HF receiver front end IC

[Ow@i$]

I am designing a HF receiver for WWV signal (10 MHz)... can its front end.. i.e Selectivity and amplification be done through an IC ??? if yes kindly give me he name of that IC ??

 

[BradtheRad]

Do you get a strong signal? It may be possible for you to get by with a simple AM detector circuit.

Start with an antenna feeding an LC tank adjusted for 10 MHz. (A reasonable proportion is a couple uH for the coil, a couple nF for the capacitor.)

Tuning it will be the challenge. You have to wait a whole second after each adjustment, hoping to hear the WWV beep!

If you have a 10 MHz crystal, it might be easier.

Feed the carrier to a diode detector and/or amplify it through a transistor or op amp, and it will power a speaker.

There are IC's for making an AM radio. I believe you'll still need the external antenna and LC tank.

 

[etmabreu]

Most (if not all) FM radio receivers work with an IF of 10.7 MHz. You may try to adapt one IC meant for FM and adapt it (at least the IF and demodulator section) to 10MHz.

 

[Ow@i$]

Thanx guys.. I just found a link which i guess will done the job for me instead of an IC, the link is :
**broken link removed**

One question now I have is, the final output of that circuit will be audio ... however WWV (10 MHz) signal also has BCD coded time information... how to extract that one???.. which i guess is Pulse width modulated.. also where in this circuit that digital part is removed??

 

[BradtheRad]

Thanx guys.. I just found a link which i guess will done the job for me instead of an IC, the link is :
**broken link removed**

One question now I have is, the final output of that circuit will be audio ... however WWV (10 MHz) signal also has BCD coded time information... how to extract that one???.. which i guess is Pulse width modulated.. also where in this circuit that digital part is removed??

Yes, interesting to see the variety of detector circuits.

Your receiver front end must avoid removing the 100 Hz subcarrier which carries the time code.

It appears you need a microcontroller to extract the code and interpret it.



http://arduino.cc/forum/index.php?topic=52887.0

 

[Ow@i$]

Thanx guys... one thing more the qrp receiver circuit that i have attached uses 40673 or ECG222 which are locally unavailable at my place... so i bought BF961... Will it be a good replacement??

 

[Ow@i$]

@ BradtheRad thanx, correct me if i am wrong but the 1Mohm and 0.001uF cap in the receiver front end (**broken link removed**) that forms high pass filter with Fc=159 hz.. isactually filtering out the Digital subcarrier??? Plz need help i am stuck there!!!

 

[BradtheRad]

@ BradtheRad thanx, correct me if i am wrong but the 1Mohm and 0.001uF cap in the receiver front end (**broken link removed**) that forms high pass filter with Fc=159 hz.. isactually filtering out the Digital subcarrier??? Plz need help i am stuck there!!!

The .001 uF capacitor blocks the gate from seeing a low-impedance path to ground through the coil. It passes the AC rf signal.

On the other hand the 1M resistor is there to provide a definite DC ground for the gate. Otherwise a disconnected mosfet gate can respond to ambient static and EM fields (including mains hum).

It is unlikely that they divert the 100 Hz of the digital carrier. But I could be wrong.

 

[Ow@i$]

hmm... you may be right... but isn't their configuration is totally satisfying the configuration of a High pass filter.???...i mean how come they would know that they don't have to filter but instead provide Blocking and definite DC ground...
i am hell lot of a confused :-(

 

[BradtheRad]

isn't their configuration is totally satisfying the configuration of a High pass filter.???...i mean how come they would know that they don't have to filter but instead provide Blocking and definite DC ground...

Yes, often we wonder 'why components don't do what they are supposed to do?'

Notice that a 1M resistor will pass little current.

In contrast, the coil L1 is low impedance as far as 100 Hz is concerned. Yes I don't believe the designers meant for low frequencies to be lost through it.

This suggests L1 is carrying a strong enough signal that the nearby 1M resistor will not reduce it much.

 

[Ow@i$]

Alright.. Thanx actually the point of filtering out the 100 Hz sub-carrier (digital information) came in my mind after your post # 5, where u wrote " Your receiver front end must avoid removing the 100 Hz sub-carrier which carries the time code."
the circuit is the receiver front end the final output of receiver is audio.. so if not that RC(1 M resister and 0.001 Cap) than were the designer is actually filtering this sub-carrier????