[ARC5] Selectivity improvement in ARC-5 receivers.

[Mike Hanz]

I think the 4th and 5th edition RSGB Handbooks are significantly better 
than any of the ARRL Handbooks in the theory area.  Walt Hutchens KJ4KV 
introduced me to them at a hamfest and prodded me into buying them, 
saying essentially the same thing.  The 5th edition begins the bridge to 
solid state, but still has plenty of outstanding info on tube circuit 
design and does have a lot of tube types used on this side of the pond. 
Highly recommended.

- Mike  KC4TOS

On 6/2/2014 1:56 AM, Brian Clarke wrote:
> Hello Ken,
>
> All is not lost, except access to the synaptic connections to your 
> long unused memory cells.
>
> The matter of which you speak is covered well at a 
> quasi-conversational level in the RSGB (1987) 'Radio Communication 
> Handbook' 5th edition, section on 'Interstage coupling' (pp 6.20 to 
> 6.25). Fred Terman (1955) 'Electronic and radio engineering' Ch 3, 
> 'Properties of circuits with lumped constants' gives a more rigorous 
> treatment with more formulae in 38 pp. The selectivity curve, ie, the 
> slope of the skirts, shown in the RSGB handbook appears as Fig 3-11 in 
> Terman. Fritz Langford-Smith (1960) 'Radio design handbook' supplies a 
> 49 pp chapter - Ch 26 'Intermediate frequency amplifiers'; it is 
> similar to Terman in terms of level and design detail; there is an 
> appendix devoted to calculating the coupling coefficient, and there is 
> a major section on selectivity and the calculation thereof.
>
> The slope of the skirts, in dB per decade, depends on the frequency, 
> the Q of the reactive elements and the coupling coefficient between 
> the coils. Q is not only that of the reactive components, but also 
> includes generator and load impedances. The coupling coefficient is 
> related to coil spacing and other matters of geometry, such as the 
> polarisation of the windings and their co-axiality.
>
> Terman's and Langford-Smith's books are for designers; the RSGB 
> handbook is for talented amateur technicians. I suspect the ARRL 
> Handbook would be similar in level to the RSGB handbook - they are not 
> really design reference manuals in the way Terman and Langford-Smith are.
>
> In short, it ain't just frequency. And ultimate stop-band attenuation 
> will depend on shielding as well.
>
> Cheers, Brian, VK2GCE.
>
>
> On Monday, June 02, 2014 7:03 AM, Ken posited:
>
>
>> This month's Electric Radio Magazine has Jeep Platt's article on the 
>> subject
>> above in it. Jeep's article is very well written and very useful.
>>
>> However, I have had a question concerning ultimate stop-band 
>> selectivity for
>> some time now after a discussion with another of our list-members 
>> during our
>> discussion on Jeep's final method.
>>
>> It is my understanding that the ultimate stop-band selectivity is 
>> determined
>> NOT by any physical characteristic of the IF transformers, but, 
>> rather, by the
>> IF frequency itself.
>>
>> I.e., at the 60 db down point, the true selectivity is determined 
>> more by the IF
>> frequency than the separation of the two IF coils.
>>
>> I vaguely remember from my EE course in filters that it was "so many 
>> db per
>> octave", or something similar.
>>
>> Can anyone here tell us what I am even talking about here, and fill 
>> in the
>> details?
>>
>> I'm at a loss, but still very confused.
>>
>> Kenneth G. Gordon W7EKB 
>
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