Cable-TV Amplifier with 5 Outlets

Here's the design of a cable TV distribution amplifier (CATV). This cable TV distribution amplifier has 5 outlets. This amplifier boosts the TV cable signal with 18dB before the signal is split into 5. The design is based around a MAR-6 MMIC. This Integrated Circuit amplifies DC to 2GHz with about 18dB, uses only 15mA and costs around 4,5 Euro.

The CATV distribution amplifier circuit is built on a piece of double sided circuit board with one trace cut out with a sharp hobby knife. It is housed in a standard metal housing, that holds the 6 F-connectors for the HF. A 7805 is used to stabilise the electrical power.

The electrical power (8..30 VDC - 50mA) enters the housing via a (1n) feedthrough-Capacitor. A single diode protects the circuit from reverse polarity voltage. A 7805 soldered to the housing (GND) stabilises the voltage at 5 Volt. Two 100nF capacitors prevent the generation of spurious signals and noise by the 7805

The HF signal enters via a F-connector. An optional attenuator (0,75 - 20 dB) gives the ability to decrease the signal strength in case you should experience interference by intermodulation products. In my situation, I ended up adjusting the attenuator at the maximum level…

After the attenuator, the signal passes through a 1nF capacitor to block DC voltages and goes into the MAR-6. The input to the MAR-6 is indicated by a dot on the body and a chamfer to the input leg.

Power is supplied to the output of the MAR-6 through a 100 Ohm resistor and a 6 hole ferrite choke (1uH). DC current will be about 15mA (3,5 Volt DC at the output of the MAR-6). Another 1 nF capacitor blocks DC and only HF signal is sent to a passive resistor splitter, made from 51 ohm carbon film resistors. Input impedance is 50 Ohm for the MAR-6. Output impedance will be a little less than 75 Ohm. The splitter is build as a 'spider web' floating over the circuit board. Each output is has a female F-connector. All F-connectors are soldered directly to the housing.

After closing the lid of the housing, the circuit should be reasonably immune to the 5 x 1.5 kW Digitenne (DVB-T) transmitters built less than 3 kilometre from my house L

Safety ground
I placed the amplifier right where the cable enters our house, and routed coax to all outlets. The housing is connected to safety-ground with a copper wire.

CATV Amplifier Power supply
For power supply, I use a non stabilised adapter. Unloaded, the output is 8,5 Volt DC, just enough for the 7805 to do its job.

Source: Cable-TV distribution Ampplifier

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25W Broadband RF Amplifier 88-108 MHz

This RF amplifier for FM 88-108 MHz with no tune (broadband) needed to cover all the FM Band. This RF Power amplifier is equiped with the famous Mosfet transistor the BLF245. Depending on the output power level you are able to provide with your FM synthesizer, you can use or not the 2N3866 driver stage included in this amplifier design.

Impedance matching network file(PDF)

All the impedance networks (Input-Output) of this RF amplifier have been determined by using the softwares: Mimp.EXE and Genesy.

Low pass filter measurements file(PDF)

This RF Amplifier need a 9 elements low pass filter ensures that its harmonic frequency meet at least a 60 dB rejection from the carrier.(RF Simulation with RFSIM99)

Gain and Ros measurements file(PDF)

The RF FM amplifier has a 27 dB gain (with driver stage) and provides 25W with a 58% efficiency.

RF Power Amplifier PCB Layout

Source: 25W MOSFET FM AMPLIFIER

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Frequency Converter 2.4 GHz to 700 MHz

It's theoretically possible to convert a 2.4 GHz wireless LAN signal to a much lower frequency to help overcome non line-of-sight issues. Many UHF television frequencies in some areas are currenty unused. Those would be great to hijack. You could then use common directional UHF TV antennas for your links. This current design is theory only.

It might even be possible to hack the local oscillator out of an old 2.5 GHz MMDS down converter and use that to drive an external frequency converter.

 

This might help overcome non line-of-sight issues most people are facing today. Fairly high antenna gain and RF output power should reduce the multipath conditions which degrade wireless data links.

The theory is to mix 802.11b channel 9 (2451 MHz) with a local oscillator frequency of 1536 MHz. The resulting IF frequency is 915 MHz, which is the new transmit/receive frequency. You then will do a little dance to the Gods to keep pagers and cellphones from destroying all your hard work.

The actual bandwith of the RF signal of the final direct sequence spread spectrum signal is 22 MHz wide, between 904 and 926 MHz - centered at 915 MHz.

You should also lower the data rate, say to 1 Mbps, this reduces the TX/RX switching times a bit.

It might also be possible to transvert down to the unused 600 to 700 MHz UHF TV frequencies. You could use those cheap, high gain UHF TV antennas and scrap cable TV hardline.

This design is for reference only, it hasn't been built completely yet. There are several quirks that will need to be worked out: the use of resistive isolation pads at various points, diplexer on the mixer's IF output, PLL loop filter values, and various switching voltages. It can be used as a start to the TAPR Summer 2003 PSR callout for 802.11b transverters.

Since in most urban areas the 900 MHz band is actual worse than the 2.4 GHz band in terms of interference, it may be possible to use this as an IF rig for lowering long coax losses, or even further transverting to the 440 or 1.2 GHz bands.

Source: 2.4 GHz to 700 MHz Converter

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