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I looked and found one thread on the subject but did not see Hans give any definite answers.? I know 1:1 is prefered and best, but the real world doesn't often give us that.? I ask because my 4SQRP tuner is not showing great results on 20M.? And I don't want to switch it's bridge (2:1 max) out to test with a digital swr meter.
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Bob
KG5GTE
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Sometimes the length of coax you are using will do this.? I
recently made a 49:1 for an end-fed half wave and installed the
antenna.? I couldn't get it to dip anywhere at all.? I checked the
coax with an analyzer and it was fine but the resonance was around
8 MHz.? I substituted another shorter piece of coax and the
antenna was spot on for exactly what I expected.
Your mileage may vary, but the coax is the first thing I'd try.
72
Chas - NK8O
On 9/14/24 17:38, Bob Parr via
groups.io wrote:
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Show quoted text
I looked and found one thread on the subject but did not see
Hans give any definite answers.? I know 1:1 is prefered and
best, but the real world doesn't often give us that.? I ask
because my 4SQRP tuner is not showing great results on 20M.? And
I don't want to switch it's bridge (2:1 max) out to test with a
digital swr meter.
?
Bob
KG5GTE
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This tuner has no bypass.? My antenna is in the neighborhood of 1.3:1 without, I think on both 40 and 20.? Just wondering how far I can push it.
?
Bob
KG5GTE
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After blowing the finals in my HB QDX, I used the zeners per
plus a 1N4148 in parallel to L14.
I did this to both the LB and HB QDX's. I run them at 11V with current limited to 1 amp. by a Drok buck/boost device.
I feed a 160 meter full wave loop through an LDG remote auto-tuner, and they see some pretty high SWR's at times. I've not had any blown finals since, YMMV.
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On Sat, Sep 14, 2024 at 06:20 PM, Don wrote:
After blowing the finals in my HB QDX, I used the zeners per
plus a 1N4148 in parallel to L14.
?
I remember seeing several posts about this and a couple other methods to help protect the finals. Including Barb's little board that uses different fet/mosftes for the power amp (shich I have, but have not used yet).? But while I may add something for protection, my question is what is the max safe SWR as built to spec?? Can a standard 9V qdx handle 2:1?? 1.5:1?? that sort of thing.
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Bob
KG5GTE
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It's very difficult to say and SWR is not how you would say it?
2:1 'SWR' can describe (among many R + j variations) a 25 ohm load or a 100 ohm load.? One will apply current stress to the PA while the other will see higher voltages.?
I suspect 1.5:1 would be ok in either case as most rigs operate fine in the real world.? Just stay away from AutoTuners
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Very simple. 1:1 is the max safe SWR. I use a 4 state tuner to
get nearly there and then fine tune while broadcasting until the
SWR indicator on the QMX reads a perfect 1:1. I have never had a
blowout after thousands of POTA contacts with anywhere from 12 to
13 volts input. Sandy KB3EOF
On 9/15/24 12:02, Bob Parr via
groups.io wrote:
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Show quoted text
On Sat, Sep 14, 2024 at 06:20 PM, Don wrote:
After blowing the finals in my HB QDX, I used the zeners
per
plus a 1N4148
in parallel to L14.
?
I remember seeing several posts about this and a couple other
methods to help protect the finals. Including Barb's little
board that uses different fet/mosftes for the power amp (shich I
have, but have not used yet).? But while I may add something for
protection, my question is what is the max safe SWR as built to
spec?? Can a standard 9V qdx handle 2:1?? 1.5:1?? that sort of
thing.
?
Bob
KG5GTE
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I try to minimize the stress I put on the finals of my radios, so I use a nanoVNA to check/tune my antennas before connecting a radio.? At about $60 and smaller than a battery pack, it's a great tool for home or portable use.
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73,
Mike, KL7MJ
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I'm not particularly careful at all. I have an MFJ-971 which I tune for max noise, then a short transmission to get as close as possible to 1:1, which I almost never achieve on either my balanced dipole, or my EFW. I've also used MFJ 949E, and QRP Guys mini tuners. I've been using QRL Labs transceivers for almost 5 years and never blown a final. I have an original QCX, two QCX minis, a QDX, and a QMX. I built them all from kit form, and I keep a bag full of BS170s in the shop just in case, because of all the horror stories I've heard here. I don't know what I may be doing differently, but I've had a lot of success with BS170s withstanding some fairly high SWRs. I suspect it may be because I don't stress myself with trying to squeeze the last milliwatt out of these transceivers.?
--
73, Dan - W2DLC
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I meant QRP Labs ...
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73, Dan - W2DLC
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I'm with Mike.?
The nanoVNA is such an incredibly useful tool, I wonder how I survived without one. It also pinpointed a feeder break to the centimeter, just one of the many magic tricks it contains.
I've also been pretty careful since I bought the QCX classic and all the radios from QRP Labs that inevitably followed. So far my spare pack of finals has remained unopened.?
73s Ted?
2E0THH?
?
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Dan,
Similar experience here. I suspect the majority of people with QRP Labs equipment have seen the same. With reasonable care to minimizing SWR mismatch and duration of the mismatch, risks are low for magic smoke exit.?
--
73, Dan? NM3A
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On Sun, Sep 15, 2024 at 10:15 AM, Sandy wrote:
Very simple. 1:1 is the max safe SWR. I use a 4 state tuner to get nearly there and then fine tune while broadcasting until the SWR indicator on the QMX reads a perfect 1:1.
I use the same tuner and have an MFJ.? I suspect I may have some issues with both that I have not yet had the time to look into further.? I also have a Rigexperts antenna analyzer, but I can't always get all the way to a 1:1.? My 4SQRP seems to make my SWR on 20M worse.? I think I can get it less that 2:1, but I finally put the analyzer on my antenna clean (no tuner) and am about 1.2:1 so I figure that is okay.
?
As I have said several times, I know 1:1 is best.? My QDX and my QMX+ (when built) are both for 9V for what that may matter.? And I can check my SWR several ways, but just wanted to know how far off of 1:1 was redlining.? So far the only answer I got was 1.5:1 should be okay.? Would like to know if 2:1 is okay (knowing that it is NOT optimal).? Just want to avoid having to replace finals... but may have to just play till I blow a set.
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Bob
KG5GTE
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I am running my QMX up to 2:1 without any issues so far, generally stop tuning at 1.5:1. Don't feel the case warming up. Doing only CW at this SWR though.
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Peter
HB9EBE
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My 4SQRP seems to make my SWR on 20M worse.? I think I can get it less that 2:1, but I finally put the analyzer on my antenna clean (no tuner) and am about 1.2:1 so I figure that is okay.
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Bob,
The 4SQRP tuner is great for matching most antennas, but I agree that it doesn't do well with an already close matched antenna.?
?
--
73, Dan? NM3A
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I'm doing a deep dive into cause of BS-170 failures.??
Currently I have finished evaluating peak BS-170 Drain to Source voltage and am in the middle of power dissipation for various SWRs.
- On 160m and 80m Peak voltage exceeds the BS-170 60v spec.? Probably should not use at 12V operation, particularly at 160m
- Using an Elecraft TI ATU there are spikes during tuning of over 100v!
I will am putting together a detail presentation.? Here are a couple of charts:
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Very well put together beginnings of a slide deck.
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Trying to come up with a fixed SWR value is difficult; Partially because like another poster said, impedance is a complex relationship and it is much more than just saying 1.5:1 or 2.0:1.
Modes of operation, duration, voltage peaks (current peaks) all interplay. Then you also have batch variations within a transistor part number (I have seen some really crazy numbers in transistors that were all supposed to be in-spec but maybe 1/2 were not).
--
Tisha, AA4HA
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Both the LPFs and non matched load reflect power back to the BS170s.? This chart shows the effect of the LPFs:
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On Mon, Sep 16, 2024 at 06:38 PM, Tisha Hayes, AA4HA wrote:
Modes of operation, duration, voltage peaks (current peaks) all interplay
Phase of the reflected power is also a crucial factor, not simply its magnitude.??
73, Don N2VGU
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Donald>
I totally agree phase of the reflected power is critical for each of the harmonics, thus affecting how the two components from the LPF and SWR will add or subtract,? and affect the peak voltage across the BS-170.? I have probably 40 scope photos and a few hundred measurements showing this.? Ultimately I will publish much of this info.
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In the past I have stated that BS-170 failures are most likely from excessive D-S voltage.? My effort demonstrates this is the case for both some bands and steady SWR and very bad for ATUs during tuning.??
Anyone with a good scope and the ability to make dummy loads of various impedances can replicate this.?
Can you do similar test?
(FYI I have the same digital scope as Hans).
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Currently I'm in the middle of determining BS170 power dissipation -? a little more difficult? since it require differencing various power dissipations.? So far I have used two approaches and now looking at a third approach to see if I can get more consistent results.
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(In the past I have been responsible for many failure analyses for NASA and the Military so I may be a little anal for Ham applications)
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Bruce Akhurst
Daniel Conklin
Ted 2E0THH
Peter HB9EBE
Tisha Hayes, AA4HA
Donald S Brant Jr