SIERRA MODS
This is a
collection of emails I've collected over time which
indicate how to put some mods into your Sierra transceiver.
Most of the mods have to do with improving the power output.
72, George N2APB
=================================================
from
Bob Follett, WA7FCU (now: AB7ST)
All of the mods, save one, have been blessed by Wayne, even if
they
don't fit his design intent of a "2 watt packpacking
radio". The
one mod he hasn't blessed is the reduction of inductance on L5 as
a
means of creating a lower matching impedance to the PA collector.
One reason is that no one (that I know of) has tested what the
mod
does to the third harmonic, in terms of -dB relative to total
power
out. Having said that, here we go:
BAND Original Sierra All mods except
PA MRF237 PA
13.7V IN 15.3V IN 13.7 IN 15.3V IN
-------------------------------------------------------------------
80M
n/c
4.2W
4W 4.3W
40M
2.5W
4.0W
4.5W 4.9W
5.8W
30M
2.1W
3.0W
4.0W 4.9W
20M
1.8W
2.6W
3.2W 4.0W
18M
1.0W
2.0W
2.9W 3.5W
Other mods include:
Q5 changed to a J310, all SM caps in modules except 80M, Meacham
"optimized LO Values", L5 reduced inductance, by
removal of 1 T on
30M - 18M, 2 T on 40M & 80M (Wayne recommends the 2:1
matching
xformer in place of the PA Collector choke instead, but I had
already tweaked all my L5's), ferrite bead on the 2N2222A.
As you can see, adding the MRF237 did make a sizable difference,
except on 80M. I haven't measured the total xmit current
draw yet,
but will. You will have to decide on how you each evaluate
the
formula of PO vs. current draw vs. cost. BTW, I got the
final for
$11 from MCM....Oh, and you need to bend the base lead to the
other
side of the case to reverse the lead layout of this device.
The biggest changes came from reducing inductance on the L5
toroid
on each module, but of course, I already had the SM caps on them
to
reduce losses once power was increased. Whats missing are
the
Meacham "optimized LO values". Here they are,
inbedded in my tune
up instructions.
You don't need any calibrated wattmeter, all you want to do is
optimize the radio. So use what you have.
1. Replace Q5 which is a J309 with a J310. They are
pin
compatable, and Wayne will start using the 310 in the next
Wilderness release. Don't expect much from this change,
maybe .1
to .2 Watts, but it helps. This is not a priority, just
something
to do on the mother board.
2. Put a ferrite bead on the base lead of the 2N2222A
driver to
eliminate VHF parasitics that show up on the higher bands.
If you
can't find one, Bob at Wilderness will sell you one...Call him.
(He also has the J310)
MODULES:
First things first. All those trimmers on the top of each
module
will, if within the proper range on their respective toroids,
have
TWO peaks as you rotate them, not counting the frequency trimmer,
C70. Re-peak the power output into your dummy load starting
with
the two PMO/BPFs, C66 & C64. Have two peaks? pick one,
and move
on. If not, you will have to modify the associated
toroid. Start
by compressing/expanding the existing turns. If that
doesn't do
it, try removing a turn. You may have to re-wind to add a turn,
but
not likely.
Then move to the XMIT BPF, C36 & C33. Same deal as
above. Now you
have as much power out as peaking those stages will allow.
That leaves the biggie, the two PI filters, L5 & L6.
You want to
remove each L5, and remove one or two turns. Remove one T
for 30M
and above, 2 turns below. What you are doing is presenting
the
final PA collector with a load of around 38 ohms rather than 50
ohms. (I might mention Wayne does not like us doing this
mod as it
MAY increase the harmonics, but no one has ever tested).
This mod
will produce your biggest power gain of all the tweaks.
Leave the
L6's alone, or slightly compress them to see if you get more
power
output. REMEMBER not to key down for for than a few seconds
at a
time.
The hard mod: on 40M and above, replace C47 C48 & C49
with silver
mica caps, preferably < 500V ones, or where you can't find the
proper SM, use polystryrene. The problem here is finding
small
SM's in large pF values. You can make any of them fit with some
bending, but its ugly!
Dave Meachem, in the Sept 95 QRPp came up with values for
"Optimized Output Filters" for the Sierra. He did
this for 50ohms
to the PA, and as I said, you will get more power by lowering the
inductance on L5. (Wayne also suggests he would rather see
you
wind a 2:1 xmformer toroid to replace the choke on the PA
collector
(This would mean you leave L5 at original value, and the xformer
would cut the impedance to the PA in half). He is probably
right,
but I haven't tried it since I already re-did all my L5's.
Anyway, the SM's are less lossy than what's in there, and you
will
pick up some free power.
BAND C47 C48 C49
----------------------
80M 910 1800 910 (These
guys are big. you may try the
Polys)
40M 430 910 430
30M 300 620 300
20M 220 470 220
17M 180 360 180
15M 150 300 150
I ordered mine from Mouser. You don't, of course, have to
do all
of them, but the higher the freqency, the more they are
needed. I
left the 80M module stock, other than the L5, removing 2 T, and I
get 4.2 W out on a 13.7V supply.
For 160, 12 and 10 meters, the optimized output filter values
are: (Per
Bob
Follet e-mail of 02/28/97)
BAND C47,C49
C48 L??
--------------------------------------------------------------
160M 1600
3000 4.10uH, 32T on a T37-2 core
12M
120
250 0.324uH, 9T on a T37-2 core
10M
120
220 0.275uH, 8T on a T30-2 core (Note: I
think
this is
a typo, and should actually
be a
T37-2 core.)
If you get through all of this, and want some more fine-level
tweaking, I have the instructions from Wayne to insure that all
the
xmit stages are performing as they should. I did this, but
only
picked up .1W, so I don't recommend it unless, like me, you have
too much time on your hands. :-)
One last thing. The easiest way to increase power out is to
increase the supply voltage. Wayne posted an E-mail about
this
about 6 mo. ago. Just make sure you replace D7, the
zener diode
rated at 36V with one rated at 43V, or even the next step
up. It's
all in the the front pages of the Sierra manual. I have a
AA pack
of 12 cells, which produces almost 16V, and I can get 4.5W out on
40M. It really is the easiest way, so don't forget about
it.
OTOH, I wanted to optimize my rig, regardless of voltage in, and
I
think the mods were worth it.
In summary, order parts, then while waiting, start with the
modules, looking for db. peak, and re-winding the L5's.
This will
show the largest power increase.
If you need some clarification, don't hesitate to shout.
73, Bob
==================================================
Sierra Mods ... Clark Fishman, WA2UNN
My friend, KF2EW just finished building a Sierra and I had given
him
some mods I found on the WEB. The 2 we did was to
change the final
transistor to a MRF237 and to change the choke feeding the +12
volts to
the final collector into a 4 to 1 impedance transformer.
Before we
changed the choke the rig put out a reading of 1 watt (actually
the
wattmeter was not calibrated for use on 3.5 MHz and the rig was
probably
putting out over 2 watts) . I had a core that they used for
the RF
choke so I wound up some #26 wire on an electric drill and wound
10
bifilar turns on the core. The center tap of the
windings(formed by the
start of one winding and the end of the other winding) goes
to the
collector and one feelead goes to +12 and the other to the output
lowpass filter. The output doubled. I took an
accurate power output
measurement and the modified Sierra was putting out 5.4 watts on
80
meters.
Have fun
Clark Fishman WA2UNN
======================================================
I modified my Sierra
for RIT/XIT and wrote it up in the Dec. '1996 QRPp
(page 60). I set it up for -1 / +6 khz XIT/RIT for split
operation in
DX pile-ups.
Also, the K2 has two VFO's which can run wide split RX/TX. (
http://www.elecraft.com )
73, Eric
=======================================================
Hi all:
A quiet weekend in Glen Rock (thankfully... no pun intended).
Thursday at
the in-laws in Hunterdon as usual and the rest of the weekend at
home. No
shopping for me, thank you very much. Call me Scrooge.
Not much operating time at N2SMH. I chose to spend my radio time
doing some
Sierra tweaking. On one of my recent West Coast trips, I picked
up a bag
full of silver mica capacitors for the express purpose of
replacing the
ceramic and mono caps in the band-module output filters. Less
loss and all
that good stuff. Some people blanch at the prospect of removing
components
from plated-through boards. Not me. A good hot iron, a roll of
braid and a
decent-quality solder sucker and off I go. Sometimes I like doing
this
stuff more than operating. Depends on what mood I'm in, I
suppose.
After replacing all the caps, I rechecked my power output.
Unscientific as
I am, I can't really report hard figures on what I gained in
terms of
output. But I did pick up at least something on all bands. Oh, I
also
replaced Q5 (buffer between transmit mixer and driver), which
originally
was a J309, with a J310 for a little more oomph into the driver.
That
seemed to help a little, too. And seeing as how I'd replaced the
stock 36V
zener at D7 with a 43 V diode, I thought I'd try running with a
higher
input voltage to see what that would do for me. At 16 V input,
I'm now
getting 3.3 W output on 40 meters. At about 13.5 V input (fully
charged gel
cell), I'm seeing 2.5 W out on 40. Didn't try 16 V input with
other bands
yet but I will sometime just for grins.
The best part was gaining a new band on the Sierra. I'd built a
10-meter
band module almost a year ago and had never been able to get any
output on
10. I knew going in that the tuned circuits would be a bear to
peak up
(extremely high Q) and try as I might, I was never able to get
even a
whisper of movement on the WM-1. I tried, oh, has to be a dozen
different
times with no luck. "Must be the toroids," I figured at
one point. Removed
*all* of them in a fit of exasperation, rewound them, and *very
carefully*
prepared the leads and reinstalled them. That wasn't it.
So this weekend, with the idea of replacing the output-filter
capacitors in
mind, I went at the 10-meter module again. This time was
different. I have
output on 10 meters! Yay! And just in time too, with solar flux
heading in
the right direction. I measured 1.1 W out on 10 once I got it
peaked. It
was simply a matter of being extremely careful and methodical.
George
(N2APB), I think you'd said that you were in the same boat with
your
Sierra. Keep trying, guy... it can be done. I think I can get a
little more
output, too. I remembered after the fact that I should also
repeak the
pre-mix trimmers. Gonna have to go back and do that on all the
modules.
Last night I had my one and only QSO of the weekend. Heard WA4CND
calling
CQ on 40. Maury was pretty weak, about 339. He answered me on the
first
call and it turned out that he was running 4 W on an MFJ rig. His
QTH is
Louisville, KY. Goes to show what a little 10.7-cm flux can do
for you.
Typically, I'd never expect to get an answer from so weak a
station. Gotta
love it.
72 David N2SMH
Glen Rock, NJ
=============================================
George:
I must admit that, to my own disappointment, there was no magic
involved in
coaxing 10-meter output. Like you, I'd been thinking about
sending the damn
thing to QRP Bob in the hopes that he could figure out what was
wrong.
Well, nothing was wrong, and there probably is nothing wrong with
yours.
Bob has told me that these filter circuits have a very sharp
peak. I don't
remember having too much trouble with my 12-meter module but I
know that
it, too, has a pretty sharp peak. As you go down in frequency,
the peaks
get broader and broader (as the tuned circuits' Qs get lower).
So it wasn't the SM caps or toroids that got it peaked, but
rather a very
methodical approach. The two trimmers involved are C33 and C36.
What I did
was to move C33 just a couple of degrees clockwise. Then, I
v-e-r-y slowly
rotated C36 over 360 degrees while intently watching the WM-1's
needle (on
100-mW scale). If I saw no movement, I moved C33 a couple more
degrees and
repeated the process with C36. Eventually, on one of these
cycles, the
wattmeter kicked up ever so slightly. Bingo! Now I knew I was in
the
ballpark and the rest was fine tuning. VERY fine tuning, mind
you. It is
*so* touchy. If you so much as breathe on those trimmers, they go
out of
whack.
I'm a pretty impatient person so for whatever reason, I'd never
before
worked up the patience to go at the process in this manner. But
this seems
to be the way it must be done.
Before you go about replacing the caps in your modules, you might
want to
consider something that I was remiss in myself. The September
1995 QRPp has
an article by Dave Meacham, W6EMD, on optimum filter-component
values for
the Sierra. If getting the absolute correct impedance match for
your filter
is an issue for you, you probably want to use Dave's values and
not the
stock values as you rebuild your modules. Me, I'm lazy and didn't
do it.
Someday I'll probably end up doing this all over again as a
result. If you
don't have the 1995 issues, I can make you a copy and send it
out. Oh, and
the December 1996 issue has a great article by Bob Follett on
boosting
Sierra output. That article is kind of what got me started on
this little
exercise. It pretty much covers the waterfront on the
possibilities for
mods to the output stages, including some previously unpublished
tweaks
from Wayne himself.
Clark and I talked about his output-stage mods at the last
meeting. I'm not
that ambitious yet. I tend to do this stuff in stages anyway. I
don't know
if I'd ever go that far, but then, I resisted putting in a KC-2
for a year
or so and now I'm very happy that I did.
The Rainbow bridge sounds like it would be a good addition. Yet
another
rainy-day project!
Pete Hoover's bandspread article was quite interesting. It
doesn't look
like too difficult of a mod, either. Something else for the brain
to
cogitate on, right? And as far as the homebrewed Sierra, thanks
for the
pointer on more pictures. I will check them out later today. That
was a
very impressive article and I told Doug that it was a highlight
of the
issue for me. When I saw that Wayne had gotten the ARRL to put
his article
in the Handbook, I figured it was a nice feather in his and
NorCal's caps.
I never *dreamed* that someone would actually try to build one
from
scratch! Nick did a jaw-dropping job. That is real homebrewing.
I'd love to
see that rig someday.
OK... lunch time. Talk to you later.
72 David N2SMH
Glen Rock, NJ
===============================================
Well, this weekend saw yet another round of playing with Sierra
band
modules, in particular the transmit bandpass filter. I'm not a
power
monger. I don't necessarily want (or need) my rig to have a full
gallon of
output. But I am interested in "optimizing" Wayne's
design. An article in
the September 1996 QRPp by Bob Follett got me headed in this
direction and
I think I'm getting close to the end... maybe.
Last time around, I replaced all the capacitors in the output
filter with
silver micas. This bought me a modest increase in output on some
bands but
not all. Recently, I was reading (and re-reading, as I often do)
old QRPp
issues and was going through Wayne's original article on the
Sierra.
December 1994 issue, I think. In that article, Wayne mentions
compressing
the winding on L6 and spreading L5 to increase output. Follett
mentions
taking a turn off of L5 as well.
So I opened up each module and starting compressing L6. Well, the
results
were quite rewarding. For example, I *doubled* my output on 10
meters from
a scant 1 W to a solid 2 W. Don't mean to make you jealous here,
George,
but the ol' WM-1 don't lie :-). I'm up to 2.3 W output on 12
meters. I saw
improvements on all bands. In my rig, 40 meters has always had
the most
output and I'm up to 3 W there with 13.8 V input. All these
measurements,
by the way, were from 13.8 V input with a 50-ohm HB load. When I
use a 16 V
supply, I'm seeing at least 0.6 W more output on all bands.
Almost 4 W on
40. Someday, I'd love to look at the waveform on a spectrum
analyzer. I
wonder what, if anything, I've done bad wrong to my harmonic
suppression.
The mystery band is 15 meters. That one is giving me fits. I
can't get
output higher than 1.9 W no matter what I do. Compress L6, take a
turn off
L5, tweak L3 and L4... doesn't matter. I even thought I lost the
module
completely at one point. After one unsolder/resolder cycle of a
toroid, I
had no output at all. Seems I had just completely altered the
tuned
circuit's peak and couldn't find it nohow. That had me worried
for a while.
But it lives... albeit at 1.9 W. It's weird when you can get more
output on
10 and 12 meters than you can on 15. Oh, and with the 16 V
supply, I get
*no* output on 15 meters. If I throttle back to 13.8V, I get my
1.9 W
again. Not sure why that is. I might have to go to the gurus on
this one
(N6KR and/or W6EMD).
In between all the tweaking, I managed to make a few contacts in
the MI-QRP
test. Not enough to write home about, maybe 15 or so. Yesterday,
17 meters
was way open. Worked K7QD in Idaho for a new QRP state (makes
40). And I
spent a good 45 minutes in a pileup for a KH8 station (that's
American
Samoa if you don't have a chart handy). No, I didn't get him. But
he was
*loud* in north Jersey, at least 569 on my W3EDP wire. You gotta
love that.
The high bands are back! Anybody work him?
72 David N2SMH
Glen Rock, NJ
============================================
As you can see, the following goes back a-ways. But I had alluded
to this
Sierra modification a couple of weeks ago. It's the one that
enables me to
use my Wilderness Sierra to check into the Knightlites net
(occasionally)
on 3686.4 MHz and to listen to 20 or 15 meters SSB while building
or
modifying other gear.
This will hopefully get you started. There was some followup
stuff I had
from off-line discussions with Wayne... as usual, I needed a
little bit of
hand-holding. I'm pretty sure I have that in hard copy at home
and I just
have to dig it up. But this is Wayne's original note to
"Rich" (not sure
who he is) on QRP-L and I took my cues from this description. It
does work
very well. The additional material I have is basically Wayne
confirming
that I had interpreted his instructions correctly and providing a
smidge
more detail, as I recall.
I would point out that output power up in the Novice band on 80
meters is
somewhat reduced. I get about 2W or maybe a bit more in the low
end of 80.
Up there at 3.868 MHz, I think I'm looking at closer to 1W. We
are
operating somewhere outside the design parameters here...
72, David N2SMH
Glen Rock, NJ
============================================
>From burdick@interval.comSun Feb 25 11:42:04 1996
Date: Sun, 25 Feb 1996 05:25:26 EST
From: Wayne Burdick <burdick@interval.com>
To: Multiple recipients of list <qrp-l@lehigh.edu>
Subject: Re: Sierra ABX, plus: VFO range switching, and receiving
USB/LSB
Hi Rich,
Glad you like the ABX mod. I use it all the time now and
really love it.
I made another mod today that you might like to try: a VFO range
switch
that lets me get up into the SSB parts of the band. It's
fun to listen to
LSB on 160 through 40, and you can listen to USB as well if you
add a BFO
switch.
To add VFO range switching:
Put a small (very small) SPDT-center off toggle switch under the
PCB, at
the far bottom right-hand corner of the front panel.
Connect the center
terminal of the switch to where the VFO tuning cap and the 180pF
cap meet.
Next, put a 33pF silver mica or NPO ceramic disc from one side of
the
switch to ground, and a 75pF from the other side to ground.
Result: about 0-150kHz in the OFF position (center),
150-250kHz w/ the
33pF cap, and 300-400kHz with the 75pF cap. You can use
different caps if
you want complete overlap. Note that the tuning is not as linear
in the
higher ranges and doesn't cover exactly 150pF. This is
because the
inductance has stayed fixed.
Also note that you may have to reduce the size of the 180pF cap
to take
account of the capacitance added by the switch, even in the
center-off
position. In my case, I had to add a 1200pF polystyrene cap
in series with
the 180pF cap to get it down to about 160pF. You may not
have to do this
if you have enough range left in the VFO setting trimmer.
To add the LSB/USB switch:
Mount another small toggle switch (DPDT, *not* center off) as
close as
possible to the BFO crystal (possibly between the RF and AF gain
controls).
The crystal must then be rewired from the switch common to C16,
the
original trimmer. The "LSB" side of the switch
then goes through the 39uH
choke to ground, and the "USB" side can go through an
additional 50pF
trimmer to ground.
To align the BFO, adjust the original trimmer in the
"LSB" position, then
adjust the new USB trimmer in the "USB" position.
Note that LSB/USB are reversed on 10 and 12 meters.
Have fun! I still hope to do an SSB adapter for the Sierra
converter
sometime, and this is the first stage of the modification.
73,
Wayne
N6KR
=========================================
See the G3YCC website
for some additional mods
[END]