THE LISTENING POST.

[VK3YNV]

The parts for the MW Band Stop filter arrived, the initial tests looked ok for the MW band but also knocked out the 160M 1.8 MHz to 2.0 MHz,
So I loaded the circuit into QUCS and ran the simulation repeatedly, changing values to try and balance the MW band rejection with the 160M band

This is the current version,

And here is the simulation from 100 KHz to 2.5 MHz

And the VNA S[1,2] sweep

The green line is the original rx-888 values, and the overall rejection of the MW band is around 20 dB, whereas the original
rejection of MW was 30 to 40 dB, but 10 dB attenuation on 160M, the modified version has minimal ( 3dB ) attenuation of the 160 M band.

The question that remains is 20 dB enough to knock out the intermod products from the stronger AM stations?
It's a very small PCB, $2 coin for comparison...

 

[BillC]

The parts for the MW Band Stop filter arrived, the initial tests looked ok for the MW band but also knocked out the 160M 1.8 MHz to 2.0 MHz,
So I loaded the circuit into QUCS and ran the simulation repeatedly, changing values to try and balance the MW band rejection with the 160M band

This is the current version,
View attachment 3498

And here is the simulation from 100 KHz to 2.5 MHz
View attachment 3499
And the VNA S[1,2] sweep
View attachment 3500
The green line is the original rx-888 values, and the overall rejection of the MW band is around 20 dB, whereas the original
rejection of MW was 30 to 40 dB, but 10 dB attenuation on 160M, the modified version has minimal ( 3dB ) attenuation of the 160 M band.

View attachment 3501

The question that remains is 20 dB enough to knock out the intermod products from the stronger AM stations?
It's a very small PCB, $2 coin for comparison...

Hi Ray, from my testing here 20 db would be enough attenuation to stop the intermod products at night, on tests conducted from here 10 to 12 db usually is enough to control the intermod products. For best overall performance an automatic Day/Night switch across the attenuator could be the go. But that adds another layer of complexity. It could be fun to build that of course. The 20 db of attenuation will really pull back the day time performance of the AM Band . There are trade offs in every direction . Looking forward to trying the new filter. Cheers.

 

[BillC]

This afternoon I mounted the 4:1 Balun / Spark Gap box to the down feed position at the loop antenna, The box will have a sheet metal roof over it, also connected the grounding rod for the Spark Gap, a Gal steel post down about 5 feet. Hope it works to reduce any spikes on the line. Check the images.

 

[VK3EB]

Night/Day switch is clever idea. LDR switch relay or time clock?

 

[BillC]

Night/Day switch is clever idea. LDR switch relay or time clock?

I might have a synchronized motor movement here, I could cut a cam and use a microswitch to pass around the bandstop filter. Fairly simple----- no electronics, perhaps, possibly.

 

[BillC]

Today Dallas fitted to RED GUM the AM Band Stop Filter as designed and built by Ray. A fantastic result, checked it out tonight absolutely no overloading from the AM stations. For daytime listening the AM signals are still mostly received at good levels. I am fairly sure that we do not really need to listen to Sydney radio stations in the middle of the day at strength 9 plus. So we will see how it works over time. Thanks very much Ray for the work with the filter.

 

[VK3EB]

New readings with MW filter in circuit. (daytime readings)

675k was -30dBm, now -57
756k was -29dBm, now -48
1260k was -33dBm, now -53

RX 1_Kiwi is better on dipole for broadcast band. 500k-1700k
RX 2_Redgum better on loop above and below MW band.

 

[VK3YNV]

Looks promising, I wonder if dialling back the MW band attenuation from 20-30 dB to maybe 10-15 dB would still get rid of the intermod overload problems?

 

[BillC]

Looks promising, I wonder if dialling back the MW band attenuation from 20-30 dB to maybe 10-15 dB would still get rid of the intermod overload problems?

Past testing showed that 8 to 10 db of attenuation on Red Gum , with the loop antenna was enough to prevent intermod products from upsetting the receiver performance.

 

[BillC]

On Wednesday morning not long after sparrow I went out to check the Listening Post, as I often do. The post was dead, no winking LED,S on any system. The Battery was sitting at 12.8 volts but power was not getting into the system. So by studying the power wiring diagram which is on the inside of the cabinet door I came to the conclusion that the Plasmatronics regulator had shut off the voltage supply from the battery between the load sense terminal and battery negative terminal. So a reset must be required,now what to do? Remove the load line from load terminal, bridge load terminal to battery negative terminal with a shorting link, just a flash discharge in reality. I then reconnected the load line to the load terminal on the plasmatronics regulator and the system started up and every thing worked and is still working. I have no idea what caused the shut down, perhaps it was a spike on the line. The Solar Panel generally provides up to 4 Amps on a bright sunny day, but that is only when the panel faces the sun directly, If I am walking past I will adjust the panel position so as to peak the charging rate. The Receiving systems within the cabinet require around 3.2 A to operate so with the solar panel at best supplying 4 A that leaves a surplus of 800 milliamps to charge the battery --- some of the time. So allowing for losses the battery might see a charge rate of 500 milliamps some of the time. I do not know of any 12 volt battery that will survive with a 500 milliamp charging rate. So with all that in mind I have hooked up various heavy duty power supplies to work as battery chargers. Power supply No. 1 commercially made in Melbourne , unregulated , variac voltage control up to 6 amps output, produces modulated harmonics on the AM band due to diode generated harmonics , not so good! , if trying to charge a flat battery very careful and continuous adjustment of the charging voltage is required so as to not exceed the 6 amp limit of the supply, No. 1 is not a good battery charger. Power supply No.2 a much heavier duty power supply by the same maker as No.1. This power supply is voltage variable with electronic voltage control and regulation, this power supply also produces lots of harmonic artifacts which are injected back into the mains wiring to my house and no doubt into the KIWIS , this power supply also needs very careful and continuous voltage adjustment when trying to charge the battery , if the voltage is brought up too quickly the overload trip will shut the power supply off. You know that the battery in the cabinet at the post can demand about 30 amps when its state of charge is low, so some form of current limiting is required, in earlier times a series globe was often used So No.2 power supply is not a good battery charger either. I hope the reader is interested in all of this. I think that I need to make a BATTERY CHARGER.

 

[VK3EB]

Wonder if the plasmatronics has some internal timer to shut down after various errors? Did this happen once before when we first setup?

 

[BillC]

Wonder if the plasmatronics has some internal timer to shut down after various errors? Did this happen once before when we first setup?

Can,t remember what happened previously Dallas but it seems to be OK now. I am setting up a shore power filter now to hopefully stop the PSU from radiating spikes and harmonics back into the mains wiring. After that I will try placing a .1 green cap across each diode in the PSU rectifier stack . Cheers.

 

[BillC]

I have plugged the shore supply filter in, there is still harmonic energy being radiated back into the house by the PSU but it is at a lower level. The next step will be to have a look at the rectifier diode set up in the PSU.

 

[VK3YNV]

That's a strange fault condition, I'm guessing that the plasmatronics shut down on low voltage, that is it disconnected the load to protect the battery from discharging too far, from memory that's a configurable setting. Then when the sun came up the battery voltage came back up to 12.8, but the plasmatronics didn't re-connect the load? That's the strange bit.

Good topic for more discussion tomorrow.

 

[VK3YNV]

More detail, from the plasmatronics manual

Low Battery Disconnect Option Low BatteryDisconnect is a feature of the PL which helps avoid battery damage by preventing the load from excessively draining the battery. You do not have to use this feature - the PL will still regulate effectively without it. Low Battery Disconnect works by turning the load off when the voltage falls below a pre-set point for a period of time. This feature is designed to trigger if the battery voltage drops for just a few moments (for example, because a motor has just been turned on). To use Low Battery Disconnect, you need to connect your load to the regulator as described on page 4, and you should also ensure that you have chosen a program where the Low Battery Disconnect feature is activated - see page 9. not Once the battery has recharged to a safe level, the load will automatically switch on again.

So, I wonder what voltage is considered "safe level"?

 

[BillC]

Checking power line noise at the Listening Post with the new "Power Line Noise Interceptor". Which really is a current transformer scaled to suit RF energy. It makes a good isolated mains tap for looking at induced voltages from noisy power supplies etc. There is a screen shot of power supply noise as generated by one of my oscilloscopes. The displayed image has not been calibrated for true level . There is a second screen showing a spectrum of noise traveling out of the Listening Post power cable to the house.

Check the images.

 

[VK3YNV]

Very curious? am I seeing peaks on the mains at 1260 kHz and 756 kHz? maybe the mains is picking up the strong MW stations?

Or am I reading that wrong?

 

[BillC]

Very curious? am I seeing peaks on the mains at 1260 kHz and 756 kHz? maybe the mains is picking up the strong MW stations?

Or am I reading that wrong?

Yes Ray there is a noise peak just below 1260 kHz too. and 756kHz is there too. Most of the other stuff seems to be hash, requires a bit of interpretation, amazing what will flow along a bit of wire !!

 

[BillC]

The Listening Post figures are good tonight Fri. 10.30

 

[VK3YNV]

Both antenna systems working brilliantly. Good result.