Cinderella Dual Band MEPT

Why Cinderella?
In the week prior to the Easter weekend, having completed my Top Band MEPT I was looking at using a similar design for a 40m unit with my 7.00MHz Crystal. Then I received an Invitation to join DL6NL and G6AVK on 14Mhz for a Holiday Weekend activation.

I searched through my Crystals, all I could find was a 5th overtone one which on its Fundamental was out of the top end of the band. With just 3 days to go there was no time to order an Xtal so I replied to Peter DL6NL “thanks for the invitation to the Party but I have nothing to wear.”

Going back to my 40m construction I wondered if I could select the Second harmonic from a Class C stage and get 14 MHz that way. I succeeded in getting a low level signal which was rather scruffy looking on the scope. I considered a Diode Ring Doubler circuit, fine if I was after a low level signal to amplify using several stages, not really simple MEPT stuff.

I moved to a digital Oscillator. Dividing digital signals is easy, doubling is not normally done, there is little information available on any techniques. If we were to put the 7.00MHz signal through enough digital gates we would get a delay of the signal. Apply the delayed signal and direct signal to a pair of XOR Gates and if the delay is correct we will get 2 pulses in one time period.
Alternatively a phase delay can be achieved with an R/C network both methods worked and on the day of the ‘Ball’ I was able to announce that ‘Cinderella has sewn a new Gown and would be coming to the Party’.

I used the Gate Delay method in a bread board ‘lash up’ with a 2n222 Driver and BFY50 PA.

The 50mW TX fared well, conditions were not good but we were all copied (Cinderella and the Two Ugly Sisters) in Nova Scotia and Northern Utah.

I am below G6AVK and DL6NL in this capture into Utah a very thin signal barely visible but I was running 3dB less ERP and of course the antennas and paths are different.

Peter DL6NL announced the switch off time for his activity Noon on Tuesday. At the stroke of Noon my Cinderella TX disintegrated into a pile of components and a single Crystal (slipper).

I embarked on the permanent version, characteristics were different without the long leads I found a combination of Capacitive Phase shift and Gate delay with critical adjustment of the Capacitor gave precise linear results.

I used to despise Veroboard. Costly,Warping Paxolin and lots of stray capacitance between the rows, however it is quick and easy for IC projects and used wisely the capacitance can effects can be minimised.

The signal generation uses two 74HC86 IC’s Selection of 7.00MHz or 14.00MHz is by the positioning of a single link.

Ideally suited as a PA is the 74LS240, having 2 separately enabled banks of Inverters. Band Selection is by a movable link for Enable and another for the Drive to either section. this means the BPF for each band can be permanently connected to its PA.

Separate plug in Band pass filters are used, this including a socket for the crystal means the MEPT is in fact universal and Multi Band.

Link swapping is no problem as the whole MEPT needs re setting when band changing, the FSK shift is doubled when the signal is doubled.

The MEPT is on its test run now using my spare PIC Keyer piggy backed on.

During the tests I tried a new method of Identification conceived to try and overcome the problem of missed identification due to missing parts of Morse Code symbols.

I now call this 5/5 It is 5WPM FSK Morse with a 5Hz shift. If I send my Call Twice and the two letters of my Major Locator Square this forms a Morse Code G in QRSS5 with a filled waveform.

Here it is into Nova Scotia, doing a fine job.

Variable Power Top Band MEPT

Manned Experimental Propagation Transmitter for Manned Experimental Propagation Tests.

A new MEPT band, for me 160 meters. I could build the same tried and tested design for all bands but the fun is in the experimenting. This Transmitter uses only 2 Transistors. NPN Crystal Oscillator DC coupled to a PNP Output Amplifier an ideal use for the old BFX29 transistors in the junk box.

Based on an old design from G3MY called the Pippin it is capable of more power than needed for a QRP Propagation Beacon. I used a DIP Switch to select collector load resistors. power levels from 5mW to 400mW are possible. The Crystal available needed pulling low, determined to use the bits from an Energy Saving Lamp I wound the inductor on the toroid former which saw previous life as the Lighting Pulse Transformer. The output capacitor and some decoupling came from the same source.

The other variation that can be made is in the construction method, I have used the Pad on Earth Plane method for VHF PA construction, it lends itself well to this project at the other end of the frequency range. I piggy backed my old test PIC Keyer to FSK via a Black LED once again used as a Varicap Diode.

Once complete I put it on test running 100mW to my 40m 1/2 wave Doublet, my e-mail being down I could not ask for reports, it would need to be spotted by a keen Top Band monitoring station, this was a week day and the week ends are more popular for 160m experiments.

When I managed to get some incoming e-mail a couple of days later I was pleased to see.

[Knightsqrss] who is on 160m? G6AVK

Later he searched the Captures for the most readable segment and deduced the call and QRA Locator. Well done and thanks Colin.

A New Narrow Mode MEPT_JT

Joe Taylor and Murry Greenman have been working on a new mode MEPT_JT. Just released this software produces and receives a 4 bit data stream with a total bandwidth of just over 6Hz.

I got it up and running yesterday morning on 10Mhz, output 100mW to a 6m CB whip with Radials and ATU Output power 100mW.
Here are the reports all in daylight.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

UTC Sync dB DT Freq Message Noise
—————————————————————
140200 3 -24 1.8 10.140079 G3ZJO IO92 20 15.1

73,

Johan on5ex

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

C:k1jtmept>mept_jt Rx 10.1386

UTC Sync dB DT Freq Message
————————————————–
232000 4 -27 0.5 10.140172 K7EK CN87 37
232600 4 -26 0.7 10.140172 K7EK CN87 37
233000 1 -28 0.4 10.140173
233400 2 -26 0.9 10.140173 K7EK CN87 37
233600 2 -27 1.3 10.140172 K7EK CN87 37
233800 5 -26 1.7 10.140172 K7EK CN87 37
234000 2 -26 1.1 10.140172 K7EK CN87 37
234200 1 -27 1.5 10.140172 K7EK CN87 37
234400 1 -26 0.9 10.140173 K7EK CN87 37
234600 7 -25 1.3 10.140173 K7EK CN87 37
234800 2 -23 1.8 10.140172 K7EK CN87 37
235000 4 -23 1.1 10.140172 K7EK CN87 37
235200 7 -25 1.5 10.140172 K7EK CN87 37
235400 3 -20 1.0 10.140172 K7EK CN87 37
235600 8 -21 1.4 10.140172 K7EK CN87 37
235800 4 -21 1.7 10.140173 K7EK CN87 37
000000 8 -18 1.1 10.140173 K7EK CN87 37
000200 8 -18 1.5 10.140173 K7EK CN87 37
000600 3 -19 1.4 10.140173 K7EK CN87 37
000800 6 -20 1.8 10.140173 K7EK CN87 37
001000 1 -23 1.1 10.140172 K7EK CN87 37
001200 3 -22 1.6 10.140172 K7EK CN87 37
001400 4 -25 1.0 10.140173 K7EK CN87 37
001600 3 -22 1.4 10.140173 K7EK CN87 37
001800 3 -22 0.8 10.140173 K7EK CN87 37
002000 4 -22 1.2 10.140173 K7EK CN87 37
002200 3 -21 1.7 10.140173 K7EK CN87 37
002400 7 -18 1.1 10.140172 K7EK CN87 37
002600 14 -14 1.4 10.140172 K7EK CN87 37
002800 2 -20 0.8 10.140172 K7EK CN87 37
003000 2 -20 1.3 10.140173 K7EK CN87 37
003200 6 -20 1.7 10.140173 K7EK CN87 37
003400 1 -22 1.1 10.140173 K7EK CN87 37
003600 2 -24 1.5 10.140173 K7EK CN87 37
003800 1 -22 0.9 10.140173 K7EK CN87 37
004000 8 -22 1.3 10.140173 K7EK CN87 37
004200 9 -18 1.7 10.140173 K7EK CN87 37
004400 9 -18 1.1 10.140173 K7EK CN87 37
004600 12 -19 1.5 10.140173 K7EK CN87 37
004800 3 -17 0.9 10.140173 K7EK CN87 37
005000 8 -15 1.4 10.140173 K7EK CN87 37
005200 5 -12 1.8 10.140173 K7EK CN87 37
005400 11 -13 1.1 10.140173 K7EK CN87 37
005600 4 -17 1.6 10.140173 K7EK CN87 37
005800 5 -17 1.0 10.140172 K7EK CN87 37
010000 3 -16 1.4 10.140172 K7EK CN87 37
010200 7 -13 1.8 10.140173 K7EK CN87 37
011000 5 -20 0.4 10.140173 K7EK CN87 37
011200 4 -21 -0.1 10.140173 K7EK CN87 37
011400 6 -20 0.3 10.140173 K7EK CN87 37
011600 3 -26 1.4 10.140172
011800 1 -33 0.0 10.140144
011800 8 -32 0.4 10.140173
044800 2 -26 1.0 10.140130 ZL1BPU RF72 30
045000 3 -26 0.4 10.140130 ZL1BPU RF72 30
045200 1 -25 0.8 10.140130 ZL1BPU RF72 30
045400 1 -25 1.1 10.140130 ZL1BPU RF72 30
050000 1 -25 1.4 10.140131 ZL1BPU RF72 30
050800 2 -23 1.0 10.140131 ZL1BPU RF72 30
051000 7 -25 1.4 10.140130 ZL1BPU RF72 30
051200 2 -24 0.7 10.140130 ZL1BPU RF72 30
051400 5 -25 1.1 10.140130
051600 2 -26 0.1 10.140130 ZL1BPU RF72 30
051800 2 -27 0.4 10.140130 ZL1BPU RF72 30
052000 1 -24 0.8 10.140130 ZL1BPU RF72 30
052200 1 -23 0.3 10.140130 ZL1BPU RF72 30
052400 6 -23 0.7 10.140130 ZL1BPU RF72 30
052600 4 -22 0.1 10.140130 ZL1BPU RF72 30
052800 5 -21 0.5 10.140130 ZL1BPU RF72 30
053000 5 -21 0.8 10.140130 ZL1BPU RF72 30
053200 1 -19 0.3 10.140131 ZL1BPU RF72 30
053400 2 -19 0.7 10.140131 ZL1BPU RF72 30
053600 5 -20 0.1 10.140131 ZL1BPU RF72 30
053800 6 -18 0.4 10.140131 ZL1BPU RF72 30
054000 1 -17 0.8 10.140131 ZL1BPU RF72 30
054200 7 -18 0.3 10.140131 ZL1BPU RF72 30
054400 3 -16 0.7 10.140131 ZL1BPU RF72 30
054600 9 -20 0.1 10.140130 ZL1BPU RF72 30
054800 2 -20 0.4 10.140130 ZL1BPU RF72 30
055000 6 -21 0.8 10.140131 ZL1BPU RF72 30
055200 2 -20 0.3 10.140131 ZL1BPU RF72 30
055400 4 -22 0.7 10.140131 ZL1BPU RF72 30
055600 2 -20 1.1 10.140131 ZL1BPU RF72 30
055800 3 -22 0.4 10.140131 ZL1BPU RF72 30
060000 6 -23 0.8 10.140131 ZL1BPU RF72 30
060200 2 -19 0.3 10.140131 ZL1BPU RF72 30
060400 9 -20 0.7 10.140130 ZL1BPU RF72 30
060600 4 -21 1.1 10.140130 ZL1BPU RF72 30
060800 4 -21 0.4 10.140131 ZL1BPU RF72 30
061200 1 -23 0.3 10.140131 ZL1BPU RF72 30
061400 2 -24 0.7 10.140131 ZL1BPU RF72 30
061600 1 -23 1.1 10.140131 ZL1BPU RF72 30
061800 1 -24 0.4 10.140131 ZL1BPU RF72 30
062000 3 -25 0.8 10.140131 ZL1BPU RF72 30
062200 2 -28 0.3 10.140131
065200 1 -23 0.9 10.140130 ZL1BPU RF72 30
065400 2 -24 0.3 10.140130 ZL1BPU RF72 30
065800 1 -26 0.1 10.140130 ZL1BPU RF72 30
093000 1 -29 1.0 10.140132
114600 2 -27 1.1 10.140132 ZL1BPU RF72 30
114800 4 -25 0.4 10.140132 ZL1BPU RF72 30
115000 1 -23 0.8 10.140132 ZL1BPU RF72 30
115200 1 -25 1.2 10.140132 ZL1BPU RF72 30
132800 3 -20 0.1 10.140173 K7EK CN87 37
133000 2 -25 0.4 10.140172 K7EK CN87 37
133200 8 -22 0.8 10.140172 K7EK CN87 37
133400 1 -26 0.3 10.140172 K7EK CN87 37
133600 3 -26 0.7 10.140172 K7EK CN87 37
133800 5 -24 0.8 10.140172
134000 8 -22 0.7 10.140172 K7EK CN87 37
134200 8 -24 1.1 10.140172 K7EK CN87 37
134400 1 -21 0.6 10.140172 K7EK CN87 37
134600 6 -22 1.0 10.140172 K7EK CN87 37
134800 9 -18 0.4 10.140172 K7EK CN87 37
135000 8 -20 0.8 10.140172 K7EK CN87 37
135200 3 -19 1.3 10.140172 K7EK CN87 37
135400 5 -19 0.7 10.140172 K7EK CN87 37
135600 14 -17 1.1 10.140172 K7EK CN87 37
140000 3 -23 0.9 10.140172 K7EK CN87 37
140200 1 -22 0.3 10.140172 K7EK CN87 37
140400 4 -18 2.0 10.140091 G3ZJO IO92 20
140400 7 -19 0.7 10.140172 K7EK CN87 37
140600 12 -14 1.1 10.140172 K7EK CN87 37
140800 4 -20 0.5 10.140172 K7EK CN87 37
141000 2 -18 1.0 10.140172 K7EK CN87 37
141200 8 -17 0.4 10.140172 K7EK CN87 37
141400 2 -22 2.1 10.140090 G3ZJO IO92 20
141400 6 -19 0.8 10.140172 K7EK CN87 37
141600 1 -25 1.8 10.140090 G3ZJO IO92 20
141600 4 -21 1.2 10.140172 K7EK CN87 37
141800 8 -23 1.4 10.140090 G3ZJO IO92 20
141800 1 -24 0.6 10.140172 K7EK CN87 37
142000 1 -23 2.1 10.140091 G3ZJO IO92 20
142200 1 -27 1.7 10.140090
142200 5 -23 0.4 10.140172
142400 4 -25 1.4 10.140090 G3ZJO IO92 20
142600 5 -25 1.3 10.140172 K7EK CN87 37
143000 1 -28 1.1 10.140172 K7EK CN87 37
143200 5 -28 0.4 10.140172
143400 1 -27 1.4 10.140172 K7EK CN87 37
143800 3 -25 0.3 10.140172 K7EK CN87 37
144000 2 -27 0.7 10.140172
144200 1 -26 0.7 10.140172 K7EK CN87 37
144400 4 -22 1.1 10.140172 K7EK CN87 37
144600 1 -25 1.5 10.140172 K7EK CN87 37
145200 1 -28 2.5 10.140090
145800 2 -28 2.1 10.140091
150000 1 -19 2.2 10.140091 G3ZJO IO92 20
150200 4 -19 1.8 10.140091 G3ZJO IO92 20
150400 3 -19 2.5 10.140091 G3ZJO IO92 20
150600 6 -18 2.1 10.140090 G3ZJO IO92 20
150800 2 -24 2.7 10.140090 G3ZJO IO92 20
151000 3 -23 2.4 10.140091 G3ZJO IO92 20
151200 3 -22 2.0 10.140091 G3ZJO IO92 20
151400 1 -23 2.5 10.140091 G3ZJO IO92 20
151400 1 -28 1.3 10.140172 K7EK CN87 37
151800 1 -29 1.1 10.140172
152200 1 -28 0.6 10.140172
152800 2 -25 1.4 10.140173 K7EK CN87 37
153000 2 -24 1.8 10.140173 K7EK CN87 37
153200 1 -27 1.2 10.140172
153400 1 -27 1.1 10.140172 K7EK CN87 37
153600 2 -25 0.5 10.140172 K7EK CN87 37
154000 1 -26 1.4 10.140172 K7EK CN87 37
154800 1 -32 1.1 10.140172
160200 2 -24 0.6 10.140172
160400 2 -24 2.5 10.140100
160600 2 -25 1.7 10.140099 G3ZJO IO92 20
160600 6 -25 0.4 10.140172 K7EK CN87 37
161200 3 -27 0.7 10.140172 K7EK CN87 37
161600 1 -25 0.5 10.140172 K7EK CN87 37
161800 1 -24 0.9 10.140173 K7EK CN87 37
162000 3 -23 0.4 10.140172
162200 4 -24 1.3 10.140172 K7EK CN87 37
162400 1 -26 3.1 10.140092 G3ZJO IO92 20
162400 2 -25 1.7 10.140172 K7EK CN87 37
162600 3 -22 1.1 10.140172 K7EK CN87 37
162800 2 -27 2.4 10.140091
162800 2 -25 1.5 10.140172 K7EK CN87 37
163000 2 -26 2.7 10.140091
163000 4 -25 0.5 10.140172 K7EK CN87 37
163200 1 -25 2.9 10.140091
163400 2 -26 2.1 10.140091 G3ZJO IO92 20
163400 3 -27 1.4 10.140172 K7EK CN87 37
164000 1 -25 2.8 10.140091 G3ZJO IO92 20
164000 1 -25 0.4 10.140172 K7EK CN87 37
164200 3 -24 2.5 10.140091 G3ZJO IO92 20
164200 3 -24 0.8 10.140172 K7EK CN87 37
164400 1 -24 1.2 10.140172
164600 4 -25 3.2 10.140090
164600 3 -25 1.2 10.140172 K7EK CN87 37
165000 3 -26 1.8 10.140090 G3ZJO IO92 20
165000 3 -24 0.3 10.140172 K7EK CN87 37
165200 2 -26 0.7 10.140172 K7EK CN87 37
165400 1 -24 2.2 10.140090 G3ZJO IO92 20
165400 5 -24 1.1 10.140172 K7EK CN87 37
165600 6 -18 1.8 10.140090 G3ZJO IO92 20
165600 3 -24 0.5 10.140172 K7EK CN87 37
165800 2 -26 2.5 10.140090 G3ZJO IO92 20
170000 1 -22 2.2 10.140090 G3ZJO IO92 20
170200 3 -19 1.9 10.140090 G3ZJO IO92 20
171000 1 -27 0.4 10.140172 K7EK CN87 37
171400 3 -21 2.9 10.140090 G3ZJO IO92 20
171600 2 -21 2.5 10.140090 G3ZJO IO92 20
171800 2 -26 2.1 10.140090 G3ZJO IO92 20
171800 3 -27 1.1 10.140172 K7EK CN87 37
172400 2 -25 0.3 10.140172 K7EK CN87 37
172600 3 -27 0.7 10.140172 K7EK CN87 37
172800 6 -28 1.8 10.140172 K7EK CN87 37
173000 1 -29 1.2 10.140172 K7EK CN87 37
173200 1 -29 1.6 10.140172
173600 1 -30 2.8 10.140089
174000 4 -27 0.4 10.140172 K7EK CN87 37

— 73, Joe, K1JT

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

C:Program FilesWSJT6>mept_jt Rx 10.1386
UTC Sync dB DT Freq Message Noise
—————————————————————
181400 8 -23 2.7 10.140093 G3ZJO IO92 20 18.8
181600 2 -24 3.8 10.140093 G3ZJO IO92 20 18.9
181800 1 -17 2.9 10.140093 G3ZJO IO92 20 19.2
182000 4 -18 3.0 10.140093 G3ZJO IO92 20 19.2
182200 4 -19 3.1 10.140093 G3ZJO IO92 20 18.9
182400 5 -23 3.2 10.140093 G3ZJO IO92 20 18.8

73 de LA5VNA Steinar

A nice mode aye?

The G3ZJO Lock

To start to understand the mechanism involved in the locking of two CMOS oscillators on the same chip we need to know a little about what goes on inside the DIL Packaged device.

Thanks to Peter G8EUX I now have an insight.

The 5 Ohm resistors and the 5nH choke which also has a resistance of around 5 Ohms are all inside the chip.

The G3ZJO Lock

My Diversity MEPT uses two oscillators on the same frequency each with Frequency Shift Keying 180 degrees out of phase. This results in a box appearance when receiving both signals, resembling a string of Paper Dolls (Origami).

The two oscillators are locked in frequency by exploitation of the cross coupling inherent in the construction of CMOS Gates.

The ‘G3ZJO Lock’ is described on my companion blog. Radioman

Diversity MEPT Propagation Beacon

This is the description and circuit of my Diversity MEPT. I have used a 74HC86 as Oscillator/Buffer and 2 x 74HC240 as PA.

Right Click and select View Image for full view.

Due to the need for critical frequency matching I decided that the best approach was identical circuits on a PCB.

Right Click and select View Image for full view.
Sorry for the error. Pin1 goes to zero volts not +V

Run on 5 Volts and using just one gate in each bank of four on the chip and an output of 35mW the 74HC240’s are not stressed.

When experimenting with oscillators using these chips I have noted that anything you do on any gate is reflected on all others, (via the power supply architecture on the chip I believe).
With the 74HC240 even enabling unused gates produces a positive move of the output frequency of a Crystal Oscillator which is using the other group of gates. I tried to use this effect to produce FSK of an Oscillator without the use of a Varicap Diode. It works, the snag being the shift is greater than we need for QRSS and the switching spike is huge.
Published designs using the 74HC240 for a single chip CW transmitter which keys the ‘Enable’ complain of incurable chirp, Hmm.

With the 74HC86 it is an opposite effect. FSK’ing of the Crystal Oscillator produces a mirror of the shift on the other gates.
I asked myself can we make use of this?
Yes, build 2 Crystal Oscillators on the same chip adjust the frequencies so they are close and they pull each other, get them very close and they lock.

Now FSK each oscillator 180 degrees out of phase, the positive shift of the high frequency one reinforces the negative shift of the other. This occurs when they are in a near fully locked state. Adjustment is tricky but once set up they seem to stay. The high oscillator with the positive shift becomes the master, if the frequencies are identical they fully lock, the Master will swamp the Slave, controlling its frequency to the extent of cancelling its shift.

Has this effect been noted before I wonder or is this the ‘G3ZJO Lock’

The Oscillators are in fact adjusted to be 10Hz apart in frequency. The Master is set to say, 10.100000Mhz, the FSK shifts it to 10.100005Mhz.
The Slave is set to aprox 10.0999990Mhz the FSK shift is adjusted to be aprox 2.5Hz. When pulling takes place this shift is reinforced to 5Hz, i.e. to 10.100000Mhz.

The Locking and shift reinforcement can be seen in action in the following picture. The two oscillators started in lock, the PCB component side was sprayed with freezer concentrated on the Master Oscillator. The Master (top trace) is seen gradually approaching the Slave as the temperature recovers. At 130 seconds from the left hand side of the display the two carriers are seen beating together, after the next shift they lock, shaky for 45 seconds, then solid.
Note how the FSK Slave shift increases when in this state.

Right Click and select View Image for full view.

Very cold starts can be a problem if the Slave starts a little too high it is swamped requiring a finger to be poked in to pull it low. (A re-set button could be provided.)
It is still early days but at normal ambient temperatures start ups are perfect and 16 Hour periods of lock have been maintained using both breadboarded and the final PCB version.
In striving for minimum bandwidth (10Hz shift) I may be running the system too tight, tests are continuing with both oscillators set for about 5Hz shift prior to locking them. This results in a final shift of around 12.5Hz, it may avoid swamping as the FSK will force them further apart.
08.03.2008. Further I have found another lock, tighter than both previously described, when in this state the negative shift can be turned to zero level. Tests will continue to establish the long term stability of this. Maybe we are getting only the mirror of the positive shift.

When testing on the breadboard I switched off my bench light and the lock went haywire, this lead my the use of Black, Infra Red LED’s (ex TV remote controls) in place of the Visible Red LED’s normally used as varicaps.

The use of two 74HC240 for the PA may be an overkill, I didn’t try using two halves of the same chip as I was aware of the undesirable effect mentioned above. They cost less than .5Euro each after all.

Another extravagance is the use of a LM7805 Regulator on each unit, again at 1.5Euro for a bag of 15 we get super regulation and isolation.

PA PCB Print View.

Osc. PCB Print View.

Finally the PIC Keyer, everyone has their own favourite method of generating FSK we just need two 180deg. outputs.

PIC PCB Component View.

PIC PCB Print View.

An Idea for a Diversity Beacon

The reception reports of MEPT Beacons come in from around the world. The first thought that goes through the mind is, what would the signal have been like using a different antenna. The comparison between a Vertical or Horizontal antenna is particularly interesting in Propagation Study.

This Diversity MEPT is the result of a long train of thoughts on the ways to achieve identifiable dual polarisation from a transmitter.

I used some of the existing techniques I have used in other Beacons and circuits I have tried before. Building identical channels for each transmitter.

I had problems with the Red LED’s as regularly used as Varicap diodes, When I switched off my Bench Lamp the frequency shifted intolerably. This gave the excuse to try the Black LED’s which are not effected at all. Yes of course they are second hand, TV InfraRed remote devices, they work fine as varicaps.

Another free, second hand component is the PIC timing Crystal a 4.43Mhz TV item from the Philips Video 2000 Recorder. The ident is selected by a push switch, yes Video 2000 front panel switch.