G8JNJ

That looks very good.

The big test is to see if the antenna you are using is good enough for the KiWi :-)

The ITU publish a noise / frequency curve (Rec. ITU-R P.372-8) https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-8-200304-S!!PDF-E.pdf (figure 2) which shows the variation in natural noise floor with frequency for various locations. 

As long as you have a receiver and antenna that is slightly more sensitive than the level shown on the graph (best case B <100KHz / >100KHz C <4MHz  / D >4MHz curves), then you don't need to worry about your receiver or antenna. 

In most cases because of the shape of the curve, this means that you only really need to concentrate on the higher frequencies, as the lower frequencies tend to have a much higher level of natural noise, even in very electrically quiet locations.

To try this for yourself, pick a suitable clear frequency, perhaps somewhere around 15 - 20MHz, where the natural noise floor is likely to be moderately low and the KiWi has good sensitivity.

Put a 50 Ohm termination on the KiWi RF input.

Zoom to level 12 (Z13 has some problems at low signal levels) and increase the WF min sensitivity slider until you can see the KiWi noise floor on the spectrum display at around -150dB.

Wait a few minutes for the display average to settle and then connect your antenna in place of the 50 Ohm load.

Make a note of the new level of noise floor on the spectrum display.

Ideally if the KiWi has enough gain and the antenna is good enough, your noise floor should rise slightly when the antenna is connected (as long as it's not due to unwanted interference). 

If you find that the noise floor increases by more than 3dB, then the KiWi and antenna you are using are already sensitive enough, as the lowest level signals you will be able to hear are limited by the natural (galactic) noise level

If the noise floor doesn't rise by 3dB (or at all) then your antenna needs to be improved.

Generally speaking, when using a good (passive) antenna the Kiwi is usually sensitive enough up to about 25MHz. On higher frequencies the natural noise floor is lower and ideally you need an antenna that has some additional gain in order to achieve a 3dB increase in the noise floor. So if you repeat the same measurement method at for example 30MHz, you may find that you can't see any change in noise level.

If you are using an active antenna, it's a bit more complicated to conduct these tests, as the amplifier will add it's own noise contribution. 

In this case you need to replace the antenna part (whip, probe or loop) with an equivalent terminating impedance. In the case of a whip or probe something like a 12pF capacitor from the amplifier input to the common (ground) rail, or in the case of a loop you need to replace the loop element with a small inductor of equal value to that of the loop (typically 2.5uH). As before look for a 3dB increase in noise when the antenna element is reconnected.

Regards,

Martin - G8JNJ

Prompted by my competitive streak, I have now modified my RF distribution amplifier so that it works properly down to 10KHz (and lower).

If I select the 'Trask' active antenna option, I can now hear the Russian 'Alpha' navigation system 'pips' on 11.9KHz.

So, if I ask really, really, nicely can I please now have a VLF sticker for my SDR :-)

Regards,

Martin

Would it be possible to embed the URL parameter extension switches in dx,jason tags ?

For example if if a tag is clicked on it would open up the appropriate extension.

e.g. 100KHz Loran, WSPR frequencies, Fax frequencies or some other extension which is applicable to the tag.

Regards,

Martin - G8JNJ

As far as I'm aware DARN is only occasionally used these days when they can afford to put some money in the electricity meter.

However there are a whole host of other atmospheric sounders and radars that can be heard almost continuously.

Here is a quick guide to some of the more obvious ones.

I also have this frustration. 

I've tried to assist where I can by sending personal emails to admins where I think I can help improve things. 

But unfortunately in some cases the Admins are more software orientated than having any real interest in the hardware or RF side of things. So it's very difficult to try to get them to improve things when either they aren't really that interested. Sometimes this is because they don't really know what sort of performance to expect, or alternatively they don't have a good enough understanding of RF to be able to understand the nature of the problem and how to go about fixing it. Just stuffing a random length of wire in to the KiWi antenna socket and hoping for the best shouldn't be the default position.

I have offered to make up filters and send them free of charge to some  Admins (where I thought the SDR was otherwise OK apart from some local overloading or interference that could be filtered out), but so far there has not been any take up (I don't to make a wide announcement and then spend all my time sending free stuff where it's not going to make any difference).

Maybe we could collectively write up some more detailed guidance notes for SDR Admins or folks considering buying a KiWi (as I notice that Farnell / Newark are now stocking the boards and kits) who are not well versed in the RF dark arts ?

Regards,

Martin - G8JNJ

I often find that I listen to one frequency whilst scrolling up or down the adjacent spectrum. If I quickly tune to a new frequency to hear what's been transmitted, it would be good to be able to quickly go back to the previous frequency without having to scroll back or retype the frequency (which I've often forgotten anyway).

I often find that I listen to one frequency whilst scrolling up or down the adjacent spectrum. If I quickly tune to a new frequency to hear what's been transmitted, it would be good to be able to quickly go back to the previous frequency without having to scroll back or retype the frequency (which I've often forgotten anyway).

Mine is fully public 99% of the time.

I don't think the bandwidth used is excessive, but I'm on a VDSL service with no user cap (as far as I'm aware).

However it does get very high usage and sometime I have to kick users off so that I can log in and use it myself.

I have a particular problem in that a lot of Dutch music pirates use my SDR all day long to monitor their own transmissions around 6MHz. 

What I really need to be able to do is to be able lock out certain frequency ranges or restrict the amount of time individual users can stay on the SDR before getting automatically kicked off. I currently have the inactivity time out set at 15mins but I may have to reduce this still further.

I now have a second Kiwi on order, so it would be good if I could link them in some way so that they both appear as one Kiwi but with eight possible connections.

I previously raised this suggestion in this link https://github.com/jks-prv/Beagle_SDR_GPS/issues/48

I know that there is at least one other station running multiple Kiwis on different ports so I don't think I'm the only Admin who may be interested in this idea.

Most of the time (when I can log in) I use my Kiwi for general short wave listening and enjoy spotting 'unusual' activity on the waterfall. I also enjoy listening to NDB's, BC stations and Amateur stations. Quite a few of my users seem to listen to HF Aero traffic as well.

I note that quite a few folks use the WSPR extension (logged as SWUKSDR) especially on the 472KHz band. I've also got antenna switching and this gets used some of the time mainly by the BC listeners in order to try and reduce interference or other stations that are co-channel.

I think the KiWi has been an excellent purchase and It's certainly re-awakened my interest in Short Wave Listening.

Well done John, and thanks for all the ongoing support and rapid resolution of any problems that may occasionally arise :-)

Regards,

Martin - G8JNJ

Mine is fully public 99% of the time.

I don't think the bandwidth used is excessive, but I'm on a VDSL service with no user cap (as far as I'm aware).

However it does get very high usage and sometime I have to kick users off so that I can log in and use it myself.

I have a particular problem in that a lot of Dutch music pirates use my SDR all day long to monitor their own transmissions around 6MHz. 

What I really need to be able to do is to be able lock out certain frequency ranges or restrict the amount of time individual users can stay on the SDR before getting automatically kicked off. I currently have the inactivity time out set at 15mins but I may have to reduce this still further.

I now have a second Kiwi on order, so it would be good if I could link them in some way so that they both appear as one Kiwi but with eight possible connections.

I previously raised this suggestion in this link https://github.com/jks-prv/Beagle_SDR_GPS/issues/48

I know that there is at least one other station running multiple Kiwis on different ports so I don't think I'm the only Admin who may be interested in this idea.

Most of the time (when I can log in) I use my Kiwi for general short wave listening and enjoy spotting 'unusual' activity on the waterfall. I also enjoy listening to NDB's, BC stations and Amateur stations. Quite a few of my users seem to listen to HF Aero traffic as well.

I note that quite a few folks use the WSPR extension (logged as SWUKSDR) especially on the 472KHz band. I've also got antenna switching and this gets used some of the time mainly by the BC listeners in order to try and reduce interference or other stations that are co-channel.

I think the KiWi has been an excellent purchase and It's certainly re-awakened my interest in Short Wave Listening.

Well done John, and thanks for all the ongoing support and rapid resolution of any problems that may occasionally arise :-)

Regards,

Martin - G8JNJ

Just about a long enough a delay to cause you to hesitate whilst speaking if you are monitoring your own transmission.