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I never thought my hobby with SDR would get me on the front page of the news paper.

I never thought my hobby with SDR would get me on the front page of the news paper. submitted by /u/SDR_Lumberjack
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Antennas • Guidelines for choosing coax cable for use >1000 MHz

Guidelines for choosing coax cable for use >1000 MHz possibly not complete, but that should suffice for a start:

Know which impedance receiver has and you know what impedance your coax cable and connector should have

Decide if you desire low loss, max. shielding or both
While low loss per dB/m (or db/ft) is desirable, if you receive interference through a bad braid shield of a cable, despite using a filter, low loss won't make you happy either.

There is no coax cable that is cheap, provides low loss, max. shielding and stable impedance,
but you can optimize

The price will differ with availability and country, and should get cheaper the more you buy
Unless you can buy a ring of e.g. 100m and share the cost with a friend, you will pay more per meter.

It's not just the coax cable price, but take into account the cost for the connectors and possibly adapter
Coax connector for a cheap coax cable of uncommon dimensions can be more costly.

Now that you know what you want, you have to choose the best cable for you

Buy only name brands coax cable

Inform yourself which coax cables, from which manufacturer and the price are available, where you live
check the cost for coax connectors and adapters

For some cable types like e.g. "RG-58" type, you need also the letters following the RG-58 or even the serial number to be able to identify which cable you will get.
If you check the Belden datasheets you will find several RG-58 type coax-cable, which differ in attenuation, shielding and therefore price.
Note: Better shielded coax cables, double shielded, with PTFE isolation, are also available in the RG-58 diameter, but are as consequence more expensive.

download the data sheets from the manufacturer and compare the attenuation and shielding factor and decide which brand name cable you can afford.

Mechanical considerations

1. bending radius, make sure that you can easily mount the cable
The best cable is not worth spending the money if you damage the cable by bending it to much. Because the min. bending radius was not observed, several hundred meter of expensive 1" coax cable had to be replaced

2. mechanical stress on coax connectors, cable, adapter and receiver
you can get SMA adapter even for thick coax-cable 1/4" or much larger, but remeber that you have to avoid mechanical force and continued stress on all component.

Attenuation and shielding
I would not call/consider any coax that has the diameter of the 50 Ohm RG-174 type coax a good quality thin cable for use at 1 GHz.
Belden identifies the attenuation in the data sheet to be 1.08 dB/m @1000 MHz loss. If you use a cable with PTFE it's down to ~0.8 dB/m @1000 MHz.
The minimum cable for a few meter should be a brand name e.g. 9201 Coax - RG-58/U Type , Belden for loss 0.476 dB/m @1000 MHz, 20 AWG solid .033" bare copper conductor, polyethylene insulation, bare copper braid shield (80% coverage), PVC jacket

While also being called RG-58 type, the 7807A Coax - RG-58 Type has less than 0.3 dB/m @900 MHz, a 17 AWG solid .044" bare copper conductor, gas-injected foam HDPE insulation, Duofoil® (100% coverage) + tinned copper braid shield (95% coverage), polyethylene jacket.

Then there are fully shielded cable, like cellflex, that have a solid cooper shielding and provide therefore 100 % shielding. In addition to the higher price, they should not be moved or bend more than a few times.

As for 75 ohm CATV-cable I bought a 100 m ring double shielded WISI MK-90 for about 50 Euro at the time. The newer MK-91 has now triple shielding and ~0.2 dB/m @1000 MHz attenuation, which is mechanically not as stable for continued moving/bending, and has to be impedance matched to 50 ohm receiver antenna input.

Power rating
While not of interest for receive only, the power handling capability of a coax cable is something to consider if you also transmit.

Statistics: Posted by snn47 — Wed Oct 09, 2019 8:17 pm

Antennas • Re: guidance for asking antenna related questions improves chances for an answer -proposal for a sticky post

@nizz -freq scan noob
I tried to rephrase and provid an example. Does this explain it better?

- transmisson line loss (cable and connectors)vs. antenna gain
guidance for choosing coax cable can be found here viewtopic.php?f=6&t=4861&p=12432#p12432
All transmission lines have an attenuation which increases with frequency.
The overall attenuation of a transmission line and connectors can be calculated by multiplying the attenuation for the operation frequency of the coax cable type used specified by the manufacturer in dB per 100 meter [dB/100 m] or dB per 100 ft (dB/100 ft) by the length of the cable used.

Each connector used between antenna and receiver will add a few tenth of a dB of attenuation, the same applies to adapter e.g. those used to convert from one connector type to another. The actual attenuation of connectors varies with the connector type (e.g. simple coax connector, threaded types like N, TNC, SMA, or Bayonet types like C, BNC, ) or for how many connections they are rated, some versions for as low as only 5 connections.

Any gain obtained by an antenna is easily offset to a large degree by the attenuation of a few meter of high loss transmission lines on higher frequencies (e.g. thin coax like RG-174)

For example you connect a monopole optimized for 1000 MHz with about 5.25 dBi via 5 m of coaxcable to a receiver

If you use RG-174 from Fairview which specifies the max. frequency as 1000 MHz and an attenuation of 1.0499 dB/m (https://www.fairviewmicrowave.com/image ... /RG174.pdf ), the cable loss for 5 m of their RG-174 would be 5.25 dB and compensate all of the antenna gain.

If you use a more rigid, but low loss ¼ inch Cellflex coax cable instead e.g. LCF14-50JFN from RFS which specifies the attenuation of 0.139 dB/m the attenuation is reduced to just 0,69 dB for 5 m LCF14-50JFN, leaving you with an antenna gain of 4.5 dBi.

Therefore it is often more sensible to use coax cable that provides low loss at the frequency you want to receive at, than trying to increase antenna gain to compensate cable loss.

Please note: unfortunately not all coax cable of the same type (e.g. RG-58) will have similar loss. There are also cheap knock off copies, with just a few strands of wire as shield without providing any real shielding, and do not reach the low attenuation by brand name manufacturers.

Statistics: Posted by snn47 — Wed Oct 09, 2019 7:57 pm

KerberosSDR • Re: KerberosSDR Developments in 2020

[*] Networked DFing - With several networked KerberosSDR units spread out around a city it will be possible to instantly direction find any signal.
I'm actively working on my own implementation of this. I would love to work together if you're interested.

[*] Hardware: Switches and an improved calibration PCB - It should be investigated if switches degrade the phase calibration or not. With switches we could eliminate the need to disconnect the antennas when recalibrating.

I am presently experimenting with the HSWA2-30DR+ from Mini-Circuits. The PCBs just arrived in the mail today and I will have results by Sunday night. This chip allows selecting between 2 antennas and an internal 50 ohm load.

Statistics: Posted by ckoval7 — Wed Oct 09, 2019 7:35 pm

Попробуй обнови или переставь библиотеки MV C++ Вы это кому?

ivanovgoga пишет:
Попробуй обнови или переставь библиотеки MV C++ Вы это кому?
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Широкополосный приёмник из DVB донгла - Страница #577

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Попробуй обнови или переставь библиотеки MV C++

endemos пишет:
Попробуй обнови или переставь библиотеки MV C++
читать полностью...
Широкополосный приёмник из DVB донгла - Страница #577

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FM Block filter before or after LNA?


I have a RTL-SDR dongle and got some time ago an LNA which works great. The problem is FM radios are now way too powerful and harmonics are messing up several parts of the spectrum. That's why a FM block filter is on the way.

Now my question is: Which way is better?

Antenna --> FM filter --> LNA --> PC


Antenna --> LNA --> FM filter --> PC

I'm guessing it's the first one so the FM filter doesn't have to stop a powered up signal but I'd like to have a more experienced opinion.


submitted by /u/EPerezF
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Choosing LNA

submitted by /u/ZbychuButItWasTaken
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No SSTV from ISS, can you confirm?

submitted by /u/derekcz
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Comment on RTL-SDR Tutorial: GPS Decoding and Plotting by Garmin Care

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