Reduced Carrier AM

[Guy G4DWV/4X1LT]

As the 'guilty party' who started off the thread in the Flexradio forum, I'd like to thank everybody here for their contributions.

Mni tnx de Guy G4DWV/4X1LT

[WA2SQQ]

I learned a lot from this Guy!
Thanks

[N2DTS]

Going from 200 to 100 watts carrier (even in a normal signal) would likely not show up much at the far end.
When testing, try reducing the overall power from 200/800 to 100/400 and see what the difference is, then do 100/800 and see.

I was always amazed how things seem to jump up from about the 25 watt level, power below that does not work very well, and someplace between 25 and 100 watts is a big improvement, then from 100 watts to 500 watts seems to do little.

In the new flex software, how is the carrier setting done, 0-100, 0-50 or what?

[WA2SQQ]

Going from 200 to 100 watts carrier (even in a normal signal) would likely not show up much at the far end.
When testing, try reducing the overall power from 200/800 to 100/400 and see what the difference is, then do 100/800 and see.
I was always amazed how things seem to jump up from about the 25 watt level, power below that does not work very well, and someplace between 25 and 100 watts is a big improvement, then from 100 watts to 500 watts seems to do little.
In the new flex software, how is the carrier setting done, 0-100, 0-50 or what?

So last night's testing was the 100/800. I'm thinking to try 50/800 tonight.
Without looking, I'm not sure what the numerical scale is. At the max position (of the AM Carrier adjustment) is where you get 25 / 100 or the 1:4 ratio. I start there and adjust the transmit output to get my 200W. From there I just back the AM Carrier slider down, to get 100W (unmodulated) out of the amp. That provides a 100/800 end result.

BTW, I see you gave up on the Anan - that was fast!

[flintstone mop]

I still hang on the thought that the carrier is reduced within the apparatus of a commercially built transmitter.
Here is an example of what transmitters WBCQ is using with this REDUCED CARRIER capabilities

http://www.transmitter.be/tmc-gpt40k.html

What you guys are doing is not connecting to a TRUE reduced carrier operation, for whatever reason you are trying to implement this in your SDR transceiver. Reducing the drive of the SDR in AM only reduces the power out of the linear and ends up as a full carrier with a lot more AM modulation on the distant receiver.
Sorry for some attitude in this reply. A little bump in the road in the hospital today. It's minor; I'll be ok
Now looking at a reduced carrier on an SDR panascope will really show you the really wimpy reduced carrier and how easily it unlocks when you try to run SAM.
What I remember seeing on WBCQ on their other services is the reduced carrier usually running in USB mode. A plain regular AM shortwave radio will receive this signal and detect it as AM because there is some sort of a carrier there.
This method is a power saving shortcut for a shortwave broadcaster and is allowed by the FCC.
WBCQ, 7415 is using a FULL carrier mode of a similar GPT 40K TX. I do not know what happened to the Harris 50KW MW50.

Thanks

Fred

[KD6VXI]

You'll find even more efficiency if you roll the bias up (increase it to more negative)  and increase the drive to compensate.

For instance,  a 500z at 3.2 kv needs about 5 to ten volts of bias.   In am,  I run 20 or more volts of bias.

My tubes run culo,  and nobody complains.

I do NOT run this way on ssb.   Needs to be switchable.

--Shane
KD6VXI

[N2DTS]

I think the net result is what counts, not how you do it.
In the TMC transmitter, they likely do it all at low level with a balanced modulator they can unbalance and get any amount of carrier out of it.
I do not see how that is different from an SDR where the same thing is done in the digital relm.
There are three separate controls, overall power output, audio level, and carrier level.
The power control changes carrier and audio, the carrier only does carrier, and the audio only does audio.

In a screen modulator, you can have a carrier control and an audio control, as you can in plate modulation.

What might be different is what happens in the negative direction, plate and screen modulation close the carrier off in basic form (no negative limiting).
In SDR, before it gets to 100% negative it starts going the other way, it inverts it and starts going positive again, but they can limit or compress the audio in only the negative direction.

I have a problem picturing what the TMC rig does in reduced carrier when you have plenty of audio to give 40KW peak on a 5000 watt carrier.
It brings the carrier up to 20KW only during the peaks?
What is the time aspect of the AGC sort of gain control look like, and how does it impact the sound?
 

[flintstone mop]

The "digital Realm" is only in the software......once it exists the computer into the SDR transceiver its back to analog transmitted the old fashioned way. We are not transmitting digital data over the air with SDR. The latest greatest Anan's and and their kind grab the analog RF into their magic FPGA (on the receive side) processors and do the digital thing in your "digital realm' and spits it out of the computer as an analog audio signal. All magic processing, for the ultimate dream receiver is obtained through the magic of computers. Specs for receivers that the best analog receiver ever conceived tube or solid state could NEVER compete with.

Fred

[DMOD]

I have a problem picturing what the TMC rig does in reduced carrier when you have plenty of audio to give 40KW peak on a 5000 watt carrier.
It brings the carrier up to 20KW only during the peaks?
What is the time aspect of the AGC sort of gain control look like, and how does it impact the sound?

As flintstone said, it is done fairly easily using software. Here is a summary:

Audio input to most station transmitters today is usually in the form of a digital audio stream,

If the audio coming in is balanced analog, it is first converted to digital using A-to-D converters and stored,

The digital data is then sent to a processing unit which does a number of things:

1. messaging of audio if necessary, such as predistortion for type of modulation (PDM, digital PA's, etx.),

2. look ahead processing to determine what carrier level and modulation is needed when the modulation envelope is created

3. digital data is released to control carrier and modulation, all happening at a high-Megahertz rate.

Phil - AC0OB

[flintstone mop]

The TMC units are very far from any type of computer control. These are 51 yr old retired military units!!!!!!!!!!!
Possible date of manufacture around 1964!!!!!!
I never mentioned use of software used in the TMC transmitters


Fred

[KD6VXI]

The method I described is exactly how Brown Boveri Co.  implements reduced carrier AM.

Now,  it's mostly done in software.   What I described wasn't, the tx's I studied where pwm,  analog input.   Circa mid to late 80s.

Nail on the head time,  they mostly all accomplish the same thing:  Saves broadcash and shortwave tens to hundreds of thousands of dollars in utility bills.....   And allows hams to use amps like the sb220.

--Shane
KD6VXI

[Steve - K4HX]

It's called Modulation Dependent Carrier Level (MDCL). There are two basic approached, Amplitude Modulation Companding (AMC) and Dynamic Carrier Systems (DCS).

In AMC the carrier and sideband power are reduced with modulation. With no or low levels of modulation the transmitter output is not reduced at all. Above a certain level, the power is reduced in a linear fashion relative or the level of modulation. At 100 %, maximum reduction occurs (usually 3 or 6 dB).

With DCS, only the carrier power is reduced and it is reduced the max amount generally when there is no modulation. As modulation increases, carrier power increases.

[DMOD]

The TMC units are very far from any type of computer control. These are 51 yr old retired military units!!!!!!!!!!!
Possible date of manufacture around 1964!!!!!!
I never mentioned use of software used in the TMC transmitters

Fred

Fred, I was referring to your reply #32  in an attempt to answer Brett's question.

Phil - AC0OB

[WA2SQQ]

So last night I did some testing with N1BCG.

I started out with 200W of carrier coming out of the amp. At peaks I was getting about 800W.
Using the AM Carrier control on the 6500 I reduced the carrier to 50W, while still achieving the 800W peaks.
Amp runs much cooler with no apparent degradation. Need to repeat this test with someone who has a mod scope.
Seems like an easy way to reduce power consumption and heat dissipation.

[flintstone mop]

The TMC units are very far from any type of computer control. These are 51 yr old retired military units!!!!!!!!!!!
Possible date of manufacture around 1964!!!!!!
I never mentioned use of software used in the TMC transmitters

Fred

Fred, I was referring to your reply #32  in an attempt to answer Brett's question.

Phil - AC0OB

Thank you Phil for your kind re-direction.
Sometimes I get a little rattled sitting in this hospital dealing with another cancer. Clarity of mind and reading responses gets scrambled and I get stupid

Fred

[Guy G4DWV/4X1LT]

Fred. Good luck in your battle. I hope you are out and about soon and fighting fit.
I recently had a longish stay in hospital and did not take any toys in (phone, books or tablet) to bust the bordom as I did not know if there were any lockable facilities available (there were not). You are lucky that you did not spend all your waking hours staring at the walls .
With vy vy best 73 de Guy G4DWV/4X1LT

[DMOD]

Thank you Phil for your kind re-direction.
Sometimes I get a little rattled sitting in this hospital dealing with another cancer. Clarity of mind and reading responses gets scrambled and I get stupid

Fred

No problem Fred.

Keep up the good fight and here's hoping for your quick return to Modulatin' in the AM mode.

Phil - AC0OB

[N2DTS]

What was he using for a receiver, and how was it set up?
An SDR in sync mode and I would expect that.
An R390a maybe not.

I would think 100 watts carrier and 800 watts pep would be ok in most receivers and save an amplifier some work.

So last night I did some testing with N1BCG.

I started out with 200W of carrier coming out of the amp. At peaks I was getting about 800W.
Using the AM Carrier control on the 6500 I reduced the carrier to 50W, while still achieving the 800W peaks.
Amp runs much cooler with no apparent degradation. Need to repeat this test with someone who has a mod scope.
Seems like an easy way to reduce power consumption and heat dissipation.

[WA2SQQ]

I don't think Clark is using any SDR equipment. If I hear you on this weekend we can do the test again.

[DMOD]

Here is Nautel's presentation on MDCL if anyone is still interested in how one company implements this for broadcashers.

About 40 minutes long and would recommend skipping the first two minutes.


http://www.nautel.com/webinar/am-power-saving-techniques/

Phil - AC0OB