Wednesday, March 31, 2010

Old radar...

For those who are making experiments on 8.97Khz and trying to get the world DX record at this "audio frequencies" goes some ideas on "antennas" a friend sent me:

I and Q ?

Phased array?



Have fun!

Tuesday, March 30, 2010

Divide by "n"

Still trying to find a way of getting a stable navtex receiver using crystal oscillator /IF combination decided to make a quick test on frequency dividers, my idea was not to make a direct conversion receiver but I guess I have no other choice unless I go to a pll system or find a combination of IF VFO with crystals matching.
With this schematic I can get 487Khz from a comon 10.245 crystal (used particulary in FM sets). If I find one 3615Khz crystal dividing by 7 one will get 516.5Khz the other NAVTEX frequency...

If you intend to use this schematic, remember I didn't looked at the output wave form but for shure it's going to need a lot of filtering. One of this days I will connected it to the navtex dc receiver block to make some tests...see below the dc receiver block with an LC vfo.

Some time ago someone gave me an old military direction finding equipment, at least the main body but not the accessories and since it's an heavy item I decided to dismantle to get some components, Inside there were some boxes I suspect were vfo's for each channel, with this looks:

Now I have some trim caps and some strange coils that I used to make an vfo for one of the navtex receiver, probably will build one of the receivers (decided to make 2) inside the aluminum box since the variable capacitor is already in place, so is one of the coils. I think this set was supposed to work around 3-4Mhz range due the size of the coils. With some extra caps I placed the resonance at 500Khz.

Testing the coil and cap as vfo:

I replaced the second NE602 working as preamplifier to an LM741 before the LM386.... now a classic DC receiver block. The combination of the coil and caps is quite stable but not enough to unatended operation.

Friday, March 26, 2010


"Surfing" in the quest to find some crystal combination that allows me to receive navtex on 490 and 518 found this funny image.... ham humor at it's best!

What about the HC49 and those litle SMD ones?

Moving on.... if the JBOT amplifier reveals uncapable to put some punch in the bands I just found the replacment, check CT1AOZ use for an GI-7B tube (or valve depends on the side of the pond) at:

Thursday, March 25, 2010

JOBT (3) Power up!

Watch out the pile up....I'm coming in..... with an fantastic 4w of output power.... I broke pile up's with less power (2 people count has pileup?)... the important is the antenna and my old aluminum tube outside the shack window, does wonders!!!
I had some coils (3 out of 4) with the wrong number of turns so I had to rebuild them because I normally count one pass in the hole is one turn but looks like that in binocular cores is one pass in both holes 1 turn. Live and learn! The diode in the ouput stage is an 1N4148 but I still have to confirm if it's not any other type.
The first coil I changed to a normal toroid since I was out of thin wire to fit in a binocular coil.
I could not get more than 4.47W but for me is enough, the lowest measure value was of 2.71W at 10Mhz. The measuring device is the uncalibrated rf probe somewhere on this blog. Calculation of power is the square of the voltage at the ouput load divided by the load. So it's the measure value plus the drop in the probe diode (assumed 0.25). If you have 10v then is (10.25*10.25)/50 = 2.10W.
The signal generator was the MFJ antenna analyser and I still tryed the amplifier at 50Mhz but only got 0.3W.... fair!
I still have to improve the temperature control since it's powering on to soon, I have to change the schematic two posts bellow in the blog. By the way in the tests the only thing I notice warm was the homebrew dummy load that was rated to only 1w.

The photo:

Wednesday, March 24, 2010

A different vfo control

Normally this blog is more about some experiences I do on my shack than current news or any other subject. Sometimes I open an exception when I find something unusual or interesting to share.
Most of you already saw some sort of VFO frequency changing be it by controlling with a variable capacitor a variable inductance, a sliding coil, a PTO, a VXO a trombone variable cap,etc,etc, you nameit.
Whell there are many different ways of "shooting the duck".... but this one for me it's the first time I see it. An original idea from "lw1ecp" worth mentioning. I am allready imaginating a smaller round ruber touching the round dial so one can make a reduction drive.

The linked image:

Must try this one of this days!

Page is at:
Also nice texts worth reading at main site:

If you need translation use for example, language is Spanish.

Monday, March 22, 2010

JBOT (2) temperature control

A good radio has to have some sort of cooling gives a nice impression.... here's mine for the JBOT (just a bunch of transistors) amplifier.
I don't ever think that the cooler is going to be needed but it's nice to have one with temperature control. It's a simple instrumentation comparator without hysteresis (it's given by the thermal hysteresis on the transistor and "sensing" diode encapsulation).
The reference diode should be near the sensing diode (but not touching the power transistor) to avoid a compensation circuit has if was the case of being a big difference between the inside and outside of the radio since the transistor capsule is in contact with the air outside of the!
I used 1N4148 diodes instead of a 2n2222 (using collector to base pins) transistor, or any other with metallic case, just because it's cheaper with diodes...

The usual crappy video, schematic is on the beginning for a change:


If you don't have 1% resistor you can try with other values, important is to get around 0v between pin 2 and 3 when both diodes are at the same temperature.

Sunday, March 21, 2010

JBOT (1)

I am sure everybody recalls his first project; the planing, the component gathering, the drawing of the pcb, the smell of the solder and probably the smell of the first resistor explosion.... anyhow it's a very nice feeling. For a while I had those same feelings with this project, I bough some transistors and start to imagine in my mind the final look the component placement in the pcb. On to the tool shop and on with some drilling and grinding...
I choosed this linear amp for my hf-radio after considering some other designs because the transistors involved are relatively cheap, easy to find and most important, I liked the concept.... just a bunch of transistors.

Component layout on the soldering side:

The back side with and without the cooler:

Why did I placed the cooler and not some heatsink? Well I have a lot of coolers removed from computer power supply and none heatsink for the TO-39 case and most looks cool and looks like an appliance!
The cooler will be activated by temperature (of course!) using probably an 2n2222 working as temperature sensor because the case can be soldered to the 2n2218 transistor case (case on 2n2222 is collector so probably will have to work around on this or use another transistor in metal case).
Measured the consumption on the cooler and is around 140mA, printed specification is 230mA, so for a 5w amp I will have 1.7w consumption on cooling!

The project is based on this design:

Linked schematic:

Friday, March 19, 2010

Mini Whip boxed.

Didn't had time for much soldering so decided to put some things in boxes.
Just placed the mini whip antenna/pre ( in the roof and boxed the power supply module. Also inside the box placed the antenna splitter ( so I can have 2 receivers connected to the same signal.

Connected one of the outputs to the TS-50 and the other is for another receiver, probably the navtex one. Removed the mic from the TS-50 just in case I feel tempted to transmit and burn the module.
Spent some time listening to Shannon volmet around 8.xxMhz and also to Santa Maria atlantic air control. If I power down the pre amplifier I can still get Shannon transmission and some air control, on a reduced signal, the box is not metalic and no shielding was placed in so that probably explains it.

Now the photos:

And the homebrew "family" growing...

Tuesday, March 16, 2010

A Navtex receiver, some tests

Today I am happy, my simple navtex receiver outperformed my TS-50 tranceiver, altough the TS-50 isn't supposed to be a performer at those frequencies neither it was connected to the loop antenna, insted it was to the outside dipole... the inportant is something that I brewed outperformended an appliance!!!
There was a schedule transmission and 1 minute before (Murphy law) it started getting a lot of static. I couldn't hear the signals in the TS-50 but they were visible in the navtex receiver.

Also changed the VFO for varicap control because I have no varicap's spare. Four nice red led's did the job. The led's are connected in pairs catode with catode then we get 3 terminal, one to ground, the other to the top end of the vfo coil, the midle, both catode, are for voltage control. Placed 4 led's at all so I can get enough frequency shift. A variable 47k pot is used to get the variable tension to the varicaps.

Some crappy photos (tm):

I decided the this receiver will be cristal controlled so I must now find a 3168Khz and a 3196Khz cristal to get the 518 and 490Khz reception. Oh well another project waiting for conclusion.

I was looking in some junk electronics boards I use to get some missing/strange parts and in one floppy drive I found an Hall sensor... this could be fun for some future project. Never the less I found no cristal on the frequencies I want.

Monday, March 15, 2010

A Navtex receiver

First I have to say that I can receive Navtex service in another way but it would be fun to make a dedicated receiver, so from the 500Khz to 4Mhz converter board I started to design an 490 and 518Khz receiver. First tests were with an low frequency oscillator near the desired frequencies ense a direct conversion receiver. The first idea was to divide a higher frequency cristal to get the oscilator but after some tests there was to much noise for pratical use.
I put my brains to a good use and came up with a nice idea using junk box cristals. If I use a 4.200Mhz cristal mixed with an 3.686 I would get 514Mhz that is 4Khz from one of navtex frequencies... 518Khz.

Problem is I get signal inversion and the decoder I am using (JavaNavtex) has no provision for that. Another issue is that I am limited to only one frequency.
Decided to make a vfo around 3168Khz (3686-518).
After some trial and error on the coil I got to the frequency... powered on the computer and there was a transmission going on....

There is one NE602 working as an audio preamplifier, you just use the input and output connecting the oscilator pin 6 to vcc. It's more expensive than using an 741 or TL series but thak's less components around (just 2 input caps if you connect from another NE602)

I managed to copy some text but the oscilator was still drifiting so had to move constantly the indicator, anyhow I got something..... now the problem is to get a stable vfo so I can let the receiver work stand alone. I am thinking in some form of pll but that adds some complexity. To be seen.

Sunday, March 14, 2010

Mini Whip

Not a great story here, just found some time ago this project on the "net" and decided to give it a go. Since I am also making some tests on a homebrew Navtex receiver this should be the ideal antenna to match it.

The crappy photos:

I used the schematic from:

The top enclousure is from small plastic bottle, the main mast is from electrical tubing conduit (VD32 local reference)
and the only changes were:
- The right most 560 cap was replaced by an 470, so as one of the dc coupling caps.
- J301 whas replaced by an BF245
- 2N5109 replaced by an 2N2219
- No 10uH coil (direct connection)
- Replaced the 470uH rf chokes by 120uH (rougthly measured)
- Didn't used the fuse or the reverse polarity protection diode.... I know what I am doing so don't try this at home!
- Dimensions on the caption area are: 30 by 45mm

I was a little skeptical on this "antenna" but from the first tests I made, it works (tested on 518, 590Khz, 10.100 Mhz and 14Mhz band), at least with some moderate strength signals. I have to make an antenna switch to make some more tests, but for now given the size of the element, it's not a bad solution for those who are tight on space.

Friday, March 05, 2010

Ferrite antenna preamp

Saw this schematic somewhere and decided to give it a try.

Honestly I only changed the output cap to a 2nF (didn't had 1.5) and don't think it will influence a lot. The variable cap and the smaller ferrite was salvaged from one of those "pound shop" like radios. Anyhow neither of the ferrites tested gave over the average results probably by being near the table with lots of cables around and not in the open.
Conclusion, it works but I will try to make another type of antenna for NAVTEX reception on 500Khz probably with some design similar to a very shorted 160m vertical antenna with a load coil. The idea is to replace a loop that I built some time ago that takes to much space and not practical to rotate.

Wednesday, March 03, 2010

HF radio - Balanced modulator + SSB IF filter

The schematic from the balanced modulator and crystal filter pre-amp are correct, just finished to place the boards in the radio and made a quick test, still need to check BFO frequency and align the impedance match on the filter.

Here's the video transmitting on 9Mhz USB (9Mhz + 1.5 Khz, more Khz minus Khz):


The boards in place:

And the current status of the front panel, the tree pot's on the lower line without buttons are from left to right: mic gain, tx gain and reception AGC (slow, fast, manual):


Due to lack of time I have to change some priorities for the next times.
This post is just a place holder for some ideas so I can recall later.
Feel free to follow some of the links bellow to see some nice designs, don't follow the ones starting with speaky...

Things to to:

- Put in place the hf radio cristal filter pre-amp and post filter mixer. I still don't know if I will use the same SBL-1 used for reception or if I will place another one dedicated for transmission.

- Make the vox circuit for the hf radio, althoug I never use vox in radios but it's nice to have some more buttons....

- Put labels in the box and make an first QSO.....if the thing works...

- Build the HF PA for the hf radio, just don't know if I will use the JBOT (just a bunch of transistors) at: (around 8 Eur in transistors for 5 w) or the nice one from sm0vpo at: (around 28 Eur in transistors for 10 w)

- Finish my other Si570 kit, put in a box with the VHF FM receiver. Change the squelch acording to this design:
(use the part on pins 9,10,11,12 of the MC3361), on my VHF FM receiver I made the conversion with an NE602 (from NE602 datasheet). My post with references is at:

- Finish an DRM receiver pcb that was sent to me when I bough the APT receiver kit.

- Place in a definitve box the 20A power supply.

- Finish another homebrew speaker built in a Cisco router dummy power supply box.

- Finish another magnetic loop antenna with coax cable that is already prepared. For use in a NAVTEX receiver.

- Put some missing components and a box on one of my first receivers, a regen one from ARRL design.

- Place in a box the ATV transmiter I have for a long time and never was tested. Put the camera connected... put an exterior antenna.

- Put in 2 plastic boxes that I allready have the tinytrack and the aprs decoder. Connect to vhf fm receiver and the computer.

- Make some more test on the VHF FM transmiter and try to get to a definitive version for shack use.

Now some interesting designs I still have to try:
- Based on the Russian mixer by RA3AAE :
- Stand alone NAVTEX receiver ...or maybe I use the 500Khz to 4Mhz converter and connect to a 4.5Mhz dc receiver... ideas..

...ufff, I have work and fun for the next century... of this days I will finish the Speaky SSB tranceiver that gave me the motivation for writing this blog

73 de Ricardo - CT2GQV