[minima] Re: SOLVED! Re: Re: Anything special about T3's capacitor to ground?
- From: Ik3nlk <mail@xxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Thu, 27 Feb 2014 10:01:36 +0100
I am happy for you! I was following your Odissea since the beginning and it's a
relief to read good news from you!
Keep going whit this fine project!
73 Giorgio
Inviato da iPhone
Il giorno 27/feb/2014, alle ore 09:48, Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
ha scritto:
> Hello everyone!
>
> It was a little past midnight and there was plenty solder smoke in the shack
> when I finally heard my minima for the first time ...
>
> Special credit to Mark who sent the decisive last message which led to
> victory. Thanks to everyone who shared comment and tips. The international
> brotherhood of electronic wizards has once again lived to its reputation!
>
> After Mark last messages, I decided to build a new mixer on a separate board,
> starting from scratch. I used new diodes that I re-matched. Picked a new
> transformer and checked it's core AL value (thanks Mvs Sarma for suggesting
> this; it was ok). Used a drill to prepare the trifilar wires, carefully
> placed the three windings, etc - gave it lots of love.
> Then I used a little piece of coax to drive the bfo signal from my main board
> and used my DDS to provide an IF at 20 Mhz. With that complete new setup on a
> new board, I still had the same problem: with the capacitor to ground there
> was no signal out of the mixer.
>
> At this point the only thing that could be bad was the BFO so I rebuilt
> another BFO from scratch on my new board.
> With the new BFO, I finally got a working setup. The audio signal was there.
>
> I then looked very carefully at the BFO on my main board and found my problem
> in 30 seconds. The 100pF capacitor that is supposed to be between the base
> and the emitter was between the base and the collector. I moved it and it
> fixed my problem. (And then considered whipping myself with a coaxial cable
> ...)
>
> I have fixed a lot of software bugs but I think with this bug I have earned
> my first home-brewing scar ;)
>
> I would have found the problem earlier if I had suspected the BFO was the
> problem. I assumed it was ok because I was getting a decent signal out but I
> was wrong.
>
> Anyway, I am now listening to 20m and 40m. It's pretty much dead now but just
> plugging the antenna in the minima, I can hear a large difference in noise
> level. I have birdies, am stations and it finally sounds like a receiver. I
> am confident there will be qsos going on when I wake up tomorrow.
>
> I hope everyone will sleep better knowing that the excellent schematic of Mr
> Farhan was not the problem - I take full responsibility!
>
> Thanks again everyone. Each evening spent on this radio is a ton of new stuff
> learnt - next steps, the transmit stages.
>
> 73!
> thomas
>
>
> On Wed, Feb 26, 2014 at 7:23 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
>> Hi Gang
>>
>> I'm back home and have just wound a 8 turn trifilar transformer on an
>> FT37-43 and coupled it up to the output of a 20MHz crystal oscillator I had
>> lying about.
>>
>> Here's the setup:
>>
>> <DSCN0332-Optimized.JPG>
>>
>> This is the signal into the BFO port (yuck - but 20MHz):
>>
>> <BFO Signal.png>
>>
>> My analogue signal generator
>> (http://g0mgx.blogspot.co.uk/2013/10/so-hows-sig-gen.html) is connected to
>> the RF port:
>>
>> <RF Port.png>
>>
>> Then I see kind of crap out of the audio port but if I alter the fine tune
>> on the sig gen I can see what looks like an audio signal:
>>
>> <Audio Port.png>
>>
>> There is a load of RF in this signal also, this is 0 to 150MHz:
>>
>> <efgjhbaa.png>
>>
>> and if I zoom in on the 20MHz, we can see the mix of the two RF signals,
>> this is 50KHz either side of the 1st peak above at 20MHz - the signal
>> closest to the centre and the largest amplitude is the BFO:
>>
>> <Audio Port SA2.png>
>>
>> 6.56 of EMRFD is probably the best reference to understand whats in these
>> signals.
>>
>> Mark
>> G0MGX
>>
>>
>>
>> On 26/02/2014 12:19, Mvs Sarma wrote:
>>> Thomas,
>>> please see whether the core qualifies for the AL value specified for
>>> FT37-43. Wind 10Turns and measure inductance. it would be AL /10. as per
>>> www.kitsandparts.com datasheet is 350 with 20% Tol
>>>
>>>
>>>
>>> On Wed, Feb 26, 2014 at 1:29 PM, Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
>>> wrote:
>>>> Mark,
>>>>
>>>> If you have a chance, I would be very interested in reading what is the
>>>> signal strength you measure here at the output of that transformer. I
>>>> might be looking at a problem that does not exist - maybe my sensitivity
>>>> problem is somewhere else.
>>>>
>>>> Mvs Sarma: Thanks for the tips. I have tried smaller capacitance without
>>>> any success and I have looked hard for solder bridge. I might try building
>>>> a new mixer out of circuit to make sure I start from scratch.
>>>>
>>>> 73,
>>>> thomas
>>>>
>>>>
>>>> On Mon, Feb 24, 2014 at 9:25 AM, Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
>>>> wrote:
>>>>> Mark,
>>>>>
>>>>> I am getting confused too ;)
>>>>>
>>>>> The radio is in RX. I believe my audio amp works ( I can receive AM
>>>>> broadcast by putting my finger on the input wire ). I can also receive my
>>>>> 3kHz tone even with my capacitor in the circuit. My problem is I don't
>>>>> receive any other signals. It's like the receiver is completely deaf
>>>>> except to very strong signals applied to the input.
>>>>>
>>>>> When you say it's normal for the input of the audio amp to be weak, how
>>>>> weak are we talking? Micro-volts? Milli-volts? Should I be able to see
>>>>> something on the oscilloscope? Maybe the very high impedance output is
>>>>> normal.
>>>>>
>>>>> If it is, then my sensitivity problem might be somewhere else. How could
>>>>> I test that?
>>>>>
>>>>> Can you confirm that plugging an antenna on the receiver makes a
>>>>> difference in the level of noise you can listen to? Plugging an antenna
>>>>> on mine makes absolutely no difference to the noise strength.
>>>>>
>>>>> thanks again for your replies!
>>>>> thomas
>>>>>
>>>>>
>>>>> On Mon, Feb 24, 2014 at 1:41 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
>>>>>> Hi Thomas
>>>>>>
>>>>>> I think I am getting confused (nothing
>>>>>> new there). If the radio is in TX then the point where your scope is
>>>>>> connected is where we would inject audio to mix with and modulate the
>>>>>> BFO signal. If we are in RX (that's my assumption) then we would only
>>>>>> expect to see the injected signal being modulated i.e. an audio signal
>>>>>> and very weak one too - most of the gain in the Minima is at audio. Is
>>>>>> the audio amp working (does it buzz when you stick your finger on the
>>>>>> input)? I am not sure what you should expect to see at that point? The
>>>>>> audio tone there will also alter and be totally dependent on the tuning
>>>>>> of the LO and hence the output of the mix.
>>>>>>
>>>>>> If your scribbles are correct then the transformer looks correct to me.
>>>>>> Without checking the signals on mine I can't help much more until I get
>>>>>> home (Thursday)....
>>>>>>
>>>>>> Mark (just boarding in Abu Dhabi & bound for London)
>>>>>>
>>>>>>
>>>>>> On 24 February 2014 08:48, Mvs Sarma <mvssarma@xxxxxxxxx> wrote:
>>>>>>> thomas,
>>>>>>> even a cheaperTA7358 and perhaps LKA1168 or so ( a compatible) would
>>>>>>> also work, I suppose
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Feb 24, 2014 at 1:29 PM, Thomas Sarlandie
>>>>>>> <thomas@xxxxxxxxxxxxx> wrote:
>>>>>>>> Raj: Yes I have all the dots on the same side. I have checked several
>>>>>>>> times now. Unless I am really reading something backwards I think I
>>>>>>>> have that covered.
>>>>>>>>
>>>>>>>> Farhan: I don't but I will look into that. Would a ne602 work too?
>>>>>>>>
>>>>>>>> It's really raging to see my 4KhZ signal get out of the mixer but not
>>>>>>>> be able to tame it into the audio pre-amp because the output impedance
>>>>>>>> is so high. What could explain this? I will take any theory ;)
>>>>>>>>
>>>>>>>> 73,
>>>>>>>> thomas
>>>>>>>>
>>>>>>>>
>>>>>>>> On Sun, Feb 23, 2014 at 11:07 PM, <farhanbox@xxxxxxxxx> wrote:
>>>>>>>>> Thomas, if you have an ade-1, just drop it into the circuit.
>>>>>>>>> - f
>>>>>>>>> Sent from BlackBerry® on Airtel
>>>>>>>>>
>>>>>>>>> -----Original Message-----
>>>>>>>>> From: Raj <vu2zap@xxxxxxxxx>
>>>>>>>>> Sender: minima-bounce@xxxxxxxxxxxxx
>>>>>>>>> Date: Mon, 24 Feb 2014 12:29:53
>>>>>>>>> To: <minima@xxxxxxxxxxxxx>
>>>>>>>>> Reply-To: minima@xxxxxxxxxxxxx
>>>>>>>>> Subject: [minima] Re:
>>>>>>>>> Anything special about T3's capacitor to
>>>>>>>>> ground?
>>>>>>>>>
>>>>>>>>> Thomas, please check all three DOTS are from the same end of the
>>>>>>>>> transformer.
>>>>>>>>> Most important that same winding start and end is correct.
>>>>>>>>>
>>>>>>>>> At 24-02-2014, you wrote:
>>>>>>>>> >Thanks Mark. That's
>>>>>>>>> > how I have been doing it. I was not sure because T1 & T2 do
>>>>>>>>> >not have those dots. Is it because phasing is not important on them?
>>>>>>>>> >
>>>>>>>>> >I have just rewound a new T3 using a new roll of #32 AWG wire on a
>>>>>>>>> >new FT37-43. I get the exact same problem. So here is a
>>>>>>>>> > picture of what I am
>>>>>>>>> >doing with some labels as to where the
>>>>>>>>> > wires go. I hope I am doing something
>>>>>>>>> >very
>>>>>>>>> >stupid and someone will be able to point it out:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Regards
>>>>>>> Sarma
>>>
>>>
>>>
>>> --
>>> Regards
>>> Sarma
>
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