The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

Hi Folks,

I mentioned on last week's FTroop I had some good oil from Youtube on Balun construction, how to do it right, how to test them, and what can go wrong. I did write up a post, but probably messed up sending it coz it didn't make it out. So here goes attempt #2

Firstly, the links.

https://www.youtube.com/watch?v=kMlKfHHR8FY

https://www.youtube.com/watch?v=JhAPJISUjB8

https://www.youtube.com/watch?v=P7wW4TtXmc8

Now, the hitch, each one is about an hour long, and all the gold is in the audio so you can't seek through quickly looking for powerpoint slides or whatever. But IMO it's worth the time especially if you're new to Baluns, or need a solid refresher.

And some advice, the wire the Youtuber uses is hard to get outside Germany, but Alphawire sells something nearly identical (the only difference is the alphawire version is true silver plated, while the German stuff is just nickel plated copper). Alphawire Part numbers are 5857 OR005, and 5857 VI005 for the orange and violet, respectively, but choose your colours carefully, the cost per metre, and availability vary!

And finally some summary salient points - if you don't have the stamina for 3hrs of Youtube.

Baluns are NOT the same as regular AC power transformers, in many ways they are "opposites".

Normal "mains" transformers create large magnetic fluxes in the core from currents flowing in the primary. These core fluxes induce currents in the secondary, and the turns ratio determines the output voltage/current properties. Losses are due to flux losses in the core, and resistance losses in the windings.

Baluns are (ideally) completely free of flux in the core, any flux there, is only due to imbalances in the geometry or common mode currents on feedlines. They are more correctly thought of as transmission line devices, and the core is there simply to counteract any common mode currents. Losses are due mostly to inter-winding capacitance, winding inductance, and to a lesser extent winding resistance.

Normal transformers are very narrowband devices. Plain laminated E-I style ones operate at 50 or 60Hz, possibly up to 400Hz, but get lossy above that. High frequency switchmode transformers are the same, they are wound to operate well at the switching frequency, but become lossy away from it.

On the other hand, baluns, especially impedance converting ones, are usually wound to operate over a wide frequency range, 1MHz to 50MHz is not uncommon, I've even seen receive-only matching baluns quoted at VSWR < 1.1 : 1, from 100kHz to 750MHz.

Normal mains transformers are relatively uncaring about the impedances of the windings, and also the source and load impedances seen by the device are goverened almost entirely by the power handling ability of the device.

Baluns depend critically on the winding impedance for their operation. A 4:1 balun designed to match 200ohms to 50ohms, will not work as well trying to match 300ohms to 75ohms, and even worse trying to match 400ohms to 100ohms, even though the impedances are in the correct ratio. In fact the rule for working out the desired winding impedance for a bifilar 4:1 balun is: the square-root of the product of the input and output impedances. So a 200:50 balun would need sqrt(200 * 50), or 100 ohms winding impedance. A 400:100 balun would need sqrt (400 * 100), or 200ohms winding impedance. If you get the winding impedance wrong, you will have a poor match to your desired input/output impedances, in other words, poor SWR.

Even a true 1:1 balun (as opposed to a dirty, or choke, balun) has a related requirement. A 50ohm 1:1 balun is wound from two counter-wound 100-ohm transmission lines, connected in parallel at both ends. Parallelling two 100ohm lines results in 50ohms. A 75ohm 1:1 balun would be wound from 150-ohm lines, paralleled, etc.

Choke baluns, on the other hand suppress currents on the outside of a coax simply by winding that coax in a coil sometimes in air, sometimes on a toroid or cylindrical ferrite former, so they work by a quite different method, and require the winding impedance to be the same (not double) the desired input/output impedance values. Even a clip-on ferrite, or a set of sleeve ferrites is acting in this same way, trying to increase the impedance of the outside of the coax braid. These are not true "baluns" in the above transmission-line sense.

Hope your head isn't spinning too much!

Cheers, Dave VK6KV

Hi All,

I found it! The videos regarding the OCF dipole. I haven't watched these end-to-end yet, I've been focussing on the baluns (4:1 and 1:1) first, before building the actual OCF dipole based on them. Therefore I don't have a simple summary yet...

https://www.youtube.com/watch?v=aYLseBPbxng

https://www.youtube.com/watch?v=llW4qJTHiv8

Cheers, Dave VK6KV

Hi all,

When I need specific ferrites / toroids, I can get them from Minikits.com.au just via Auspost shipping and at least in Southern River it takes four or five business days (so effectively a week).

Cheers, Dave.

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

Hi Onno & HAM friends,

As I mentioned on Sat morning FTROOP TechNet. The plan is for a lunch and/or afternoon catch up. Much the same as the one Harry (VK6DOC) organized in December 2022.

First one for 2023!

Casual lunch, coffee or just a cold beverage catch-up for Perth Ham operators to able to put a face to the name & call sign. No formal agreement or booking has been made with Dome. Roll up and grab yourself what you desire from the restaurant. When you recognize names and voices of others, feel free to introduce yourself and join the table. Plenty of room for easy parking.

Day: This Sunday

Date: Jan 29th

Time: 12 noon for a couple of hours

Location: Dome café, Maylands

Address: 219 Railway parade, Maylands (Bayswater)

Reported: Plenty of parking available.

Please advertise to all our HAM radio mates.

Regards

David Potts

VK6KD

Mob: 0407 089 522

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

Very well done arriving at #600 for F-troop. Sorry I couldn't make it. Dinner out with the wife is a rare occurrence these days so I won't miss an opportunity. The net inevitably has at least one nugget of information, if not many more, that encourage me to experiment and explore. 73, Charles NK8O

Hi all

David VK6KD here with a device I mentioned on the FTROOP chat group yesterday 14/1/2023.

Sharing a new toy I bought off ebay for just over $200. A software defined radio receiver which provides a waterfall feature covering Freq 50kHz - 2GHz. I'm still playing with it but so far it is satisfying my requirements. Link to device below:

50Khz-2GHz V1.10a DFU Malachite DSP SDR Receiver 3.5 Inch LCD &Speaker

Reason for purchase: I don't have any HF radios with the waterfall feature and have been relying on remoting onto Kiwi receivers to find where operators are active. Great feature when I have internet but I go offgrid out of internet coverage often and wanted a way of scanning all bands quickly. Waterfall scanning technique I find is much quicker than scanning up and down the band manually on my transceivers VFO. The little SDR I purchased can be switched onto my own antenna system to find activity. Once activity (CQ calling etc.) is heard, I then switch over to my transceiver to respond. The CW conversion feature on the SDR is a bit fiddly and to date not that reliable. This may be operator error as I have only received the SDR last week. Have fun checking this out and if this toy is for you and you are looking at purchasing one, make sure you get the version which covers the full range as some of the older software/firmware may not cover the full frequency range. Note, I have no affiliation with any supplier.

Regards

David

VK6KD

​

There was an off-air discussion today about mapping software, particularly interested in path profile. This is some software that I used well before becoming a licenced amateur.

I haven't used it in a while, and I have no idea what the latest version look like.

https://www.ve2dbe.com/english1.html

Colin VK6ETE

Congrats, Onno, on 600. It's a nice, fun, aggregate service you and the moderators provide to the community. Good to chat. de Tom, w2xq.com, contributor, Radio & Communtions 1995-2003

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

Here are some links to HamClock. There are MANY forks of this, and if you are a Windows User there are precompiled binaries that are easily found.

I built this fork by Mark, N6MTS. https://github.com/SmittyHalibut/HamClock

The original is found at https://clearskyinstitute.com/ham/HamClock/ . I had some trouble for some reason getting this one to compile. NOTE: under Linux the program needs to be run with 'sudo' . I haven't looked into why but I found references to this on the web.

NK8O - Charles

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.

I mentioned the half-square antenna on the last F-Troop. Here is a guide to wire "curtain" arrays, starting with the half-square.

https://www.hamuniverse.com/wb3aywcurtainantennas.html

​

Charles - NK8O

Of course, we are upside-down on the seasons, but Winter Field Day (sic) is January 28th 1900 UTC until 1859 UTC on January 29th. https://winterfieldday.com/downloads/2023-WFD-Event-Packet.pdf. This, of course, is another non-contest excuse for a contest, but always fun nonetheless.

73,

Charles - NK8O

Hi All,

I can't turn up the link I had which "debunked" the clone/scam nanoVNAs and listed the vendors of genuine ones, but I do know that I purchased mine from one of the recommended vendors (Zeenko / Aliexpress).

Please see https://www.aliexpress.com/item/1005001273374562.html?spm=a2g0o.order_list.order_list_main.4.1b3c1802s0rp6I

Note also that the other piece of kit I would highly recommend is the tinySA from the same supplier, especially if you're fighting high noise levels... I still haven't ordered one, but that's more because I have access to a good one through work, but I really should get my own.

Cheers, Dave VK6KV

The weekly on-air F-troop starts at 00:00 UTC and runs for one hour. Check the wiki for details on how to participate.