Archive for the ‘qrp’ Category
Even better low-pass filters for transmitters
November 27th, 2016 | 
Author: The last issues of QEX have featured two interesting articles by Gary Cobb, G3TMG. He outlines the advantage of using Zolotarev designs for the harmonic suppression filters of transmitters, giving even better suppression of the second harmonic than the more common Chebyshev or quasi-elliptic filters.
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| Chebyshev low-pass filter from the GQRP data sheet (issue 1) |
My interest in this was triggered by the test of the Ultimate 3 QRSS/WSPR kit from QRP Labs in the Nov 2016 QST. The review was positive overall, but it was remarked that the harmonic suppression does not meet FCC requirements (-43 dBc or better). I am not sure whether this is due to PCB layout issues, or if better filters can alleviate it, but I note that the design uses the simplest filter of the ones I have listed here.
The evolution of filters for use for harmonic suppression follows at least these three steps:
- Chebyshev type I filters with equiripple in the passband and a monotonically falling, maximally flat stopband. A 7-pole version with three inductors and four capacitors in a pi-network has been around for a while, in e.g. the old recommendation from the GQRP club. It was based on the QST paper “Low-pass filters for amateur radio transmitters,” Ed Wetherhold, W3NQN, Dec. 1979. Two designs for a 20 m filter were given there:
1) Max. ripple in passband: 0.00731 dB, attenuation at 28 MHz: 40.7 dB
1) Max. ripple in passband: 0.00960 dB, attenuation at 28 MHz: 34.5 dB 
Second-harmonic optimized low-pass filter from the
GQRP data sheet (issue 2)An improved stopband was the topic of W3NQN’s article “Second-harmonic optimized low-pass filters” in QST Feb. 1999. Here there is one additional capacitor as the central inductor is made into a parallel resonance which gives a zero in the stopband, based on an idea by Jum Tonne, WB6BLD. The design goal is that this zero should be at the second harmonic frequency. W3NQN proposed to call this a Chebyshev filter with a zero (CWAZ) filter, but it is more correct to call it a quasi- or pseudo-elliptic filter as remarked by G3TMG. It increases the attenuation at the second-harmonic in the 20 m design to better than 60 dB. This design is the basis for the current (Issue 2) G-QRP technical sheet. This would also be interesting to test in the QRP Labs Ultimate 3 transmitter kit.
Zolotarev low-pass filter from the Nov/Dec 2016 QEX article G3TMG in the new QEX articles has noticed that the passband is over-specified in the above filters as the lower 60% or so of the passband is unused. The Zolotarev design allows for more passband ripple in this part where it does not matter. The advantage is even better stopband attenuation. A measured example for a 60 m filter has a passband ripple of 0.17 dB and a stopband attenuation at the second harmonic of 71 dB. This filter has the same component count as the previous one, but the filter is no longer symmetric like the two previous ones. The increase in second-harmonic suppression is not as great as the going from the first filters to the second, but should still be worth the effort.
The papers, which are well worth reading, are:
- Gary Cobb, G3TMG, Zolotarev low-pass filter design, QEX, July/Aug 2016.
- Gary Cobb, G3TMG, A more efficient low-pass filter, QEX, Nov/Dec 2016.
The post “Even better low-pass filters for transmitters” first appeared on the LA3ZA Radio & Electronics Blog.
Even better low-pass filters for transmitters
The last issues of QEX have featured two interesting articles by Gary Cobb, G3TMG. He outlines the advantage of using Zolotarev designs for the harmonic suppression filters of transmitters, giving even better suppression of the second harmonic than the more common Chebyshev or quasi-elliptic filters.
|
| Chebyshev low-pass filter from the GQRP data sheet (issue 1) |
My interest in this was triggered by the test of the Ultimate 3 QRSS/WSPR kit from QRP Labs in the Nov 2016 QST. The review was positive overall, but it was remarked that the harmonic suppression does not meet FCC requirements (-43 dBc or better). I am not sure whether this is due to PCB layout issues, or if better filters can alleviate it, but I note that the design uses the simplest filter of the ones I have listed here.
The evolution of filters for use for harmonic suppression follows at least these three steps:
- Chebyshev type I filters with equiripple in the passband and a monotonically falling, maximally flat stopband. A 7-pole version with three inductors and four capacitors in a pi-network has been around for a while, in e.g. the old recommendation from the GQRP club. It was based on the QST paper “Low-pass filters for amateur radio transmitters,” Ed Wetherhold, W3NQN, Dec. 1979. Two designs for a 20 m filter were given there:
1) Max. ripple in passband: 0.00731 dB, attenuation at 28 MHz: 40.7 dB
1) Max. ripple in passband: 0.00960 dB, attenuation at 28 MHz: 34.5 dB Second-harmonic optimized low-pass filter from the
GQRP data sheet (issue 2)An improved stopband was the topic of W3NQN’s article “Second-harmonic optimized low-pass filters” in QST Feb. 1999. Here there is one additional capacitor as the central inductor is made into a parallel resonance which gives a zero in the stopband, based on an idea by Jim Tonne, WB6BLD. The design goal is that this zero should be at the second harmonic frequency. W3NQN proposed to call this a Chebyshev filter with a zero (CWAZ) filter, but it is more correct to call it a quasi- or pseudo-elliptic filter as remarked by G3TMG. It increases the attenuation at the second-harmonic in the 20 m design to better than 60 dB. This design is the basis for the current (Issue 2) G-QRP technical sheet. This would also be interesting to test in the QRP Labs Ultimate 3 transmitter kit.
Zolotarev low-pass filter from the Nov/Dec 2016 QEX article G3TMG in the new QEX articles has noticed that the passband is over-specified in the above filters as the lower 60% or so of the passband is unused. The Zolotarev design allows for more passband ripple in this part where it does not matter. The advantage is even better stopband attenuation. A measured example for a 60 m filter has a passband ripple of 0.17 dB and a stopband attenuation at the second harmonic of 71 dB. This filter has the same component count as the previous one, but the filter is no longer symmetric like the two previous ones. The increase in second-harmonic suppression is not as great as the going from the first filters to the second, but should still be worth the effort.
The papers, which are well worth reading, are:
- Gary Cobb, G3TMG, Zolotarev low-pass filter design, QEX, July/Aug 2016.
- Gary Cobb, G3TMG, A more efficient low-pass filter, QEX, Nov/Dec 2016.
The post “Even better low-pass filters for transmitters” first appeared on the LA3ZA Radio & Electronics Blog.
Taking your QRP signal to the next step.
I was reading NY4G's blog a week or two ago and came across a great post that I wanted to share with my readers. I emailed him about reposted it but never heard back so here goes.......It is full of great DXing tips!
DXing Tips For Little Pistols Like Me
OK I admit it I am more often than not a little pistol. More than likely, I am trying to make a contact at 5W.
Keep in mind two things - the heavy lifting is done not by you but by the DX who is trying to dig you out
of the mud. Some are more willing than others. Of course, the second thing is your persistence. If you
don't go away after he has worked stronger stations - chances are he will try to work you.
Taking your QRP signal to the next step.
I was reading NY4G's blog a week or two ago and came across a great post that I wanted to share with my readers. I emailed him about reposted it but never heard back so here goes.......It is full of great DXing tips!
DXing Tips For Little Pistols Like Me
OK I admit it I am more often than not a little pistol. More than likely, I am trying to make a contact at 5W.
Keep in mind two things - the heavy lifting is done not by you but by the DX who is trying to dig you out
of the mud. Some are more willing than others. Of course, the second thing is your persistence. If you
don't go away after he has worked stronger stations - chances are he will try to work you.
Here are some additional tricks to slay that DXing dragon I learned from Brian Smith WO9I. Some are
Here are some additional tricks to slay that DXing dragon I learned from Brian Smith WO9I. Some are
verbatim and some are paraphrases. Some I omitted but most I kept. Some I added to from my own
experience. Here is the URL: http://www.ybdxc.net/2014/10/14/25-dxing-tips-for-the-little-guy/
(1) "Sharpen your sword. Never embark on a DX quest without first tuning-up your rig. Make sure
(1) "Sharpen your sword. Never embark on a DX quest without first tuning-up your rig. Make sure
your PA is not putting out into a high SWR situation - wasting your meager power into heat as
feedline loss. Sometimes you get only one shot at a rare station before the rest of the world
catches up with you."
(2) See which bands are open before starting the hunt. Bandconditions.com is a good resource.
(2) See which bands are open before starting the hunt. Bandconditions.com is a good resource.
A reading of 100 for a band indicates that your 1 watt or 5 watt signal stands a good chance
of being heard. Yet another way to do it is to listen for the band beacons. Make sure your foray
into the ether is worth the effort. WWV (at 5, 10, 15 and 20 MHz) gives propagation info at 18 minutes
past every hour. Look at the cluster and listen for on-going QSOs. See how strong the signals are in
the cluster spots - even if it is a country you don't need. If you are looking for an entity in the
Balkans - see how loud the DX are around your hunting ground.
(3) Never send “CQ DX.” Rare and even not so rare DX station seldom answer such calls, especially
(3) Never send “CQ DX.” Rare and even not so rare DX station seldom answer such calls, especially
when transmitted by weak signals.
(4) Use the contests. If you could operate only a few days a year, I’d pick the weekends of the major
(4) Use the contests. If you could operate only a few days a year, I’d pick the weekends of the major
international contests such as the CQ World-Wide, the ARRL DX Contest, CQ WPX, and so forth. I
gnore your score; the idea is to bag DX,you need for whatever - DX Marathon, DXCC, band slots.
These events are like for the little kid in the candystore - except you are truly a little kid
(or a small fry). During contests, the bands are crawling with stations, some rare and some not so
rare. If you are doing DX Maraton - you need most of if not many. The QSOs are short, and best
of all, wide dispersal of the big guns.
(5) After the contest, hang around, to see if rare stations—particulary DXpeditions—want to hang
(5) After the contest, hang around, to see if rare stations—particulary DXpeditions—want to hang
around to see if anyone else wants to work them. The big guns are usually in their holsters by
then, which is exactly why you’re still blazing away.
(6) Peek into the DX alleys, which are usually located just inside the General band
(6) Peek into the DX alleys, which are usually located just inside the General band
(14.026 Mhz, etc.). On non-contest days many rare stations hang out here. However, these are also
the most congested places of all. But hey, sometimes the propagation gods smile on you.
(7) Know when to quit. Don’t spend your life trying to break pile-ups; when the band’s open,
(7) Know when to quit. Don’t spend your life trying to break pile-ups; when the band’s open,
there’s plenty of good stuff elsewhere (usually from the same region), and lots of big guys don’t
know how to root it out. How to tell good odds from bad? Good odds: the DX station is booming,
the op is working stations quickly, other station from your call area are getting through, and/or you
don’t hear much competition. Bad odds: weak DX station, slow op, propagation favours other call
areas, pile-up is loud and limitless.
(8) Nail the newcomers. Now for real guerilla tactics: Move to the slow edge of a band and,
(8) Nail the newcomers. Now for real guerilla tactics: Move to the slow edge of a band and,
tuning slowly accross it, listen for the sound of any station coming on the air, such as a
“tuning up” signal, “QRL?” or of course, CQ. Should one of these surface, stop immediately and
listen for an ID. (Ninty-nine times out of 100 it wont be rare DX, but trust me: that 100th time will
more than make up for it.)
Late means wait. As you’re hunting stations coming on frequency, also check for QSOs that are
Late means wait. As you’re hunting stations coming on frequency, also check for QSOs that are
about to end (“73,””TNX FER QSO,” etc.)—and wait for an ID.
(10) Develop DX ears. DX signals rarely sound like statesiders. They’re weaker and more
(10) Develop DX ears. DX signals rarely sound like statesiders. They’re weaker and more
unstable (and those which cross over the North Pole sound “fluttery”). Teach your eardrums
the difference.
(11) Be watchful for 10 or 12 meter openings. Ten meters is the little guy’s equalizer. When the
(11) Be watchful for 10 or 12 meter openings. Ten meters is the little guy’s equalizer. When the
surf’s up on 10, the DX comes in waves, and a puny signal (even a 5 watter) floats just fine.
Ten meters tend to open to a small geographic area at a time (meaning less competition); also,
signal strength can fluctuate wildly within a few minutes. If you find a new one that’s too weak to
work, lock on to it and relax. Within 15 minutes its signal may peak, giving you a clear shot.
(12) WFWL (work first worry later). If an exotic-sounding station appears, don’t look up its
(12) WFWL (work first worry later). If an exotic-sounding station appears, don’t look up its
QTH—pounce! I once heard a 3B8 sending CQ. “What’s a 3B8?” I wondered, but the second he
stopped transmitting, I chased him. Only after the QSO did I discover I had just worked Mauritius.
Rehearse. Rare DX stations are sometimes barely audible, or covered with QRM. A trained ear
Rehearse. Rare DX stations are sometimes barely audible, or covered with QRM. A trained ear
can pull them through, but an untrained ear hears only clutter. So hone your hearing. Practice
working common DX stations (such as G’s and JA’s) with faint signals.
(13) Upgrade. Much of the delectable DX swims in the extra portion of the band. Thus reeling it
(13) Upgrade. Much of the delectable DX swims in the extra portion of the band. Thus reeling it
in is often a question of “How low can you go?” Remember, only 7 percent of all American
amateurs can operate in these murky depths.
(14) Rock around the clock. DX conditions vary with the time of day, so don’t just operate from
(14) Rock around the clock. DX conditions vary with the time of day, so don’t just operate from
7 to 9 o’clock every evening. Vary your routine: Stay up all night on a Friday, rise before dawn
on a Sunday. Remember, sunrise and sunset can produce interesting conditions, so try
them often.
Turn lemons into lemonade. “Bad breaks” aren’t always what they seem. Sometimes they even
Turn lemons into lemonade. “Bad breaks” aren’t always what they seem. Sometimes they even
work to the little guy’s advantage. Example 1: While trying to work a weak ZK1
(South Cook Islands) during a contest. I was dismayed when a loud Californian began blasting
away on a nearby frequency. Then I realized that because of the W6, most people who were
casually tuning around wouldn’t hear the ZK. During brief lull I caught his “QRZ?”, jumped in,
and nailed him instantly. Example 2: A T3Ø (West Kiribati) operating SSB dodged a stateside
pile-up by QSYing to a U.S. CW-only frequency. Just one American moved with him—yours
truly, who fired up a key and worked him cross-mode.
(15) Talk the talk. Even with Q signals, all CW stations don’t sound the same. DX stations favour
(15) Talk the talk. Even with Q signals, all CW stations don’t sound the same. DX stations favour
expressions such as “TKS” (instead of American “TNX”) and “DR” (as in “DR OM BRIAN”).
Soviets often close with “DSW” (a Russian good-luck term). And of course, stations whose
transmissions alternate between “599 K” and “QRZ?” are often worth working. Familiarity with
international callsigns helps, too, as I learned one evening in 1988 when I tuned in Y88POL.
Just another East German, right? But wait! East German suffixes usually have only two
letters … hmmm. Moments later I worked a new one—Antartica.
(16) Less is Morse. Not only CW is less popular than SSB (decreasing your competition), but
(16) Less is Morse. Not only CW is less popular than SSB (decreasing your competition), but
it’s more effective in marginal conditions—a plus for weak stations.
Read the news. Serious operators learn about DXpeditions and such by subscribing to publications
Read the news. Serious operators learn about DXpeditions and such by subscribing to publications
such as QRZ DX? and The DX Bulletin. And for those with packet capability, lots of DX packet
clusters spot rare stations.
(17) Never assume. Once, during a Boy Scout jamboree weekend, I heard a Liberian station with
(17) Never assume. Once, during a Boy Scout jamboree weekend, I heard a Liberian station with
a special callsign, using scouts as ops. No one was answering its CQ, probably because
everyone believed the station was working only fellow Scouts. But when I asked, “Are you
working only Scout stations?” I was rewarded with a “No, you’re 5 by 6”—and a new one.
(18) Beat the bushes. Many people think all the primo DX hangs out on the low ends, but
(18) Beat the bushes. Many people think all the primo DX hangs out on the low ends, but
that’s a fallacy. Ever work Moroco? I did—on a 10 meter Novice CW frequency! And I once
heard Zimbabwe on 21.080. Moral: Don’t just look in the clearings; rummage through the high
weeds, too.
Listen for swan songs. Normally, when sunspots are high, upper HF bands such as 10 and
Listen for swan songs. Normally, when sunspots are high, upper HF bands such as 10 and
15 meters close in the evening. During their final moments, however, strange conditions
sometimes occur. Try to catch each band just before it gives out (see whether any signals are
audible; if so, tune around). As the band dies, most of your competition will give up and
head south. I bagged my first CEØ (Easter Island) under such conditions.
(19) Check and double check the DX call. Don’t just scribble down a DX callsign; make
(19) Check and double check the DX call. Don’t just scribble down a DX callsign; make
absolutely certain you heard it correctly. On CW I’ve worked lots of ops who can’t tell a “4” from
a “V” or an “H” from an “S.” Missing even one dot in a call sign can turn a prize catch
into a busted QSO.
Do they have to be LOUD to work them????
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| Learning a QRP lesson |
1. He was in and out right at the noise floor.
2. He was not at the QRP watering hole so he was running most likely some kind of QRO power.
3. What chance did my QRP 5 watt signal have if I could barely hear QRO signal?
When RA3XM stopped calling CQ I threw my call out there and can you believe he came back to me on my first call!! I was shocked that I made the distance, it was not a long QSO but I did get a 559 signal report and I passed along to him a signal report, my name and that I was running QRP. It became crystal clear to me of something I read on more than one occasion from seasoned QRP op's....you may come across signals that are in and out of the mud, don't short change yourself ( I have done so on many occasions) thinking "they are QRO and in the mud they are never going to hear my peanut signal. Instead throw your call out there and you may be surprised......and when RA3XM came back to me from the noise I was surprised and pleased to make the contact. Spinning the dial once again I hear AN400R booming in (Spanish special event station) I gave him a call and and made that contact as well. On this outing it was not as simple as calling and making a contact there was F6EJN, DK7OB, AN400C, IT9RZU, MI0GH and AN400C all who I called and was not heard. A valuable lesson was learned on this outing.....even if the station calling CQ is in the mud give them a call and you (I was) may be surprised they come back to you.
Do they have to be LOUD to work them????
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| Learning a QRP lesson |
1. He was in and out right at the noise floor.
2. He was not at the QRP watering hole so he was running most likely some kind of QRO power.
3. What chance did my QRP 5 watt signal have if I could barely hear QRO signal?
When RA3XM stopped calling CQ I threw my call out there and can you believe he came back to me on my first call!! I was shocked that I made the distance, it was not a long QSO but I did get a 559 signal report and I passed along to him a signal report, my name and that I was running QRP. It became crystal clear to me of something I read on more than one occasion from seasoned QRP op's....you may come across signals that are in and out of the mud, don't short change yourself ( I have done so on many occasions) thinking "they are QRO and in the mud they are never going to hear my peanut signal. Instead throw your call out there and you may be surprised......and when RA3XM came back to me from the noise I was surprised and pleased to make the contact. Spinning the dial once again I hear AN400R booming in (Spanish special event station) I gave him a call and and made that contact as well. On this outing it was not as simple as calling and making a contact there was F6EJN, DK7OB, AN400C, IT9RZU, MI0GH and AN400C all who I called and was not heard. A valuable lesson was learned on this outing.....even if the station calling CQ is in the mud give them a call and you (I was) may be surprised they come back to you.
Portable QRP operations in the park.
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| Hunting for that one contact |
