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0 votes
1 answer
59 views

Use of filters for weak SSB when there is no QRM

On bands like 10m when there is often little or no QRM (just gaussian noise), are the "Noise Reduction" filters intended to make weak phone signals more understandable? My subjective view is ...
4 votes
1 answer
92 views

How to properly simulate a crystal filter being pulled?

After reading k1zmt's answer to the question of how to change the resonant frequency of a quartz, I wondered how to simulate a quartz filter to check that result. I went with the following model of a ...
2 votes
1 answer
69 views

Identify filter on schematic

I am analyzing the Baofeng UV5R schematic. And trying to identify which filter was used in input UHF/VHF RF stage on RDA1846. It seems to me that it is a 3rd order Butterworth bandpass filter. But i ...
2 votes
1 answer
97 views

Why does the Elecraft KX2 filter show a dip in the middle when I reduce the filter bandwidth?

This is a waterfall made in gnuradio with a simple audio source->waterfall block at 12ksps. The filtering I'm talking about is therefore all on the Elecraft KX2. At the top of the waterfall the ...
9 votes
2 answers
301 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. I'm trying to monitor their actual performance with noise filtering. In my set up I ...
6 votes
1 answer
196 views

How to achieve highest Q-factor in inductors for 6-160m amateur bands?

When building filters for ham bands (direct sampling SDR frontend) - it is common to build filters using 2,6,10,12 material toroids. Are there any recent developments that offer lower losses / higher-...
9 votes
1 answer
456 views

How do you choose an inductor wire gauge for high-power RF?

At 100 watts in a 50-ohm system, the current flowing through an inductor would be about 1.41 A, thus a 26-AWG wire should be plenty since they are chassis-rated for 2A and for just a few windings that ...
0 votes
1 answer
68 views

How do you protect your radio when testing custom RF circuits at ~100W?

We are designing a UHF/VHF diplexer for a satcom project and targeting support for 100W. Our radio can transmit near 100W but of course we want to protect it in case there is a failure of some kind. ...
17 votes
4 answers
19k 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,...
0 votes
1 answer
179 views

Can I reverse a passive high pass filter?

Can the passive high pass filter be used in reverse? (exchange TX and ANT) I have a passive HPF, but I don't know if it is possible to reverse the port using.If I do this, will it cause the HPF to ...
1 vote
0 answers
63 views

How to determine if filter is well matched?

Hello i'm in process of creating band pass filters for my ham radio. I calculated the filter for 80m band basing on this website: And recreated it in reality: Then I started measuring it with ...
1 vote
0 answers
56 views

Multiple Transmitting Antennas On Different Frequencies In Close Proximity

I am working on a project where I’m going to have multiple transmitting antennas in very close proximity (in a nosecone of a rocket). There are 3 different radio systems. Our 433 MHz 1 watt telemetry ...
1 vote
1 answer
89 views

Does a filter or inductor's power rating matter in its passband, or only in the attenuated frequency range?

I would like to build a high-pass filter that would block reception of signals from the United States' FM broadcast range (88–108 MHz) while still allowing me to transmit VHF ham signals (around 146 ...
0 votes
1 answer
82 views

How do you create a DC-blocking ground-shunt that looks inductive in an "L" match?

We are optimizing an impedance match with s2p models for an LNA and found that an "L" match with a serial cap and shunt inductor will optimize to provide +3 dB of output, versus using serial ...
4 votes
1 answer
965 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
2 answers
298 views

What's the difference between LPF and BPF in context of bandwidth setting?

I'm used to simple RX/TX bandwidth configurations, on my VHF FM rig it's either narrow, normal, or wide. It seems to be much more complex on my new HF SDR rig, and the instructions don't say anything ...
2 votes
1 answer
315 views

How do I choose between T37-2 vs T37-6 for this High-Pass Filter?

My RTL-SDR V3 is being overloaded by an AM broadcast so I'd like to build a high-pass filter to block the AM broadcast band. I thought I'd start simple and try making the one shown in Fig 3 of "...
2 votes
2 answers
154 views

Second filter is not working on my mcHF kit

I'm building my first kit, it's the mcHF SDR radio. I've started with the low pass filters. The radio has four of them: I tested the first filter with a NanoVNA and got a result that resembled what ...
2 votes
1 answer
292 views

Coupling Capacitor of an Antenna

I have a simple question about general meaning & importance of the coupling capacitor in following part of a simple receiver circuit: Is it true that the proper reason why this coupling capacitor ...
1 vote
0 answers
232 views

Crystal Filter Impedance Matching

I downloaded a 2-meter receiver schematic using an IC for the dual conversion IF strip. The first 10.7MHz IF uses a crystal filter with a terminating impedance of 1800//5pF. The output impedance of ...
1 vote
0 answers
66 views

Narrow bandstop filter not requiring ground connection in SMD package

I’m designing an antenna that I’ll implement on a printed circuit board. The antenna will be working on both sides of 900 MHz, so it’s not exactly for ham use. I’m planning to use a bandstop filter in ...
12 votes
1 answer
3k views

What is a "roofing filter"?

What are roofing filters? Are there different kinds of things that are called roofing filter? Why would a circuit or component be called a roofing filter instead of just a IF bandpass filter? Why ...
2 votes
3 answers
249 views

Maximum frequency for discrete components bandpass filter

What is the maximum frequency that can be practical to build a filter with discrete components? I need a band pass filter for 1090Mhz.
4 votes
2 answers
1k 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 ...
0 votes
0 answers
146 views

Is 6 kHz bandpass filter wide enough for listening to SW broadcasts?

I'm considering buying ICOM IC-718 as a main rig and also to use it for SWL. Read contrasting opinions on the Internet, with an article reviewing dedicated SW receivers saying "That receiver's ...
1 vote
1 answer
289 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 ...
9 votes
5 answers
834 views

What limits a PIN diode or varicap from being used in a "Software Defined [Radio] Filter"?

A PIN diode varies its capacitance based on a DC bias, and a Varicap exhibits this effect even more clearly. What limits the use of "solid state variable capacitors" like these for ...
4 votes
1 answer
1k 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 ...
6 votes
2 answers
2k 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 ...
3 votes
2 answers
848 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
1 answer
141 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?
1 vote
1 answer
306 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
1 answer
606 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 ...
2 votes
1 answer
158 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 ...
6 votes
0 answers
216 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'...
2 votes
2 answers
1k 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 ...
0 votes
1 answer
112 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 +/...
3 votes
2 answers
45 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 ...
5 votes
2 answers
766 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 ...
1 vote
2 answers
1k 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
1 answer
94 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 (...
2 votes
1 answer
184 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 ...
0 votes
1 answer
443 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 ...
3 votes
1 answer
91 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
2 answers
194 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 ?
3 votes
3 answers
1k 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: ...
13 votes
4 answers
1k views

Why do today's transceivers use LC filters rather than crystal filters?

Going through a number of schematics for today's receivers (Elecraft KX3, for example) I note that most use LC circuits for filtering. The wikipedia article for Crystal Filters suggests, however, ...
3 votes
0 answers
91 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. ...
1 vote
1 answer
146 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
1 answer
843 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 ...