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QDX and QMX+ (soon at least) what is the max safe swr?

 

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.?
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73, Dan? NM3A
 

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
 

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.
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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
 

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.?
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73, Dan? NM3A
 

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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I meant QRP Labs ...
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73, Dan - W2DLC
 

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.?
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73, Dan - W2DLC
 

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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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:

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.
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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
 

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
 

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
 

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.
 

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.
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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:

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
 

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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