[Premium-Rx] Receivers for MW and 160 meters.

[Karl-Arne Markström]

If a modest tuning range is sufficient, many different architectures for an LO source
can be used. One idea would be to use the HP8640 concept, starting with an high-Q
VHF/UHF cavity oscillator and frequency dividers to reach the required LO output frequency.

Another would be to use a fractional-N synthesizer on, say, 100 times, the LO frequency.
Such a synthesizer (like the one used in the SRT CR91) can be built having a step size of 1 Hz (at 160 MHz) and 
phase noise of better than  -110 dBc/Hz at 10 kHz offset.
Division to an output frequency of 1 MHz would improve the phase noise to maybe 
-145 dBc/Hz at 10 kHz offset

A third approach could be to use the old fashioned direct synthesis (R&S XUA, Adret 6100) methods,
and use frequency dividers to further improve the phase noise close to the LO center frequency.

Any LO source using a DDS will need to utilize a "clean-up PLL" to suppress the discrete spurious sidebands
inherent in the DDS frequency generation scheme. It is hard to tell if it can improve the spurious level to the
required -120 to -130 dBc.

Linrad was mentioned as a more suitable "back-end" for an high-performance receiver.
I cannot do anything but agree, it is open-source, Linux-based and "Made in Sweden".
The omission of Linrad was an oversight in my case.

73/

Karl-Arne
SM0AOM


73/

Karl-Arne
SM0AOM

----- Original Message ----- 
From: "Jerry" <gh1lockett at bak.rr.com>
To: <premium-rx at ml.skirrow.org>
Cc: <sm0aom at telia.com>
Sent: Friday, February 11, 2005 9:12 PM
Subject: Re: [Premium-Rx] Receivers for MW and 160 meters.


> I forwarded this thread of notes on to a friend of mine, Bill 
> Carver-w7aaz, who has built more than his share of high performance 
> receivers/transmitters over the years and whose basic IF strip is built 
> into the CDG2000 high end homebrew transceiver project that has/is being 
> built by a lot of folks..  He had this to say:
> 
> 
> I looked at that "PTS" synthesizer. It looks fine for phase noise,
> obviously a DDS-based design. But, like every other DDS, they have
> inband spurs. Those are specified as -75 dBC.
> 
> So your receiver, in addition to being tuned to the desired frequency,
> is also tuned to a myriad of other places and down 75 dB. Would you be
> impressed by an xtal filter with skirts down 75 dB? It would work, it
> would sound good, but the first time someone 10 KHz away moved your
> S-meter you'd be pissed. That sounds like my 75A4, cica late 50's, with
> mechanical filter blowby.
> 
> According to data sheets a well-filtered pair of AD9951s in quadrature,
> at HF, should produce an output that's comparable to the PTS. Either is
> fine for proof of concept and casual, but it is  NOT  providing
> performance of a premium receiver. We need a synthesizer design that
> makes an LO with spurious down at least 100 dB to be acceptable, 120 dB
> to be considered "premium" receiver performance.
> 
> Karl-Arne, SM0AOM, proposes a receiver that should have reasonable
> performance. It is totally dependent upon (1) synthesizer cleanliness
> and (2) the 24 bit ADC. All the emphasis is on digital today, the 24 bit
> audio ADC will get nothing but better. The only undefined block is the
> synthesizer:  what does Karl-Arne propose for that synthesizer? I am
> ready to build it.
> 
> Pass that back. I don't need a detailed schematic, just a block diagram
> with some performance numbers scribbled in.
> 
> Bill
> 
> 
> 
> Sent: Friday, February 11, 2005 7:09 AM
> Subject: Fw: [Premium-Rx] Receivers for MW and 160 meters.
> 
> 
> : Interesting comments..
> :
> : Jer
> : ----- Original Message ----- 
> : From: "Karl-Arne Markström" <sm0aom at telia.com>
> : To: <premium-rx at ml.skirrow.org>
> : Sent: Thursday, February 10, 2005 10:54 PM
> : Subject: Re: [Premium-Rx] Receivers for MW and 160 meters.
> :
> :
> : I certainly agree with prevoius posters that nothing can be 
> substituted
> : for front-end selectivity.
> : Off-channel signals that have been eliminated through preselection
> : simply cannot cause problems downstream.
> :
> : Proper choice of mixers (the SS-1R has been mentioned) helps a lot, 
> and
> : if paired with preselection
> : and a low-noise oscillator as in the G3PDM receiver design the results
> : can be spectacular.
> :
> : To take up previous discussions about diplexers, it is my firm belief
> : that lumped-constant
> : diplexers intended to smooth out impedance variations near the 
> passband
> : from crystal or mechanical
> : filters would be impractical.
> :
> : The exception may be the route taken in the E1700/E1800 where a 90
> : degree hybrid absorbs the
> : impedance mismatch from crystal filtering behind the mixer.
> :
> : A proposed design for a very high-performance MW and 160 m receiver
> : would in my opinion look
> : like this:
> :
> : 4 dB Cohn-filter preselector with a - 3dB passband of 0.5 to 1 % of 
> the
> : centre frequency;
> :
> : Push-pull MOSFET feedback low-noise amplifier, Gain 10 - 12 dB, NF < 2
> : dB and IP3 > 50 dBm;
> :
> : A passive power divider to the I and Q signal paths, each with a
> : high-level "Tayloe-mixer" driven from a
> : low-noise frequency synthesizer via high-speed logic I and Q LO 
> drivers;
> :
> : Passive low-pass filtering in each signal path in the mixer;
> :
> : Low-noise I and Q baseband preamplification before 24-bit A/D
> : conversion;
> :
> : "Software Defined Radio" signal processing a'la the SDR-1000 software
> : downstream
> :
> : Such a receiver, as modeled in HP/Agilent "AppCad", shows an NF of 
>  6 -
> : 8 dB, an IP3 with 10 kHz spacing of around
> : 40- 45 dBm (30 kHz spacing IP would probably be impractically high to
> : measure with "normal" lab gear).
> :
> : Should the ultimate in sensitivity be needed (for example when using
> : Beverage antennas in extremely quiet locations), the preselector and 
> the
> : low-noise amplifier (preferably preceded with some filtering) could
> : trade places.
> : This would yield a receiver with a noise figure of around 4 dB and a
> : dynamic range of >110 dB in SSB bandwidths.
> :
> : 73/
> :
> : Karl-Arne
> : SM0AOM
> 
> 
> 
> 
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