Sunday, May 26, 2024

Test of a cheap PCB based end fed half wave antenna

There is a nifty little PCB based end fed antenna Unun and winder being sold in the Chinese stores online. It does look a lot like the ones sold by QRPGuys. The kit comes with the BNC socket, a capacitor, a toroid, some cable ties, the butterfly nut and bold, and a length of enamelled copper wire. It doesn't come with the antenna wire. 


I cut the wire for a 20m band antenna. The flatness of the SWR curve suggests rather high losses in the toroid.


For a 20m band antenna there is enough space to wind the wire around it but I think it wouldn't be enough for lower bands.


Strung up near the house it certainly brings in CW and FT8 signals well on 20m. 


The capacitor doesn't look like a high voltage type and I wouldn't want to transmit more than a very few watts into this. I could substitute the capacitor and toroid. It's very compact and something to throw in the travel bag but I wouldn't trust this for extended digital transmission.

Thursday, May 23, 2024

Switched to Starlink

During my recent frustration with the Telstra supplied NBN fixed wireless I ordered Starlink. This morning the box arrived. More compact than I had anticipated.


The "out of box" experience is excellent, I would say it matches Apple's standard.


I put the "dish" (really a small flat panel) on the roof facing south and powered it up.


The app contacted a satellite and then asked me to rotate it 9 degrees. Within minutes it was working and speed is better than any internet I've ever had.


That Speedtest is run on a Wifi connected Mac. The Starlink app's Speedtest is faster but I assume testing at the router rather than what you really get. 


Not bad. I'm amazed at the ping latency given that I'm using a satellite internet service.

There's a small obstruction which I'm hoping to eliminate by moving the panel. It might even be the ladder which is propped up near the antenna.


I've cancelled my Telstra / NBN service who, incidentally, just wrote to increase the price. Starlink is a bit more expensive per month and I had to pay AU$600 for the gear. It's certainly better value per bandwidth and their customer support seems much better. I like the honesty of showing outages proactively. 

If you have a good view of the sky it's worth considering.

Wednesday, May 22, 2024

NBN Fixed Wireless frustration

Where I live, in country Victoria, internet is via NBN fixed wireless. I pay AU$100 a month for unlimited. Signal strength was not full bars and would sometimes drop in rain - probably because the signal path goes through trees. Speeds were about 20-30Mbps download and that was enough for streaming video and video calls.

A few months ago, there was some sort of upgrade and speed jumped to over 50Mbps download. I was very pleased.


About a week ago there were three days of disruption due to an NBN "upgrade". At the end of that period, signal strength had dropped and speed was down to sometimes 2Mbps.


I tried the normal things, turning off the NBN box for periods of time and back on again, hoping it would re-sync or something. We have a Facebook group for local residents and I posted there asking if other people were seeing the same thing. Two others said yes so presumably there are others as well. A few of us reported a fault via our providers. I'm with Telstra so started the process via the chat. 

Note that they don't make it easy to report a problem and, I guess correctly, they said the connection was working.

The support people clearly use a script and even though I listed all the steps taken so far they seem oblivious of this and asked me again.

There are frustrating terminology issues. They asked about the "modem" and I thought they meant the NBN fixed wireless modem but in fact they meant the Telstra Wifi router. 

It's strange that they have no visibility of other customers having issues and NBN rarely seems to be aware of any problems. Surely a network operator has monitoring in place?

After several hours doing things including plugging a laptop in to the NBN device via an Ethernet cable they agreed there was a problem and escalated to NBN. A technician was booked to visit my house in four days time. Another local said she had an appointment on Tuesday. You might think they'd visit all properties at the same time.

In the end all of our visit appointments were cancelled and magically the signal strength is now better than ever and bandwidth looks better than ever.


However, during the outage period I decided to order Starlink. The gear should arrive within the next few days and I'm fascinated to try it out. I have some concern about obstruction from some tall trees.

It's great to have another option.

Update

Amusingly Telstra just emailed to say the price is going up.



Technology news on ABC radio

Talked through the technology news on ABC Nightlife last night: Telstra lay-offs, Microsoft announcements, new features coming to Android 15, age verification for porn access being trialled, a concerning bug in iOS 17.5, NBN fault frustration and a possible way to avoid car sickness.

Listen here.

Tuesday, May 14, 2024

Moorabbin Radiofest

The Moorabbin RadioFest was a terrific show this year. The turnout looked good to me although I'm told it was down on past years.


It was great to see a vendor, VK Radio, was there with some amazing commercial radios to play with.


I came away with a home brew antenna tuner. The biggest purchase I saw was by Dave, VK3ASE, who seems very pleased with his receiver purchase.


Congratulations to the organisers who did an excellent job.

Saturday, May 11, 2024

Extreme geomagnetic storm effect on 10m

Although I follow space weather with some interest it's rare to see it reported in the general news. Recently I repaired my 10m band dipole which had been eaten by a tree and I left it receiving WSPR. Over the past 24 hours you can see that my reception essentially stopped which is not something I've ever observed.


Here's the current status according to the Bureau of Meteorology's Space Weather Service:

I did not see aurora but it's been cloudy here in Victoria. Things are now returning to normal:




Friday, May 03, 2024

Testing Unun losses

In his recent feedback, Richard, VK3TXD, suggested I measure the loss in the Unun built with Jaycar LO128 core by making a second one and wiring them back to back.


On the spectrum analyser, I set the range from 5Mhz to 30Mhz and the plot shows a very slow loss over the range. Note that the tracking generator is at -10dBm.


In the middle of the frequency range the loss, going through two transformers is 3.26dB. 1.63dB for one Unun. Richard commented that 2 turns of primary winding is not good so I added a turn. Here's the plot.


The loss in the middle of the range, going through two transformers is slightly less at 3.24dB. In my test, hardly measurable. Of course with an extra turn on the primary the impedance transformation is much less so more turns on secondary will be needed.

Perhaps I'm not measuring this correctly but I'm not seeing the dramatic problems that were predicted.

Thursday, May 02, 2024

Constructive feedback on my naive end fed half wave from Richard, VK3TXD

After posting the last story on my very simple end fed half wave antenna I received some suggestions for improvement from Richard, VK3TXD. In the past he has sent me some antennas and match boxes he has constructed. He was concerned that if he left this as a comment I might take it as heavy criticism, but no, I am very grateful for his suggestions.

Richard writes:

Some suggestions for you. In no particular order. Some terse notes. Do feel free to query, happy to discuss.

1. Check toroids before use. The Jaycar ones often have a sharp lip. Sand it off with emery type paper. Sharp lips are the enemy of enamel wire.

2. The cap. You mentioned HV. My experience with the altronics ones was poor. They were super lossy. I strongly suggest Silver mica. 500V is good for 100W and more. No need for higher.

    VNA measurement will show the difference easily.

    You used 150pf. That looks a little high.

3. I used 0.8mm diam enamel wire for 100W. I use 0.63 wire for 50W. Not sure what you used. Using 1mm or more is pointless. [I used 0.63mm]

4. The LO1238 is quite good. If anyone criticises you and says you should use a Fairrite core or similar, ask if they've done measurements. I have. The differences are within margins too close to error. Some people say you should use #52 or other material.  Same come back.

5. Spread out winding increases loss. It makes flux linkage between turns more difficult. Close wind. Shorter magnetic paths are better in all regards.

6. 2 turn primary tapping is not good. For 160m, 80m, 40m, the efficiency will be really poor. On 10m it starts to come good. Use a 3 turn primary. <<-- please test with VNA, the difference is quite surprising.

One thing. On 10m the 3 turn primary may be fractionally worse on 10m. On all other bands the loss will be substantially less.

    With 3 turn primaries, 160m and 80m are ok.

7. Teflon tape wrapping the toroid is pointless. Some people have a fetish for it. It will make the experimenter _feel_ good, but at 100W, it makes zero difference - I've not had flashover ever and never used tape. I think I've sold about 70 UnUns using the same toroid.

8. At 400W, yes, 400W, the 100pF 500v silver mica cap will fail. A user admitted that. I _really_ don't recommend it. I am not convinced the EFHW is a good solution to > 100W as the electric field will be very high, and the instantaneous voltage on the hot end of the UnUn will get disgusting-high.

9. Be prepared to need a 1:1 to tame the common mode current. The unit I sent you has an inbuilt 1:1. It is not perfect, the coax sits in the high intensity field, but no user has reported a problem.

Craig VK3NCR tried a 1st version without the 1:1 and on 10W from his IC705 it garbled voice peaks. His radio hated it. The 2nd version with 1:1 cured it.

   1:1 baluns and common mode current seems to be a dirty little secret few own up to.

10. On 13th May for a few days Stan VK3BOT is going mobile. He is using my UnUns. https://www.vk3frc.org.au/post/an-invitation   if you get a chance to have a QSO and mention me. VK3NCR and VK3BOT

11. There are some other good options for toroids......

Try stacking 2 LO1234's = super glue together. This has a shorter magnetic path and the efficiency is quite a bit better than the LO1238. How much better.....use the VNA <smile> This one is in fact my favourite,


Try stacking 3 of the LO1230 (smaller ones) and use 0.63mm wire. I put 50W into these. These are very efficient also. I did a mounting sled for use in a jiffy box. It is quite good.

12. Oh. On YouTube checkout "mm0opx" - he's done a lot of work. Also "evil lair electronics". And "Steve Ellingtn" has a nice video on the small compensation coil you can use to make the bands line up better.

13. I've not really mentioned my thoughts on efficiency and antenna mounting. Let me know if you are interested. The above data-dump is a bit intense for now.

14. My favourite so far. The 2 stack LO1234.

Tech notes. 

The smaller diameter has a shorter magnetic path which aids efficiency. Being taller helps increase the magnetizing impedance but not so much as to make 10m unusable.

Below is based on 2 stack LO1234 UnUn with 2 stack 1:1 as well. It goes into a rather nice and small box. Stan and Craig have them now. Drilling the ends is disgusting, it is super tight tolerance so I made drilling templates. I'm happy to send you files if you want - personal use etc. Oh. I've been using some stainless wing nuts and bolts recently. Some users want them.



My sincere thanks to Richard for his detailed feedback and suggestions. I will certainly try some of them.

I put up the antenna this afternoon and had a QRP contact on 20m with a station west of Sydney (about 800km away). I mentioned this to Richard who replied:

Having success with a home built antenna is THE BEST isn't it. I find it a pleasure. I bet you smiled! <I would have>

The resonance moving up the band to 100% normal and caused by capacitive coupling being frequency dependent (don't quote me on that)...as F goes up, more coupling to ground hence resonance goes up. Something like that.

That Steve Ellington Video I mentioned. Chase that down. Seriously. He explains it well and a small loading coil 2m from the UnUn will fix it <<<---worthwhile (and fun). I use some 19mm (?) placcy pipe and about 8 to 10 turns.

Why 2m along? Steve explains. It is all to do with the current profile moving by each band and hence the loading coil has a different effect by band. You can get it quite close to spot on.

One thing. The SWR being that low quite often means there is a fair amount of loss in both efficiency of the UnUn, but also in radiation. Unless noted, your coax will be on the ground and its outer sheath is acting as the radial and radiating into....the ground. Hence loss.

I've nec modelled the EFHW. Very naive models tho. A good thing about it is that on 40m, wth 20m of wire, the point of highest current is 1/2 way up the wire. If you are using a  9 or 10m squid pole and inverted L, it is nice and high in the air and the pattern is quite NVIS. On 20m, the high current point is lower and it looks more like a vertical with lower lobes, hence you get the best of both worlds - 40m NVIS and 20m DX. It all depends on mounting etc of course.

I like to have the 1:1 in the same box and use 2, yes 2, radials. I found the SWR was better. I mount in inverted-L with a 1 to 1.5m elevation of the unun. The radials radiate, so get them into the air.

That capacitor looks good actually! It may be a SM type. In truth...this only comes into play marginally on 20m rising to significantly on 10m.

The spec-an if it has a tracking generator can do a loss measurement. The nanovna can save the file tho. The spec-an may offer it - I don't know.

You can open a .s2p file with a text editor. It is just all the measurements that were used to plot the data. It is in complex (real imaginary - or real and phase angle) format. See Dan's post on the math.

On the NanoVNA. Download a PC program (or mac?) and use that connected to the nanovna. That will have a means to save the data to file. It is of type ".s2p" and from that I can plot swr and loss with the code I wrote with help from Dan as mentioned.

Use the 'logmag S21' test - and be sure to calibrate and use the same fly leds in the calibration. Accurate measurement is not a trivia exercise.

NOTE....the 50 ohm side pigtails can make a big difference to SWR. I've found keeping these short makes a big difference..

The ohm meter test is all very well, but the EFHW can have quite high voltages on the top end of the UnUn. The ohm meter is not great for this kind of test, you are not testing with what it will experience. That is why at 400W I would get nervous. At 100W the voltage should be less than 500V even under an adverse SWR.

Ta on the neatness. I have wound many. Using 0.8mm wire makes it a lot easier.

Efficiency....the worst balun you could possibly make will have loss up in the 3db region, so losing 50% of the power. This will be turned to heat in the ferrite core. You might juuuuust her that kind of loss.

Guess, but from experiments, on 40m a 2 turn primary may have round 40% loss worst case. The 3 turn primary halves that and slightly better. The  stack of LO1234s is a bit better again.

I tried stacking LO1238's. That helped on 160 and 80 and 40. On 20m it was worse than 1 core and on 10m it was terrible. Looks good tho!

The hard truth. You won't hear the difference unless it is a marginal signal on SSB. A more efficient UnUn will get less hot, so even on 10W it will run a little cooler. SSB is very lenient. All change if you use digital. It makes a huge difference there. Core heating under digital can be over 10 times, and maybe 20 times more than SSB because of higher average power.

Feel free to publish. A very small mention would be fine. I'm sure you will write it better than me. You can make a few posts out of it exploring that compensation coil, and trialling the smaller 2 stack, and loss testing etc. I've spent a lot lot lot of time playing with all this.

Gotta go. I'm cooking dinner!

Cheers - Richard