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20 Watt QRPLabs Dummy Load for Sale?

Mark K0ABD
 

 
Hi Folks,

I'm in the process of learning how to make a simple & lightweight QRP diploe antenna. Meanwhile, I'd like to practice CW & get aquainted with my QCX40. 
 
From what I understand, I shouldn't power on the rig without an antenna or dummy load. 
 
This rig will accept any 50 ohm 5-20 watt dummy load with a female BNC connector, right?
 
Would anyone be interested in selling an assembled QRPLabs 20 watt QRP dummy load?
 
If not, maybe a suggestion on another quality one for sale by a different vendor?
 
Thank you,
Mark, K0ABD
 

Marty NR3Z
 

Mark,
    QRP Guys also has a QRP dummy load kit for $10.  All parts are through hole and very easy to build.  I have also built the QRP dummy load from  3rd Planet Solar / KC9ON to learn how to solder SMT part.
72,
Marty NR3Z
Skitch@...
NR3Z@...

jjpurdum
 

Another possibility is to modify the DL that was featured in QST (Nov, 2018), but downsize it for QRP use. We did that and it looks like this:


We used a 250W RF resistor (eBay #401311455234) which costs about $5. Our experience is that, with a 4"x1" aluminum heat sink (eBay #332908504318), you can get about 10-15 seconds of "tune time" with a 250W resistor running at 35W. With a massive (read non-portable) heat sink you might be able to approach its rated dissipation, but don't count on it. (We tried 100W and, after about 5 seconds, the top half of the resistor went into low earth orbit). The software is essentially the same as the QST version and also used a small OLED to display the power. (Yes, this is sort of a plug for our upcoming book, which does feature the Mini DL.)

Jack, W8TEE


On Thursday, November 7, 2019, 8:36:27 AM EST, Marty Squicciarini <skitch@...> wrote:


Mark,
    QRP Guys also has a QRP dummy load kit for $10.  All parts are through hole and very easy to build.  I have also built the QRP dummy load from  3rd Planet Solar / KC9ON to learn how to solder SMT part.
72,
Marty NR3Z
Skitch@...
NR3Z@...

Steve in Okinawa
 

You may have had a defective 250 watt resistor if it popped with 100 watts on a large heat sink. I can run 100 watts indefinitely into one mounted on an old CPU heat sink with a small PC fan. Having said that, I DID blow up a 100-watt termination mounted similarly when I slightly exceeded that rating for an instant, and also destroyed a 250-watt termination when I lost track of what a linear amplifier was putting out. Currently have 4x 250 watts on order for a dummy load for said amplifier, Cantenna-style. 

jjpurdum
 

There's always a chance that we had a defective resistor. However, the heat sink isn't all that big, because we wanted it to fit in a shirt pocket, yet still have a power display and the ability to tune QRP loads. After the one blew up, we watched the temperature with an infrared temp gun and the 250W got very toasty very quickly at 100W. I'm sure your heat sink is much larger and, better safe than sorry.

Jack, W8TEE

On Thursday, November 7, 2019, 9:46:16 AM EST, Steve in Okinawa <sfab43@...> wrote:


You may have had a defective 250 watt resistor if it popped with 100 watts on a large heat sink. I can run 100 watts indefinitely into one mounted on an old CPU heat sink with a small PC fan. Having said that, I DID blow up a 100-watt termination mounted similarly when I slightly exceeded that rating for an instant, and also destroyed a 250-watt termination when I lost track of what a linear amplifier was putting out. Currently have 4x 250 watts on order for a dummy load for said amplifier, Cantenna-style. 

Steve in Okinawa
 

OK, your heatsink sounded larger than pocket-size. The resistor spec sheets show how quickly they derate with temperature, so there might be little to gain using a higher nominal power resistor. My QRP load here uses a 100-watt resistor but quickly gets too hot to touch with 25 watts in.

Richard G4TGJ
 

It's fine to power on your QCX without an aerial or dummy load provided you don't transmit. You can set it into practice mode so that you can send without actually transmitting.
--
73
Richard
G4TGJ

Mark K0ABD
 

Hi Richard,

The reason I brought this up is that another QRPLabs Group member told me he fried the output transistor of his QCX40 when turning it on after assembly.

You're saying that it is totally safe to turn on my QCX40 & practice, without an aerial or dummy load, just as long as I don't transmit?

This means I don't need to wait to familiarize myself with my new rig until I obtain one of these.

Although, if I start to build my own from kits it would be a good idea to get one.

thank you,

Mark/K0ABD

Mark K0ABD
 

On Thu, Nov 7, 2019 at 08:36 AM, Marty Squicciarini wrote:
QRP Guys
Marty,

Someone else contacted me via email & suggested that. Currently I have no soldering iron. I'd like to wait until I can get a decent one, because from what I now understand I can't skimp on a soldering iron. I'll have a look at that website to see if they offer an assembled one for sale.

thanks,

Mark/K0ABD

Mark K0ABD
 

Thanks for replies, all.

I would have responded sooner, except I had no internet yesterday & only partially on Wednesday.

Mark/K0ABD

Alan G4ZFQ
 

You're saying that it is totally safe to turn on my QCX40 & practice, without an aerial or dummy load, just as long as I don't transmit?
Mark,

Totally safe if you do not make a mistake and transmit!
The reason a dummy load is recommended is that it has happened in the past. Since then the firmware has been modified to make it less likely, but not impossible.
Also it has been said that alignment sometimes works better if a load is present although that is not so important.

73 Alan G4ZFQ

Mark K0ABD
 

I appreciate the response, Alan.

Nice to know I don't have to wait until I get a dummy load/antenna to start practicing. This rig may have been built in 2017 or 2018. I just got it & haven't powered it up yet because I don't have a battery. After I obtain one I'll have to check the firmware to ensure it's the latest.

thanks,

Mark

Mark K0ABD
 

Thanks all for the helpful suggestions. I also appreciate those who have contacted me directly via email & taken the time to instruct me.

Marty NR3Z
 

I agree with you in that you don't want to skimp on the soldering iron and I think on the SoftwareControlledHamRadio  list there were a few recommendations.  I have the Hakko Fx888D and it is worth every penny.
72,
Marty NR3Z
Skitch@...
NR3Z@...



On Fri, Nov 8, 2019 at 7:28 AM Mark K0ABD via Groups.Io <mboston72=yahoo.com@groups.io> wrote:
On Thu, Nov 7, 2019 at 08:36 AM, Marty Squicciarini wrote:
QRP Guys
Marty,

Someone else contacted me via email & suggested that. Currently I have no soldering iron. I'd like to wait until I can get a decent one, because from what I now understand I can't skimp on a soldering iron. I'll have a look at that website to see if they offer an assembled one for sale.

thanks,

Mark/K0ABD

Mark K0ABD
 

OK, Marty, thanks.

Mark K0ABD
 


I'd rather not take any chances in destroying this new rig. I think I'll wait until I get a dummy load before turning it on.

What about this?

Mcbazel Surecom Male PL259 Plug DC to 1.0GHz 25W Watt 50 Ohm Dummy Load

Or this?

Mcbazel Surecom PL259 Male Plug DC to 1.0GHz 15W Watt 50 Ohm Dummy Load

According to the reviews it can be used for HAM antenna setups.

Then, I would just need a male BNC to female SO239?

thanks,
Mark/K0ABD

Bill Cromwell
 

Hi,

If you want to convert form the BNC connector on your radio to SO-239 you should get a short jumper cable to connect the the two fittings. The greater weight of that SO-239 hanging on your BNC connector will ruin your radio antenna connector in a short time. With the jumper cable tyhe weight can lay on the table. Been there - done that.

73,

Bill KU8H

On 11/8/19 2:40 PM, Mark K0ABD via Groups.Io wrote:
I'd rather not take any chances in destroying this new rig. I think I'll wait until I get a dummy load before turning it on.
What about this?
Mcbazel Surecom Male PL259 Plug DC to 1.0GHz 25W Watt 50 Ohm Dummy Load <https://www.amazon.com/Mcbazel-Surecom-0014-0154-PL259-1-0GHz/dp/B07MP1ZJHB/ref=sr_1_1_sspa?crid=2L76DDGMJZRKL&keywords=pl259+dummy+load&qid=1573240859&sprefix=pl259+dumm%2Celectronics%2C156&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzT1I5SkZWTFFETVZEJmVuY3J5cHRlZElkPUEwMDk2NTE0MU5EM0I4VExKVkk5SCZlbmNyeXB0ZWRBZElkPUEwMzI3MDUzMVkwREVRM0pWTVg5MSZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=> Or this?
Mcbazel Surecom PL259 Male Plug DC to 1.0GHz 15W Watt 50 Ohm Dummy Load <https://www.amazon.com/Mcbazel-Surecom-0014-0153-PL259-1-0GHz/dp/B07MH6WPZL/ref=sr_1_21_sspa?keywords=pl259+dummy+load&qid=1573241538&sr=8-21-spons&psc=1&smid=A263LSCPZJCHO0&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFRSkxRQlc2WktOVzYmZW5jcnlwdGVkSWQ9QTA5NDI1NTEzVlhHNTBNRktZUEtGJmVuY3J5cHRlZEFkSWQ9QTAzMjY5MjkzSlFaSlpRQUdGU0xNJndpZGdldE5hbWU9c3BfYnRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==> According to the reviews it can be used for HAM antenna setups.
Then, I would just need a male BNC to female SO239 <https://www.amazon.com/DHT-Electronics-coaxial-adapter-female/dp/B00CW5JT58/ref=pd_bxgy_23_2/142-5041965-0985129?_encoding=UTF8&pd_rd_i=B00CW5JT58&pd_rd_r=06e4eefd-3c88-425d-bb2d-0c79811187b0&pd_rd_w=aELqw&pd_rd_wg=L4RLr&pf_rd_p=09627863-9889-4290-b90a-5e9f86682449&pf_rd_r=HXQGNK8H8PTANQ0A2HXQ&psc=1&refRID=HXQGNK8H8PTANQ0A2HXQ>?
thanks,
Mark/K0ABD
--
bark less - wag more

N3MNT
 

I would use something like this with the dummy load you suggested above.  No strain on Radio BNC.
https://www.amazon.com/SO239-Female-Coaxial-Antenna-Mobile/dp/B01IT2GS42/ref=sr_1_12?keywords=bnc+male+to+UHF+female&qid=1573253033&s=electronics&sr=1-12

Shirley Dulcey KE1L
 

Even without a kit, most home builders can assemble a do-it-yourself dummy load.

The essential ingredient is a collection of ordinary carbon composition or carbon film resistors that add up to 50 ohms in series, parallel, or some combination of the above, and can handle enough power. I have a homemade dummy load that consists of three 2W 150 ohm resistors soldered to the body of a PL-259 at the near end, and connected to a short piece of insulated wire at the far end. That's an old connector designed for crimping onto RG-58, but the same concept will work with a standard size PL-259. I bought the resistors a while back at a store that carries repair parts for TV repair shops.

You can also use a larger number of lower wattage resistors mounted on perfboard. One possible configuration would be 20 1/4W or 1/2W 1K resistors connected in parallel. There would be a fair amount of soldering to do for that configuration but the build would otherwise be straightforward.

For a QRPp load you could use a smaller number of resistors in various connections. Two 100 ohm resistors make a simple arrangement. Higher power arrangements would include 5 10 ohm resistors in series, and eight 100 ohm resistors in a series-parallel arrangement. (Four parallel strings of two 100 ohm resistors in series.)

Any of these ideas should produce a dummy load that is adequate for the HF bands, and can be built entirely out of parts that many hams will have in their parts collections. If you want one with good VHF performance it's probably better to stick with one of the kit designs.



On Fri, Nov 8, 2019 at 2:12 PM Mark K0ABD via Groups.Io <mboston72=yahoo.com@groups.io> wrote:
OK, Marty, thanks.

Mark K0ABD
 

Bill,

I appreciate this tip that will prolong the life of my rig! I just ordered that on Amazon.

Mark/K0ABD