# All Questions

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138 views

### Comparing antenna effeciency

Let's say I have three dipoles, one is resonant at some frequency and is matched at the antenna, the second is shortened with loading coals and is also matched at the antenna, the third is shortened ...
1k views

### How to mark SWL contacts on eQSL?

I fairly frequently get SWL reports via eQSL. I'm never quite sure what I should do with them. I know that eQSL has SWL capabilities, but I can never tell if I'm actually stating that a contact was ...
9k views

I was reading about EchoLink and came across this rule under "Access Policies": 2. No "SWL" (listen-only) access is permitted. EchoLink is a two-way system by design, and there is no mechanism ...
1k views

### What should be the modulation when transmitting APRS signal?

Is it SSB or NFM or other type of modulation?
111 views

### Must all three VEs hold the required licence class to “prepare” an examination, or just one?

47 CFR § 97.507 states that: (a) Each telegraphy message and each written question set administered to an examinee must be prepared by a VE holding an Amateur Extra Class operator license. A ...
219 views

### Designs for a multi band vertical/collinear antenna for the 1.9 gigahertz range [closed]

I'm starting to research building a multi-band antenna in the 1.9 gigahertz range. I see them offered on wireless routers, and they use them in cellular sites. Can anyone provide a reference or quick ...
6k views

### How can I calibrate a SWR meter?

I would like to build my own HF (1.8 - 30 MHz) SWR meter, however I'm not sure how I can calibrate the meter without an accurate power source. I'm targeting a power capacity of 150 W so I can use it ...
3k views

### Does effective grounding of mobile (vehicle) antenna mounts address common-mode currents?

While researching how best to install my mobile amateur radio in my car, I didn't understand if there was optimum Antenna Feedline Length for mobile installations? Understanding that this is caused ...
305 views

### Why is gain used?

It always confused me why 100 watts out of your transmitter could radiate 200 watts coming from a high-gain antenna. Why is the term gain used instead of directionality?
4k views

### Is there an optimum Antenna Feedline Length for mobile installations?

I bought a ham radio antenna mounting kit for my car that includes ~16' of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259. I asked the sales person if it is ...
931 views

### Using wirewound resistors in a dummy load

I have a bunch of high-wattage 50 ohm resistors lying around, but they are wirewound. If I use them as a dummy load for transmitters 144 MHz and down, how bad would that be? Since they probably will ...
3k views

### In USA, is it legal to hear police or ATC frequency? [closed]

In USA, is it legal to hear police or ATC (air traffic control) frequency?
136 views

### What are specific areas that some people get into within amateur radio? [closed]

I just got licensed a few weeks back and have been connecting with repeaters on my 2m/7cm HT. My plan is to get a mobile antenna for use in the car and make an antenna for home operation. While those ...
408 views

### What does the “USER” programmable key function do on the Yaesu FT-897D?

I was just reviewing the manual of my Yaesu FT-897D to remind myself of useful functions I might have forgotten about, and I found the programmable function keys, which can be set to any of “All Multi ...
987 views

### Is a VHF antenna on a vehicle's body a bad idea?

For context, I'm brand new, with nothing but an HT & 19" dual band (2m/70cm) whip on it. While I'll likely go with a magnetically mounted vertical antenna, I've been thinking of other more covert ...
241 views

In a slide on calculating link budget, detrimental effects to a link included “Radio pollution (selectivity, blocking, IP3)”. What is radio pollution? Specifically, what are selectivity, blocking, ...
2k views

### How would a time-difference-of-arrival receiver with two antennas know which side the signal is from?

An easy TDOA design by Byonics was published with the following schematic: It appears that the antennas are switched at a rate of 640Hz, which allows a 640Hz tone to be heard in the radio when the ...
6k views

### Why is the electric field orthogonal to the magnetic field from an antenna?

I've read in several places that the electric field is 90 degrees orthogonal to the magnetic field, and both are orthogonal to the direction of the wave from a transmitting antenna. What causes this? ...
715 views

### Why are there no amateur allocations in the LF and VLF spectrum?

Amateur radio enthusiasts have slices of spectrum at every magnitude of spectrum MF and above, but in the US none are below MF. Why are there no spectrum allocations below 160M?
656 views

### Audio Morse Code to CW converter?

What kind of circuit can be constructed and/or could be used to convert audio containing Morse Code sounds (say from an old practice tape, or from computer generated audio) into key, switch or relay ...
162 views

### How do PL tones make it through so much noise?

So sometimes I hear people trying to get into a repeater with pure noise, and no audible audio on their transmission. With the repeaters that require a PL tone, how can the PL tones get through all ...
1k views

### What is a “dip relay” and how does one use it to build a transmitter?

Reading a discussion on low parts count transmitters, I came across this description, which lacked schematics and build instructions: Re: PROJECT 14: THE WORLD'S SMALLEST TRANSMITTER Are y'all ...
5k views

### Why prefer LC oscillators rather than RC oscillators in RF design?

I don't recall ever seeing an RC oscillator driven RF transmitter or receiver. What prevents people from choosing RC oscillators in RF design?
4k views

### What is the expected microphone input voltage level of a handheld transceiver?

Ok, so I'm looking to inject some computer generated CW into a little handheld rig by wiring direct into the mic input line. What sort of voltage is expected on this input, are we talking uV, mV or ...
3k views

### Does a FCC amateur license cost money?

If I wanted a FCC Amateur license, is this going to cost me anything? That includes tests, application fees, filing fees, and anything else but hardware.
7k views

### How do I change my registered address with the FCC?

I just moved, and I want to change my registered address with my call-sign. Is there a form or something somewhere that I can fill out? Do I have to mail it, or can I turn it in to the FCC or ...
1k views

### Where to apply for an amateur LTE radio license in the USA?

Where do you apply for a license to operate on the LTE radio spectrum for amateur radio in the USA? Can this amateur license be used to operate a cell phone independent of a carrier?
121 views

### multiband mimo ad-hoc wireless connections from different spectrums [closed]

I'd like to create a multiband MIMO ad-hoc wireless network. Can I turn on every GPS, WIFI and Bluetooth radio of a mobile device and synchronize data transfers at extreme speeds between a small, ...
104 views

### Estimate Path Loss

I am wanting to setup a simplex path that is 7KM from base to base in relatively flat ground. How can I estimate the path loss, and what do the numbers mean when I find them? I am wanting to do it ...
517 views

### Morse Code Key Grease

I just got an old brass key at a hamfest, and it appears to be in pretty good mechanical condition, aside from some dirt and dust. Taking it apart, the key (apologies for not knowing the exact ...
401 views

### AM vs SSB weak signal

I know single sideband is much better than FM for weak signal receiving. I know that SSB is just like AM, but with the unneeded parts removed. For weak signal propagation, like EME and aurora, would ...
2k views

### Antenna RX vs. TX

If I only want to receive radio signals and not transmit, are there any differences in the way I design the antenna I need to use, or is it the same either way? I was going to pick up a Realtek ...
2k views

### Why is optimal polarization different for fm as to SSB/CW

On the article "7db for 7 bucks", which is an article about building a simple three element 2M yagi, they stated that vertically polarizing the antenna is better for FM work, and horizontally ...
944 views

### What is Circular Polarization?

So I just learned that a satellite does not send out a circularly polarized signal, it just switches orientation slowly when it topples through space. I thought that because they were spinning, the ...
223 views

### What will I need to receive the ICE/ISEE-3 transmitter?

The ICE/ISEE-3 spacecraft, launched in 1979, is due to pass by the earth in August, 2014. It was commanded to power down completely years ago, but it appears to have failed to do so, and while it ...
2k views

### Are satellites Left or Right hand circularly polarized?

I'm thinking of building some helical antennas for satellite work. I want to know which way to wind them. If satellites are spinning randomly, how can we know if they are left hand or right hand ...
314 views

### Measurement Confusion

I am building a simple antenna from this article 7db for 7 bucks. I am confused on the measurements for the antenna: It looks like there are two pieces of 18 inch PVC pipes connected to a T fitting. ...
734 views

### Coherent CW synchronization?

When using coherent CW, how is the receiver frequency and/or Morse Code dot clock synchronized to the transmission precisely enough to allow for synchronous decoding?
2k views

### What does the Friis transmission equation represent and how is it derived?

I've read that the Friis transmission equation can be applied to calculate path loss in ideal space. However, I'd like to better understand the factors that define it and what it represents, and why ...
8k views

### Grounding VHF base station antenna

I'd like to install an outdoor dual band VHF/UHF base station antenna, a simple pole antenna like the Comet GP-1. I live in an area where lightning is rare, but not unheard of. Should I drive ground ...
3k views

### What is the theoretical performance of a 2m 1/4 wave ground plane antenna when used at 70cm?

If I have a 2-meter 1/4 wave ground plane antenna with 1/4 wave radials bent down at approximately 45 degrees, what kind of performance in terms of SWR and gain pattern can I expect when using it on ...
204 views

### SDR software support for National Instruments USB-4431 ADC?

I have an opportunity to purchase one or more of these 24 bit, 4 channel, 102ksps USB ADCs, but before I do I want to understand how difficult they would be to use with existing SDR software. Are ...
6k views

### Why is antenna aperture a function of wavelength?

Wikipedia says: It can be shown that the aperture of a lossless isotropic antenna, which by definition has unity gain, is: $$A_{\mathit{eff}} = \frac {\lambda^2}{4 \pi}$$ We also see this emerge as ...
1k views

### How would this RF field strength meter be calibrated?

I'm interested in an RF field strength meter that doesn't have to be lab quality, but still gives enough information about the RF field to know if an area exposed to RF is above the safety limits ...
3k views

### If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom?

I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there. My ...
99 views

### Transmitting Offset for sats

I found some pages on info for satellites, and I got different results. Some said to shift the transmit frequency as well as the receive, some said to keep the transmit the same, but shift the receive ...
684 views

### How would I calculate antenna gain?

The concept of antenna gain is pretty important for calculation of link budget and is something I've had contact with. I know that it tells me how focused the waves emitted by the antenna are and I ...
2k views

### Is the bandwidth of an LCR resonant circuit independent of the capacitance?

Is the bandwidth of an LCR resonant circuit independent of the capacitance, if the inductance and its series resistance are kept the same, and the Q is high? This question and the calculation ...
2k views

### How does SDR demodulation differ between wideband and narrowband FM?

What is the difference between software demodulation of an IQ signal between wideband FM and narrowband FM? Both seem to look at the 2nd difference in unwrapped phase angles of IQ samples.
295 views

Can a regenerative shortwave receiver (especially an old vintage unshielded tube or transistor model) connected to a wire antenna generate HF interference? If so, what are some ways to prevent one ...

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