Dick
Are the signals for which you experience the unusual  carrier level
variations typically the stronger ones that you are comparing? Is the lowest
frequency at which they AM the carrier the same in each case?
And what about the rx LO in all the rxs involved (including Andy's
Watkins-Johnson)? Are they synthesised or not and are any specs re phase
noise on the LO available?
Just wondering if this is yet another example of reciprocal mixing
problems?
Off to bed-it's 2am here!
73
Dave
ZL3FJ

----- Original Message -----
From: "Dick Rollema" <[email protected]>
To: <[email protected]>
Sent: Wednesday, July 31, 2002 1:20 AM
Subject: Re: LF: Re: Power of Donebach 153kHz TX

To All from PA0SE

Andy, G4JNT wrote:



>I've just made a check of both Droitwich and Donebach transmissions using
>the WatKins Johnson WJ-8711 receiver here at work.  Using the narrowest

IF

>bandwidth of 56Hz, setting manual gain control, and monitoring the output
>tone using Gram on its widest setting I cannot detect any variation in
>carrier level with modulation on either of the two transmitters.  The

level

>meter, which indicates actual signal level, accurately calibrated in dBm,
>also shows no significant variation with modulation. There is perhaps 1dB

of

>variation on Donebach ( due to fading ?)  and nothing on Droitwich.
>
>I'm very sure (read 99.9% certain) Droitwich has no amplitude

modulation -

>viewing it on a vectorscope in the past shows only the phase variation.

So

>perhaps you are seeing some secondary effects introduced by the receiver

?

>
>Andy  G4JNT
>
>I repeated the reception using the Wandel & Goltermann PSM-5 selective
>voltmeter and  a wire aerial instead of the loop. The results were
>identical to the SPM-12 and the loop aerial: variation in strength as
>read  on the meter on Donebach, Droitwich and Dutch 747kHz and steady
>readings on other LF and MF transmitters.  The variations follow the
>modulating signal so it is not a matter of conversion of a data PSK or

FSK

>signal into AM.

It would be interesting to know what other amateurs  find? Or provide an
explanation of the anomaly?

73, Dick, PA0SE

>


>< I am pretty sure Donebach uses some form of controlled carrier

modulation,

> >apart from the phase modulation mentioned by Walter.
>
> >Our Dutch MF transmittters at 747kHz and 1008kHz are also made by
> >Telefunken (400kW at daytime).  The 747kHz transmitter uses controlled
> >carrier to save power and expenses; the 1008kHz one does not. The

carrier

> >at 747kHz, as measured by the SPM-12 at 25Hz bandwidth, shows the same

kind

>
> >of fluctuations as the Donebach one, the 1008kHz carrier is steady.
>
> >Remarkable is Droitwich at 198kHz. There the carrier goes downward

during

> >modulation!
>
>
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