As the synthesiser in the MA1723 is very similar to the one used in the
RA1792,
I would estimate the total sideband noise to be about - 90 dBc/Hz at 5
kHz spacing.
However, it is likely that noise from the signal processing chain that
makes its way
through the final "roofing filter" would be the major contributor to
the transmitter "close-in noise".
Research at the ITT-Standard Radio company in the 80's (presented at
the Nordic HF Conference HF92), also showed that the low-level parts of
a solid state power amplifier had to be designed
more or less as a low-noise receiver front-end in order to provide a
noise floor that could be
negligible compared to the broadband noise floor coming from the
exciter.
Many of the simpler HF exciters for shipboard use had such a high
broadband noise that they
could make duplex operation onboard a ship impossible, and this could
only be cured by the insertion of a "post-selector" between the exciter
and the power amplifier.
The Collins HF-8010 family and the SRT TD90 family (measured noise
floor of - 155 dBc/Hz at 100 kHz from the carrier) were among the best
exciters available in these aspects.
73/
Karl-Arne
SM0AOM
----Ursprungligt meddelande----
Från: g4fph@mjha.co.uk
Datum: Jul 3, 2006 10:18:56 AM
Till: amps@contesting.com
Ärende: Re: [Amps] 4CX10 000J / Racal MA1723
Peter,
Do you know how clean the synthesiser is in the
MA1723? I have often wondered, as its quite an
old design, but never had the equipment to measure it.
The old Racal TX I use from time to time on-air
features an MA1723 as the exciter, followed by a
Class A solid state stage (drawing about 10 Amp
at 28 Volt with a pair of BLW96 to give 10 - 20
Watts for the valve [passive] grid!), followed by
a single 4CX1500B. The valve section, has two
motor driven roller coasters (for L1 and L2 in
the Pi-L) and enough solenoids and relays to keep
this OM amused. The TX has full auto tune (about
5 seconds tune time for any freq. between 1.6 -
30 MHz) and is truly a thing of beauty.
If anyone has an unwanted spectrum analyser,
please send it to me. I'll wait in all day for
delivery and post any useful measurements I make back here pro bono!
Regards.
Mark.
-----------------------------------------------------
At 17:27 02/07/2006, Peter Voelpel wrote:
>Why not,
>if you don´t bother the power bill you can easily achieve a super
clean
>legal limit signal which will be much better then any ham linear.
>Of course it needs to be be driven by a transmitter with best purity,
>perhaps the PT-8000C could be nice or a Racal MA1723 with a 4CX350J
or
>YL1050 in class A as the driver ;-)
>
>73
>Peter, DF3KV
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.
com] On
>Behalf Of Jan Erik Holm
>Sent: Sonntag, 2. Juli 2006 17:55
>Cc: amps@contesting.com
>Subject: Re: [Amps] 4CX10 000J
>
>surely no ham would use a thing like that, or?
>
>/ Jim SM2EKM
>----------------
>
>Peter Voelpel wrote:
>
> > All the J-types are low distortion, gain of both is about 20db
> >
> > 73
> > Peter, DF3KV
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.
com] On
> > Behalf Of Joe Subich, W4TV
> > What are the differences between the 4CX1000J and 4CX10000D -
> > particularly to explain the 10 KW vs. 15 KW output difference
> > in the "normal operation" figures on the Eimac short form
> > catalog (www.cpii.com/eimac)? Of course, with a listed gain
> > of 4.5, it would seem to take 2500 W or so to drive either of
> > them to their full capability ...
> >
>
>
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*******************************************
Mark Hill - G4FPH
E-mail: g4fph@mjha.co.uk
Current web pages at: www.g4fph.net
Old web pages at: www.qsl.net/g4fph
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