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Farhan VU2ESE'sTwo Tone Generator

 

Hi everyone,

I started building the two tone rf generator from Farhan's ?site to add to my test equipment. I have finished the first section (ie oscillator #1) and tested it to see how it functions. On his website Farhan mentions in the calibration procedure that one oscillator should give about 200mV p-p. I can only get about 40mV, anyone has any suggestions or thoughts as to why I am measuring such a low peak to peak voltage?

I have double checked the component values and am confident of their ratings so I am very confused at the moment...

Any thoughts and suggestions are highly appreciated.

73 Elia, M0ZHN
Jack, W8TEE
 

I love seeing builds like this! Dave Richards, AA7EE, carries it to an art form (notice Han's BPF in the photo):

Inline image


A visit to his site is just plain enjoyable to me.

Jack, W8TEE


On Wednesday, June 30, 2021, 10:14:41 AM EDT, M0ZHN via groups.io <eliamady@...> wrote:


Hi everyone,

I started building the two tone rf generator from Farhan's ?site to add to my test equipment. I have finished the first section (ie oscillator #1) and tested it to see how it functions. On his website Farhan mentions in the calibration procedure that one oscillator should give about 200mV p-p. I can only get about 40mV, anyone has any suggestions or thoughts as to why I am measuring such a low peak to peak voltage?

I have double checked the component values and am confident of their ratings so I am very confused at the moment...

Any thoughts and suggestions are highly appreciated.

73 Elia, M0ZHN


--
Jack, W8TEE
 

Elia,
40 mv is really low. Can you measure the rf voltage at oscillator emitter and collector of the amp?

On Wed 30 Jun, 2021, 7:51 PM Jack, W8TEE via , <jjpurdum=[email protected]> wrote:
I love seeing builds like this! Dave Richards, AA7EE, carries it to an art form (notice Han's BPF in the photo):




A visit to his site is just plain enjoyable to me.

Jack, W8TEE


On Wednesday, June 30, 2021, 10:14:41 AM EDT, M0ZHN via <eliamady=[email protected]> wrote:


Hi everyone,

I started building the two tone rf generator from Farhan's ?site to add to my test equipment. I have finished the first section (ie oscillator #1) and tested it to see how it functions. On his website Farhan mentions in the calibration procedure that one oscillator should give about 200mV p-p. I can only get about 40mV, anyone has any suggestions or thoughts as to why I am measuring such a low peak to peak voltage?

I have double checked the component values and am confident of their ratings so I am very confused at the moment...

Any thoughts and suggestions are highly appreciated.

73 Elia, M0ZHN


--
Jack, W8TEE

1625062749374blob.jpg
IMG_20210630_150833376.jpg

 

Hi Ashhar,

At the oscillator emitter the voltage is 72mV peak-to-peak.
At the amp collector it is about 9mV

Both with a 49.9 ohm load. Something is quite wrong now, the max output is only 5mV at the attenuator output.

Faulty transistors?

Elia, M0ZHN
Terry VK5TM
 

Bit hard to tell from the photo, but is the transformer wired correctly?
--

 

Are you sure your oscillascope is not on 10x vs 1x? It seems to be exactly 10 times down. Check some dc voltages with the scope and the bandwidth settings too.


On Thu 1 Jul, 2021, 7:28 AM Terry VK5TM, <vk5tm@...> wrote:
Bit hard to tell from the photo, but is the transformer wired correctly?
--

John Cunliffe W7ZQ
 

Looking at the schematic of the output combiner, are you really using 150 ohm resistors for a 50 ohm system? Every similar output combiner I have ever build for a 50 ohm system has 50 ohm resistors.
https://www.vu2ese.com/index.php/2020/06/19/two-tone-generator/

John
Mark - N7EKU
 

Hi,

I would think it depends on its purpose -- is it made for feeding a mixer or feeding a mic amp?

M
John Cunliffe W7ZQ
 

I would think it depends on its purpose -- is it made for feeding a mixer or feeding a mic amp?

The one I was referring too was the one on his site that was available from the above link and was for a RF system. I did not dig farther to see if he had an audio version.
 

We are discussing the rf two tone generator. The emitter should show at least 500mv of RF.?
I still suspect measurements. It is like this, the oscillations need the amplifying device to saturate for the oscillations to sustain. They wont do that at such low outputs.
Can you check the voltages at the three leads of both the transistors?

On Fri 2 Jul, 2021, 2:28 AM John Cunliffe W7ZQ, <n2nep@...> wrote:
I would think it depends on its purpose -- is it made for feeding a mixer or feeding a mic amp?

The one I was referring too was the one on his site that was available from the above link and was for a RF system. I did not dig farther to see if he had an audio version.

 

Right, I did some DC measurements as follows:

Oscillator Transistor
E-7.02V
B-5.81V
C-11.91V

Amplifier Transistor
E-2.94V
B-3.61V
C-11.84V

Next I checked the scope probe and scope settings, Ashhar was spot on correct, the probe was set to x10 but the scope was expecting a x0.1 so when I changed the probe scale setting on the scope to x10 I got the correct 200mV output of the circuit :)

I knew the probe was set to x10 but I did not know that the scope also had an input scale setting..... Well never too old to learn

Thank you everyone for your help with this, as with most issues it is usually the simplest things that are mostly ignored?

73 Elia, M0ZHN
 

Excellent!


On Fri 2 Jul, 2021, 4:42 PM M0ZHN via , <eliamady=[email protected]> wrote:
Right, I did some DC measurements as follows:

Oscillator Transistor
E-7.02V
B-5.81V
C-11.91V

Amplifier Transistor
E-2.94V
B-3.61V
C-11.84V

Next I checked the scope probe and scope settings, Ashhar was spot on correct, the probe was set to x10 but the scope was expecting a x0.1 so when I changed the probe scale setting on the scope to x10 I got the correct 200mV output of the circuit :)

I knew the probe was set to x10 but I did not know that the scope also had an input scale setting..... Well never too old to learn

Thank you everyone for your help with this, as with most issues it is usually the simplest things that are mostly ignored?

73 Elia, M0ZHN

 

So I finished building the two tone generator and did a test of a small rf amplifier using an MMIC. The datasheet says OIP3 is 29dbm, using the two tone generator and my tinySA (using the web interface for more accurate measurements) I got -26dbm! Quite pleased with this :D
 

I have built an improved two tone generator that provides additional isolation. I use? two stages of common gate amplifiers on each channel. I needed this for sbitx where I could inject -10 dBm per tone.
The IMD measurements are very easy to do and one wonders why more people don't do them.

On Wed 7 Jul, 2021, 5:58 AM M0ZHN via , <eliamady=[email protected]> wrote:
So I finished building the two tone generator and did a test of a small rf amplifier using an MMIC. The datasheet says OIP3 is 29dbm, using the two tone generator and my tinySA (using the web interface for more accurate measurements) I got -26dbm! Quite pleased with this :D

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