Sensitive VHF reciever/scanner under 200$?

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leviterande

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Hi, I am not sure if this is the right section to post this so pardon me if this was wrong. I am working in a lab and making a series of experiments inside and outside buildings. I want to pick up various very weak signals at specific frequencies above 100mhz. NOTE: I am going to connect the receiver to a spectrum analyzer to analyse the transmission carrier wave itself. I wonder if you could help me pick the best one for the job under 200$ , that would be really appreciated

Requirements:
-detect very weak signals in the range around between 100mhz to 200mhz(higher than 200mhz is fine ofcourse too)
- high sensitivity/ good signal to noise ratio
- selectivity:very narrow bandwidth if possible

I read amplifying nowadays is not a problem and that you could install various antennas and preamps etc. But the most crucial thing is the sensitivity and signal to noise ratio if I understand correctly. So sensitivity is a priority I guess to pick weak signals?
I searched the net and ebay and there is a plethora of instruments, there are all from modified usb dongles, unknown unmarked smaller boxes without specifications on ebay, to handheld wideband small scanners, and stationary wideband receivers and scanners.

Which should I look for?
What is the best bang for buck to fulfill my requirements above do you think?
thx
Karl
 

natedawg1604

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Hi, I am not sure if this is the right section to post this so pardon me if this was wrong. I am working in a lab and making a series of experiments inside and outside buildings. I want to pick up various very weak signals at specific frequencies above 100mhz. NOTE: I am going to connect the receiver to a spectrum analyzer to analyse the transmission carrier wave itself. I wonder if you could help me pick the best one for the job under 200$ , that would be really appreciated

Requirements:
-detect very weak signals in the range around between 100mhz to 200mhz(higher than 200mhz is fine ofcourse too)
- high sensitivity/ good signal to noise ratio
- selectivity:very narrow bandwidth if possible

I read amplifying nowadays is not a problem and that you could install various antennas and preamps etc. But the most crucial thing is the sensitivity and signal to noise ratio if I understand correctly. So sensitivity is a priority I guess to pick weak signals?
I searched the net and ebay and there is a plethora of instruments, there are all from modified usb dongles, unknown unmarked smaller boxes without specifications on ebay, to handheld wideband small scanners, and stationary wideband receivers and scanners.

Which should I look for?
What is the best bang for buck to fulfill my requirements above do you think?
thx
Karl
Can you clarify what type of research/measurements you are doing? In general "non-professional" hobbyist scanners (i.e. any scanner sold by Uniden, Radio Shack, GRE etc) are not known for superb sensitivity or selectivity. Indeed, very few (if any) scanner manufacturers even publish technical specifications for sensitivity or selectivity within various frequency ranges.

If your measurements are confined to a particular frequency range, you should consider buying a device specifically engineered to operate within that range. For example, you might consider buying a used "professional" VHF radio on Ebay and find someone who can disable the transmit functions.
 

leviterande

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Aug 4, 2014
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Can you clarify what type of research/measurements you are doing? In general "non-professional" hobbyist scanners (i.e. any scanner sold by Uniden, Radio Shack, GRE etc) are not known for superb sensitivity or selectivity. Indeed, very few (if any) scanner manufacturers even publish technical specifications for sensitivity or selectivity within various frequency ranges.

If your measurements are confined to a particular frequency range, you should consider buying a device specifically engineered to operate within that range. For example, you might consider buying a used "professional" VHF radio on Ebay and find someone who can disable the transmit functions.
Thanks for the lightning quick reply!
I understand, used equipment can be great deal but I had no luck in the used business, unfortunately.
I intend to analyse the waves via a spectrum analyzer (S.A). As you know noise is part of our life so when you tune in for example on a radio station and see the waves on a (S.A) you will see noise on all frequencies on a certain amplitude. The radiostation frequency amplitude however is "much higher" . The signals I am going to detect however are going to be much lower I believe. I expect them to be at the same level as the noise itself /slightly higher. All I want is to see if the signal is detected.

Say for example I put an intentionally very weak 100mhz transmission signal a distance from my receiver(say a few meters). The question is can I see this signal if I have a sensitive receiver+ S.A.. I think yes. By noticing that the "noise" around 100mhz range in the S.A has became higher/more changed than before.

How much the amplitude of this 100mhz signal is higher than the noise is what it is all about I believe. and that depends on sensitivity and cleearity as far as I see .. I am not a shortwave radio expert so thats why I wanted to ask here what kind of equipment would fit my bell best for the money.
Iis it scanners or wideband receivers I should look at? I guess, scanners are better than wideband receivers since scanners are directed at higher frequencies, correct? or am I way wrong?
for instance: there are many types, handheld types like this YAESU VR-160 AM/FM/WFM PROFESSIONAL COMMUNICATIONS HANDHELD RECEIVER | eBay and trunk trackers and there are these "black boxes" 25-1300 MHZ RECEIVER FM/AM/SSB HAM RADIO SDR HF/VHF/UHF + SPECTROSCOPE + ANTENNA | eBay like this w/o any specs anywhere. which general type do you think I should direct my interest at?

Thanks
Karl
 

leviterande

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Messages
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I forgot to add that the weak signals are not necessarily artificial, I mean, they are not broadcasts, conversations or the like. It complicated to explain in detail. All I know for certain is the frequency range. SInce they are not artificial signals and are instead from nature, I dont know how they are modulated .I dont know for sure under what category they fall, if they are FM , or AM or CW or a mix. I assume however that the signals are basically auditory - range-pulses of 100mhz-200mhz. so they would look like 100mhz CW or AM?

I cant know the exact modulation (it could even be a full CW )so, what I want to ask is, (ignoring for now the sensitivity problem)does it matter what kind of reception a radio must have in order to listen to say just a specific frequency?. or do I have to know both the signal´s frequency and the signal´s modulation form in order to search for it? cant I just "free search" the air for a specific frequency.

hmmm..I think however honestly my wondering is far from clear ..
 

WA0CBW

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In general the receiver must be able to select the specific signal you want to analyze. If the signal is a CW signal there is no modulation. Therefore there is nothing (no modulation) to detect. To "hear" the signal you need to mix another signal with it in the receiver giving you a tone. For the sake of discussion a CW signal has zero bandwidth. (Actually it is a few hundred hertz wide). Take that same CW signal and amplitude modulate it. The width of the signal now becomes twice the highest audio modulating frequency. If I modulate it with a 3KHz tone then the bandwidth will be 6Khz wide and contains 3KHz of upper sideband and 3KHz of lower sideband. The receiver might use a diode detector to rectify the carrier and sidebands thus recovering the original modulated signal of 3KHz.
So to answer your question the receiver needs to be able to tune to the desired frequency, have a bandwidth wide enough to pass only the desired signal and sidebands and a demodulator able to remove the modulation frequencies. A spectrum analyzer will allow you to view the carrier and its modulation characteristics. Since a spectrum analyzer may not be as sensitive as a good receiver you would have to get closer (or amplify) the signal you want to analyze. Now what are you trying to do with the receiver? I guess you could hook the spectrum analyzer up to the receiver IF but the signal has been kind of modified after going through the mixer and IF amplifers.
BB
 

leviterande

Member
Joined
Aug 4, 2014
Messages
5
In general the receiver must be able to select the specific signal you want to analyze. If the signal is a CW signal there is no modulation. Therefore there is nothing (no modulation) to detect. To "hear" the signal you need to mix another signal with it in the receiver giving you a tone. For the sake of discussion a CW signal has zero bandwidth. (Actually it is a few hundred hertz wide). Take that same CW signal and amplitude modulate it. The width of the signal now becomes twice the highest audio modulating frequency. If I modulate it with a 3KHz tone then the bandwidth will be 6Khz wide and contains 3KHz of upper sideband and 3KHz of lower sideband. The receiver might use a diode detector to rectify the carrier and sidebands thus recovering the original modulated signal of 3KHz.
So to answer your question the receiver needs to be able to tune to the desired frequency, have a bandwidth wide enough to pass only the desired signal and sidebands and a demodulator able to remove the modulation frequencies. A spectrum analyzer will allow you to view the carrier and its modulation characteristics. Since a spectrum analyzer may not be as sensitive as a good receiver you would have to get closer (or amplify) the signal you want to analyze. Now what are you trying to do with the receiver? I guess you could hook the spectrum analyzer up to the receiver IF but the signal has been kind of modified after going through the mixer and IF amplifers.
BB
I want to find out weather I can detect the weak signals or not. After lots of search it seems that the IC r6 is the most fitting as it seems to be the most sensitive of all others?
 
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