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Trouble with Audioguru's FM Transmitter circuit

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Nigel Goodwin said:
Even a slight amount of soldering skill prevents any heat damage, there's no need for temperature controlled irons to do so.
Hi Nigel,
I mentioned my Weller temp-controlled iron because there are some people still using a plumber's 100W soldering gun that gets so hot that its tip gets badly corroded and the solder's flux instantly disappears.
They might need about a full 10 seconds to make a bad solder joint while my temp-controlled iron makes an excellent joint in about 1/2 second with much less heating.

I also recommend using 63/37 rosin flux core solder. It "sets" abruptly like a Schmitt trigger. Ordinary 60/40 solder slowly solidifies causing bad joints if anything moves. :lol:
 
As it happens, I didn't take my own advice, with regards to the crocodile clips on diodes. I fixed 1N4148 diodes striagt to the board, with no extra lead or anything. Worked ok though. I did leave a gap for the transistors though, seeing as its only ealing with audio frequency this time, it should cause no problems.

I use an Antex 15W iron from Maplin. Used to use a big 30W thing from a DIY shop, for £3.50, :lol: , the difference is astounding. Anyone using any cheap iron for PCB, its well woth your while getting a decent one. I can make most joints almost instantly with it. Only sometimes will I have to give it another attempt, usually if the solder doesn't flow to both sides of the lead.
 
audioguru said:
I mentioned my Weller temp-controlled iron because there are some people still using a plumber's 100W soldering gun that gets so hot that its tip gets badly corroded and the solder's flux instantly disappears.
They might need about a full 10 seconds to make a bad solder joint while my temp-controlled iron makes an excellent joint in about 1/2 second with much less heating.

Actually I've got a 100W Weller soldering iron at work!, it also has the usual Weller curie point temperature control system.
 
Sorry for not replying for so long. Had exams.....

panic mode said:
if the wire is really from coax cable it is definitelly not enameled and it looks like bare copper wire - not enameled.

I am quite sure that it is enamelled wire. No electrical continuity between any 2 points on its surface.

audioguru said:
Hi T_an,
Where did you find that 250V candy-striped old cap? Its inductance is probably more than your inductor!

U noticed that only now? It was already seen in that other photo that I had posted. So it has high inductance, eh? Those are 330 and 470 nF caps. Probably I'll get some other type.

audioguru said:
The 1mm wire for my coils is so stiff that you can stand on them and they don't change.

Where did u get coils like that? My coax wire is pretty stiff, but not as stiff as what u r saying.
 
t_anjan said:
So it has high inductance, eh? Those are 330 and 470 nF caps. Probably I'll get some other type.
They are for coupling audio, so their inductance doesn't matter. They just use as much space as about 10 of my modern ones!

Where did u get coils like that? My coax wire is pretty stiff, but not as stiff as what u r saying.
I got the 1mm thick wire from a speaker's crossover coil. I tightly wound my coils around a 3mm screwdriver shaft. With the enamel removed from the ends, they fit perfectly in the holes of my Veroboard copy. :lol:
 
Hi and g'day mate!
Hey, it's spring time outside today. The snow that we had yesterday is gone. I'll steal my daughter's old bike, go for a spin and check the range.
My FM dial is full so I must keep away from the biggies and the many low-power (only a few thousand times stronger than my transmitter) foreign language stations, but I don't know where they are.
Google has 137,000 links for FM stations in my city, languages and religions that I never heard about before, 3 universities and many more. I'll just jam the weakest one for a few minutes.
 
Yeah, besides the 100 real stations, there are 136, 899 copies of my FM transmitter here!
 
Hey Pike,
My Mod4 FM transmitter goes about 1km very clearly, line-of-sight before being drown-out by a "real" FM station on the same frequency. It's too bad that my area doesn't have a vacant FM station frequency available, it might go 5km.
I didn't notice any RF frequency change when I took it from my 22 degrees C home to 13 degrees C outside.
I tested its range with the tones from my son's alarm clock. When I placed it about 1m from my souped-up clock-radio playing an FM station's music, its reception sounded exactly like the real station on my stereo and my car radio, except in mono. Very low distortion and wideband audio. :lol:
 
What would be the total output power of that transmitter??

My one in the other thread only goes about 40 metres before it starts becoming directional. (Australian standards allow only 10uw :x, screw that and this complying kit.)
 
Hi Pike,
I don't have an RF power meter. My transmitter's brand new 9V alkaline battery was used for a long time yesterday so today it measures 8.25V. The circuit's mic, preamp and regulator don't draw much so most of its power is in its output and some in its oscillator. Today it measures 39mA, so its input power is 322mW. If it is 70% efficient, its output power is 225mW. It is probably a lot more with 9V. Its power drops a lot when I shorten its 30" antenna.

Australia's limit is 10mW according to Silicon Chip mag. I don't know Canada's limit but somewhere I read 100mW. I'll ask the RF cops when they come to arrest me! :lol: :lol:
 
Hi T_an,
Where did you find that 250V candy-striped old cap? Its inductance is probably more than your inductor!

Hi Panic Mode,
My FM transmitter works fine with a 9-turn closely wound coil made from 1mm enamelled wire on a 3mm former, and also this project from where I got the idea:
Hi, I am trying to build this circuit (project 54) using veroboard.
Can you give advice on the component layout and spacing :
 
Hi T_an,
Where did you find that 250V candy-striped old cap? Its inductance is probably more than your inductor!

Hi Panic Mode,
My FM transmitter works fine with a 9-turn closely wound coil made from 1mm enamelled wire on a 3mm former, and also this project from where I got the idea:**broken link removed**
Hi, I am trying to build this circuit (project 54) using veroboard.
Can you give advice on the component layout and spacing :
**broken link removed**
 
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Your parts are way too far apart. The traces connecting the parts have too much inductance when they are so long.

The traces must be cut to length so that extra length is not a capacitor to a trace beside it.

Mine has many more parts and is still much smaller than yours.
 

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Thanks a lot for your comments!
Besides this problem, I concern about other things as well:
- How about relative position of the components ?
- Let's say we have to use wire to connect 2 points. The wire should be in the metal side,right ? (Veroboard has metal side and non-metal side). Then does the length of this wire affect the performance of the circuit)
 
Thanks a lot for your comments!
Besides this problem, I concern about other things as well:
- How about relative position of the components ?
- Let's say we have to use wire to connect 2 points. The wire should be in the metal side,right ? (Veroboard has metal side and non-metal side). Then does the length of this wire affect the performance of the circuit)

At VHF layout is critical - everything will affect performance.

Normally wires are placed on the plain side of veroboard.

As Audioguru has posted (many times) a fully working example, why not simply copy that?.
 
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Most resistors and capacitors jump from one copper trace to another, but jumper wires are used on the plain side of Veroboard (not on the copper side). Look at the jumper wires in my pic.
 
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