G8JNJ

DRM Heard

G8JNJ

January 2020

All India Radio 15030KHz heard in UK at 13:14

IF Level: -10.9 dB
SNR: 6.7 dB
DRM mode B
Chan 10kHz
ILV L
SDC 16
MSC 64 QAM
Protect: A=0 B=1
Services: A=2 D=0
Medium range use, multipath resistant

Services:
1… (more)

DRM Heard

G8JNJ

January 2020

All India Radio 15030KHz heard in UK at 13:14

IF Level: -10.9 dB
SNR: 6.7 dB
DRM mode B
Chan 10kHz
ILV L
SDC 16
MSC 64 QAM
Protect: A=0 B=1
Services: A=2 D=0
Medium range use, multipath resistant

Services:
1… (more)

Problem with audio - Chrome [fixed, Windows 10 settings issue]

G8JNJ

January 2020

The issue was not associated with just the KiWi or cookies and I subsequently found that it affected other websites with audio enabled too.

After a lot of messing around I discovered that the problem… (more)

Problem with audio - Chrome [fixed, Windows 10 settings issue]

G8JNJ

January 2020

The issue was not associated with just the KiWi or cookies and I subsequently found that it affected other websites with audio enabled too.

After a lot of messing around I discovered that the problem… (more)

Electric fence noise

G8JNJ

January 2020

Modern electric fence energisers have 'pulse shaping' which minimises noise from the energiser itself, so most problems are associated with arcing or insulation breakdown.

One quick test is to… (more)

Electric fence noise

G8JNJ

January 2020

Modern electric fence energisers have 'pulse shaping' which minimises noise from the energiser itself, so most problems are associated with arcing or insulation breakdown.

One quick test is to… (more)

v1.360+: DRM extension now available

G8JNJ

January 2020

Hi John & All Happy New Year to everyone.

Even if it's not possible to decode DRM because the KiWI is occupied, could it be made so that you can still open up the DRM schedule screen so that you… (more)

Multiple "Sweepers" on my Cascade

G8JNJ

December 2019

It's Over The Horizon Radar (OTHR)

https://en.wikipedia.org/wiki/Over-the-horizon_radar

There are Six 'usual suspects'

These four tend to sit on specific frequencies for long periods of time.

Cyprus (… (more)

Questions About the Mini-Whip Antenna

G8JNJ

December 2019

Just a couple of additional thoughts following on from Stu's post.

Both techniques of screening and choking are important, but they perform different functions and have to be applied appropriately.

"… (more) Quad shielded" coax can be many things, but these days many of them are just marketing hype.

In the past coaxes with multiple screens that were insulated from each other were used for video distribution in TV studios, where it was necessary to separate 'clean' and 'dirty' electrical grounds from each other, so that very low level noise didn't get introduced into the analogue DC to <10MHz video circuits.

Quad shielded coax as referred to these days, tends to be a generic term that means it incorporates other cores around the inner, and some of these may simply be to provide additional mechanical strength or protection, such as steel reinforcing strands.

It's best to avoid coaxes that have a plated steel cored center conductor and also those with aluminium foil screen or aluminium conductors.

All of these can cause problems on the lower frequencies where the conductor skin depth is not adequate for the purpose on the LF bands.

Common mode noise is carried on the outside of the coax screen, and so as long as the skin depth of the conductor is sufficient, it will remain there and any additional screening won't make much of a difference.

The problem arises at the ends of the coax where it is terminated, and makes a transition from balanced to unbalanced due to the current on the outside of the outer screen.

Common mode chokes are required to reduce the amount of common mode current that can be carried along the outer of the screen and can be re-radiated to be received by the antenna. It can also be directly re-introduced into the balanced signal path of the coax by incorrect termination of the screen at that transition point.

The frustrating thing about common mode chokes is that it's a bit like playing 'Whack a Mole' as soon as you put a choke in one place, the current distribution changes and the noise can pop up on a different frequency. Some degree of experimentation is required to find the best placement, and this often changes when you connect new items of equipment, or even in some cases when you simply plug another item of electrical equipment such as an extension lead, and the long mains cable modifies the RF current distribution on various surrounding structures.

I have used an E-Probe mounted above the metal roof of an industrial building full of various items of consumer electronics and server farms. The trick is to use the metal roof (and frame of the building) as the ground plane for the antenna, but to ensure that the coax has lots of common mode chokes fitted on the 'building side' of the ground plane connection, so that noise from within the building is not introduced onto the antenna itself.

Regards,

Martin - G8JNJ (less)

Multiple "Sweepers" on my Cascade

G8JNJ

December 2019

It's Over The Horizon Radar (OTHR)

https://en.wikipedia.org/wiki/Over-the-horizon_radar

There are Six 'usual suspects'

These four tend to sit on specific frequencies for long periods of time.

Cyprus (… (more)

Howdy, Stranger!

G8JNJ

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Reactions

DRM Heard

DRM Heard

Problem with audio - Chrome [fixed, Windows 10 settings issue]

Problem with audio - Chrome [fixed, Windows 10 settings issue]

Electric fence noise

Electric fence noise

v1.360+: DRM extension now available

Multiple "Sweepers" on my Cascade

Questions About the Mini-Whip Antenna

Multiple "Sweepers" on my Cascade