More filters

Some time ago I bought 3 isolated filters, one LSB, one USB and the other for AM, the idea is to use them as secondary filter for the "Trevo"....or maybe for some other project.

This time I bought another set, including the board where they all seen to come from. It looks some sort or IF part of a radio, it has the MC1350, MC1496 for SSB/mixing/amplifying. Just can't find any reference about the board.

Anyhow, the idea is to remove the filters the IC's and parts for other projects.

It's cheaper to buy the 3 filters than a single one from a major brand, if they are good or not, that's another story.

Have a nice week!

ps: Updated here with more info

Another kit

I always liked planes, when I was a kid my father was a plane maintenance mechanic, althoug I only went with him very few times to the hangars it was allways something that fascinated me.

Maybe one day I will try to fly one, I think planes and trains are the only transportation mean that I'm not certified to "drive"...

Passing trough the local supermarket there was some promotions on plane kit's, so why not!?
So far I've built two, one for each year that I've been in Ireland.

2013:

and 2014:

...this Year still didn't spotted the promotion...

PS: If you think it's easy to make, think again, you really need some patience to do it , tough that's no rocket science.

 Have a nice day!

Trevo bandpass filter - I

Slowly I'm getting the "Trevo" transceiver built.

I'm trying to get now the bandpass filter to some usefull state.

Here's the progress with the inclusion of relays for switching.

...decision that I already regretted after soldering all those small relays, each one is an inverter, so it takes two for each band, and I'm also grouping two separate sets (one for the low bands, the other high bands)...and still missing almost all the coax from the filters to the relays!


General schematic is this one:

...adapted from the "Speaky" transceiver without the diode switching part.

The filter includes a tuning voltage that is applied to C21, kind of pre-select with varicaps, input is applied on L2(3,4), output goes on L3(3,4) or vice-versa if you care....


The varicaps are going to be changed to diferent type from the ones in the "Speaky" because they are made of un-obtanium so I expect to do some changes in the filter componentes values.
The baseline is the following:

I never testes this configuration for the 160m band so I might have to change design for that band. Will probably include also one option for VLF bandpass or a filter bypass.


Still a lot to be done.

Have a nice week!

FT-707 repair (10) Finding replacement coils

As stated on a previous post of the FT-707 repair series I had to remove two coils from the 10m A and B local premix oscillator, to use on the 40 and 30m band because there was a previous owner that really made a mess out of it.
Now I'm the the process of finding replacement ones, the coils are a non existing item and there is not much information on their specs so I got some coils from the junk bin and started to find which ones would work by winding them on a trial and error process.
For that I replicated the oscillator part from the technical manual on a small PCB:

..the assembly:

 ..this way it's easier to test multiple coils.

The output of the circuit looks similar to this when the coil is ressonant or near ressonance:

 After some testing I already have one coil finished and in place, it's not perfect but for now fits the bill:

I used some IC terminals to test in the board also and if needed replacing latter on:

 ..it was easier this way to avoid do much soldering on the board.

 The coil is marked "3392" and comes from an unknown board that my guess was used on a wallkie-talkie (has cristal holders and a side switch), whatever that coil match's in terms of specs or inductance to is unknown to me, I have to build and inductance meter yet.
I run 2 turns for the secondary and 6 for the primary for 10m B band, the removal or increase in the coil number is done by testing with a crystal upper in frequency and also lower of the main one for test and see if the output increases or decreases, eg: if more amplitude on a 50Mhz than on a 35Mhz for a 42Mhz center frequency I assume the higher the amplitude the closer to the resonance frequency so has low inductance and more turns needed (keeping the same parallel cap, 39pf).

If you look closer still missing the first coil for the 10mA, top of the right column of coils, I already have one tested, just not in place, marked "3410 E 0" that works with a 14Mhz crystal (42Mhz overtone), just waiting to find a suitable crystal for 42.5Mhz, the one I previously placed there doesn't want to oscillate on overtone, was placed before proper testing and was removed.

Now it's like this:

 ... except that the band is already on the correct band position...as soon as I have the 10m A in place I might leave 10m C and D with the CB frequencies :)


Have a nice week,

Arduino digital out, 4 to 16 decoder/demultiplexer

.. .Using an 74HCT4514 ...

Controlling the VFO for the "Trevo" transceiver from the Arduino poses a small problem, the Arduino doesn't have enough output lines to control all the bandpass filters so I had to come up with a solution. There are some I2C IC's that would expand the digital output pins and do the job but I think that's like killing flies with a cannon so I went to a more "old school" approach.

The 4514 series IC used here, in high speed version (HCT not realy needed), is a 4 to 16 decoder with input latches, the latches are not needed on this case since there will be no signal change from the command lines.

Basically you input a 4 bit (parallel) binary and you have 16 digital outputs according to the truth table here:

This is the assembly (LED's were place on the first 3 outputs to check that is working correctly)

And the control schematic from the Arduino:

Sample code to output high (1) on Q1 of the 74HCT4514, pin 9:

// start sample
// setting the pins on the Arduino
pinMode(13, OUTPUT); pinMode(12, OUTPUT); pinMode(11, OUTPUT); pinMode(10, OUTPUT);
// send the data "1000"
digitalWrite(13, 1); digitalWrite(12, 0); digitalWrite(11, 0); digitalWrite(10, 0);
 // end sample


...now I still have to code the rest so that a band change activates the correct output...

Have a nice weekend!

Mixers tested

Here's some of the passive mixers I normaly use.

From top to bottom, ADE-1, TUF-1, SBL-1 all 7 dbm level.

I've been experiencing with the ADE-1 using the IF out as input for the VLF range and it works nicely, contrary to one could think. I'll post in the future the experiments.
I'm also favoring more this mixer since it's the cheapest of the 3.

The SBL-1 I use in HF range but also made a VHF transceiver using it for the reception part.

The TUF-1 only used it on the "Speaky" kit, might replace the ADE-1 in the "Trevo" transceiver design with it.

Have a nice week.

FT-707 repair (9) No external VFO

Looking back, this is the 9th issue found between the two sets, hopefully will be the last!

The problem with the "blue" FT-707 was that the external VFO was not working with the set, it was working with the other set so the VFO is ok.

I started looking at the diagram, for sure the issue is in the connection to the external VFO, the VFO ligt's and controls the radio if you press the RX but no frequency, only the 91Mhz symptoms of no VFO:

Started by testing the switch inside the plug with a make shift adapter (the shield of a plug):

One of the poles in the plug swithc put's inline a 50 ohm resistor so it's easy to test from the RF board, pin 3 of J05 "memo out".

All the connections were tested and all with continuity....what is going one here? Something is not right!

Let's bring the heavy troubleshooting stuff.... the oscilloscope, before that,  just powered on the radio once more and the external VFO was working!... Hum!?, probably the contact creaner I aplied on the swithc changed things... good, let's close the lid before it breaks again.... then is when it stops again, ahhh, a broken cable for sure, some touches on the cables and voila the culpit (external vfo in):

The press of the lid against the cable would disconnect and that's why when I did the testing it was all ok. live and learn!

For now this will end the FT-707 repair series, they only need a god tuning and some cleanup, if something major "arrives" will post here.

Have a nice week!