Hi Group,

How difficult is it to put a balance modulator inside an radio that generates
AM to get Double Side Band suppressed carrier? Where can I get a circuit for a
balance modulator?

Is it possible that someone listening to a DSB with a USB receiver will not be
aware that there is another sideband on the LSB side?

Has anyone is this group ever experimented with DSB?

de KJ4UO

PDRUNEN wrote:

Hi Group,

How difficult is it to put a balance modulator inside an radio that generates
AM to get Double Side Band suppressed carrier? Where can I get a circuit for a
balance modulator?

Is it possible that someone listening to a DSB with a USB receiver will not be
aware that there is another sideband on the LSB side?

Has anyone is this group ever experimented with DSB?

de KJ4UO

If you mean converting an AM transmitter to DSB it may not be trivial if
the radio modulates the finals -- generally a DSB or SSB transmitter
generates the energy at a low level and amplifies it up with a linear
amplifier, while an AM-only rig may very well have a class-C final RF
amp who's power supply is audio-modulated.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

If you mean converting an AM transmitter to DSB it may not be trivial if
the radio modulates the finals -- generally a DSB or SSB transmitter
generates the energy at a low level and amplifies it up with a linear
amplifier, while an AM-only rig may very well have a class-C final RF
amp who's power supply is audio-modulated.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I seem to remember some conversions about 30 years ago where another final
tube was put in and the grids were fed in push pull and the plates were in
parallel or single ended. Forgot where the audio was fed but think it was
either the grids or screens. If there is room in the transmitter it was not
really that much of a job.

PDRUNEN ) writes:
Hi Group,

How difficult is it to put a balance modulator inside an radio that generates
AM to get Double Side Band suppressed carrier? Where can I get a circuit for a
balance modulator?

Is it possible that someone listening to a DSB with a USB receiver will not be
aware that there is another sideband on the LSB side?

Has anyone is this group ever experimented with DSB?

de KJ4UO

Most of the work on DSBsc in amateur circles is about simplicity. They aren't
using it for the benefits of having two sidebands, complete with the receiver
circuitry to take advantage of it. It is used because it's cheaper than a
complete SSB transmitter. And yes, the intent is that you use a sideband
receiver to receive it, at which point it cannot be differentiated from
an actual single sideband signal out of the transmitter.

Indeed, unless one has a a synchronous detector, it will be difficult to
properly demodulate the DSBsc signal unless one strips off the extra sideband.

With SSB, if the reinserted carrier is off a bit, you simply have output
that is somehwat shifted in the spectrum. But if you have a DSB signal,
if the carrier is not reinserted right in the middle of those two sidebands,
the two sidebands will not translate to the exact audio frequency, and
the output will be horrible. Strip off the extra sideband, either at
the transmitter or the receiver, and it's an SSB signal that the product
detector is dealing with.

So decades ago (and likely it's still the case) the reason most times
DSB transmitters appeared in ham magazines was because it was simpler
to generate DSBsc than an SSB signal. And all of the articles would
talk of how the guy at the other end would likely never notice.

As for modifying an AM transmitter, the trick is to find one with a balanced
output stage. If you've got two tubes there, likely it can be made into a
balanced modulator. And one thing that is forgotten is that it makes no
difference whether the signal is generated at a low level and amplified,
or generated at a high level. Indeed, in the latter case you eliminate the
long string of linear amplifiers.

Michael VE2BVW

Where can I get a circuit for a
balance modulator?

P.D.-

Many, if not most SSB rigs generate DSB-SC and flter-out the unwanted sideband.
Therefore, it may be easier to generate DSB by modifying an existing SSB rig,
replacing the SSB filter with a wideband AM filter.

I haven't listened lately, but years ago there was a foreign broadcast station
just above the Fifteen Meter band, that was broadcasting DSB-SC. The carrier
wasn't completely suppressed, so I suppose this is "VC" or Vestigal Carrier! I
think the station was out of Quito, Ecuador.

This station was intended to be received using a synchronous detector. I had
no trouble receiving it on my SSB rig. I could even get music to sound OK by
careful adjustment to match their frequency.

73, Fred, K4DII