Has any build this Tx?

[shankar]

Hi,

I want check before I build myself, if any one has build this circuit

http://homepages.tesco.net/ada.tippett/Radio3.htm

What is that Black colored element L1 says 10nF? inductor/capcitor (confusion with unit specified nF)

Thank you
Shankar

[AndyOne]

Shankar,

It says 10uF, it is safe to assume the designer meant 10uH. L1 is an RF choke which stops the signal getting into the positive rail so it isn't critical almost any value around the figure quoted should work.

Andy.

[shankar]

Andy,

Thank you, I am going build this

[Daniel7866]

Hi,

I want check before I build myself, if any one has build this circuit

http://homepages.tesco.net/ada.tippett/Radio3.htm

What is that Black colored element L1 says 10nF? inductor/capcitor (confusion with unit specified nF)

Thank you
Shankar

Hi,

I have build two of them. Work great. The black element is a rfc coil. 2 1/2 turns 0,4mm copper wire on a ferrite bead FX1115.

Daniel

[shankar]

Daniel,

Thank you. I want to know, if I wish you to add crystal from local shop, what could be rating for that?, is it 17.5MHz?

Shankar

[Daniel7866]

Shankar,

I don't know where you are living and frequency will depend.

If you use the 35MHz band then use a Futaba crystal only since this circuit is designed for that. Crystal oscillates at half frequency so 17.5MHz range is good.

If you use the 40/41MHz band then also use a Futaba crystal. But since this crystal now runs on 1/3 frequency (13.5MHz range) you need to modify some values. What I did when I modified mine from 35MHz to 41MHz was:
C3=72pF (56//16 ;) ); C5=270pF; C6=150pF;C7=18pF.
This kept frequency deviation within 3kHz. 1.5kHz apart from center frequency.

Also my aerial is different than that showed on the drawing. It is a 124 cm center loaded telescopic aerial. Center coil is 30 turns 0.8mm on 11mm dia mandrel. 22 turns in 41MHz.


Powered by 9.6volts this Tx has a outstanding range :)

Daniel

[shankar]

Daniel,

I live in india, I use three different bands (35Mhz, 40Mhz, 27Mhz ) (surface) for rc cars.. Even I have 40Mhz Rc for mini helicopter ... Then It might not a problem in using these frequencies... You have give a lot of information ... According to you it looks me I have to use Futaba crystals.

Thank u
Shankar

[JLSalas]

What changes are needed to work at 72 Mhz?

Is this a full range tx?

JL

[minifly]

daniel,
just looking at your antenna and have a few questions:

how did you calculate how many turns/what inductance coil to use?

more importantly, what would it be for 35mhz? :p ;)

is it a base loaded antenna or a helical antenna?

[Daniel7866]

Minifly,

The original 35MHz Tx kits I purchased yeeeeeeeears ago included a center loaded aerial. The coil has 30 turns on it. Did you calculate something different? ;) .

Since I was too lazy to calculate the coil for 40/41MHz band... I just asked the factory Micron ;) .

JL,

I did no investigation for the 72MHz band. I guess you need to change more than some caps.

Range test Micron Tx/Rx on 41MHz: loss of solid communication at about 250 meters open field, Tx aerial collapsed. Not too bad :D .


Daniel

[minifly]

do you know what diameter core (is there a core?) the wire is wrapped around? also what guage (approx) wire it is?

thanks.

[Daniel7866]

Hi Julian,

I've stripped insulation from the coil so U can see. The fifth section of the aerial is cutted. The PVC(?) mandrel is glued on it leaving approx 1cm free space inside. Coil is 30 turns 0.8mm dia copper wire. Sorry about wire guage, I can't convert it :rolleyes: .

Hope it helps,

Daniel

[vintage1]

You can put this coil at the bottom of th antenna as well - on the circuit board..and use one with a variable ferrite slug tio tune it to maximum output.

See an eariler thread on transitter power problems for a handy little meter hat reads radiated power enough to tune up a tramsmitter.



Not sure if all crytsals are half frequency. In my day we used third overtone at 27Mhz..

Not sure if the 'frequency doubler' is, in fact, that at all, in that circuit..by and large the tuned circuit on the collector of the Xtal osciillator will supress the fundamental so the crystal itself will oscaillate at the correct 35Mhz frequency.


Ther is nothig magic about making a transmitter..but the problems occur in three or four specific areas.

(i) getting it spot on frequency. Crystals can and are pulled a long way from cut frequency and you need a frequency counter to set up teh colsd and capacitirs spot on.

(ii) Getting the sidebands out..those two coils and capacitors to the right of the power stage are critical in stoping the thing transmitting on sub and super harmonics of the main frequency. Without a spectrum analyser ($5k or more of kit) its a bit of guess work tuning them .Especially if you move te transmitter to a fairly different frequency like 72MHz

(iii) getting the best power out. That can be done using a current meter in the supply and a simple home made field strength meter.

[minifly]

vintage, and any others...
would it be possible to use a base loaded rx antenna on a tx? or is this completely unfeasable?

is there a large difference between the performance of helical and base loaded antennas?

thanks.
minifly, on a steep learning curve :rolleyes:

[j.s laura]

What is the dotted lines between the rf section output and the antenna in the circuit diagram.

How have you connected the antenna to the pcb rf out put. By a wire,cable, or directly to the PCB as in commercial sets kindly let me know.

In INDIA only 27MHz is legal, can you kindly suggest how this circuit could be used with Hitek or Futaba 27MHz crystals.

Regars

J.S Laura

[Daniel7866]

What is the dotted lines between the rf section output and the antenna in the circuit diagram.
Could be a coax cable as on my first Micron Tx.
How have you connected the antenna to the pcb rf out put. By a wire,cable, or directly to the PCB as in commercial sets kindly let me know.
My second Micron Tx has aerial directly screwed on the pcb.
In INDIA only 27MHz is legal, can you kindly suggest how this circuit could be used with Hitek or Futaba 27MHz crystals.
From a previous post it looks that you can use 35 and 40MHz too. For the 27MHz band I would first modify c3/c4/c5/c6 and check my work with a frequency counter (100Hz resolution or better) to keep hf deviation within local regulations. Also check sidebands with a spectrum analyser. Sorry not saying you the values for caps you need to change. It's up to you.
Regars

J.S Laura

Daniel

[vintage1]

vintage, and any others...
would it be possible to use a base loaded rx antenna on a tx? or is this completely unfeasable?



Not at all. I did in fact use just such. Its not QUITE as efficient as center loading, but all modern TXes from the big manufactirers use this.

Or an equivalent.


is there a large difference between the performance of helical and base loaded antennas?

thanks.
minifly, on a steep learning curve :rolleyes:

I think so, but am not sure. With antennae, there is no subsitute for size.

Old 27Mhz ground based kit used a full 8'6" quarter wave,and grounded the other half to a stake driven in the ground.

Commercial transmitter use grounding mats of steel reinforcing mesh buried in the earth.

They wouldnt do all that if a coil on a pole worked just as well :D