Use 2: i.e Antenna followed by Filter. The small insertion loss of the filter shouldn’t be a problem.
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Update!! @abcd567 I have found a similar board like the Skordo Filter + LNA one which you’re using. This is found from a from a Indian website(similar to Aliexpress based in India).
It cost’s around $52.82. I have also compared with the Skordo and didn’t found any differences.
It’s a waiting game now. Once again thank you @abcd567 for posting your setup. It was very helpful.
Great question - you can usually start an aurgument with this one!
In general, I agree with @jimMerk2, but site specific conditions may need to be concidered.
In a high-noise location, accepting the insertion loss of the filter will give better results.
In a low-noise location, placing the filter after the amp negates the filters insertion loss, also filters noise generated by the amp.
Its a high-noise location in my case based on the results of the scan.
I have just finished my 12 elements coco and its testing day 
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Your snd my situations are similar. Like you, I live in an apartment in a high-rise building, and not allowed to install anything on roof or outer walls of building. As a result my installation, including antenna, is indoor. Height is not an issue, it is rather very good. Also coax length is only a meter or two. Both these factors are to my advantage The main problems are:
(1) The 360° View is restricted to nearly 220° by my own building
(2) Part of this 220° view is further obstructed by nearby high-rise building.
(3) There are Cell/Mobile phone antennas installed on roofs of my building as well as nearby building. As a result the RF interference is very high and if I remove the filter, my reception drops to less than 50%
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Yep, seems to be tough conditions. + In my case, the nearby airport is a low traffic one(about 80 departure and arrivals) making the stats very poor. Peak hit was 280 aircraft’s.
The testing of recently crafted12 elements coco is heart breaking as its under performing when compared with 8 elements coco. The top element(1/2 wave) is shorted at the end.
I would like to swap the top element like your mentions here
and few others like 1/2 wave, 1/4 wave with center wire projecting in air, center wire shorted to braid etc.Does it make any big differences @abcd567 @geckoVN
I’ve never read a theoretical (mathematical) explanation for the short or 50R resistor below the top element, so try it without.
The design is very dimentionaly sensitive, so don’t give up if your first doesnt work (most don’t).
You need to use a quality brand of coax with datasheet you can trust and you want the highest Vf you can find.
The greatest influence on the Vf is the inner dilectric, so you want foam or cell dilectric for the best chance of success.
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@geckoVN I have made my both coco’s based on https://www.balarad.net/ in which his calculations are matching with the VF of the coax which I have used. Here’s the data sheet from the manufacturer of the coax.
8 element coco plotted a maximum range of 222nm once without any filter or LNA. So there might be some dimensional errors in the 12 elements coco. Also I noticed that lower end of 12 coco is slightly bend towards one side(as the holding pipe length is not enough). Does it downgrade the performance?
Also I didn’t understand what’s meant by Jelly flooded
“Jelly Filled” has a greater resistance to moisture penetration and is commonly used where the cable is buried.
The “jelly” is petroleum jel. Sold retail as Vasaline or similar.
What material is the suport pipe?
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To get a CoCo lengths right, nominal VF is not accurate enough for this kind of antenna.
If you can find / purchase a Vector Network Analyzer ($$$) or NanoVNA ($), you can measure the exact VF of your coax at 1090MHz. Be sure your NanoVNA covers the 1090 MHZ range. Here is a good starting point to see how to measure the VF: measure velocity factor with nanovna at DuckDuckGo
Example Amazon NanoVNA: AURSINC NanoVNA-F V2 Vector Network Analyzer 4.3inch 50KHz-3GHz HF VHF UHF Antenna Analyzer Ham Radio, 5000mAh Battery, Measuring S-Parameters Voltage Standing Wave Ratio Phase Delay Smith Chart: Amazon.com: Industrial & Scientific Find one based on the spec’s and reviews. Truly amazing what these little devices can do.
As you build your CoCo antenna, connect it to the NanoVNA as you add each segment and check for the Resonant frequency of the evolving antenna. You want the lowest Standing Wave Ratio, (SWR) to be as close to 1090 MHZ as possible. Based on your measured VF, cut the first coax length to a bit longer than the formula length, then trim the coax length by tiny amounts to increase the frequency. To lower the resonance frequency, replace the top segment with a slightly longer segment and repeat. Continue until you feel you have enough segments. Note: bit of a diminishing returns by adding more and more segments. Every 3db gain increase requires doubling the number of segments. 8 segments seems to be a sweet spot for CoCo’s. Don’t ask how I know that.
If your antenna will be outside or just need some protection, suspend it inside a weatherproof tube. White PVC contains materials that attenuate these frequencies, so you may want to use some other piping.
As my granddad said “Almost nothing worthwhile is ever easy”. Have fun and build a KickArse Antenna. You will never regret success. This is making me want to build another CoCo!
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Its a 1meter long PVC conduit. But the antenna is not inside the conduit as I got poor results when I tested the coco inside the conduit.
I have planned to move the 8 elem coco to a new PVC conduit(bigger one) with the proper connectors like T, Angle sections to build a nice antenna mast.
Also will try to include a provision in the mast to test my cantenna’s.
I’d look for a different support if you’ve demonstrated “this” pvc conduit is a problem.
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@wiedehopf Cantenna’s and spiders are my first preferences before making these coco’s(As I have read coco’s are failures most of the times).
The measurement was 69mm and performed good as I got a range about 140-150nm with first(left) antenna. The second one(right) was made with 10 legs(with a bobbin to hold the radials) but the results are same as first one. My glue gun was broken, so I’ve burned the stick directly over the bobbin to fix the radials.
I have got 170nm peak range with the bigger cantenna and few messages from obstructed views too(when compared with coco)
Let me move the coco to new mast and I’ll update the test outputs here(Inside and outside the conduit)
For me the spider seemed to work a bit better with the whip a bit shorter.
But it’s not typically a huge difference.
I wouldn’t worry about cantennas at all if you have spiders already.
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Does it make any major flaws in the performance?
The 12 element coco testing has been done and I saw a downgrade in the performance when compared with 8 elements coco. I assume the problem is with the topmost element.
So today I’m going to do few changes to the 12 elements coco by replacing the top element.
- 1/2 wavelength top element with a 1/4 wavelength center conductor up in the air
- Same as 1st + 1/4 conductor shorted to the coax shield using a piece of coax center conductor
- Same as 1st + 1/4 conductor shorted to the coax shield using a resistor of 100Ohm (I didn’t get a 50 or 75ohm resistor in local shop)
All your suggestions and feedback’s are welcome. @geckoVN @abcd567 @wiedehopf @astrodeveloper
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Welcome to the forum! Since you have strong GSM interference, a 1090MHz filter + LNA would help. The RTL-SDR wideband LNA may still amplify GSM signals, so a dedicated 1090MHz filtered LNA or a separate SAW filter before the LNA would work better.
If you can’t find one locally, check with ham radio groups or electronics suppliers in India. Looking forward to your test results!
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I made my first 2m ham antenna like that lol.
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