Questions tagged [antenna-system]

The system composed of an antenna and a feed line, and possibly also an RF ground connection, antenna tuner, balun, phasing device, et cetera.

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2
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3answers
707 views

VHF 50 Ω Antenna Over 75 Ω TV Coax

I have a 50 Ω VHF airband antenna which I’m planning to install in my loft, for use with a RaspberryPi-based RTLSDR scanner/receiver. I already have a UK-standard UHF/Freeview antenna using standard ...
8
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5answers
412 views

How did hams manage to tune their antennas before VSWR meters?

In the early 20th century --back when the hobby was still new-- before VSWR meters and antenna analyzers were invented, how did radio operators know whether they were tuned for maximum power out? ...
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3answers
108 views

Using 75 Ω instead of 50 Ω coax feed

Can I replace my old 50 Ω coax with RG6? It's cheaper and less loss at VHF/UHF. I would match by L/2 multiples of coax to repeat input and output impedance or L/C matching networks at each end. Is ...
7
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5answers
1k views

What is an antenna tuner? Why bother with resonant antennas in the first place?

There are a lot of antenna tuners on the market that have various capabilities in terms of how they can allow random radiators to work with our transceivers. What exactly do they do? My ...
8
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3answers
523 views

Stealth HF station setup advice

I need some advice on setting up my first HF station in a somewhat restricted townhouse community. If I had a detached house with a backyard I’d probably already have everything setup. But with this ...
7
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3answers
178 views

Passively reducing ground loss?

Would a disconnected wire or conductive mat below a low height antenna reduce ground losses? A tuned length of wire under a wire antenna might be suitable for NVIS gain. But would a bunch of space ...
5
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6answers
233 views

Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka “antenna tuner”)?

I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to ...
4
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1answer
171 views

Is it safe to run two barefoot rigs on one antenna with an AB switch?

I have a Daiwa CS-201A two position switch. The single side is connected to by quarter wave vertical (40m). The A and B sides are connected to an IC-7300 and TS-830S. The switch is claimed to have ...
2
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1answer
147 views

Bow Tie antennas impedance

I see on the internet that a radio amateur made bowtie antennas for transmitting and receiving on the 2 meter and 10 meter bands. They produced very good SWR bandwidth when fed with 50-$\Omega$ coax. ...
6
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1answer
110 views

Why does adding 50-ohm BNC Ethernet terminator(s) in parallel to my 4-element yagi improve my radio's reception? (70cm)

I have this radio, with a rubber duck antenna, and a repeater twenty miles away to my north-northwest. If I set my radio on the top of a cabinet in my bathroom, I receive the repeater fine. I can't ...
4
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2answers
103 views

What additional information do I get from an RF ammeter, as compared to a regular SWR/wattmeter?

I've grown up using SWR/power meters. They're "simple" devices: They show forward and reverse power, and show the standing wave ratio. They, however, do not show antenna efficiency. New hams are ...
7
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2answers
5k views

Phasing harness for antenna array

I understand that certain antenna designs (particularly phased arrays) require feeding each radiating element with a certain number of degrees of phase separation in order to achieve a desired ...
4
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1answer
65 views

How to model passive elements when simulating an antenna?

So I started writing an antenna simulator program to design antennas for my needs. To calculate the electric field vector at every point, I split the active element of the antenna into a large number ...
4
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2answers
246 views

Share wide band antenna with multiple transceivers

I'm trying to incorporate several transceivers on my board design; I need WiFi (2.4 GHz) SatCom (~1.6 GHz) RF (~900 MHz) and GNSS (~1.5 GHz). I need to combine them into one antenna. I found a wide ...
17
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5answers
4k views

How does the signal know where the cable ends and the antenna starts?

I know very little about antennas. I know, that for a certain frequency the antenna needs a certain lengths for good sending/receiving conditions. Often the antenna is at the end of a cable. Why doesn'...
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3answers
176 views

Output power curve of an antenna

My approach is that a radio wave is made from zillion of accelerated electrons which emit zillions of photons. Since the current flows in a open circuit, the antenna generator works against something ...
7
votes
2answers
631 views

What are some ways to ground a transmitter+antenna in an enclosed attic?

If I want to minimize "RF in the shack" and lightning hazard, what some good ways to ground a transmitter and indoor antenna in a top floor room or attic with no exterior access? (say a multi-story ...
0
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1answer
197 views

guard planes in differential antenna PCB designs

The designs I have seen all seem to have this surrounding stitched-to-the-ground copper pour surrounding them. Why put it on a differential antenna PCB like below ? And why are those thin lower left ...
4
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1answer
252 views

Are Elevated Radials Necessary for Elevated, 5/8-wave “Ground-Plane” Antennas?

Currents at the base of an elevated, 5/8-wave, vertical ground-plane (GP) transmit antenna are lower than when that vertical conductor is 1/4-wavelength. Does this mean that the performance of the ...
2
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1answer
105 views

Stacking DB8 “bedsprings”

I'm trying to receive a UHF TV signal 86 miles away. Considering the height of the transmitting antenna and the height of the receiving antenna, I should be able to just make line-of-sight between ...
9
votes
6answers
1k views

While backpacking, is it worth mounting the antenna to the backpack frame (above my head)?

I am planning a trip with a large group in 6 weeks. We will be spread out in small groups on a trail in a mostly desert plateau landscape perhaps 5 miles apart, but mostly in a straight line. I'm new ...
2
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2answers
298 views

G5RV Jr. fed with ladder line and coax

I am a new ham and I was just given a G5RV Jr. I have about 20 feet of coax plus about 60 feet of 450 ohm ladder line I can feed it with. Can I extend the G5RV Jr. feed line with the ladder line I ...
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1answer
101 views

How is RF Power at Receive Antenna Output Terminals Calculated?

Is the Friis equation sufficient to make this calculation? Must other considerations also be evaluated?
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2answers
101 views

True near field distance for a short monopole antenna?

Antenna properties: Height x Diameter = 3.3 inches x 1.4 inches Test Frequency: 900 MHz (Wavelength = 33 cm or 13 inches) I see some conflicting formulas to calculate the near field distance for ...
5
votes
5answers
223 views

Signal path to maximize RFI rejection in an urban environment

Urban ham here (Cambridge, MA - FN42ki - KC1JZE) looking for tips to make this hobby possible in the city. I rarely can hear both sides of HF phone transmissions, and have yet to make contacts despite ...
6
votes
1answer
143 views

Two antennas on different sides of a building

I live in the 4th floor of a building with one side facing south and the other north. I am able to use my 2M mobile base transceiver with a mobile magnet mount antenna placed just outside the window. ...
3
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1answer
130 views

How high an SWR can the USRP 2901 (B210) handle?

I connected a USRP 2901 (B210) to an amplifier I designed. The USRP seems to shutdown every time I try to transmit. I guess I messed up with the input impedance matching on the amplifier. Is it the ...
4
votes
3answers
166 views

Radio stops receiving as soon as the antenna is threaded all the way

Is it normal for the antenna conector of the radio to have 18ohm resistence between the inner socket(signal) and the thread (ground)? When I connect the antenna works fine if only the inner plug ...
3
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1answer
87 views

Electrical Earth

I have moved to a new flat which is on the 4 floor, luckily the landlord has let me put an OCF dipole outside with coax feeding through an existing hole in the window frame. I'm looking for some ...
6
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4answers
1k views

Why do we distinguish between balanced and unbalanced?

I hear all the time, "you need a balun between your balanced dipole and unbalanced coax to stop the common-mode current" when it seems the proper advice is "you need something to stop common-mode ...
5
votes
3answers
445 views

Lightning strikes nearby and coaxial cable

A direct hit on my home by lightning is very, very unlikely. However, many lightning strikes that hit Earth nearby are by far the main hazard for ham radio gear (in my opinion, after 60 years in the ...
9
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1answer
171 views

Does Coax Limit the Maximum SWR a Transmitter 'Sees'?

A recent discussion about SWR led to the assertion that a length of coax cable will ultimately limit the SWR to which the transmitter will be exposed. By experimenting with an SWR calculation tool ...
7
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3answers
2k views

Antenna for a cramped attic

Brand new Ham. I bought a cheapo UV5 right before I got my call sign. I want to set up a decent 2m/70cm station for starters and I realize that a better radio is important but wanted to knock out the ...
7
votes
3answers
340 views

Attic Dipole - Impact of Ethernet over CAT5/6

I've been thinking about putting 20m and 10m dipoles up in my attic (HOA), but I also intend to soon put some Ethernet cable to a WAP (with PoE) through the attic. I was intending to feed this with ...
4
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4answers
356 views

TV strong station has no signal when coax is connected

Right, not directly ham radio related, but this puzzles my ham brain. I have several TVs connected to a distribution amp connected to an outside antenna. All but one work fine, and the one won't ...
2
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2answers
221 views

Using one of two antenna tuners connected in series

I have: A Kenwood TS-590SG. 2 antennas up, a tri-band beam and a fan dipole. I run both antennas to a MFJ-998 auto tuner. I also have a MFJ versa tuner IV. The auto tuner works good for 80-10 meters ...
6
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6answers
760 views

Use a TV coax and balun for a poor-man's OCFD?

Can I use TV coax and a cheap TV balun to build a poor-man's OCFD? Marginal performance is acceptable if it saves money. If I could listen to 10% of transmitters within a 100 mile radius that would be ...
0
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2answers
432 views

Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?

I'm studying for my foundation license (in the UK) and I have these diagrams: Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does ...
1
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1answer
151 views

Two devices + one antenna

What I have: GSM 900 repeater 900 - 2400 MHz MIMO antenna 2xSMA MIMO 4G Router works with 1800 MHz LTE Is it a good idea to connect GSM repeater via SMA splitter to one of the antenna cables? Will ...
0
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2answers
52 views

Determing short or open location in antenna system

I have a G5RV antenna. It used to work fine. I had it disconnected for several months. Now I can't get it to load. I think there may be a short or open in the coax. Is there a way to determine how ...
2
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2answers
461 views

Grounding Help - Where To Route My Wires

Here is my situation. My antenna mast is on the opposite side of the house from my ham shack, same with the power service entrance. I have installed ground rods roughly every 16 feet with #6 wire ...
0
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2answers
608 views

G5RV Jr and Ladder Line feed Lying Flat on the Roof?f

a semi-old, mildly grumpy, damn lazy new General Class Op, back after nearly 40 years since last license. Live in an old 2 story Mediterranean Sunset District Avenues home with a flat, beam-bitumen-...
1
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1answer
240 views

Wide bandwidth HF power combiner schematic and formula

I want to build (not purchase) a wide bandwidth power combiner. It should combine signals from 2 TFD antennas cut for 15 MHz lower frequency and used for receive only. Upper frequency is 30 MHz so ...
2
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2answers
230 views

Using two antennas with IC751A — one for transmitting and another for reception

Is it safe to use one antenna for transmitting (main antenna PL connector) and another for reception connected to ANT IN connector at the backside panel?
3
votes
3answers
611 views

What is the point of high gain antenna with respect to the maximum EIRP

OFCOM states that the maximum EIRP within the UK for 2.4 GHz is 100mW. Simply put, what is the point in being able to buy 2.4 GHz high gain antennas which can say do 24dBi, which already puts the ...
5
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4answers
952 views

What exactly is impedance?

I see "impedance" used everywhere. Equipment has an input and output impedance. Antennas and feedlines all have this 'impedance' thing. For someone that understands DC electronics, Ohm's law and a ...
2
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2answers
127 views

How to safely connect a digital output to a receiver's antenna input?

Suppose I have a 3.3 or 5V GPIO digital signal (from an Arduino or Raspberry Pi, etc.), periodically toggling at some HF or VHF frequency. Since it has such a "dirty" spectrum, I don't want to hook ...
1
vote
3answers
326 views

High SWR on a Jeep with Spare Tire Mount

I just installed a spare-tire mount and Browning BR-180 dual band antenna on my Jeep JK. Initial SWR testing show nothing higher than 1.4:1 across both bands so I didn't try to tweak it. Then I put ...
0
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1answer
272 views

Using the VHF port for 6m on an Icom IC-706mkIIg transceiver

My Icom IC-706mkIIg transceiver has two output ports: one for its VHF/UHF bands (i.e. 2m/70cm) one for the HF bands, and also 6m! I have a couple of broadband VHF/UHF antennas whose transmit specs ...
1
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2answers
124 views

Serial matching stub combined with RF choke

If I use RG6 coaxial cable in odd multiples of 1/4 wavelength as a serial matching stub, can I also use it, without modifying the length, as a coiled RF choke balun at the antenna feed point?