Amateur Radio Wiki - User contributions [en]

Capacity hat

2013-08-20T13:41:19Z

LDighera: Added top hat photograph, but it needs to be re-sized

'''Capacity Hats'''

by Lou Rummel KE4UYP

Capacity hats will reduce the amount of inductance necessary to resonate the antenna, and increase bandwidth. But contrary to popular belief they add nothing to the radiation resistance. For a component of an antenna to increase radiation resistance it must itself radiate.

It is true if you put a Capacity hat on top of a short mobile antenna it will change the antennas efficiency but what happens is the current on the radiating element moves further up to the top.

Because the current is now further away from ground this lowers ground loss. So the ratio of radiation resistance to ground loss and Omni Loss resistance, which is the reduction in the amount of inductance needed for the loading coil, goes down.

Although it is true that the input impedance of antennas using Capacity Hats is higher than coil loaded antennas this is not an indication of an increase in radiation resistance, for the same reason that a folded dipole with 300 ohms impedance has the same radiation resistance as a standard 73 ohm dipole.

[[File:15m_tophat_P1020593.JPG | frame | Figure 1: Capacitive hat added to 40-meter wire dipole elements lower resonant frequency so that it lies within the 15-meter band. Source: KJ6YVT ]]Related Wiki pages: [[Antennas]], [[Electronic Theory]]

{{antennas}}

File:15m tophat P1020593.JPG

2013-08-20T13:05:03Z

LDighera: Figure 1: This capacitive hat was added to each leg of a 40-meter dipole element to cause it to resonate at a lower frequency within the 15-meter band.

Figure 1: This capacitive hat was added to each leg of a 40-meter dipole element to cause it to resonate at a lower frequency within the 15-meter band.

Beam

2013-08-20T04:06:21Z

LDighera: Added Hex-beam stub

Related wiki pages : [[Antennas]], [[Bands]], [[Propagation]]

[[Loop]]

[[Quad]]

[[Quagi]]

[[Yagi]]

[[Hex-beam]]

{{antennas}}

RTL2832

2013-08-20T03:17:16Z

LDighera: Added external link to SDR-Radio Console program that promises to be a new way forward for SDR software.

The '''RTL2832''' is an IC produced by Realtek Corporation to demodulate DVB-T (digital TV) signals and send them to a host computer over the USB bus. It has an additional mode designed to allow reception of consumer FM radio, and this is achieved by capturing I/Q samples and forwarding them to the host computer for demodulation and playback.

This feature was discovered by a Linux kernel developer while writing a Linux driver for devices using this chip, and the discovery was quickly put to use by implementing drivers for SDR programs such as [[HDSDR]], turning these devices into cheap [[Software Defined Radio (SDR)]] receivers. As the devices have a wide tuning range (typically continuous from 64MHz to 1.7GHz) they are very flexible.

As so many devices have been produced based around this chip, it is difficult to reliably tell which devices are suitable for use with SDR. There is a community maintained list on Reddit documenting [http://www.reddit.com/r/RTLSDR/comments/s6ddo/rtlsdr_compatibility_list_v2_work_in_progress/ which devices are known to work].

== Capture bandwidth ==

The SDR mode of the chip is theoretically capable of capturing up to 3.2MHz of the RF spectrum at one time, however the largest sample rate successfully received without sample loss is 2.8MHz. This means any signal to be demodulated must fit within 2.8MHz of the RF spectrum. For comparison, a consumer FM radio signal has a bandwidth of around 120kHz, and a TV signal (with audio) is 6-8MHz.

== Frequency range ==

The '''RTL2832''' chip does not perform any RF tuning itself, so it must be paired with a suitable tuner chip to enable signal reception. At the time of writing, the available USB devices use one of the following tuner chips:

{|class="wikitable"
!rowspan=2| Tuner !!colspan=2| Advertised frequency !!colspan=2| Actual frequency
|-
! Min !! Max !! Min !! Max
|-
| Elonics E4000 || 64MHz || 1700MHz || ~30MHz || ~2100MHz
|-
| FC0012 || ? || ? || 30MHz || 945MHz
|-
| FC0013 || ? || ? || ? || ?
|-
| FC2580 || ? || ? || ? || ?
|}

As the tuner chip dictates the frequencies available for reception, the Elonics chip is typically favoured as it has the greatest frequency range.

== External links ==

* [http://sdr.osmocom.org/trac/wiki/rtl-sdr rtl-sdr] at the osmocom wiki
* [http://wiki.spench.net/wiki/USRP_Interfaces Balint Seeber's wiki] with instructions and downloadable installer for getting HDSDR working with an RTL2832 device under Windows
* [http://v2.sdr-radio.com/ SDR-RADIO.com] MS Windows console for SDR receivers and transceivers. By: Simon Brown (HB9DRV)

[[Category:Software-defined radio]]