What do you use?

nhfdcadet

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New Hartford, Ct
What kind of equipment would you recommend for signal finding in the VHF and UHF Bands?
I currently rely mostly on signal strength and a directional antenna, but i'm sure there's better ways. Any advice?
 

N8RDF

(vanity call, "Radio Direction Finder")
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Check out this thread here: How many times have you participated in a Transmitter Hunt?
 

mmckenna

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From the land of sky blue waters!
I've had to track down interference on repeater inputs. I have a service monitor and a spectrum analyzer. The spectrum analyzer was helpful to narrow down the frequency the interference was on, but the slight delay in processing made it not a good method to track it down with a directional antenna.
Ultimately the thing that worked was a basic hand held radio with an RSSI readout and a Yagi antenna. Took a while since it was intermittent transmissions, but it worked. Was able to walk right up to the source. As you get closer, a attenuator can be handy. I used some inline coaxial attenuators.
 

N8RDF

(vanity call, "Radio Direction Finder")
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Also, if you haven’t read the book, google THRDFS by Moell and Curly (sadly, free download available)
 

N8RDF

(vanity call, "Radio Direction Finder")
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Brighton, MI
High budget- DDF2020T doppler with gps option
Mid budget- yagi antenna and attenuator with xcvr or scanner
Low budget- handheld radio and body fade technique
Reminder#1- vhf and uhf will have lots of reflections and multipath, take several readings around a single spot before deciding the direction
Reminder #2- having great clubs doesn’t make an expert golfer. Practice a lot with known signals before trying unknown ones.
 

vagrant

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As mmckenna noted, one will typically end up on foot during the search, so you're reasonably set with your dual band directional antenna and a receiver/transceiver with a reasonable signal level meter. One that displays RSSI is great. Attenuation definitely comes into use and turning your back to the signal with a directional antenna in front helps to also narrow the direction when you get close. Remember 360° turns are prudent. Also, do not forget harmonics. Your dual band antenna will come in handy if you're looking for 146.565 and dial up 439.695 when the signal becomes stronger. This is very handy when the radio will not attenuate further and you don't have an inline attenuator to add. Additionally, if the signal appears to be using a vertical antenna, turning your directional antenna horizontal may add up to 20 dB of attenuation for a quick and easy option.

As to equipment, I use an Icom R30 which offers adjustable attenuation. I use the dual band Elk Log periodic for the directional antenna. While I have stuck with the Elk, I have used much lower cost receivers over the years.

Good equipment helps, but trial and error from practice is the best investment.
What kind of equipment would you recommend for signal finding in the VHF and UHF Bands?
I currently rely mostly on signal strength and a directional antenna, but i'm sure there's better ways. Any advice?
 

Ubbe

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Sep 8, 2006
Messages
6,198
Location
Stockholm, Sweden
I while ago I had dead carrier transmission that jumped around on almost all VHF marine channels. When it transmitted on ch16 and the rescue channels the rescue team asked people to check their microphones and when it sent a carrier on the big ships announcement channels they complained about a swoshing sound in the radios. That continued for a couple of days but nothing was done about it so I went out with a scanner and pointed the antenna horizontal and tried to find the weakest signal, where the antenna pointed, and turned 180 to check that it wasn't stronger from the opposite direction. I ended up at some houses pretty close to a radio amateur. I talked to our FCC about it and they came out with a car equipped with a doppler direction finder with 8 antennas on the roof.

It turned out that I had been chasing the reflection from a concrete wall that supported a road on a hill and the actual signal where obscured from a hill to my much lower search position. FCC found the source at the other side of the hill and turned out to be another radio amateur that had salvaged an old discarded marine radio that he used for listening to marine traffic. He had left that powered on connected to a roof antenna while he was on vaccation and the radio had suddenly began to sporadicly transmit and change channels by itself. So if using direction type of method you should probably increase your search area much more than what you think would be necessary to avoid hunting for reflections.

At work a bought a Ramsey kit doppler direction finder that came with four telescope antennas and magnet feets and it costs something like $250 and worked really well.

/Ubbe
 

burner50

The Third Variable
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Dec 24, 2004
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NC Iowa
I used to do them daily. It's not that difficult.

A old settop dipole antenna and a 3" piece of PVC to whatever flavor of receiver you have that shows received signal strength with little delay. If it has a speaker for you to listen your ears will tell you more than the receiver will.

Back when the FCC cared about CATV leakage, it was a job I did a couple times per day. We used to have leak detectors mounted in our trucks.
 

PA8W

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Nov 14, 2017
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I mainly use "dopplers" or automatic amplitude RDF's of my own design.
Sometimes with the aid of MapApp, an Android mapping app I wrote to present my bearings on the map, plus the bearings my homebase-doppler is producing.
Leaving the car I switch to homemade Moxxon directional antennas (Ever hunted in a dense corn field with a yagi?)
Building the tools actually is my core hobby, but of course I do need targets to test them and -even more important- improve my skills.;)
 

Sparky_ND

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Jun 26, 2021
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I've used a combination of almost all the methods mentioned already, but this certainly looks interesting.....

KrakenSDR
 
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