Questions tagged [filter]

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3
votes
1answer
50 views

Looking for origins of a crystal filter schematic used in uBITX

Here is a crystal filter used in uBITX transceiver: I've never seen such a topology in any other transceiver and decided to invest some time in exploring it. Turned out it's quite interesting. Eight ...
3
votes
2answers
98 views

SSB Transceiver Architecture - USB with Crystal Filter

I'm planning to build a 20m SSB transceiver and I want to get the overall architecture straight in my head first. Here's what I'm thinking so far, a single conversion superhet design with a 9MHz IF ...
3
votes
1answer
51 views

Tradeoffs: varicap vs. air variable capacitor for Rx bandpass?

What might be the tradeoffs between choosing varicap diodes versus air variable capacitors in the design and construction of tunable bandpass filters for HF receivers?
8
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2answers
123 views

How to effectively test and interpret the “working range” of a ferrite core with a signal analyzer?

I have a couple of Ferrite beads that are advertised as effective for suppressing conductive noise around 150kHz which I'm trying to monitor their actual performance with noise filtering. In my set ...
1
vote
1answer
85 views

Looking for a convenient audio frequency spectrum analyzer

I would like to have a convenient tool to measure filters and amplifiers in 20 Hz - 20 kHz frequency range. Currently I'm doing this with a signal generator, an oscilloscope and LibreOffice. It's not ...
2
votes
1answer
86 views

What is an Audio Peaking Filter?

What is an Audio Peaking Filter? And how might that be different from an ordinary (narrow) CW bandpass filter, or from tunable audio filters (with fully configurable upper and lower cutoffs)? Does a ...
3
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0answers
144 views

DIY Triplexer for HF (low), 6m (med), and 2m/440 (high)

I'm looking at picking up the TYT TH-9800, which is a Quad-Band FM radio on 10m/6m/2m and 440 (I'm lucky enough to have some 6m and 10m repeaters in the area). I know there exists quad band antennas ...
2
votes
1answer
84 views

How to select capacitor for diplexer use

Follow-up on this question: How to prevent cracking the capacitors in my diplexer? Short story: 2m/70cm diplexer, to be used up to 50W. Schematic from Elsie: S21/S11: I don't know exactly what to ...
5
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0answers
57 views

Choice of PCB coil design for filter inductor at ca 20 to 400 MHz, 5 W

Looking at the diplexer schematic from this nice question, I realized this can completely be done in PCB-formed elements (minus the connectors). (As a kind of counter-action to the original question'...
3
votes
1answer
198 views

How to measure quartz crystal motional parameters using a VNA?

I want to measure quartz crystal motional parameters with a VNA, unfortunately all Google searches I've done have lead me to nothing in concrete. I know how to get an impedance curve and measure the ...
2
votes
2answers
282 views

What is the current state of the art in CW filters?

In the 1970s I made a CW “filter” based on a phase locked loop that detected a specific audio frequency, and this drove an NE555 oscillator: the result seemed at first like a “zero bandwidth” CW ...
3
votes
2answers
42 views

Problem of two SAW fitler?

When I series two SAW filter, why the attenuation less than sum both of them in stop band region. Each of them (in stop band) have 60dB attenuation but when series them, the attenuation is equal to ...
0
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1answer
37 views

Combining two CFU455IT +/-2kHz (4kHz) ceramic filters to get a +/-1.25kHz (2.5kHz) filter for SSB

Can I put two of these cheap (less than 3USD) and common CFU455IT +/-2kHz (4kHz bandwith -6dB ) ceramic filters in series to get a lower bandwidth good for SSB TX? If I'm correct I will get -12dB at +/...
6
votes
2answers
429 views

Looking for a schematic of a DIY circulator

I would like to build a simple HF, VHF or UHF circulator to get a better understanding of how these devices work. Sadly at the moment I'm unaware of any articles or books that provide corresponding ...
6
votes
2answers
189 views

Wide band TX capable band-pass filter for VHF and Airband

I want to share the same antenna for VHF (TX/RX 144-148 MHz) and for Airband RX-only (116-136 MHz). I live on a very congested area where filter is a must, so I'm looking for the best solution for my ...
0
votes
2answers
283 views

What kind of filter should be used at the output of HF linear amplifier?

I am looking for a output filter to use with a HF linear amplifier called miniPA70 which is available through several online auction sites. The circuit is available here : http://iu3idf.blogspot.com/...
2
votes
1answer
38 views

In which cases do SAW filters improve performance?

I am looking for ways to improve reception between two of my devices. The communicate on the 868 MHz ISM band with a 2-GFSK modulation. The problem is that one of them is heavily shielded by metal (...
0
votes
1answer
118 views

What is the most common CW audio filter center frequency?

For older receivers with a fixed (crystal?) audio filter for CW, what is the usual center frequency of the audio bandpass of the filter? Or cut-off frequency for low-pass CW filters? For newer ...
2
votes
1answer
74 views

voltage rating for RF filter components

I want to design a PCB for a diplexer for Satellite operations. I want to use SMD capacitors and possible inductors to get some experience with soldering SMD components. What should the voltage rating ...
3
votes
1answer
76 views

Help understanding transmission loss of trivial circuit

I was trying to DIY a VHF/UHF diplexer, and got some weird readings from the VNA. By debugging I reached this trivial circuit: Which has the following frequency response: I'm trying to figure out ...
1
vote
2answers
112 views

If I parallel two crystal filters together, will that double the bandwidth? [closed]

Will the bandwidth be doubled ? And will the impedance be halved ?
2
votes
3answers
230 views

Under what circumstances does intermodulation become an issue in a filter after LNA setup?

I'm reading about using software-defined radio for picking up ADS-B signals at 1090MHz. There is this blog which considers (among others) a setup as follows: ...
3
votes
0answers
83 views

Where did the LP to BP transformation $ \frac{\omega ^{2}-\omega_0^{2}}{\omega\cdot BW} $ come from?

I'm not sure this question is appropriate for this site, but I feel that if anyone knows about a filter, a radio ham knows! And as a ham myself I feel I need to understand this important area better. ...
2
votes
1answer
95 views

How to match crystals using NWT?

I want to build an ladder SSB filter using 8 MHz quartz resonators. I don't have frequency meter but I have NWT-70. How can I match crystals to build a good filter? What kind of parameters should I ...
1
vote
1answer
344 views

Raspberry Pi rpitx for SSB with filter?

Using rpitx, we can transmit SSB using a single GPIO port from the Raspberry Pi. This of course uses square waves so creates a lot of harmonics. If I were to use a ...
1
vote
1answer
115 views

How can I improve my Es'Hail 2 reception?

I'm using an RTL-SDR to receive Es'Hail 2. My chain is as follows in order: 60 cm TV Satellite dish pointing 2 degrees off Es'Hail 2 Universal LNB (from TV company, not really a stable frequency). ...
2
votes
2answers
70 views

Daisy Chaining AM filters to help with IMD

I live near an AM transmitter, and the input of my RTL-SDR becomes overloaded. I've added an AM filter and it's really helped, however I still get a very strong AM signal with some IMD all over ...
1
vote
1answer
138 views

ICOM IC-910h How much bandwidth does it listen when receiving USB and FM?

CD-audio has a bandwidth of 22kHz. CW usually has a bandwidth between 3 to 5 kHz. But I am wondering what is the bandwidth my Icom IC-910H can listen to in both, the SSB and the FM mode? Also, what ...
5
votes
2answers
309 views

SSB filtering in the frequency domain?

I'm not sure whether it's more appropriate to ask this question here, or in the dsp.stackexchange. But I'll try here first. There seems to be a lot of information available on the filtering and ...
1
vote
2answers
88 views

What's the practical significance of the source impedance in an RF filter?

I'm reading through a tutorial on filter design and Bartlett's bisection theorem. It gives an example of a filter with 2.909k terminations: Then, the right side of the filter is scaled by a factor of ...
6
votes
2answers
2k views

How can the design of an RF filter also encompass impedance matching?

I'm installing an antenna which will require a matching network. (A fixed network: the load will not change.) I'm also building some low-pass filters to reduce transmitted harmonics. It would be a ...
4
votes
2answers
2k views

Small band-pass filter for HT?

I'd like to add a band-pass filter to my Baofeng UV-82 to make it comply with the spurious emissions requirements. Ideally it would be a rigid device with SMA or BNC connectors that would fit between ...
3
votes
1answer
286 views

How can I determine if out of band interference is affecting my AIS reception?

AIS I am receiving ship AIS messages. These are low power, digital messages periodically sent on two marine channels close to 162mhz. This frequency is surrounded by FM broadcast, weather radio, and ...
2
votes
2answers
1k views

Baud rate/frequency/bandwith/characters per second

I'm trying to filter a noisy serial line that comes in to a radio (mostly as a thought excercise in line filtering). The data comes in on a RS-232 line, 9600 baud, 8n1. I've found a lot of ...
0
votes
1answer
227 views

Cell Phone Filter / Interference?

How do cell phone filters filter out all the extraneous EM waves and noise (especially noise) when you get a call? I would expect a phone to have a bandpass filter to get rid of most noise but even ...
6
votes
2answers
610 views

Filtering for PSK31 demodulation

What's the ideal filter for PSK31 demodulation? That is, something that minimizes ISI, while having a narrow bandwidth to reject adjacent channels, while being reasonably matched? Most PSK modes use ...
4
votes
2answers
382 views

SDRPlay RSP1 and broadcast band (AM) interference

I heard the SDRPlay RSP2 has an AM notch filter, but I don't want to spend that much money. How is the RSP1 for broadcast band interference? Will I need a preselector? I already have an MFJ-1020c ...
5
votes
1answer
2k views

What frequency to set trap on?

I plan to build trapped multiband dipole so I read lots of documentation I found. There is one thing that confuses me: various authors recommend setting resonant trap frequency differently: some say ...
2
votes
2answers
111 views

Filtering VHF FM on my DTV signal

I've noticed that when I transmit on my HT when I'm watching TV (OTA), the signal drops and the screen goes blank (or digital "static") and then returns when I stop. I've replicated the issue by ...
3
votes
4answers
437 views

Are directional couplers ever used in duplex repeater systems?

I understand that most single-band repeaters will use a tuned cavity duplexer to isolate the received signal from the transmitted signal, since the frequencies are very close and extremely sharp ...
7
votes
1answer
404 views

Super-low-tech VHF low-pass filter construction?

Related to this question: Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero? Is it possible to build a super-low-tech low-pass filter for VHF harmonic suppression without a PCB or ...
1
vote
1answer
71 views

Diplexer termination?

When using a 2M/70cm diplexer for low-pass filtering (or with only one antenna on one of the two "outputs"), should the unused connection be left open, or terminated? (using a suitable impedance, ...
2
votes
2answers
101 views

What function do high-pass filters in a direct conversion receiver perform?

Use case: I'm considering hacking into my SoftRock RXTX to bypass the filters, then add external filters. I'm wondering if I can use just the low-pass filters I've already built, or if there's a ...
13
votes
4answers
10k views

Where are the baluns for VHF and higher? How can one be made?

In another question, commenters recommended that I look into adding a 1:1 balun to a dual-band dipole to eliminate the feedline as a radiator. As I understand it, a 1:1 balun also functions as a choke,...
2
votes
1answer
406 views

What is shape factor of a resonant circuit?

I have seen the shape factor of a resonant circuit defined in different places as both "the ratio of the -3dB point to the -60dB point", and elsewhere as "the ratio of the -6dB point to the -60dB ...
3
votes
1answer
464 views

Tuning a SAW filter?

Does anyone know if it's possible to shift the center frequency of a SAW filter? I'm only talking about 0.1% shift, say from 433MHz to 437MHz. Can it be done or is the center frequency baked into the ...
1
vote
1answer
131 views

What dimensions to choose when winding your own inductor

Suppose you want to make a wilkinson 3-way splitter with lumped components Given the following circuit, you need a 31.5nH inductor The inductor can be wound various ways: 3 wdg, 1 cm diameter, 2.36 ...
7
votes
2answers
555 views

How to calculate if low-pass filtering is sufficient?

An answer on this question Suggested method for boosting 0.05 watt transmitter up to 10+ watts? suggests putting a filterless 19dB amplifier between the HackRF (or similar general-purpose SDR) and a ...
1
vote
1answer
207 views

Toroidal inductor and transformer basics

In basic terms, using an Ultimate3S Beacon (above) as an example, what do the various toroidal components do exactly? How do they accomplish this? In construction terms, does it matter if the wound ...
4
votes
1answer
715 views

Cellular VHF Interference

I just got my license a week ago. Installed a new VHF/UHF radio in my car and everything seems to be working great. I've been heard at distant locations and picked up signals from repeaters that are ...