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Take an inductor and test it at 100 khz which many cheap testers use.? Then do it again with a more costly instrument which more then likely will test at a higher frequency then 100 khz.? This same inductor will read differently.

Lee, w0vt

Well the tool we used was certainly ancient, and did not worry about frequency. But, in any case, indeed experimentation may be required. I was trying to do something a bit difficult (getting it to work on both 20m and 30m if C1 is tuned and alignment is done of the other 3 variables) but should not have reduced L4 to just 8 turns, thinking L4 was part of the LPF which I'm less worried about. So I'll restore L4 to proper or close value, and then see if I should change T1 from 31-3-3-3 to 30-4-4-4 as I think the 30m signals are a little down or rather, lacking in volume. I suspect that is due to T1. Before I made those changes, and when I had part of T1 wound or connected opposite direction, the volume was loud, but signals were very heavily attenuated, as would be expected. Just that taking out T1 and putting it back, though this time I have left VERY long legs on the underside of the board, is a headache, I'll have to find a way to label each leg with the correct hole number as I pull it out.

This is indeed a very educational project, now I've learned that frequency does or doesn't really matter too much in the measurement, but especially that cores vary 5 or 10 percent even such small ones so a couple of turns is a possible effect of that variance, and not just the spacing in the winding which is less of an issue. This is really a wonderful project for education and giving a boost to amateur radio, as well as CW. I also look forward to running it as a WSPR beacon, plus hope it will help me into the outdoors and to do a little more exercise, perhaps even contemplate pedestrian mobile.

Take an inductor and test it at 100 khz which many cheap testers use. Then do it again with a more costly instrument which more then likely will test at a higher frequency then 100 khz.? This same inductor will read differently.

Lee Are you you using a standard, does either of these meters give the correct result? "More costly" does not necessarily mean more accurate.

Paul says get an Ebay meter, can anyone recommend one that is definitely accurate? I got one that claimed 1% yet was about 15% when I checked.

John makes a good point, we measure the apparent inductance. Stretching/compressing alters capacitance not inductance although the in-circuit effect is much the same.
But one of the papers Graham pointed to gives examples of stretching/compressing high frequency low inductance coils changing inductance due to leakage.

I'm not sure actual measurements are going to be useful to most QRP Labs constructors. Unless one has accurate standards measurements on ALL meters must be regarded with a degree of suspicion.
In practical terms "try removing one turn and observe the effect" is better advice to a beginner than to recommend getting meters of dubious accuracy which might further confuse them.

And "remove one (or more) turn and observe the effect" is best done temporally if possible, undo the turns but do not cut the wire until tested. The free loop of wire will not usually have any effect and may be rewound if the desired change in performance is not achieved.

73 Alan G4ZFQ

Folks, I Just want to shed light on the effect of spreading or squeezing
windings on inductance of toroids. The Micrometals app note entitled "Iron
Powder Cores for High Q Inductors" states:

"Another characteristic, which affects the apparent inductance, is leakage
inductance. Leakage
inductance acts in series with the coils self-inductance. This is a result
of uncoupled flux and
becomes most apparent in high frequency, low inductance coils particularly
when the turns are
not evenly distributed around the core. Here is an example where a T50-17
is wound with 10
turns #20 (μ = 4).
In cases like this where it is possible to drastically change the
positioning of the turns, and the
permeability of the core material is low, very large differences are seen.
In higher permeability
materials this affect is much less. In a number of applications, toroidal
coils are tuned by this
means. "

In the example described for a T50-17 wound with 10 turns, induuctance could
be varied from 0.22 microhenries to 0.39 microhenries by simply varying the
coil spread from 360 degrees to 120 degrees!!

Steve K1RF

Great news! I took off L4 and rewound, as I had reduced windings to just 8 (!) thinking it was part of the LPF of L1-L3 and trying to make the QCX work on both 30m and 20m... I put back 4 turns, bringing it to 12, and 30m is alive and well, as good as the main rig I think, only perhaps a bit better: it seems to pick up less local noise in the filter compared to the same width filter in the commercial rig. I just worked 4W/OZ1AA on 30m (in Timor) who gave me the obligatory 5NN but copying VK5EEE callsign on the second pass was certainly not bad! JA's are booming in too... lovely receiver, really lovely!

I'll measure power output tomorrow as I can't measure here, but I think I've got at least 3W perhaps more. Before I fixed the number of windings on L4 I had 3W out on 30m at 14V and increasing to 18V did not affect the power at all -- probably due to a drastically low number of turns on L4 (turn number suited to 15m rather than 30m). Output signal is very clean and well shaped. The built in Morse Key is easy to use.

I did not take off T1 as that is no small job -- I have made an unusual number of windings for 30m instead of 4-4-4-30 which everyone should stick to for 30m, I made it 3-3-3-31 but it still seems fine. Perhaps sensitivity may be even better if that is possible, with the recommended number. One odd thing: in theory this should receive OK even on 20m, but at around 12.505 MHz any frequency higher than that an awful machine-gun pulsing noise comes on the receiver. Any ideas what may be causing that?

And now a second contact: Josh N7XM in Nevada, his 2ele Yagi up 33m :-) my 2x6m doublet up 9m and end on to USA (about 2 S points DOWN direction USA!) he gave me RST 449 and he was RST 589 -- this is great FUN !!!

With 80W, I'd have been around 2S points stronger, so 3-5W QRP is plenty in good conditions, and if the dipole was broadside USA, 4 S points, thus matching his S8. Looking forward to contacts with Europe, given my dipole is broadside to Europe, and even looking forward to QCX to QCX contacts... Look out for me early morning European time via Long Path, usually active around 10119.

A note: naturally as the filter is 200Hz, tuning steps of 1kHz or 0.5 kHz could miss stations -- Josh was on 10105.2 but still heard him on the edge. But most stations do use CW on a full round 1kHz, few are in between. QRP stations however can have a huge advantage by NOT being on exactly a .0kHz (round 1kHz) because almost everyone else is. If you operate on an "in between frequency" you will likely have no QRM at the other side.

73 all -- and the fun building this kit hasn't ended: enclosure case, loudspeaker (with amp if needed), portable antennas, mods, solar panels, EMP Faraday cage... ;-)

Update: in trying to make T1 for both 30/20m I wound 31,3,3,3 but RX on 10MHz is as good as my commercial rig if not better, so that's OK.

My low pass filter, to open it up for 20m I wound the toroids for 17m or so... but did not change the 30m capacitors so I have twice the capacitance it should.... since I'm going to use this perhaps only on 30m, maybe I better replace those capacitors and.or rewind that if it is affecting output power?

My output power is unclear: on an external watt meter that a friend says is reliable, but is not a QRP watt meter as such, on the 20W range it shows 2.5W out at 13V, but using the internal test RF power digital meter of the QCX shows 5W. At 20V (don't do that for long!) the external watt meter shows 3W whereas it should be around 10W.

So it seems power is a bit low and isn't rising significantly with voltage increase. Would this be due to LPF? In spite of this I had DX QSO's last night without problems. WSPR got me to EA8 from VK.

I guess now it is some experimenting with L1, L2, L3 to see if I can improve output power.

One issue: side tone does not seem to be working well though it was, at present it only comes on at higher volume and then very loud. Will have to check circuit etc is clean.

For an experiment today for those in Europe, if you can listen in the early morning your time, I'm running in CW Beacon mode on 10119.1 kHz once per minute, 25 second long transmission while busy with house chores. Would be interested if you can hear me and do send any RST reports to vk5eee at vkcw.net