[R-390] Straight Key Night

[Don Reaves]

If this year's Straight Key Night is like last, here is a chance to exercise
your R-390A narrow CW filters.  Lots of crowded, slow speed signals bunched
up in the bottom half of the 80,40,20 meter ham bands.  Many of the signals
you hear will be rarely used vintage transmitters, so there is a challenge
to twist knobs and track the chirpers and drifters and weak sigs.  Just what
R-390 receivers were born to do...

New Year's Eve 7pm EST to New Year's Day 7pm EST.
Details at  

http://www.arrl.org/contests/rules/2006/skn.html

Hope to work some of you. Happy New Year

W5OR
don at reatek.com
w5or at comcast.net




> -----Original Message-----
> From: r-390-bounces at mailman.qth.net 
> [mailto:r-390-bounces at mailman.qth.net] On Behalf Of 
> Flowertime01 at wmconnect.com
> Sent: Thursday, December 29, 2005 7:22 PM
> To: R-390 at mailman.qth.net
> Subject: Re: [R-390] Trim Caps on Mechanical Filters
> 
> DW Holtman ask,
>     
> Was the modification that installed variable caps (C-569 
> through C-571) in 
> the input and output of the mechanical filters in the If 
> module applied at Depot 
> during rebuilds, or just put on newly manufactured modules? 
> 
> There are two flavors of mechanical filter caps in production.
> What you see is what you get. The field never went back and 
> "upgraded" the 
> caps in the IF deck.
> 
> Early production had selected fixed caps.
> 
> Later production had 4 caps under the can and 4 more on the 
> side of the deck. 
> These units also had 4 more holes in the side of the frame to 
> access the side 
> caps.
> 
> If you have an IF deck with side caps and no side holes in 
> your frame, you 
> have a swapped in IF deck. Conversely if you have holes in 
> the frame and no caps 
> you have a swapped out IF deck. This will start some chatter 
> and likely get 
> us another dead carcass. So near the new year and such tasks 
> to be dealt with. 
> 
> There was much todo about what to do if you had to replace a 
> mechanical 
> filter in a deck that did not have trim caps. The last word 
> in 1975 as I was 
> getting out of service was still to just put the filter in 
> and ignore the cap 
> optimization problems. Wisdom from management powers was that 
> once the caps were 
> properly trimmed they needed no further adjustment. If you 
> measured the output 
> before you tweaked on the trim caps, you likely found your 
> diddling produced no 
> further gain. Experience in the field did not support this 
> wisdom from higher 
> management. It was standard procedure to tweak all the filter 
> trim caps on 
> every PM event. We wondered why there was no modification 
> work order to at least 
> add the top caps to the IF decks. We could see why no one 
> wanted us drilling 
> into IF deck and installing caps in the bottom side. 
> 
> I think if we look at decks with and without trimmers on the 
> bottom side, we 
> will see that the decks have a lot of differences to allow 
> the caps to be 
> inserted. There was just not a big blank chassis wall space 
> there waiting for 
> additional caps. The extent of these changes may have been 
> why no field 
> modification was ever kited and fielded. The idea of 
> providing new decks with caps was 
> just a non starter from spending and contract point of view. 
> Letting someone 
> drill holes in the frame to trim decks in place was not a 
> popular subject.
> 
> We always wondered how much better a deck would have been if 
> it had had 
> adjustable caps. Decks without trimmers still passed signal 
> to noise test like 
> every other receiver, so we believed the assembly folks did a 
> good job testing and 
> selecting the fixed caps.
> 
> One myth was the early production was "selected" to closer 
> specification. 
> Once Collins had a big pile of good but not good enough 
> filters, a proposal was 
> produced and sold to get the trim caps in and the less exact 
> filters in. Myth 
> was that a well trimmed deck never needed adjustment. I have 
> no evidence to 
> support that statement.
> 
> Hope this provides you some insight on the subject.
> 
> Roger AI4NI
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