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SW-3B issue

I have just bought from Venus trading…SW-3b, a 3 band 5w radio.

Like many other similar radios this has a little LED which light which is supposed to light up/illuminate on transmitting and on the small screen there is a graduated ‘bar’ graph(?) indication of power output. This is shown in the link, but i’m sure most of these small radios are similiar.

I’ve field tested the radio twice, using a linked dipole from SOTA Beams which uses 6m of RG174 feeder and an 11.5v battery. . No led lights up and there is NO bar graph indication on the screen that shows it is transmitting other than, “TX” being displayed.

I’ve also tested it from my home QTH using a similar length of coax to a simple dipole via a tuner which I use with my home radio a 10w Ten-Tec radio… No LED lights up and again there’s no power indication on the screen I’m transmitting other than “TX”.

However, If I use a dummy load the LED lights up and there is a horizontal bar the full width of the screen. I asked the company about this and they suggested I measure the power output which I did using an 11.5v battery. This showed an output of 5v. and the LED worked and there was a horizontal bar showing I was putting out 5 watts on the radio.

My technical ability exhausted at this point I took it to a an amateur whose technical skills I’d rate very highly. Using his extensive test equipment the radio was shown to put out 5 watts, including altering the SWR readings by varying and even connecting it to a 2m aerial giving an SWR of 4:1. In all the tests the radio worked as it should, the LED illuminated and the bar graph on the radio showed 5 watts going out.

Conclusions
a) He suggested I may have incorrectly used or checked my linked dipole. So I did another test this morning using my home aerial with the same type of coax to a simple dipole. I was able to exchange RST with the first ham I answered. No LED lit up - no bar graph etc., etc.,

b) He did comment that a 6m length of RG 174 coax may be so ‘lossy’ that there was not enough power going out of the radio to illuminate the LED and./or the bar graph.

c) I have used myYou-Kits HB-1b many times using the same linked dipole and through my home QTH aerial and I always get a display output showing ;a power output of up to 5watts.

d) I have been picked up by the RBN network over most of Europe in the couple of times I’ve used this radio.

QUESTIONS

Has anyone else used RG174 with a SW 3b ??

Has anyone experienced similar issues with this radio?

Is it the fault of my ‘lossy’ SOTA beams linked dipole & home aerial ??(I have no other aerials to use/test)

Should I simply insist on returning the radio as it is faulty?

David

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If you don’t have a method of measuring power, frequency and checking for out of band harmonics then you shouldn’t be operating a transmitter.

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Thank you for your helpful reply. Yes I do have a power meter and yes I did check the frequency output which was 100% accurate.

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Hi David,
Can you try a choke balun or add a ferrite clamp(s) on your RG174 ?

73 Éric

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You can try also to put your dummy load just after your 6m of RG174 and check again :wink:

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So you can measure the output into a dummy load and it was correct and the display worked.
That says the radio is functional.

The loss in your 6m RG174 at 20MHz is under 1dB. So you’ll be looking at about 4W at the far end.

It then depends on the circuit for measuring output power. Could be there is significant RF on the coax which is affecting the power measuring circuit. Choke balun would be what I would try next. You can do that by coiling the coax like a solenoid about 10cms in diameter. 6 turns should do. You want it ideally at the far end. But you can see if winding the coax at the rig end around something lossy like your hand and holding it close to your body affects the result.

Dummy load at the far end of the 6m coax would be worth looking at.

6m coax at 20m is pretty close to a 1/4 wave and it may be affecting the impedance seen by the radio, could be enough to upset the power circuitry if it depends on the load looking like close to 50Ohm.

EDIT, Ah, Eric has suggested similar. Also try inserting a 2m patch lead in the feeder and see if you get a better reading.

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I have an SW-3B in regular use with a Sotabeams linked dipole fed with 10m RG174 from time to time (although usually an EFHW but that’s not specific to your question) so pretty much the same setup

Mine is the slightly older model so the bar graph does not give an indication of TX power (as per the original version design) but the red led does indeed light up and TX flash in the display.

Perhaps it’s some peculiarity of the new model and the meter display mod is not quite right

Dec
ei6fr

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Hi David,

I do.
I use the same RG-174 for KX-2, HB-1B & SW-3B.
The length is 5m.
It works same well.

73, Jarek

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HI,

Has anyone else used RG174 with a SW 3b ??
The coaxial cable has nothing to do with your problem. Except if it is faulty. (short-circuit)

Has anyone experienced similar issues with this radio?
No, mine works as expected.

Is it the fault of my ‘lossy’ SOTA beams linked dipole & home aerial ??(I have no other aerials to use/test)
Any type of antenna should work ! Your dummy load is the losiest antenna you can use… :slight_smile:

Should I simply insist on returning the radio as it is faulty?
Try to contact Venus Trading first, they are normaly helpful. Maybe they already encountered this problem.

b) He did comment that a 6m length of RG 174 coax may be so ‘lossy’ that there was not enough power going out of the radio to illuminate the LED and./or the bar graph.
I can’t understand how your friend can suggest you this issue !! The LED is inside the SW-3b, so you can put 1km of cable, it will still light up !

The LED is connected via a voltage rectifier/doubler directly at the antenna output.
So, if it doesn’t light up, my only guess is that you have a short-circuit directly at the antenna connector. But if this is the case, you should have noticed it and if you receive correctly, it is probably not the problem.
Even weirder, you say that you got good RBN reports, so everything is just fine.

Your problem is very weird. There is no logical explanation…

73 Patrick

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As Patrick @TK5EP has stated, the RG174 coax cable is quite adequate on the lower HF bands and even on 28 MHz it is still not significantly lossy enough to be a concern.

And if the coax was lossy, the radio would be seeing a good load and should behave much like it does on a dummy load. But on the other hand if it was that lossy, you would not hear stations with the receiver and you would not be spotted by the RBN.

Many many activators have used and still use the SOTABEAMS linked dipoles with this feedline. I have made a trap dipole and fed it with this coax too, it works fine.

Is it possible that the light outside is strong enough to make the display of the radio invisible? Can you try the dummy load outside in the sunlight?

73 Andrew VK1DA/VK2UH

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Did you ever get resolution to your problem? I have 2 SW3B’s and feed them with 36” RG-316 directly to a Trail-Friendly 10/20/40m antenna. Both transceivers show red LED output (bright) and bars on meter every time I transmit.

They work equally well concerning your issue with 13.8v/11.1v/9v power inputs.

I might add KL7KN produced a great operating/troubleshooting guide for the SW3B. I believe you can find it on the Venus website.

Erik
KE8OKM

I hope so Eric.

I just got this email back from Dale at Venus Technology today:-

"
" Hello David
Yes,we’ve tested the radio which is working fine.

The issue for the new SW-3B is that we’ve added the power meter to it,so the power meter requires the DC current path,for some antennas without DC current path,the power metet may not work.
So we added a small inductor to the output,now all type of antennas are working great.

Will be shipped back to shortly.

Dale"

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