G8JNJ

Hi Lonecrow,

I think the problem could be a very strong out of band VHF Digital TV signal that is being down-converted to a frequency that is being aliased by the KiWi to the frequency range you are seeing.

The reason for trying the Airband filter is to see if it reduces the unwanted signal that may not be suppressed sufficiently by the transvertor's built in filters.

The 30MHz low pass filter will help test to see if the problem is the down-converted un-signal that is being aliased by the KiWi sampling frequency from somewhere around 70MHz to 18MHz.

As I say, it is only a theory at the moment.

Regards,

Martin - G8JNJ

Hi Lonecrow,

Looking at the spectrum and using the new peak hold function, the noise has a fairly well defined 'shape' that could possibly be a VHF Digital TV transmission using the ATSC standard.

I have a theory about how this could be occurring, but a bit of testing is required to prove it.

First - does the noise go away when you disconnect the Air Band antenna ?

If it does then try.

1. Adding an aircraft band Band Pass Filter to the input of the transvertor.

Something like the "bandpass filter BPF 118-136MHz for Air band" that are sold on Ebay.


2. Adding a 30MHz low pass filter between the transvertor and the KiWi.

Something like the "ZETAGI F27 FILTER ANTI TVI FREQUENCY 0-30 MHZ 300W" or some other CB TVI filter as sold on Ebay


Do either (or both) of these things appreciably reduce the level of the interference ?

Regards,

Martin - G8JNJ

Hi John,

Thanks for fixing it.

I only accidentally noticed it when I realised that the auto notch was no longer removing a strong carrier.

Regards,

Martin - G8JNJ

Some of the 5GHz link kit I've had problems with in the past used Power Over Ethernet which was very noisy. In fact any POE kit seems to generate a lot of unwanted noise. This is a major issue with my Kernow KiWi http://kernow.hopto.org:8073/ which is currently using a temporary active monopole mounted above a room containing POE kit.

Also some of the Bias Tees that are used with Mini Whips don't have adequate filtering on the DC path, so any noise picked up from the power supply or DC connecting cable gets transferred directly onto the RF path and into the receiver.

However Mini-Whips and other E-Probe antennas tend to be noise magnets due to their unbalanced design and high value of feed point impedance, which makes it very difficult to choke off or completely eradicate noise that is picked up on the feed cable. Balanced active antennas and active loops (which have a much lower value of feed point impedance) are much better in this respect.

Regards,

Martin - G8JNJ

Does the KiWI GPS antenna work OK with your other GPS receiver ?

Is the KiWi GPS antenna placed on a metal surface ? This helps because the antenna was designed to sit on a motor vehicle roof which acts as a ground plane / reflector. It doesn't work as well if there is no metal surface below it.

When mounted outside in the clear and on a metal surface the GPS antenna and KiWi receiver can work quite well.

Regards,

Martin - G8JNJ