receiver 15 MHz

[sofiehem44]

Need help from experts!
Criteria are as follows:
A. sensitivity 0.1 uV.
B. ASK is received, (amplitude shift keying).
C. frequency: 15 MHz. (not to be used in USA).
D. type RS232 in TTL level.
When ASK is now used, carrier = 1, no carrier = 0.
I'm using Multisim 13 and have run into a wall.
So far not easy to solve.

 

[Nigel Goodwin]

Firstly, forget the 1/8th wave antenna - it cannot work, it will be resonant at 80MHz.

I don't really think it's going to matter

As seems common with these sorts of threads the OP won't even tell us what he's trying to do, has never looked at how radio receivers are designed, and even denies it's a radio. He's even miraculously now jumped from 15MHz to 40MHz.

Chances of him ever building anything are slim to less

 

[sofiehem44]

Firstly, forget the 1/8th wave antenna - it cannot work, it will be resonant at 80MHz.

To reduce antenna size, you add a loading coil either at the base or part way up the antenna, to make the overall item resonant at the appropriate frequency.

You can buy commercial ones:

Mobile spring loaded reduced 1/4 λ antenna whip (40 MHz) - Renaironline

G40DKF 1/4 (M5) Mobile spring loaded reduced 1/4 λ antenna whip especially made for use in connection with "G"-type mounts (bases) on vehicle roof etc. QUANTITY DISCOUNT PRICES

renaironline.co.uk

Mobile spring loaded reduced 1/4 λ antenna whip

Mobile spring loaded reduced antenna whip made for use in connection with "G"-type mounts (bases) on vehicle roof.

www.scan-antenna.com

Or make them yourself - here is a calculator to work out dimensions:

Coil-Shortened Vertical Antenna Calculator

Build an effective, shortened vertical antenna by adding a loading coil. This online calculator tells you the amount of inductance your loading coil we need to have.

www.66pacific.com

Secondly, look at proper radio receiver designs - the collector loads should be parallel resonant tuned circuits, not just chokes.

Also you need a bandpass filter (tuned circuit) between the antenna and the first transistor, otherwise that can be overloaded by any signal at any frequency.

I've not clue what that jumble of bits in the middle of the diagram is supposed to be!

Add resistors or chokes in the positive power connection between low level and high level stages, with each stage having it's own decoupling caps.

You have something like that on the collectors - but the bases are still fed directly from the non-decoupled positive power, so can pick up stray signals.

This gives a reasonable example of the first stage, the "front end" of the receiver; it's actually a converter so ignore the IC and later parts - but the first stage & RF bandpass filtering, plus the power decoupling, are good examples of what you should be aiming for.

http://www.hvde.nl/electronica/rx/6mt_converter/6mt_converter.png

Many thanks for all the suggestions, I'm starting from scratch again.....

 

[sofiehem44]

I don't really think it's going to matter

As seems common with these sorts of threads the OP won't even tell us what he's trying to do, has never looked at how radio receivers are designed, and even denies it's a radio. He's even miraculously now jumped from 15MHz to 40MHz.

Chances of him ever building anything are slim to less

The problem arose when I realized that the antenna became a bit large. Then the mystery of what the receiver is to be used for: ASK receiver! In this context, very little data to be transferred between vehicles and a fixed station. (16 bits) Wrong code, send again.

 

[Nigel Goodwin]

Again, the issue arises of illegal broadcasting, a serious offence in any civilised country. The chosen frequencies seem 'unusual' as well - but as you never give any actual details, we can't make suggestions.

 

[rjenkinsgb]

From the users name, they appear to be in Sweden?? (Sofiehem is a Swedish municipality).

If that is the case, there does appear to be a legal frequency near 40 MHz, for telemetry??

From this document, translated by Google:

ShieldSquare Captcha

www.pts.se

(Part 3 section 71) 40.66–40.80 MHz: Radio transmitters for radio control and telemetry. Maximum power: 100 mW erp. Channel frequency: 10 kHz.

40.0 MHz is not allowed, and there are other allocations for different services closer to that.


The 10KHz channel restriction does mean well-designed and properly tested equipment for both transmit and receive though - which does seem unlikely from the events to date.