IET
Decrease font size
Increase font size
Topic Title: Difference between low level and high level modulation?
Topic Summary:
Created On: 07 April 2012 10:04 PM
Status: Read Only
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 07 April 2012 10:04 PM
User is offline View Users Profile Print this message



ubercool

Posts: 19
Joined: 11 September 2011

Can anybody please tell me the difference between low level and high level modulation? Also could you provide me with specific examples and advantages and disadvantages of each?
 16 April 2012 10:12 PM
User is offline View Users Profile Print this message



eswnl

Posts: 144
Joined: 29 November 2008

It describes where the modulation takes place in the RF chain between signal and transmitter from what I have read.

See: http://www.edaboard.com/thread248568.html

If you look it up and then perhaps give us all a detailed explanation so we all understand.
 20 August 2012 08:45 AM
User is offline View Users Profile Print this message



electricaltestinguk1

Posts: 11
Joined: 12 July 2012

HIGH LEVEL MODULATION:
parameter:
1. power level: modulation takes place at high modulation level.
2. types of amplifier: highly efficient class c amplifiers are used.
3. efficiency: very high.
4.devices used: vacuum tubes or transistor for medium power applications.
5. design of AF power amplifier: complex due to very high power involved.
6.applications: high power broadcast transmitters.

LOW LEVEL MODULATION:
parameter:
1. power level: modulation takes place at low power level.
2. types of amplifier: linear amplifiers are used after modulation
3. efficiency: lower than high level modulators.
4. devices used: transistors, JFET,OP-AMPs.
5. design of AF amplifier: easy as it is to be done at low power.
6.applications: sometimes used in tv transmitters(IF modulation).

I'm sorry for my answer I just search it for you.
 20 August 2012 10:28 AM
User is offline View Users Profile Print this message



cblackha

Posts: 79
Joined: 21 January 2003

Did you mean high and low LEVEL or high and low ORDER?

Either way - I would suggest 2 seconds on Google and then post a more specific question, which should then get you a more specific answer.
 01 September 2012 06:48 AM
User is offline View Users Profile Print this message


Avatar for kylemmisael.
kylemmisael

Posts: 2
Joined: 30 August 2012

Low level modulation: Class B (75%max) power amplifiers are used which offers better quality modulation i.e low distortion probability. Minimize generation of harmonics.
The advantage of using a linear RF LP amplifier is that the smaller early stages can be modulated, which only requires a small audio amplifier to drive the modulator.


High level modulation: Class C (90%max) power amplifiers are utilized which improves greatly the efficiency of the transmitter but low in quality i.e higher distortion level is expected.
A large audio amplifer will be needed for the modulation stage, at least equal to the power of the transmitter output itself. Traditionally the modulation is applied using an audio transformer, and this can be bulky. Direct coupling from the audio amplifier is also possible (known as a cascode arrangement), though this usually requires quite a high DC supply voltage (say 30V or more), which is not suitable for mobile units.

-------------------------
Acne cream
 05 November 2012 10:53 AM
User is offline View Users Profile Print this message



cloudserver

Posts: 3
Joined: 05 November 2012

Low level modulation can possible to control by software(including DSB with carrier, SSB suppressed-carrier and independent sideband, or ISB). And high level are based on high-efficiency class-D and class-E power amplifier stages, modulated by varying the supply voltage.
 08 March 2013 12:34 PM
User is offline View Users Profile Print this message



richardjohn

Posts: 5
Joined: 08 March 2013

you must check teletopix.org his blog can help you.

Modulation
 15 May 2013 06:43 PM
User is offline View Users Profile Print this message



kengreen

Posts: 400
Joined: 15 April 2013

Yes ... and NO.

I think I am correct in saying that high level mod is the most popular because it results in the highest efficiency with low distortion.
The easiest design is to anode mod the PA (final) stage. The drawback is the extremely high h.t. required. You will find it used in Amateur rigs ( 'ware fingers) and all most high-power broadcast transmitters - I have no knowledge of the design of television broadcast transmitters apart from the fact that you could set up home in the P.A. cum rf-generator. Again anode mod seems the most logical.

Low-level modulation is carried out before the drive to the P.A. - of necessity in an FM chain - but kit means that the PA must cause as little distortion as possible - a Linear Amp. Class A, Class AB and Class B are up for choice but Class C is a definite no-no.

Techniques such as ssb etc use low-level mod because, when the modulation-ignal is zero then so is the carrier.

Kn reen




at the P
.A

cal.
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.