Plz help me convert FM receiver to 2m for a Foxhunt

[ramesh2000]

2m receiver

Hello everyone

I am Ramesh and am planning to take part in a Radio Detection Event (A foxhunt).
For the event I have to build my own receiver(readymade not allowed but can use ICs)
Morse code will be transmitted b/w 144-146 Mhz FM.

Plz help me out:

1) I have never really built anything so complex so I was thinking of modifying an existing FM(88-108 Mhz , schematics are relatively easy to find on the net) circuit to work at 144-146 Mhz.

I figure that I'd need to change a couple of capacitors and I'd be done.Plz tell me if this is true..and if yes , how should I go about it? Can any1 plz suggest a schematic and what modifications shld be done to it?

2)I have searched a lot for 144 Mhz FM receiver but haven't found any good schematics...Plz could some1 tell me ?

3)Has any1 taken part in these competition?Can you tell me your experience?And any other info a first-timer like me would need to know??

Thanks!!!
Ramesh

 

[dpechman]

convert fm to m

i dont have any expertise in rf, but i growup reading electronic magazines and i have tryied some radio toys many years ago. i remember to cut 2 or 3 turns from the main coil in superregenerative radios to reach 144Mhz. the capacitors you can try some value lower of original.
check this one **broken link removed**
this seems very sensitive, but will give you the idea.
in more elaborated schematics i have no experience.
regards

 

[cyberrat]

fox hunting receiver 2 m

You will also need a directional aerial and signal meter otherwise your not going to find them.

Foxhunts are fun, take some sandwiches as it can take a while to find them

 

[ramesh2000]

simple receiver 144 mhz

Thanks a lot for yor reply!

I read the link , but wasn't able to understand everything very well.Bt will certainly read up on that

Can any1 tell me how the simplest FM radio using a popular IC (like TDA7000 , etc) works?As in which capacitor/inductor controls what?

Here is a link which attempts do do something similar...Can any1 plz tell me how the original FM radio was made?
www.qslnet.de/member/la3za/dokumenter/CheapVHF_SPRATWinter04.pdf

Thanks

Added after 10 minutes:

@cyberrat

Ya , I know that Directional antenna etc. are imp , but being a first timer I am worried just about building the basic receiver I'd be more than happy if my receiver actually detects something.

Plz plz help me out.

PS:If I do make it , i'll certainly take sandwiches along!

 

[dian]

2meter resiever circuit

try this link
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=5168, for pc controller 2m receiver, its easy to modification

or
www.open-circuit.co.uk/rox1.php

or this one
http://www.geocities.com/hagtronics/2_meter.html

regards
Dian Kurniawan

 

[ramesh2000]

tda7000 144mhz

Thanks for those links!
But unfortunately I am unable to find many of the components in India.Worse , the shop owners have no clue about the replacements(They are merely traders , have very little understanding of electronics).

That is why I'd like if someone could explain me how a basic FM IC driven circuit works.

Like TDA7000 , etc. , so I could simply modify the existing capacitors and be able to boost the range to 144-148 Mhz.

Also could some1 list the most popular/easy to use FM ICs?

Plz help me out .

Thanks

 

[dian]

simple 2m receiver

TDA7000 designed for FM broadcast 88-108MHz like the data book said. How ever there's some people said TDA7000 family (TDA7088) have ability to operate until 150MHz. You may try to changes the oscillator frequency, (pin 5 & 6 in TDA7000) by changes the smallest value of L and C.

Other method is try to make a down converter for this chips.
*. create fixed freq oscillator (using crystall) (ie. 45MHz)
*. mixed it with input freq (ie. 144MHz to 148MHz)
*. give the mixed signal to TDA7000 (ie 144-45 = 99 to 148-45 = 103)

try this link for your TDA7000 modification
**broken link removed**

 

[Audioguru]

2m receivers.

The TDA7000 was a horrible obsolete old "FM radio".

 

[pranam77]

2 meter receiver

Converting a FM radiop is very difficult. Dedicated kits built with FM reciever IC's but those are fixed frequencies with crystals as refernce. You may go for any regenerative recievers whic are available on the net. But those too will not have a PLL option. You may have to tune manually. Any ways... Best of luck

 

[ramesh2000]

fox hunt circuit

@Dian

Thanks ! I don't understand everything you said bt I am reading abt it.

@Audioguru

Plz suggest some newer and better FM chips

@Pranam
Plz tell me more.I dont care if I have to manually tune it.

In fact I'd be glad even if my receiver picks up something(forge the morse code signal) , cuz that'd give me a big hint as to where the transmitter is.

Is there any simple antenna/ckt that can pick uup "some" signal at 144-146 Mhz(with/withouut decoding the FM)?

 

[Audioguru]

superregenerative receiver 144mhz

With radios so cheap lately, nobody makes a good radio IC anymore. Even the Sony radio IC is not made and the newer Philips IC is also not made anymore.

 

[Borber]

how to tune a reciever fm 88-108mhz

Here are two projects:

**broken link removed**

https://www.darc.de/ardf/technik/junior2/junior2.html

 

[pranam77]

144-146mhz circuits

Hai Ramesh, Thanks for pressing the "Helped me" button. Its my pleasure to have helped some one. I have attached here two articles related to regen receivers. The article from QST describes the regen principle and the other is a VHF regen receiver which cover 140 to 150 MHZ. Good luck.

 

[Audioguru]

modifying fm radio for 2m

I guessed correctly that somebody would post a one-transistor regen "radio" in this thread.

 

[pranam77]

simple receiver fm

Audioguru..you guessed right. Ramesh wanted exactly that which is very easy to build with too littele components. Ramesh...Thanks for pressing the "Helped me" button. Its my pleasure to have helped some one. Good luck in the Fox hunting contest.

 

[ramesh2000]

pll 2m 144mhz

Hey every1 , thanks a lot for your help.I am evaluating varios designs and will see whcih1 to build.

Also can you guys help me out with the antenna?
I am planning to use the simplest 3 element Yagi Antenna (1 reflector , 1 driven and 1 director).
The construction seems very easy.

But can some 1 plz explain me the bare basics?As in what orientation wrt hidden transmitter do I get to hear the loudest signal(on my earphones )?

Thanks

 

[Audioguru]

fm receiver modifcation

The sound level from a sensitive FM tuner does not change with RF signal strength from the transmitter.
The sound volume from an AM tuner changes with RF signal syrength if its AGC is disconnected.

Is the fox transmitting AM or FM?

Most foxes transmit FM so the receiver uses an RF signal strength indicator circuit to determine the direction that is sensed by a moveable directional antenna.

 

[pranam77]

norwegian regen receiver

Hai Ramesh. The answer to this question is a bit difficult. Ok....here it is. Basically to get best reception fron any antenna it should be tuned to minimum SWR and maximum gain using any Antenna analyser or transciever with a SWR meter. For hunting the fox you need a signal strength meter which will display the received signal strength of the transmitter and you need to move towards the direction,in which you get more and more strength. It is possible only if you use a commercial receiver in which you will have a calibrated S-Meter in analogue or LCD bar graph form. You cannot guess the signal strength by heraring the signals. Rest of my answer is given by Audioguru. Good luck