Hi Power FM mic V5

Hi Shail
I have found that a lot of transistors like a little more capacitance between the emitter and collector than the one shown in Harry's drawing. I use around 10pf and have used as much as 22pf but don't go higher than that.  Check the bios voltage on T1 and if it's ok the try a different cap on the RF oscillator.
 If you were not very careful getting the coil like Harry's you could also be out of the FM band as well.  I would use about a 22 PF tuning capacitor to help give it a winder range if you haven't tried that all ready.

Hi Harry,

I have made the Hi power FM mic V5 however there is no reception in the FM receiver.
How do I check my circuit ? I have checked all the parts are correct however I need to know from you the testing points on the PCB. I have a digital Multimeter for testing. Please help me. This is the 2nd time I am making this project. The first time I made it 6 years back, it worked very fine but now its not working.

There are loads of LC meter circuits published, it is just a question of selecting the most convenient.

For my part it is not often that I need to measure an inductor or capacitor as the ciruit I am building is usually geed enough as a test jig. Tuned circuit and GDO can be quite usefull.

But it is all a case of personal preference.

/Harry

Such sort of LC meter may be a good companion to a beginning RF ham:
LC meter. The starting bid is cca 30 EUR here, but similar device can be self-build for even less. The schematic and program must be somewhere on the web.

BR from Ivan

Hi Harry,
an inductance meter never can supersede a multimeter. My opinion is:
1 - a multimeter - undoubtedly !
2 - a RF bridge - valuable for measuring L, C, resonance frequency, antennas, RF cables, matching circuitry etc. A GDO can serve similarly, but requires more skills of his users.
3 - a fast digital scope with FFT or at least with a built-in counter.

VBR from Ivan

That is an interesting comment Ivan.

Everyone has their favourite piece of test equipment and mine is the GDO. I have always been good at estimating coils and then using the GDO to test tuned circuits, and maybe making adjustments. But the GDO is also useful for antennas, coaxial cables and even measuring capacitance.

The GDO frequency range is quite wide but as far as inductance and capacitance gos it does not have nearly enough range.

So if you were to choose the three most useful pieces of test kit, then you No 1 would be the Inductance meter? What would the other three be?

I must admit that I have become "spoiled" by having a spectrum analyser with tracking generator. That with a directional couple and a bridge can measure just about anything from 10kHz to 2GHz. But beside that my three would have to be:

1 - Multimeter
2 - Grid Dip Oscillator
3 - Frequency counter

But I often use the project I am assembling as a test-bed for certain components during construction.

Very best regards from Harry - SM0VPO

Hi,
IMHO an inductance meter is one of the most useful devices for a RF ham. It can be an LCR meter, a RF bridge, a GDO with several known capacitors etc. I always had problems when winding or re-using coils before I bought a bridge.

BR from Ivan

If you look ion my homepages there are several pages dedicated to PCB coiols. One of them is a multi-layer coil that I used for the HF band. PCB artwork and coil "winding" data is also there.

BR Harry

Coils are always a problem - especially for beginners like me

I have purchased the necessary materials and am going to try and etch some PCB's - and to play around with etched coils

Thanks again

It is funny but the biggest problems I ever have with my homepages is that of coil winding. If one experiments it really matters not what gauge of wire you use, and turn spacing has but a small influence on the inductance.

Coils themselves have a "root law" (look at the formula) so if a coil is doubled in inductance then the frequency will only fall by 30%.

But in this particular case the coil has nothing to do with frequency :-)

Questionas and answers are free, but mistakes comne with a price. Feel free to ask if you are in doubt.

Very best regards from Harry - SM0VPO

Thanks Harry

I understand what you meant now

The inductance was about 0.04uH which is nothing more than an extra 1/2-loop, or about 25mm wire formed into an omega sign. It is not exactly all that critical as it does not affect the operation at all, other than improving stability when you touch the antenna.

Best regards from Harry - SM0VPO

Admin wrote:
Remember also to use a 1/2-turn coil to feed TR3.
This is NOT shown on the circuit diagram but is needed for matching the
capacitive input of TR3 and preventing TR3 from causing the frequency
to become unstable.

Harry,

Just one last clarification please with regards to your statement above.

Do you mean literally a half turn coil? I'm not sure I know how to do a half turn, haha
Would this be like a 180 degree half circle? Pardon my ignorance, I
might have misunderstood. What inductance value do I need to aim for
with this coil?

You are most welcome. The object of my homepages is to help and learn. I think that I have learned the most over the past 14 years.



Have fun - Harry - SM0VPO

Hi Harry

Thanks for helping me out

Admin wrote:
The inductor is 0.182uH (calculated) and there is a page on my homepages for coil winding in the electronic calculators page. In general (about) 6mm Dia. coil with about 6 turns of wire will do the job. Use some form of stif wire, like 0.5mm Dia.

Thank you, this will help me greatly.

Admin wrote:
Remember also to use a 1/2-turn coil to feed TR3. This is NOT shown on the circuit diagram but is needed for matching the capacitive input of TR3 and preventing TR3 from causing the frequency to become unstable.

Do you mean literally a half turn coil? I'm not sure I know how to do a half turn, haha Would this be like a 180 degree half circle? Pardon my ignorance, I might have misunderstood. What inductance value do I need to aim for with this coil?

Admin wrote:
As for construction method, look at ny 500mW HF PA. That construction method is always good and sound for 1-off's, and expecially for VHF RF work. You can also see the same technique used on the HF oscillator project.

Finally, I am pleased you like the homepahes. You may like to know that it is running on a Raspberry-Pi computer

I love the dead-bug construction style, I've build every single FM band circuit I can find on the internet. I still need to get to the point of etching my own PCB's but this way is cheap, easy and works well for me. I will look at your 500mW HF PA for some tips on the style.

Really - it runs on a Raspberry Pi? That is fantastic! I received mine about two months ago and still need to find the time to play around with it.

Hi Willem,

Praise indeed, thank you very much :-)



The inductor is 0.182uH (calculated) and there is a page on my homepages for coil winding in the electronic calculators page. In general (about) 6mm Dia. coil with about 6 turns of wire will do the job. Use some form of stif wire, like 0.5mm Dia.

Remember also to use a 1/2-turn coil to feed TR3. This is NOT shown on the circuit diagram but is needed for matching the capacitive input of TR3 and preventing TR3 from causing the frequency to become unstable.

Incidentally, TR3 does NOT really provide any gain, but buffers the tuned circuit from the antenna. The coil on the PCB is also done for stability.

As for construction method, look at ny 500mW HF PA. That construction method is always good and sound for 1-off's, and expecially for VHF RF work. You can also see the same technique used on the HF oscillator project.

Finally, I am pleased you like the homepahes. You may like to know that it is running on a Raspberry-Pi computer, see www.raspberrypi.org

Very best regards from Harry - SM0VPO

I bought the kit for the "Hi Power FM mic V5" from Harry - its excellent. Really stable and performs better than some of the so-called "high-power" FM transmitter kits I've bought.

I have a question, suspect I've asked this on the old forum but I take it the old posts are lost.

I want to rebuild the V5 circuit dead-bug style - to practice my soldering and construction techniques. What would I use in terms of air-core inductor to replace the current inductor that is etched into the PCB?

I'd appreciate any help - I want to understand how to calculate something like this. I see calculators on the web to calculate air-core inductors but I don't know what the inductance is on this circuit with regards to the etched coil on the PCB

Thanks to Harry for such an excellent circuit.

PS: Harry, please consider selling a kit for your V6 and V7 transmitters. It seems that electronics is a dying art and it is so wonderful to have a site like yours with great designs