The brochure includes some unique information …
… as well as some information that can also be found elsewhere on our site …
PDFs – Published in Three Formats (Revised 5 AUG 2013)
8 July 2014 – The filters have arrived (ahead of schedule) and will begin shipping tomorrow. Our internal designation for this manufacturing lot is #2714, identifying the week and year it was received.
2 June 2014 – We commissioned the next batch sans a preorder waiting list, to shorten the procurement cycle.
26 May 2014 – The latest manufacturing lot has sold out.
9 May 2014 – The filters have arrived from INRAD. Our internal designation for this manufacturing lot is #1814.
29 January 2014 – The next production run has been commissioned. We expect it will arrive on Friday May 16th, give or take a week.
22 January 2014 – We are currently accepting preorders towards the next production run.
18 October 2013 – Batches four and five have arrived and been shipped.
6 August 2013 – The fourth batch has sold out and we have commissioned a fifth batch.
10 July 2013 – Batch #4 has been commissioned.
19 June 2013 – Batch three has sold out.
17 February 2012 – Wayne ➚ confirmed that Elecraft ➚ is not much closer to offering switchable dual-bandwidth filters, than they were when the K3 was first announced. (“Still a gleam in my eye” as he put it.)
On Its Own Merits
Considering the Big Picture
700 Hz “pairs nicely” with INRAD’s 400 Hz filter and also with their 1,500 Hz filter. By this we mean that there’s optimal spacing between them. (Not too much, and – just as importantly – not to little.) This “pairing nicely” aspect of 700 Hz was one of the major factors that led to our commissioning INRAD to design and manufacture this filter for us.
Expanding on the notion of “pairing nicely”, a useful analogy is to think of your filters as “tools”. In this context, choosing which filters to get is like outfitting a toolkit with an assortment of screwdrivers in preparation for a DXpedition, but with the stipulation that you may only bring five with you. Unless you only expect to use these screwdrivers to repair eyeglasses, you’d be wise to select a wide assortment of sizes.
The same rule applies to K3 filters. You might be able to justify choosing the four narrowest (500, 400, 250, and 200 Hz) for your K3, if it will only ever be used for running under the most extreme CW contest conditions, with numerous close-in S9+25 signals.
The drawback of this strategy is that there is a diminishing return whenever any two filters have fairly similar widths, ultimately reducing the “contribution” each filter can make to your K3’s maximum “potential” crystal filtering flexibility. (The extreme case – to demonstrate this point – would be to imagine installing two identical filters in your main or in your sub-RX!)
Yes, under some band conditions you might be able to discern a difference between two 8-pole filters of very similar widths. Specifically, between INRAD’s 500 and 400, or between their 400 and 250. But the difference is unlikely to be so dramatic as to warrant installing both of them.
Please don’t misunderstand … these three filters – the INRAD 500, 400, and 250 Hz – are perfectly fine choices; it’s just that installing all three, isn’t three times better than only having one.
Compared to INRAD’s 1000 Hz Filter
At first glance the 1000 Hz might seem to be more flexible, since it can also be used for 1000 Hz digital formats. That is, until you take a closer look and realize this filter is only about 975 Hz wide at minus 3 dB. Thus a narrow SSB filter might be better suited for these modes; especially for weak signal work. But more importantly, a 700 Hz filter is sure to outperform a 1000 Hz filter, at passband widths below 700 Hz but above the point where your next narrowest filter is automatically selected.
Compared to INRAD’s 500 Hz Filter
500 Hz might actually be the better single-filter “solution” for casual CW contesting. Especially if your primary objective is to only use one filter slot for CW. Coincidentally, 500 Hz is both too wide and too narrow to “pair well” with most other CW filters anyway. Further, 500 Hz is somewhat of a one-size-fits-all compromise and as such, it doesn’t do anything particularly well. Specifically:
Still, a 500 Hz filter might work just fine for you, provided that:
Our guess is that there multiple contributing factors, including: because they have higher priorities; because the up-front effort/cost to add it to their product lines is prohibitive; and because the demand isn’t sufficient to make doing so worth their while.
785 ± 15 Hz. We estimate the shape factor at 1.7. Our original intention was to offer a 750 Hz filter, something midway between INRAD’s 500 and 1000 Hz. We specified 700 Hz, knowing the minus 6 dB width would be several percent wider. In hindsight, perhaps we should have specified 675 Hz? However, at the time our primary concern was that we didn’t want something too similar to INRAD’s existing 500 Hz filter, and we have fulfilled on that intention.
They are right now … but only because the latest batch arrived much earlier than expected. (This batch is much smaller than usual and will likely sell out before the end of August.)
These custom filters are available exclusively through unpcbs.com. INRAD ➚ does not offer them for sale on their website. If they were available directly from INRAD, there would be no reason for us to offer them.
Overall, the filters in the July 2014 batch have a center frequency of 8215.013 kHz, i.e. a plus 13 Hz offset. Enter [ +0.01 ] into the “FLx FRQ” Config menu, to compensate for this +0.00016% deviation.
Overall, the filters delivered in May 2014 have a center frequency of 8215.027 kHz, i.e. a plus 10 Hz offset. Enter [ 0.01 ] into the “FLx FRQ” Config menu, to compensate for this +0.00012% deviation.
Overall, the filters delivered in October 2013 have a center frequency of 8215.027 kHz, i.e. a plus 27 Hz offset. Enter [ 0.03 ] into the “FLx FRQ” Config menu, to compensate for this +0.00033% deviation.
Overall, the filters in the February 2013 batch have a center frequency of 8214.955 kHz, i.e. a minus 45 Hz offset. Enter [ -0.04 ] into the “FLx FRQ” Config menu, to compensate for this -0.00055% deviation.
Overall, the filters in the June 2012 batch have a center frequency of 8214.98 kHz, i.e. a minus 20 Hz offset. Enter [ -0.02 ] into the “FLx FRQ” Config menu, to compensate for this -0.00025% deviation.
Upon adding a new filter, you should use the “FLx GN” Config menu to compensate for the relative differences in insertion loss across your filters. Whereas the K3 manual recommends 1 or 2 dB for 400 and 500 Hz filters, we estimate that the difference between the 2.8 kHz and 700 Hz filters is actually closer to 3 dB. (Specifically, minus 3 dB at 2.8 kHz versus minus 6 dB at 700 Hz.) Still, 2 dB is probably a good starting point.
Note that the objective here isn’t to compensate for all of the insertion loss. Rather, it is to use the minimum gain necessary so signal levels do not fluctuate objectionably when switching filters. Most likely, you’ll find the best setting for 700 Hz is between 1 and 3 dB. Getting the best results might entail changing the loss compensation of one or more of your existing filters.
In the rush to send the filters, all domestic orders were shipped without the required mounting hardware, i.e. (1) 4-40 zinc pan-head Phillips machine screw and (1) lock washer. Most of you will have already the required hardware on hand, or will be able to obtain it locally. However, international customers may experience difficulty finding non-metric parts. We will provide this missing hardware upon request.
Caution! Be sure to use a 3/16" (4.8 mm) or 1/4" (6.4 mm) long screw! Anything longer might extend into the filter and damage it!
Overall, the filters in the December 2010 batch have a center frequency of 8215.06 kHz, i.e. a plus 60 Hz offset. Enter [ 0.06 ] into the “FLx FRQ” Config menu, to compensate for this +0.0007% deviation.