Radio Receiver problem

Thread Starter

Zeeus

Joined Apr 17, 2019
521
Trying to get 7Mhz people communicating but unfortunately getting radio stations :

Not the issue for now..The receiver : antenna to bandpass filter then through Rf amp

Between the filter (for 50 ohm output ) and Rf amp (50 0hm input) is the problem

There's a cable linking the filter to amp input (coupling) capacitor (100nF). My hand has to be touching this cable for there to be sound at the end

Problem is clear??

Please how to fix?

Thanks
 

KeithWalker

Joined Jul 10, 2017
797
The problem is not very clear. Did it work correctly before or has it never worked? What is the center frequency and bandwidth of the band pass filter? Which part of the coupling cable do you touch to get radio stations; the insulation, the shielding or the center conductor?
 
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Thread Starter

Zeeus

Joined Apr 17, 2019
521
The problem is not very clear. Did it work correctly before or has it never worked? What is the center frequency and bandwidth of the band pass filter? Which part of the coupling cable do you touch to get radio stations; the insulation, the shielding or the center conductor?
Centre frequency is meant to be 7Mhz but it peaks at about 7.8Mhz : didnt measure bandwidth

It works (can hear stations) only if my hand is touching the cable (insulation). I removed the cable and used a capacitor directly from filter to amplifier (my hand also has to be touching this capacitor to get audio)
 

vu2nan

Joined Sep 11, 2014
144
Hi Zeeus,

The problem is either with the antenna or the bandpass filter.

Have you connected the antenna direct to the RF amplifier or direct to the receiver and checked?

What's the antenna you're using?

Regards,

Nandu.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
521
Hi Zeeus,

The problem is either with the antenna or the bandpass filter.

Have you connected the antenna direct to the RF amplifier or direct to the receiver and checked?

What's the antenna you're using?

Regards,

Nandu.
Yeah , will redo the BPF....The antenna is (Wires wrapped around a rod then one end is connected to the BPF and the other end is connected to a long wire (the other end of this wire is loose)

Will connect the antenna directly to amplifier to see (Although, will want this BPF before)

Thanks

Yeah it works, from antenna to amplifier : so BPF is the problem : Thanks

but why getting radio stations? it's Direct conversion Receiver : BPF, mixer ( with 7Mhz Jfet oscillator) then audio amplifier

Thank you
 
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Thread Starter

Zeeus

Joined Apr 17, 2019
521
Hi Zeeus,

The problem is either with the antenna or the bandpass filter.

Have you connected the antenna direct to the RF amplifier or direct to the receiver and checked?

What's the antenna you're using?

Regards,

Nandu.
Want to reduce noise totally..what's a good way to troubleshoot, to find out where noise is coming from
 

MrChips

Joined Oct 2, 2009
20,874
Why is the wire wrapped around a rod?
Ferrite core antennas are used for picking up magnetic fields below 3MHz.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
521
I see...will use the wire (about 1m) directly without the rod to see

but why picking up radio stations and not 7Mhz communication

is there a way to measure noise from each transistor?

Yeah working without rod
 
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Thread Starter

Zeeus

Joined Apr 17, 2019
521
Hi Zeeus,

Can you receive the 7 MHz signal from your signal generator?

Regards,
Nandu.
Don't understand..You mean to test the filter with 7Mhz from generator? Tried this and it was peaking at 7.8Mhz (so used amp) after filter
Remaking filter

this is your question?
 

vu2nan

Joined Sep 11, 2014
144
Hi Zeeus,

Your receiver should be tuneable and working on around 7 - 7.1 MHz to hear radio amateurs on 40m. Your signal generator should be tuned to that frequency and your receiver adjusted to receive that. Could you do that and confirm?

Regards,

Nandu.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
521
Hi Zeeus,

Your receiver should be tuneable and working on around 7 - 7.1 MHz to hear radio amateurs on 40m. Your signal generator should be tuned to that frequency and your receiver adjusted to receive that. Could you do that and confirm?

Regards,

Nandu.
I see...Just tested only the filter with signal generator...Remaking the filter then will test

Thanks

Is there a way to measure noise from each transistor?
 

Thread Starter

Zeeus

Joined Apr 17, 2019
521
Any pics of your radio and setup please?
Will post schematic after boring school

Please how to "troubleshoot"? to find out noise from transistor? where to place low pass filter to reduce noise?

Like how to make it better like real radio with less less noise
 

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Dodgydave

Joined Jun 22, 2012
9,071
Looks like an homemade radio kit, can't give you advice until we see the circuit it uses, your problem is too many pcbs, this introduces too much extra capacitance..
 

Thread Starter

Zeeus

Joined Apr 17, 2019
521
Hi Zeeus,

Could you upload the schematic of what you've built?

Regards,

Nandu.
Could have uploaded yesterday... This is exactly what i have i believe..From the output of the audio pre-amp to LM386 (circuit from datasheet).
Vs is signal after bandpass filter but removed it in real life to make another

Not really "working" on spice... The oscillator buffer not working

This is the bandpass filter used.. want to make another with k and q values

Anyways, what can do better? what's wrong?

Thanks

Guessing, should leave 51 ohm resistor at the point before the mixer : although didn't observe much difference
 

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