russian Physical and Chemical Society. The date is celebrated in the Russian Federation and Bulgaria as "Radio Day".
28 March 1896 : Anniversary of Marconi's first audio transmission. (Marconi is known for his development of the telegraph and we have found no evidence of a first in audio transmissions).
2 June 1896 : Marconi patented a radio device.
27 July 1896 : Marconi's first public wireless transmission of Morse code....."

Have a nice week!

Phone call

Last Friday night got a phone call from a friend:

(F: friend)
(M: me)

M: Hello
F: Look, the name Yaesu-Musen tell's you something
M: Yes
F: The number FT-7 tell's you something?
M: Yes, it's a qrp I think
F: And the markings: FL-110
M: Hum, I think it's a linear to match the FT-7
F: I have here this equipment, do you want to have a look?
M: How did you get those?
F: Never mind!
M: Are you at home tomorrow?
F: No, will be out.
M: Just wait there! I will have diner latter!

My friend isn't a radio amateur so I drove to see what he was up to.
A friend of him who is/was (giving up) radio amateur gave him this equipments and he handled to me for testing.

Saturday morning I went to the sack so I could test both equipments.
The FT-7 isn't esthetically perfect (althoug the mic is) but the FL-110 look's like it was never used. They came in the original box but only one power cable so will test the FL-110 against the TS-50 on 10w out.

After powering up the FT-7 I started to get some interference in audio, I thought immediately that there was a problem with the radio but later the TS-50 was with the same, so it was due to band conditions. I did got some signals on 20m but then audio started to fade away (on the FT-7) so the radio has some problem for sure.
Then I disconnected the FT-7 and connected the FL-110 to the TS-50. Power up, and it lit the normal LED. Transmission test.... zip, nothing, nada, not even the operate LED, I switched to AM to get a bigger carrier to activate the RF switch, I have to test with the external activated switch but I think there's some problem internally.

Conclusion, two inoperative equipments...for now... I told last Friday to my friend that we will put the equipment at his home, connect an antenna and let him decide to make the ham radio exam. He told me he was going to think about it, I understand he's position, I guess he is a little fed up of radios, he's an air traffic controller!

Saturday, February 11, 2012

AM for the "BITX"

Nothing more simple than adding AM reception to the BITX transceiver, Right?

I was over confidence on this one, having done SSB I thought AM was going to be child's play..... a simple rectifying diode, a low-pass filter and that's it! I missed something in between for sure!
Was getting nothing at all, getting a whistle or getting to low after some days testing and a lot of soldering after I came up to my first acceptable version....oh did I mentioned that the idea was to use only the same values of components of the BITX V3 design? NO? Yes, that was the idea, even so I had to use 9 different values of resistors, diodes and caps (all standard values and no IC's or coils) but I also added airband reception in between except I'm using an external VFO. If the 2SC2570 can be used as VHF oscillator then the count will stay at 9....will try that in the future (7 for the AM part and 2 for the airband input filter).

Since this is the first working test, no schematic will be provided, I need to improve a little bit and try to reduce the number of different components.

Here's the lousy video, live audio was greater than the one captured on mic, I guess that if my mobile phone was a toaster all would came out burned!
Not all the components you see in the video are part of the design :)

Have a nice weekend!

Wednesday, February 01, 2012

It's a BITX...

...Not to take literally....

Some time ago I used parts of the "bitx" transceiver for a small receiver, mainly the first mixer and the crystal filter, for the SSB demodulator and audio I used the NE602/LM741/LM386 combination, it worked good but never finished it (at least give it a decent box).
Now decided to use some this parts (all the RF receiving strip) for a NAVTEX receiver since I found in the crystal box one that oscilates around 9.510 Mhz... so with more 490Khz (one of NAVTEX frequencies) and it sits in the middle of "bitx" IF (10Mhz). Since I was building basically all the receiver part why not make a full version, so here part of the build process...

First tests using the ADE-1 mixer:
Now fast forward and some soldering....bellow image from top to bottom upright pcb's the 9.5Mhz oscillator the 4Mhz vfo (horizontally laid) and the 10Mhz BFO (with LSB/USB, two white variable caps)

I add already build last time the first mixer with diodes but now decided to use an ADE-1 mixer, also for the SSB demodulator one was used.

The first problem was in the audio stage... supposedly the easiest part, I was getting smoke in one of the limiting resistors, luck (and experience) avoid a total burn out, after some tests and some bad words I found the issue, I was looking at an LM380 schematic and not the LM386 used on the transceiver (remember to always have only one schematic in front of you).

Second issue that was driving me nuts was the lack of gain, I had gain in the amplifier after the crystal filter so I tough that there was some issue with the crystals, but they had been tested in "real live".... I ended up making the post crystal amplifier of "bitx" version 3, no luck... more bad words and another day to think about the issue, I decided to replace the ADE-1 (was suspecting of it) in the SSB demodulator and made the original bitx mixer, it worked first time with a lot of gain...more bad words thinking I had ruined one ADE-1 mixer (their expensive you know?). Decided to check the ADE-1 small adapter PCB that I made, yups, that was the issue, a small short from a tiny little piece of cooper... oh well, now it works again with the ADE-1 just because I have more mixers than binocular cores...

Can you spot the multi-turn carrier null pot of the original "bitx" schematic?

Now again with the ADE-1 in the SSB section (lower right part of the image)

I still need to finish the VFO (done but not tuned) because I was driving the first mixer with the Si570 kit (it's easier when doing tests). The idea is to put a switch between VFO (4-4.350 Mhz) and Fixed channel (9.510) for NAVTEX. obliviously a switched band pass filter for 14Mhz and 500Khz...

Have fun!