[R-390] Distribution Amplifier

[Bob Camp]

Hi

A couple of things you could do with the ARRL distribution amplifier:

1) The MAX 496 is a direct drop in for the MAX 497. The 496 has the 
same spec's except it has half the gain and significantly less 
distortion above 10 MHz.
2) Change out the 75 MHz high pass filter for one that cuts off at 30 
MHz. If you are running into a '390 there's nothing good going to 
happen with signals and distortion above 30 MHz.
3) C14 is the input blocking capacitor. The guys who did the AMRAD whip 
antenna came up with the fact that making this cap smaller trades off 
lightning protection for low end response and noise figure. If AM radio 
is not an issue dropping this part back to 0.001 or even less might be 
a good idea.
4) In the same way putting a coil of some sort in the location shown 
for R2 could help for ESD and lightning. Of course a DC short can cause 
problems of it's own.

Please don't take this as a bash of the design. It looks like a *very* 
well done design. I suspect it works very well just like it is shown in 
the article. All I'm trying to suggest is that it might be possible to 
optimize it for R-390 type use.

	Take Care!

		Bob Camp
		KB8TQ




On Apr 21, 2004, at 12:35 AM, Dennis L. Wade wrote:

> Bob brings up a good point that I think is easily overlooked.
>
> The project has two area in which gain is applied, the distribution
> section, and an optional rf amp ahead of that.  In correspondence
> with the author, I expressed my concern that unknowing builders would
> carelessly include as much gain as they could before the front end of
> their receivers and I suggested some article language cautioning its
> use.
>
> As I'm sure all of us know, most HF receivers seldom need another rf
> stage, not to mention the '390 series.  As Bob points out, IMD and
> other bad things are more likely to happen even without the added
> gain block.  I hope potential builders of the distribution device
> keep that in mind.
>
>                Dennis
>
>> Hi
>>
>> Well don't throw out all the glow in the dark stuff quite yet .....
>>
>> The video amplifiers that form the heart of the ARRL project are
>> pretty darn nice little chips. However they are not rated for IMD and
>> their harmonic distortion numbers begin to climb as you go past about
>> 10 or 12 MHz. That isn't to say they fall apart. Far from it they
>> probably work pretty darn well considering what they are.
>>
>> What they are not is the tuned RF front end on an R-390. I would be
>> very interested to see how they do when attached to a couple hundred
>> feet of wire with the bands open ...
>>
>>  Take Care!
>>
>>   Bob Camp
>>   KB8TQ
>>
>>
>>
>> On Apr 20, 2004, at 1:04 PM, Scott, Barry (Clyde B) wrote:
>>
>>> Looks like a really well-designed project; however, I'm afraid if I
>>> built it, I'd start looking for 6 more receivers...
>>>
>>> Barry(III) - N4BUQ
>>>
>>>
>>>> Hi, Pete, and ALL,
>>>>
>>>> The author and designer of the multicontroller has a neat web
>>>> site that
>>>> describes the project pretty well.  Go to:
>>>>
>>>> 	www.w8zr.net/multicontroller/
>>>>
>>>> In speed reading the QST article just now, I did not see a
>>>> noise floor
>>>> specification mentioned, but he is using new Maxim MAX497CPE
>>>> video amplifier ICs
>>>> each containing four 275 Mhz low-noise amplifier/buffers.
>>>>
>>>> I, too, am very interested in getting his kit and building it
>>>> for all my receivers.
>>>>
>>>> Marshall Dues  WB5MYO
>>>> Katy, TX
>>> _______________________________________________
>>> R-390 mailing list
>>> R-390@mailman.qth.net
>>> http://mailman.qth.net/mailman/listinfo/r-390
>>>
>>
>> _______________________________________________
>> R-390 mailing list
>> R-390@mailman.qth.net
>> http://mailman.qth.net/mailman/listinfo/r-390
>
> -----------------
> "If you can remain calm, you just don't have all the facts"
>
> Dennis Wade
> KG6ZI
> Carmichael, CA
>
> _______________________________________________
> R-390 mailing list
> R-390@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/r-390
>