[Hallicrafters] Revolutionary Signal Generator

[Julian Bunn]

I have the same question about the Jung Jin: works for me and does all that.

It seems that everyone has their own favourite RF sig gen, and it's 
almost a religious conviction :-)

Julian

Charlie wrote:

> 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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>
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