THE LISTENING POST.
- Thread starter BillC
- Start date
VK3EB
Active member
Hi Bill, we have some competition a new SDR, nice low noise site south of ACT, west of Cooma.
snowlinesdr.vk1hf.com:8073
more info
snowlinesdr.vk1hf.com:8073
more info
Last edited:
Just had a quick look at the snowline SDR, looks like a really good low noise site, seems like lots of patterned interference across wide sections of the bands, I wonder it it's solar regulator related or it's the woodpecker?
11.15 pm RX1 on top of list 41/32 Nice work!!
11.15 pm RX1 on top of list 41/32 Nice work!!
At the present time I am working on a common mode current choke for the co-ax feed to RX 1 V Loop, it seems to have reduced some of the modem noise around 2 megs by a good margin, more testing needed.
I noticed that pattern on snowline too Ray. I read somewhere that vertical patterned bars are caused by internally generated noise, switchmode power supplies etc and atmospherics show up as horizontal streaks along the frequency spectrum. We watch with interest the snowline venture.
e
I noticed that pattern on snowline too Ray. I read somewhere that vertical patterned bars are caused by internally generated noise, switchmode power supplies etc and atmospherics show up as horizontal streaks along the frequency spectrum. We watch with interest the snowline venture.
More work on the Listening Post . Chasing noise I placed a capacitor from B + to ground, at the battery of cells ,that seemed to knock some noise off. Soon I will solder a bonding wire to the CGI cladding in two places on each wall sheet right around the hut, that bonding wire will be connected to multiple grounding stakes driven in about 5 feet. The roof cladding will also be bonded by soldering every sheet to a copper wire. There will be two runs of roof bonding wire ,so the 4 ends will be bonded down to the wall bonding wires and thus to ground. We might end up with an RF tight box/hut which might stop stray noise from entering the Vertical loop. We shall see how we go.
VK3EB
Active member
Wanting to replace our current non standard figure 8, 240v power cable as feeders on the loops with some homemade balanced line I asked ChatGPT for help.
Question.
Dimensions of open wire line with 1mm conductors for 450 ohms impedance.
Answer.
For a two-wire open-wire transmission line in air, the characteristic impedance is well-approximated by:
Z0≈276log10 (2sd)Z_0 \approx 276 \log_{10}\!\left(\frac{2s}{d}\right)Z0≈276log10(d2s)
Where
You specified:
Solve for spacing sss
450=276log10(2s1 mm)450 = 276 \log_{10}\left(\frac{2s}{1\,\text{mm}}\right)450=276log10(1mm2s) log10(2s1 mm)=450276=1.630\log_{10}\left(\frac{2s}{1\,\text{mm}}\right) = \frac{450}{276} = 1.630log10(1mm2s)=276450=1.630 2s1=101.630≈42.6\frac{2s}{1} = 10^{1.630} \approx 42.612s=101.630≈42.6 s=42.62≈21.3 mms = \frac{42.6}{2} \approx 21.3\ \text{mm}s=242.6≈21.3 mm
Result
For a 450-ohm open-wire line using 1 mm diameter conductors:
Center-to-center spacing ≈ 21 mm
(Conductor-to-conductor gap ≈ 20 mm)
If you want, I can generate a table for other impedances or conductor diameters, or provide construction guidelines (spreaders, materials, mechanical spacing tolerances, etc.).
Yes.
Open-Wire Line Dimensions (1 mm Conductor Diameter)
Using the standard formula:
Z0=276log10(2sd)⇒s=d2⋅10Z0/276Z_0 = 276 \log_{10}\left(\frac{2s}{d}\right) \quad\Rightarrow\quad s = \frac{d}{2} \cdot 10^{Z_0/276}Z0=276log10(d2s)⇒s=2d⋅10Z0/276
Where
Spacing Table (1 mm wire)
Excellent result.
My RSGB and ARRL reference books collecting dust now.
Question.
Dimensions of open wire line with 1mm conductors for 450 ohms impedance.
Answer.
For a two-wire open-wire transmission line in air, the characteristic impedance is well-approximated by:
Z0≈276log10 (2sd)Z_0 \approx 276 \log_{10}\!\left(\frac{2s}{d}\right)Z0≈276log10(d2s)
Where
- Z0Z_0Z0 = desired impedance
- sss = center-to-center conductor spacing
- ddd = conductor diameter
You specified:
- Desired Z0=450 ΩZ_0 = 450\,\OmegaZ0=450Ω
- Conductor diameter d=1 mmd = 1\,\text{mm}d=1mm
Solve for spacing sss
450=276log10(2s1 mm)450 = 276 \log_{10}\left(\frac{2s}{1\,\text{mm}}\right)450=276log10(1mm2s) log10(2s1 mm)=450276=1.630\log_{10}\left(\frac{2s}{1\,\text{mm}}\right) = \frac{450}{276} = 1.630log10(1mm2s)=276450=1.630 2s1=101.630≈42.6\frac{2s}{1} = 10^{1.630} \approx 42.612s=101.630≈42.6 s=42.62≈21.3 mms = \frac{42.6}{2} \approx 21.3\ \text{mm}s=242.6≈21.3 mm
ResultFor a 450-ohm open-wire line using 1 mm diameter conductors:
Center-to-center spacing ≈ 21 mm
(Conductor-to-conductor gap ≈ 20 mm)
If you want, I can generate a table for other impedances or conductor diameters, or provide construction guidelines (spreaders, materials, mechanical spacing tolerances, etc.).
Yes.
Open-Wire Line Dimensions (1 mm Conductor Diameter)Using the standard formula:
Z0=276log10(2sd)⇒s=d2⋅10Z0/276Z_0 = 276 \log_{10}\left(\frac{2s}{d}\right) \quad\Rightarrow\quad s = \frac{d}{2} \cdot 10^{Z_0/276}Z0=276log10(d2s)⇒s=2d⋅10Z0/276
Where
- d=1 mmd = 1\,\text{mm}d=1mm
- sss = conductor spacing (center-to-center)
Spacing Table (1 mm wire)| Impedance (Ω) | Required spacing sss (mm) | Gap between conductors (mm) |
|---|---|---|
| 300 Ω | 11.2 mm | 10.2 mm |
| 350 Ω | 15.0 mm | 14.0 mm |
| 400 Ω | 18.0 mm | 17.0 mm |
| 450 Ω | 21.3 mm | 20.3 mm |
| 500 Ω | 24.8 mm | 23.8 mm |
| 550 Ω | 28.6 mm | 27.6 mm |
| 600 Ω | 32.8 mm | 31.8 mm |
| 650 Ω | 37.5 mm | 36.5 mm |
| 700 Ω | 42.8 mm | 41.8 mm |
Excellent result.
My RSGB and ARRL reference books collecting dust now.
Hi Dallas. I have just a moment ago fitted the Spark Gap / Gas Arrestor / bleed / 9:1 balun box to V Loop 1 , for RX 1. It seems to be working OK . The grounding wire is connected under the head of a wall sheet mounting screw, the lower end of the wall sheet is buried in the soil. Do you have the copper wire to make balanced feeder? A good look up on your part , all that information at a stroke, how quickly we adapt to the (New World).
The image shows the Balun box mounted under the Listening Post roof.
The image shows the Balun box mounted under the Listening Post roof.
Last edited:
VK3EB
Active member
Coming together nicely Bill
The homemade ladder line will use the current fig 8 cable just need to seperate the wires and install the little spacers and lock in place, probably have a spacer every 50cm but can move as required. 1mm wire and 25mm spacing equals approx 500 ohms impedance.
A sample…..
The homemade ladder line will use the current fig 8 cable just need to seperate the wires and install the little spacers and lock in place, probably have a spacer every 50cm but can move as required. 1mm wire and 25mm spacing equals approx 500 ohms impedance.
A sample…..
VK3EB
Active member
Ray, parts from the garden section bunnings using water sprinkler components, long riser tubes cut to length and little threaded joiners which screw into ends. all good for UV environment. could be a 3D printer project but not having a printer I have made before already having a jig to make it simple.
https://www.bunnings.com.au/pope-450mm-rigid-riser-with-adaptor-10-pack_p3120413
https://www.bunnings.com.au/pope-450mm-rigid-riser-with-adaptor-10-pack_p3120413
thanks for that
i tried hunting around bunnings for something to use in ladder line , i was going to use bic biro's as spreaders but couldn't get them cheap enough (or find enough freebies
) so I printed some spreaders off on the 3d printer
VK3EB
Active member
Attention Bill.
Narrowcast Greek (1683kHz)
Two stations on same frequency one in Melbourne one in Sydney. Sydney Tx is 280Hz high in freq so night time can hear the beat.
This SDR in south-west can receive station at good strength, which confirms off frequency, also audio high distortion assume over modulation?
The ACMA as a regulator basically useless in this area of narrowcasting.
Narrowcast Greek (1683kHz)
Two stations on same frequency one in Melbourne one in Sydney. Sydney Tx is 280Hz high in freq so night time can hear the beat.
This SDR in south-west can receive station at good strength, which confirms off frequency, also audio high distortion assume over modulation?
The ACMA as a regulator basically useless in this area of narrowcasting.
Those types of station seem to lyke distrtion.
I think it's these guys. 1683am The Hellenic Radio Station of Australia
https://1683amgreekradio.com/
https://1683amgreekradio.com/