[Elecraft] Re: K1 on 10 meters: helpful advice
Sandy, W5TVW
ebjr at i-55.com
Mon Dec 26 16:48:27 EST 2005
Keep us posted on this guys! I plan ultimately to build a 17/10 meter board.
Already have a 160/80 meter board to go with my 40/30/20/15 meter
4 band board.
I'm in no rush as it will be a while before 10 gets "decent" again except for
the usual summertime "Sporadic E" type stuff and the perennial
North-South path to South America. I can work the Argentine/Brazilian
Venezuelan stations already on 20 or 15 so don't need 10 meters for them!
73,
Sandy W5TVW
----- Original Message -----
From: "Stephanie Maks" <va3uxb at maksystems.com>
To: "wayne burdick" <n6kr at elecraft.com>
Cc: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Monday, December 26, 2005 3:30 PM
Subject: [Elecraft] Re: K1 on 10 meters: helpful advice
| Hi Wayne,
|
| Thanks very much for the additional information! Most of my
| guestimated values for the 2-band board seem to match those that were
| in the email you sent; the only ones I was way off on were C16 & C20.
|
| I actually found a cheap source of fundamental 36MHz crystals.
| They're about $4.00 each, the only catch is they're surface-mount. I
| just solder leads on them and use them in the normal crystal mounting
| holes.
|
| Yesterday I was at work most of the day with a lot of time to think
| and surf the net, and found one email that I'd missed in my earlier
| research:
| http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-06/
| msg00789.html
|
| Based on that email, I reduced the value of RF-R11 from 82 ohms to 33
| ohms. I now get up to almost 3 watts out on 10 meters. I'll have a
| go at adding the L-network at J7-P8 as described in the email you
| provided and see if that improves things any further.
|
| I also went a little crazy last night with experimentation, and
| decided to have a shot at my 'ideal' 4-band filter board: 80 / 40 /
| 20 / 10 meters. I've got a design in mind to provide 4 separate low-
| pass filters, but it will mean some drastic surgery to the filter
| board, and I won't have room for the noise blanker any more. As it
| stands now, on the test bench, I have a full 5 watts output on 80,
| 40, and 20 meters, and 2 to 3 watts on 10 meters. The board's two
| existing low pass filters are set-up for 40 and 10 meters. So while
| I can currently listen on all four bands, I won't be transmitting on
| 80 or 20 just yet. The key for me though is, I know what is
| required, what the values are, and have a good idea how to lay it out
| physically, so basically I know it's possible.
|
| Thanks again for the info and suggestions!
|
| Happy holidays and 73 de
| Stephanie Maks
| va3uxb
|
|
|
| On 26-Dec-2005, at 14.44.01, wayne burdick wrote:
|
| > Stephanie (and other interested parties),
| >
| > I have some additional thoughts on modifying the K1 for 10 meters.
| > I also found some old e-mail from another customer who attempted
| > it. Between the two, I believe you'll be able to do this successfully.
| >
| > When I designed the Norcal/Wilderness Sierra, which uses the same
| > I.F. as the K1, I realized that a 36-MHz crystal would be
| > expensive, so I came up with an alternate mixing scheme where the
| > LO is below the band rather than above it. The RX and TX image
| > rejection isn't quite as good with this technique, but that
| > probably doesn't matter since the band-pass filters are narrow.
| >
| > Here's the normal conversion scheme (high-side injection):
| >
| > RF 28.000 - 28.100
| > + IF 4.915
| > ------------------------
| > = LO 32.915 - 33.015
| > + VFO 3.085 - 2.985
| > ------------------------
| > = XO 36.000
| >
| >
| > Here's the alternate scheme using low-side injection:
| >
| > RF 28.000 - 28.100
| > - IF 4.915
| > ------------------------
| > = LO 23.085 - 23.185
| > + VFO 3.085 - 2.985
| > ------------------------
| > = XO 26.170
| >
| > I.e., you can use a 26.170 MHz fundamental crystal. Advantages of
| > this frequency vs. 36 MHz include: (1) more power output from the
| > NE602 premixer oscillator; (2) cheaper; (3) possibly available from
| > Wilderness Radio. If Wilderness doesn't have any, you might try
| > ICM. I think the ICM part number for the basic crystal type (not
| > including frequency) would be #436162.
| >
| > Low-side injection results in one additional minor issue: the
| > sideband gets inverted. This just means that the CW pitch will
| > change in the opposite way from the other bands as you tune. VFO
| > readings should still be accurate.
| >
| > Looking back through old K1 design notes, I found an e-mail from
| > another customer (Bob Larkin, boblark at proaxis.com) who put his K1
| > on 10 meters. He used an overtone 36 MHz oscillator, requiring
| > changes to the basic band module. A 26.17-MHz crystal would be
| > simpler, as I described above. But Bob's notes on getting adequate
| > power output on this band are quite useful. I have attached them
| > below. Let me know if you try this! If we have a couple of
| > customers successfully complete the mods, we'll offer it as an
| > option kit for use with the 2-band module.
| >
| > 73,
| > Wayne
| > N6KR
| >
| > * * *
| >
| > The RF filter was designed to have 2.2 dB IL in 50 Ohms and has 3
| > and 40 dB
| > bandwidths of 1.8 and 18.5 MHz. Inductor were the regular 1 uH.
| > C16=C20=270
| > pF, C17=C19=33 pF, C18=1.5pF (if the latter is not available, use 0.75
| > inches of the gimmick capacitor).
| >
| > The LPF is an interesting topic. I did not try a direct scaling of
| > the other
| > filters. This might work adequately, and would be good for someone
| > to try.
| > Instead I designed a 2-coil modified elliptic filter. The goal was
| > to move
| > the cutoff frequency far enough above 28 MHz to minimize the
| > insertion loss,
| > and to put an elliptic null at the second harmonic, 56 MHz. The
| > final design
| > cutoff at 34.9 MHz and had a measured insertion loss of 0.17 dB at
| > 28 MHz
| > and 65 dB at 56 MHz. L11 is 0.28uH (9T T37-6, over 75%), L12 is
| > 0.22uH (7T
| > T37-6, tight wound--probably should be 8T spread out). C24=94 pF
| > (two 47 pF
| > in parallel, one on top, one under), C25=164 pF (two 82 pF), C26=75
| > pF. The
| > capacitors in parallel with the inductors are mounted below the
| > board and
| > arranged to be flat against the board to clear the bottom board parts.
| > Across L11 is 13 pF (two 6.8 pF in parallel), across L12 is 36 pF.
| > This is
| > quite a few parts, but the measured performance is great.
| >
| > Now the K1 was on 10-m, but the transmitter didn't put out any
| > power! There
| > wasn't enough drive to make the Class C Q7 draw current. I made two
| > changes
| > to fix this. Both of these have the potential to alter the
| > performance on
| > other bands, particularly 15 and 20-m. I attempted to evaluate these
| > effects, but I only have the one K1! Both changes are attempting to
| > compensate for the drop in gain of Q6 and Q7 with frequency. My 10-m
| > performance seems to still be limited by drive to Q7.
| >
| > First, U9 has more gain available. I put 270 pF across R11,
| > boosting the
| > gain on all bands above 40-m.
| >
| > This produced a fraction of a Watt, but not enough drive, yet. So, I
| > measured the impedance looking into pin 8 of J7, in transmit. At 28
| > MHz,
| > this was 5+j8 Ohms. So I added an L-network to match this closer to
| > 50 Ohms.
| > At the J7-P8 side of D9, I inserted a .12uH (6T #32 on T12-6,
| > tight) and on
| > the J7-8 end put 200 pF to ground.
| >
| > Now at 13.8 V I get 3W, and at 12V about 1W. All spurs are at least
| > 48 dBc.
| >
| > As a by-product the output on 15-m is easily 7W. The power control
| > seems to
| > still be able to work fine and on my K1 the spurs were still
| > essentially
| > where they were on all bands.
| >
| >
| >
| > ---
| >
| > http://www.elecraft.com
| >
|
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