The Ideal, The Perfect, The One!

[clapp]Thanks Digger Rubby ducky your the one, 1/4 length dipole antenna, folded back on its self.
Was never very up on antennas didnt get round to taking ham exam.
but from what your saying would your 1/2 pipe design look like 2 half cylinder parabolics?
That would be more robust than mesh parabolic dish.Would focusing be similar?
So half cylinder with 1/4 wave stub at focul around 31mm for 2.4G (length being critical for frequency).
I was also thinking we are only looking for signal loss so only need transmit to single antenna?

Cheers Jeff


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		Quote:			Posted by goldigger
	Actually, I was thinking a couple pieces of aluminum vent pipe... but a 1/4 wave antenna, at 1.7 gigaHertz, is about 17 inches long! At 3.5 gigaHertz, is near to 8.4 inches... still too big! Maybe cut the pipe length wise, for a reflector. Use a rubber ducky made for 2.55 gHz? goldigger

I'm still wondering how the moisture in the soil will affect the overall reading. I've been out of here for a while with a nagging, indecisive hurricane but I have still been thinking and studying (no progress yet )

Why not, Brian... Post the schematic and let's have a look see!

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		Quote:			Posted by goldigger
	Forget the rubber ducky.... it was calculator error and a joke (and a bad joke at that.) Moisture in the soil should be relative, that is, it should not change, over the relatively short time you scan, unless soil types vary greatly. OK. I will whomp something up and come back to the forum, with it. But in the immortal words of Danny Kaye: *But first, ve danze!* That is, I will finish my catch-up, lo out, do the schematic, and log back in. goldigger

I'll catch it tomorrow. I had a rough day and tomorrow promises to be rougher so I best get off here and get some rest. Lookin' forward to seein' your schematic, bro.

Take care all and HH,
Ken

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		Quote:			Posted by bludger
	Yeh maybe single transistor varactor colpitts as a vco to sweep band, or sort of harmonic rich ghz oscillator must be something? Adjust uhf amp feedback so it oscillates, must be standard circuits around. Just cooking dinner in microwave hope its not looking for gold leaking the 2.45 ghz had it for 16 years and still going good,1000W magnatron would boil away those soil moisture problems Ken battery life would 'nt be good Look forward to seeing your design too Digger. Regards Jeff.

I could have uploaded yesterday but could not find this section! I searched and looked at all the likely forums but NOTHING! Today..... there it is.... it pops up and slapped me in the face! Wo!

OK. The *circuit* is an expression of thoughts, that is, some ideas, and how they MIGHT be implemented. Also, the *box,* in the circuit is a stripline oscillator, on one side and an enclosure for the oscillator parts, on the other side. The box dimensions should be about 2:1

When calculating, using a varactor, I found it difficult to achieve the full frequency scan, so I would suggest two parallel stripline oscillators fed  with the same scan (sawtooth) voltage.

goldigger

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		Quote:			Posted by bludger
	good low component count use of same ic for saw and neat amp, should make it easy to put together   i'm not good with rf, the construction of the stripline, never dealt with one before that i can think of. Is the box dimensions width and height crucial too and the coupling to the antenna is that a loop to the antenna connector? Regards Jeff

I guess there is a formula for striplines but if you make the box about 1/2 as wide as it is long, should work. I usually figure the wire length as 300/mHz X 100 so you have centimeters,  then divide that in 1/2 for the 1/2 wave length and if it is a copper tube, multiply this by 0.95, but if it is #14 wire, use 0.97.

Thus for 2600 mHz : 100(300/2600) = about 11.5 cm. for full wave and 5.77cm X .97 (wire!) = 5.6 cm  If you make the box 8cm long and 3 to 4 cm wide/deep, it should work. Then solder the wire, centered at one end (drill a small hole to hold the wire and at the other end for one varactor or tiny trimmer cap), use about #14 house wire is good. The other end has back to back varactors soldered between the rod  end and the top of the box. the junction of the varactors has a 47k or 68k or 100 resistor, running square away from the rod to a pass-through capacitor (.0005 t0 .001ufd), this is for the tuning voltage (sawtooth.)

The link (about 300R) is a narrow loop with 2 or three turns. Each end can go to BNC plugs on the same side.... this goes to the *antenna,* which will provide the changing load, on the oscillator..... I think I explained the rest??? (A 1/2 turn, bent wire, grounded one end, is a 50 ohm link. Like an upside down L)

Maybe I should draw an enlarged picture of the stripline general idea???

Anyway, if one oscillator can not cover from 1.7 to 3.4 gHz, 2 boxes would be needed: 1.7 gHz to 2.6 gHz and 2.5 gHz to 3.4 gHz.... this makes a big change in box size  and rod length. The low one, centered on 2.25gHz and the top one centered on 2.95gHz are: 6.75cm rod and 10 by 5 cm box; 4.9cm rod with a 7.4 by 3.7 cm box..... this is the inside dimensions of the boxes, and they can be made of 2 side copper, pc board, soldered together.  Just make all boxes on a large piece of pc board.

Physically, it is simple, its just getting the dimensions right. If you have one of those small 2 or 4 gHz frequency counters, it helps..... build the low frequency one first and make sure it works, then the higher frequency one can be checked with 2 Schottky mixer diodes by mixing 2.25 gHz with 2.95 gHz to get 700 mHz (without modulation, in the center of the  tuning voltage ranges. There is a way to tune the rod, to get your perfect frequency: a thin square of *finger stock* with a center hole and 2 fingers for the rod. it slides towards the varactors to make the rod effectively shorter, thus higher in frequency. If you use this idea, start with a rod slightly longer than calculated. (at leas 1/4 inch or 6.4 mm longer)

It is all moot if you can not get UHF transistors that will work at these frequencies. Look at the fT rating; this is the maximum amplification frequency, but they will oscillate beyond this frequency.

The MMIC amps may work as oscillators but they have a fixed in/out impedance of 50 ohms, so a link has to be used to connect the input of the MMIC and another link (of the right phase) to connect the output of the MMIC, the stripline is then the sole determinant of frequency. Also, do not exceed operating current of the MMICs.

Have I helped or totally clouded the issue?? 

goldigger

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