A 1928 Hartley

After seeing my 1934 transmitter a friend asked if I was doing anything special for the Bruce Kelley Memorial 1929 QSO Party coming up in December. Last year I put my TNT transmitter and SW3 on the air. This year it might be interesting to try a Hartley oscillator.

As ham radio approached January 1, 1929, and the more rigorous standards, the ARRL encouraged hams to improve their stations. One improved transmitter design was a single tube Hartley oscillator described by Ross Hull in the August 1928 issue of QST. Bruce Howes, W1UJR, covers this design on his web site here.

I've been searching through my junque box looking for the parts I need. The first step was a parts list and an enlarged scan/photo of the transmitter. After picking through multiple boxes and peanut butter jars I've lots of possibilities. Now it's a matter of sorting through what I have for the parts that match the original design.

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Designing a Combiner for VHF/UHF

Here's is one way of combining several antennas on VHF/UHF is by using a power combiner (or power splitter if you prefer to look at it from that angle). Using the principle of impedance transformation in a quater wavelength transmission line, a proper matching can be made between antennas and the downlead cable.

To build a RF combiner you need to design a coaxial quaterwave line, having a characteristic impedance Zo, determined from Zo^2 = Z1*Z2, where Z1 and Z2 are the impedances being matched. This is normally done by using tubing - round or square - with air as dielectricum.

Simple impedance calculation
The characteristic impedance for the two types of lines are:

a = the diameter of the inner round conductor.
b = the inner diameter - or side lenght - of the outer conductor.


Combiners for 144, 432 and 1296 MHz
2-way combiner for 144 MHz.
4-way combiner for 432 MHz.
2-way combiner for 1296 MHz.

Exact impedance calculation

See more : 2.4 GHz Power Amplifier - RF Power Meter -  UHF Power Amplifier

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40-900 MHz Signal Amplifier-Booster

This is a small amplifier of signal that cover the frequencies from 40 to 900 MHz. Those frequencies include TV in VHF and UHF and also radio in the frequencies of 88 - 108 MHz, strip of FM. The signals in up to 20 dB, becoming possible to receive even the weakest signals. Below is the circuit diagram.

The circuit is built in turn of an UHF broadband transistor, BFR 90. This transistor can operate as loud as 1.6 GHz in frequencies, and it has an gain of 23 dB. The signal of the antenna is applied the input of the circuit and for C5 it is coupled to the base of the transistor. It is amplified and of the collector of BFR90, through C2 and C1 it is taken the input of RF of the radio or receiver of TV. The circuit operates with a battery of 9V small that, because of the very low consumption of the circuit, it will last plenty of time.

Here's Printed circuit boards and component layout of the signal amplifier

Characteristic and Specifications technique for signal amplifier-booster with BFR90

• Answers of Frequency: 40 - 900 MHz
• Gain: 20 dB
• Maximum level of output: 90 µV
• Input-output impedance: 75 ohm

Signal Amplifier Circuit's Parts List
R1 = 82 Kohm
R2 = 270 ohm
R3 = 1,5 Kohm
R4 = 120 ohm
C1,C3 = 100 PF
C2 = 2.2 pF
C4,C5 = 1 nF
D1,D2 = 1N4148 diode
Transistor = BFR90, BFR91, BFR90,
Several = PCB, solder, battery 9V, metallic box, clip to battery, etc.
L1, L2=diameter: 5 mm thread diameter:0,5 mm turns: 8

See more : Stereo FM Transmitter

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FM Transmitter With BF494

This is a small circuit fm transmitter using transistor BF494 . The reach of the transmitter will depend a lot on this antenna, of the feeding of the circuit and of the place where will happen your operation.

With a feeding of 6 V (4 piles AA) and an antenna of about 40 cm of length, we can arrive to the 200 meters. With a smaller antenna, or in place with many structures of iron (flagstones) the reach will be sensibly reduced. A common wall without metallic structure is not obstacle for this transmitter.

Below the circuit schematic and Printed circuit board fo the fm transmitter

Parts List of the micro fm transmitter

Transistors:
Q1 - BC558
Q2 - BF494
Resistors:
R1--4,7 KΩ
R2--220 KΩ
R3--22 KΩ
R4--10 KΩ
R5--6,8 KΩ
R6--47 Ω
Capacitors:
C1--10 µF/16 V - ELECTROLYTIC
C2--4,7 µF/16 V - ELECTROLYTIC
C3--10 nF - ceramic
C4--4,7 pF - ceramic
C5--100 nF - ceramic
CV--trimmer from 3-30 to 5-50 pF
Other:
MIC--microphone of electret of two terminals
L1--Reel - to see text
S1--simple Switch
B1--3 to 6 V - 2 to 4 small piles
The--antenna - to see text Printed circuit board or bridge of terminals, box for assembly or hollow book, support for 2 or 4 small piles, threads, it welds, etc.


Source: Toni Eletronica

See more : Stereo FM Transmitter

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FM Transmitter 2N2218

Here's simple FM transmitter circuit using transistor 2N2218. Micropohone is a microphone of electret of two terminals and the antenna should possess from 15 to 40 cm.

Below is schematic circuit of the fm transmitter

Printed Circuit Board (PCB) and Component Layout of the fm tranmitter

Parts List of the fm transmitter
Resistors
R1 = 2,2 kΩ
R2 = 4,7kΩ
R3=5,6kΩ
R4 = 47Ω
Ceramic Capacitors
C1=4,7 nF
C2=2,2 nF
C3 = 4.7pF
C4 = 100 nF
C5 = TRIMMER CV 3-30 PF.
Transistor:
T1 = 2n2218 or equivalent.
Other:
L1 =  5 turns of enameled thread 22 AWG, diameter of 10 mm.
B1 = Battery of 9 volts alkaline.
Mic1 = electret microphone.
Several = printed circuit board, antenna, box, etc.

Source: Toni Electronica

See more: FM Transmitter Circuit

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Camping and Picnic Table QRP

This last weekend we planned a campout at Frontenac State Park. We've picniced there several times but have never camped over night. No camping trip packing list is complete without my K1. (This time we did forget the blankets and pillows but the K1 was loaded.)

I ended up getting several chances to ham. After a quick listen on 20 and discovering the CQ WW RTTY contest in full swing I moved to 30 mtrs for the weekend. The antenna was a 45' endfed wire (1/2 length wave on 30 mtrs) in a tree next to the campsite. It was approximately broadside to the NNE but did a great job into the northeast US. Between Saturday and Sunday I worked W3XAF (MD), KB3TJS (MD), W0IMD (CO), AA3TH (PA), WA1IIE (ME) and KD3DK (PA).

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Making 1 to 4 Balun for Matching Impedance

Here's the way to match 75 Ohm to 300 Ohm impedance. In case of making balun for 200-300 Ohm folded dipole antenna to 75 Ohm transmission cable.

Please see table on image above to determine velocity factor for different cable type.

Please check out my 4 Watt FM transmitter!

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Audio Limiter/Compressor for Electret Desk Microphones

This electronic circuit is audio limiter compressor specifically designed to use with very low-cost electret desk microphones. Overcomes the heavy attack/decay problems with diode rectifier VOGAD circuits.

A TL074 IC was used with a dual supply of +/-5v Note the lack of rectifier diodes in the feedback loop, instead the circuit uses high gain BC848(smd BC108) This uses the full wave rectifier effect to give a non-linear compression level avoiding the worst of the 'pumping' normally noticed with discrete diodes. R38 sets the compression level/bias point to suit the hfe of the selected transistor. Note Q2 is a P channel Junction FET eg J176.

Source: http://www.g8ajn.tv/projects.htm

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VHF Video Transmitter 60-200 MHz

Here's a simple video transmitter for VHF TV channel will accept baseband video input, hence it can be driven by most CCD cameras and VCR video outputs. It ouputs roughly 80mW and when used with a 40cm telescopic antenna over 100 metres range is possible.

The transistor of the video transmitter can be a BC108, BC546, BC337 or a 2N2222. L1 is wound on a 10 mm air former. Use 6 turns 24 SWG for frequency 60-80 MHz, 4 turns for 150-180 MHz, and 2 turns for 180-200 MHz

You can use this with a monochrome or color video signal. To transmit sound just build the wide band FM transmitter and tune it to the audio channel.

See more : Audio Video RF Modulator - PLL FM Transmitter - Circular FM Antenna

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40W Broadband FM RF Power Amplifier

Here's broadband RF power amplifier for FM amplifier design is based on Motorola MRF171A MOSFET. The amplifier was constructed in a small aluminium diecast box. RF input from transmitter and output connections are made by coaxial sockets. The power supply is routed through a ceramic feedthrough capacitor bolted in the wall of the box.

This constructional techniques results in excellent shielding, preventing RF radiation escaping from the amplifier. Without it, significant amounts of RF radiation could be radiated, interfering with other sensitive circuits such as VCOs and audio stages, also significant amounts of harmonic radiation could occur.

Any RF power amplifier must be followed by a low pass filter (LPF) to reduce the harmonics to an acceptable level. What this level is in a unlicensed application is a moot point, but as the output power is increased, more attention must be be paid to the harmonic suppression.

In this RF power amplifier design used a 7 pole Chebyshev low pass filter. A Chebyshev was chosen as the phase and amplitude ripple within the passband was not critical, and the Chebyshev gives a better stop band attenuation than compared to say, a Butterworth. The design stopband was chosen to 113MHz, giving a 5MHz implementation margin from the highest desired passband frequency at 108MHz and the start of the stopband at 113MHz.

The next critical design parameter was the passband ripple. For a single frequency design it is normal practice to choose a large passband ripple, for example 1dB, and tune the peak of the last passband maxima to the desired output frequency. This gives the best stopband attenuation because greater passband ripple results in more rapid stopband attenuation. A seven pole filter has 7 reactive elements, in this design four capacitors and three inductors. The more poles, the better the stopband attenuation, at the expense of increased complexity and more passband insertion loss. An odd number of poles is required as both the input and output impedance was designed to be 50R.


40W Broadband FM RF Power Amplifier

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More 1934 Transmitter

Remember the safety problem with my 1934 transmitter? One of the phone plugs is for metering and the other is for the key. If, in the heat of the moment, I get the two mixed up and plug the key into a B+ metering jack, I'll have over 300 volts on the key.

To protect myself I tied a length of string and a plastic cable clamp to the key phone plug (any lump of plastic would work). After the key is plugged in I slide the cable clamp under the front edge of the transmitter. The string is short enough that the plug can not be removed without getting the clamp out from under the transmitter.

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RF Low Pass Filter 1.8-145 MHz

This lowpass filter circuit is a very basic filter. It required to remove the harmonic frequency content of the transmitter and can be used on frequency 1.8 - 145 MHz.

The cut off frequency of the filter can be achieved by making C2 and C4 variable trimmer acurate filtering. All coils are 22 SWG wound on 10mm Air former spaced at 2mm.

For making coils of the lowpass filter, download this RF Calculation Software and the list of Wire Gauge below.

Source: Ajpotts

See more: FM Transmitter

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A 1934 transmitter - On the Air

Yesterday I set up my 1934 transmitter up with my NC101X and tried the pair out on 80 meters using my endfed 105' inverted "L" antenna only about 10'-20' off the ground. The station worked fine.

At 21:45 I had a nice QSO on 3570 with NG9D in Plainfield, IL. Lynn's signal varied from 589 to 599+. He reported that my 589 signal sounded fine/stable.

Also shown in the picture is my iambic keyer set up to key older tube rigs.

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More 1934 transmitter - It Works!

I've finished wiring my 1934 transmitter, powered it up and it works! With about 300 volts on the plates of the 46s and the 47 it loads to 15-20 watts input and 7-10 watts output. It sounds great also.

One change I made from the Bill Orr design is to connect the 47 screen to regulated 150V rather than a resistor network off of B+.

This transmitter is not without some personality, though. Only the amplifier stage is keyed so the oscillator stage runs continuously. On key up any energy from the oscillator that makes it to the antenna will be heard as a faint back wave. We'll see if this is objectionable. The second personality trait is, unfortunately, pretty nasty. When using the rig, one phone plug is for metering and a second is for the key. If in the heat of the moment I get the two mixed up and plug the key into a metering jack I'll have over 300 volts on my key. I'm planning something that will keep me from accidentally removing the key plug.

Eventually I plan is to mate this transmitter with my National FB7X for a complete 1934 station that I'll use in the 2010 AWA Linc Cundall OT CW Contest.

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FM Bandpass Filter 97.5 MHz

This type of filter circuit is a bandpass filter for FM band 88-108 MHz. This bandpass filter is in fact a combined highpass and lowpass filter. The first stages are a high pass and the last stages a low pass. We ripped it out the newsgroup alt.radio.pirate too bad, we can't remember who posted it. We tested the schematic with a simulation in MicroSim PSpice A/D Analog/Digital Simulator, Version 6.2 - April 1995. You find the output on this page.

This is An overview with PSpice from 10 MHz to 400 Mhz :

An overview with PSpice from 70 MHz to 150 Mhz looked like the next picture. Too bad PSPice didn't interpolate the points more detailed, this is why the curve is angled and not bowed!

Source: FM Bandpass Filter 97.5 MHz


See more : Audio Video Modulator - FM Transmitter - Ring FM Antenna

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