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Problem in a powerful FM circuit design

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new life

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in fm transmitter circuit , i found aproblem in it
as one of it's componants is 2 coils each one 0.001µH
but there is no IF
i sold the 2 coils and connect the circuit but it didn't work
i can't solve this problem
if any body know about the matter plz tell me
thanks alot
 

Re: problem in fm ciruit

hi
could u semd the schematic?
 

Re: problem in fm ciruit

ok this is the circuit diagram
**broken link removed**
 

Re: problem in fm ciruit

**broken link removed**

hi

here is a link i found 'off the top'

if you use search strings maths {bool or more complex see there rules }
in any search engine

you can null or remove rubbish by ++ definaly add or -- definatly remove
always add this -- to remove any other thing to the end of any string

so


air++spaced+coils+RF++helix+coils+core+cored--

just paste to google or altavista there is lots more links to info to get very specific info

http://www.google.co.uk/search?hl=e...&ct=result&cd=1&q=helical+coils+100mH&spell=1

here for the right coils to use


these coils are in essance easy to make but realy a molded one is best

tip is to look for ex equipement and map the colours of known types to save cash

i do this

rake the heep
hehe
:D

ps dont use too high a Q types keeps bandwidth wide and benifits power use

on my own site and the
**broken link removed** other pages in the link sections

youll find links to the coils specs sheets and other details

i think 3T 7mm + 1.2 all round so 8.2mm coil .22 mm wire i think! if i was lost on an island
 

Re: problem in fm ciruit

Another variant of coils:
inductors are 0.1uH, 6 to 8 turns of 22-gauge hookup wire close wound around a 1/4-inch diameter non-conductive core such as a pencil.
 

Re: problem in fm ciruit

Here is a little simulation I did for a friend on the RF section of this transmitter after he complained of some TV interference after building this.

Basically I modified the circuit slightly by taking the feed for the final RF amp from inside the tuned circuit, as this helps filtering out harmonics. The coupling cap was reduced 10 times to minimize loading the tank circuit. The osc feedback cap was increased slightly for reliable oscillations. The result is still the same output level around 10mW but the 2nd harmonic is reduced another 10dB. Also there's about a 6dB improvement in phase noise.

The simulated results proofed to be close when measured on the actual circuit after modification.

The last variation has another extra emitter choke added, resulting in about 50% more power at the wanted frequency and even more harmonic attenuation.

Also lowering the value of the 47k to around 33k it is possible to get up to 20mW while still keeping harmonics low. That is a 100% increase in RF power with much lower noise and harmonics as the original circuit.

Just thought it may be helpful to others.
 

problem in fm ciruit

i'm realy sorry
i want an easier solution to my problem
as i can't over it till now
 

Re: problem in fm ciruit

Also it will draw around 53mA at 10mW and about 55mA at 20mW (black trace) so one of these small 9V batteries won't last very long. If you plan to use it on a power supply make sure it is well regulated.

And for those interested, the final modification we played with adding some DC feedback to reduce flicker noise in the oscillation device gives 13dBm (20mW) and another 6dB lower phase noise. Overall improvement 100% RF power, -10dB TV band harmonic and 12dB reduction in phase noise. It should be possible to improve the phase noise some more by lowering the 100k feedback resistor but then 2nd harmonic starts to rise. With 82k feedback simulation results give 2nd harmonic at 2dB higher and lower PN@10k (-112dBc), PN@100k (-132dBc). So you win some and loose some.

It is amazing how well the measured results compared. I have uploaded images to show original to final improvement. Average carrier noise (related phase-noise)was measured on a mod-meter for easy comparison. Close-in noise can also be observed on the analyzer display.

If you need more power, use my last circuit but with 2N4401's instead of 2N3904's. It can handle a bit more power. Current will go up to around 84mA (22mA in osc and 62mA in amp) and RF power just over 100mW. Just remember that this power can get you into trouble in most countries and the 2nd harmonic, although still 30dB below the carrier is now at about -10dBm enough to cause TV interference. You will need some extra LPF to get the harmonics down more. Picture shows results of the 2N4401 version we tested before and after adding the filter. 29pF indicates variable cap set value.
 

Re: problem in fm ciruit

here is the full details on the transmiter without confusing you

1st please if you have a simple digital camera
take a medium resolution photo of your built unit

lets see its guts


save it as .jpg and send it to a post here

so.. here is the project
with coils details

**broken link removed**

remember to wind the coils in the right ... ! direction

it should wind anti clockwise from + rail to the transistors

i like this circuit but its just too big

ill find you a better one in my archive of bugs

hehe
**broken link removed**
here is a good one high gain and nice audio extended range and battery

to extend the range of a bug use a passive repeater
find a good spot and use two small vhf 2 el yagi with a preamp circuit inbetween
gives an extra gain

i build them into light bulbs and use the neurtal

then monitor from blocks away

good circuits repository

**broken link removed**

dont just ask

experiment

you need a few tools like a radio and a meter setup to measure its current use when running
 

Re: problem in fm ciruit

For all those that were asking for more power, well here is a design. This uses the output of the last circuit I posted at about 100mW. The power transistor can be a 2N3866 or 2N4427 and both work well. The transistor runs quite cool and needs only a small push-on heat sink. The values in brackets are my settings to obtain maximum output. This is quite close to my initial design values. On both 0.7W and 1W out the 2nd harmonic is 20dB below the carrier. This may need more filtering not to cause interference. Mount the 3.3k resistor directly over the 1uH choke.

Use responsibly not to get into trouble with the authorities!

I have added another cap to reduce the harmonics more.

Also tested with a BFS22A transistor. Work ok, but output slightly lower (~830mW) as this transistor needs a bit more drive being a 4W device. Overall the 2N4427 is the best choice, giving me 1.3W @ 12V and 0.8W @ 9V with about the same harmonic performance.

I think it is good to stop here at this point. I am not planning to a design for a higher output, so please don't ask, PM or email.
 

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