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Type: Posts; User: biff44

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1. ## Thread: what is the significance of the transit frequency and maximum frequency of oscillatio

by biff44
Replies
5
Views
382

### Closed: Re: what is the significance of the transit frequency and maximum frequency of oscill

they are only roughly related.
More important...is the negative resistance of your active device higher in value than the resistance of your resonant tank circuit.
2. ## Thread: Issue with bias tee in RF noise circuit

by biff44
Replies
1
Views
280

### Closed: Re: Issue with bias tee in RF noise circuit

hmmm.
Peaks and dips? Sounds like something in your circuit is acting like an antenna?
OR the source you are driving it with has harmonic RF output, so try a battery driven potentiometer...with...
3. ## Thread: what happens to RF choke while doing ac analysis

by biff44
Replies
5
Views
381

### Closed: Re: what happens to RF choke while doing ac analysis

do you mean "RF CHOKE", which is an inductor that deliberately has high loss, and an "INDUCTOR", which deliberately has low loss (i.e. high Q)? Makes a big difference in the answer

by biff44
Replies
2
Views
288

### Closed: Re: Fixed load of wave guide

theory of small reflections! a tapered wedge is a subset of impedance matching taper designs.
5. ## Thread: Tuning of varicap diode in a magnetic loop antenna based on modulating signal

by biff44
Replies
7
Views
553

### Closed: Re: Tuning of varicap diode in a magnetic loop antenna based on modulating signal

i understand your concept, and it might work.
consider though that FM and PM are related. So if you have a source that is FM modulated, and you now vary the resonant frequency of the actual antenna...
6. ## Thread: Input and output matching in Distributed amplifier

by biff44
Replies
11
Views
795

### Closed: Re: Input and output matching in Distributed amplifier

i am not an expert at IC design...but i would look at EACH element of the active device, look at what resistive impedance the input and output want to be at, then choose an input transmission line of...

by biff44
Replies
5
Views
962

### Closed: Re: Matching 75ohm antenna to 300ohm receiver

Here is the deal. If your length of 300 ohm cable is short (less than 1/8 wavelength) it does not matter.

Only if you have a long transmission line is it a concern

Balanced to unbalanced...
8. ## Thread: How does discontinuities cause reflections?

by biff44
Replies
5
Views
425

### Closed: Re: How does discontinuities cause reflections?

you need to read a entry level paper on how a transmission line works.
It is easy to digest, but a little beyond the scope of a forum such as this to explain it all.

Basically, a transmission...
9. ## Thread: patch antenna polarization

by biff44
Replies
4
Views
780

### Closed: Re: patch antenna polarization

Sorry, i was afraid i was not being clear.
152387

Let me try to ask this in as simplified a way as i can.
Lets say i transmit a signal, and send it to a 3 dB equal phase splitter. The two...
10. ## Thread: Smith chart of λ/4 Transmission Line

by biff44
Replies
20
Views
1,261

### Closed: Re: Smith chart of λ/4 Transmission Line

The theoretical answer to your questions is: The smith chart is a bilinear transform from the impedance to the reflection coefficient domains. Such transforms follow certain rules.

It is an...
11. ## Thread: DC blocking caps selection for a Filter(Band pass)

by biff44
Replies
3
Views
298

### Closed: Re: DC blocking caps selection for a Filter(Band pass)

the prototype filter test circuit uses blocking caps, so one could suppose the input is a DC short circuit. So you need the caps IF that port is connected to an active device that has DC bias on it....
12. ## Thread: High dynamic range preamp in direct conversion wideband receiver

by biff44
Replies
8
Views
1,790

### Closed: Re: High dynamic range preamp in direct conversion wideband receiver

direct conversion receivers are subject to more interference effects from undesired received signals, because there are no IF filters to help to remove them. So adding a broadband...
13. ## Thread: patch antenna polarization

by biff44
Replies
4
Views
780

### Closed: patch antenna polarization

Antennas question.....I know if i have a transmitting antenna that is circularly polarized, and a receiving antenna that is vertical polarized...i will get low link loss no mater how i rotate that...
14. ## Thread: 100MHz soil moisture sensor

by biff44
Replies
8
Views
1,954

### Closed: Re: 100MHz soil moisture sensor

Yes you could use insulated probes....but the probes can get dirty and wet that way. A non contacting method would be better for repeatability reasons
15. ## Thread: Is it really "heating" used for beam scanning in Echodyne's radar?

by biff44
Replies
4
Views
422

### Closed: Re: Is it really "heating" used for beam scanning in Echodyne's radar?

It looks like a multi element phased array, where the elements are spaced out electrically with different time delays. As you sweep the frequency, each time delay imparts a different phase shift, so...
16. ## Thread: Metamaterial unit cell structure of Metawave's radar used for beam steering.

by biff44
Replies
3
Views
581

### Closed: Re: Metamaterial unit cell structure of Metawave's radar used for beam steering.

metamaterials are useful for slowwave structures. It is possible that they are using that property to make the antenna "look" like the antenna elements are spaced out further electrically, than they...
17. ## Thread: No commercial 10MHz-50MHz antenna ? How to build?

by biff44
Replies
6
Views
451

### Closed: Re: No commercial 10MHz-50MHz antenna ? How to build?

Yes! We ALL like using waveguide at 10 MHz. That way if it is raining, we can park our cars inside of it so they do not get wet
18. ## Thread: RF Limiter not working as it should

by biff44
Replies
4
Views
348

### Closed: Re: RF Limiter not working as it should

For one thing, diode based limiters usually trip on around, say, 100 milliwatts or so. Expecting one to turn on at -30 dBm is pure folly.

by biff44
Replies
1
Views
298

### [SOLVED]Closed: Re: DDS vs PLL RF Link Budget

back in the day, people used analog ramp generators and a PLL-like tracking system to make a linear chirp. BUT it had serious linearity problems, and had a reset issue too.
SO although a DDS might...

by biff44
Replies
11
Views
728

### Closed: Re: Where can I get my transmitter/microwave link tested

20 years is a long time. Odds are the electrolytic capacitors have failed by now
21. ## Thread: 100MHz soil moisture sensor

by biff44
Replies
8
Views
1,954

### Closed: Re: 100MHz soil moisture sensor

I would NOT assume that 100 MHz is free from such effects. Soil conductivity will of course influence a reading, and i am sure the ionic content in fertilizers will change the conductivity.
22. ## Thread: Using spiral inductor after SRF

by biff44
Replies
3
Views
389

### Closed: Re: Using spiral inductor after SRF

my off the top of my head comment would be: if you end up needing negative inductance inductors in your filter, you must have way too much parasitic inductance/transmission line length in your...
23. ## Thread: 100MHz soil moisture sensor

by biff44
Replies
8
Views
1,954

### Closed: Re: 100MHz soil moisture sensor

it is a pretty crude circuit.
Analog devices makes a number of impedance analyzer chips for use in things like capacitance meters, but they are all around 1 MHz signal frequency.

Maybe someone...
24. ## Thread: Fast low duty cycle pulse oscillator

by biff44
Replies
4
Views
401

### Closed: Re: Fast low duty cycle pulse oscillator

From a project i did a long time ago, i recall microwave oscillators taking a good microsecond or two to fully stabilize after start up. That is because the transistors go from being off, to ON, and...
25. ## Thread: Good wire for small antenna

by biff44
Replies
6
Views
521

### [SOLVED]Closed: Re: Good wire for small antenna

by small antenna, do you mean "electrically small"?
If so the resistance in the wire will be CRITICAL if you want it to radiate any power at all. I have even used solid silver wire in certain...
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