[Hallicrafters] Revolutionary Signal Generator

[Charlie]

So tell me again why an "antique" HP 8640 isn't the best solution?  It has a 
digital display, accurate, very stable, shielded, covers IF to UHF, has 
calibrated output, can be swept, has built in level controllable AM & FM, 
runs by itself, and is relatively inexpensive.  Some popular options allow 
it to survive 50 watts into it's outhole and can double the freq to over 1 
giggle hurtz.   AND they used to sell new for about 10 large, so it ain't 
Heathkit.

By the way, I use a Wavetek  (paid $35 for it)  audio generator for the 50 
kHz IF's.

Charlie k3ICH

.
----- Original Message ----- 
From: <Troglodite at aol.com>
To: <Hallicrafters at mailman.qth.net>
Sent: Thursday, May 25, 2006 2:48 PM
Subject: Re: [Hallicrafters] Revolutionary Signal Generator


> To all interested,
>
> There are two problems with the simple DDS approach which are difficult to
> solve. If it were easy, we would see inexpensive digital RF generators in
> profusion.
>
> The first problem is that the signal as it comes from the chip is riddled
> with "spurs." This is an easy to fix for a narrow tuning range, but 
> becomes more
> difficult as the range increases.
>
> The second problem is that if you expect to use this for receiver 
> alignment
> and testing, you really need a calibrated output attenuator. You need to 
> be
> able  to get down to the microvolt range. To do this, you have to put the 
> noisy
> parts  in a can, and use feedthrough capacitors for all the control lines.
> This means  the processor too. The only RF exit should be the output. The
> attenuator should  be mounted in a shielded box as well. Great care needs 
> to be taken
> to prevent RF  leakage.
>
> You can live with minor impurities in the waveform - at least for 
> alignment
> purposes. Ever look at the output waveform on the inexpensive commercial 
> RF
> generators? Some of them deliberately distorted the waveform so that it's
> harmonics could also be used. But if you want to measure receiver 
> sensitivity,
> you need that calibrated output, and to get it you will need good 
> shielding.
> Without it, you will have an instrument no better than the inexpensive 
> ones,
> except that it is more frequency stable and accurate.
>
> Regards,
>
> Doug Moore
>
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