Receiver Sensitivity

[Sshalita]

I know that the antenna has a great effect on receive (RX) quality, but I am wondering if there are any differences between the receiver engine/module contained in the various scanner models. This question is specifically for portable/hand-held units.

Aside from specific features, like trunking and other enhanced digital capabilities, do the higher end scanners have better RX capabilities (e.g., are they more sensitive) than lower-end models or do they all use the same RX engine? The same question can be asked for RX sensitivity between brands such as Uniden versus Whistler?

Right now I am using a BC125AT and am struggling to monitor Low VHF (39-45 Mhz for CA CHP). I upgraded the antenna to a Diamond RH77CA (thanks to reading threads on RR) and it helped, but it's still not great. It then dawned on me that there may be more sensitive receivers out there, hence the question. For what I am monitoring the BC125AT is sufficient, but I would consider upgrading if there was a more sensitive/powerful receiver.

Would be interested to hear comments.

 

[ko6jw_2]

Scanners from the major manufacturers have similar specs. The higher end models have better sensitivity. Not commercial grade, but generally adequate. Sensitivity is not usually the problem. Greater sensitivity will probably result in more overloads and intermods.

Others may want to debate the merits and demerits of some receivers and they are welcome to do so. However, as you seem to realize it's more about the antenna system.

Good low band reception requires an antenna designed for that band. The Diamond is really intended for amateur use in the two meter and seventy centimeter bands. Yes, it is a good antenna, but it is not designed for 39-45Mhz. In fact, it may do worse than a simple telescoping antenna because it has a fairly narrow bandwidth and its response will fall off below the two meter band.

A quarter wave antenna for 42Mhz would be about 66 inches long. At about 18 inches the Diamond is way too short. Radio Shack used to sell a telescoping whip with a center loading coil that worked OK on low band. Don't know if they still sell them. GRE used to sell rubber ducks that covered low band. Again not very good, but better that the stock antennas.

Unfortunately, with the general move to UHF, low band antennas are harder to find. Just a plain telescoping whip and a long as you find will do a good job.

 

[Ubbe]

It's normally done so that a portable scanner, that have less of an antenna and sees lower signal levels, gets a higher sensitivity set in the amplifier but then also have a higher risk of getting overloaded or de-sensed when using a bigger antenna or getting too close to strong transmitters. One way of reducing the risks are to use more and narrower filters that always are put between the amplifier and the antenna connector. Modern Uniden scanners have lots of filters and Whistler have fewer. Old scanners and budget level ones also have fewer filters. A portable scanner are always a compromise between size and performance. If portable scanners would be just as effective as a mobile/base one, we all would be using them as they can be used both home, in car and wherever you go, so much more versatile. But that is not the case.

Professional receivers and even most single band HAM radios have very narrow filters that are track tuned to the exact frequency you are monitoring and that often makes them receive better than any multiband scanner. Even a cheap TYT MD380 for less than $100 receives better than scanners but have limited features and cannot trunk track and only scans 32 channels in each scanlist with or without CTCSS/DCS. It's perfect for monitoring some weak signal transmissions. Rumors have it that the latest batch of MD380 have changed to a direct conversation receiver, like the same concept the Uniden SDS100 uses, and have lost some of its excellent performance but is still better than a scanner and can also be connected to bigger antennas.

/Ubbe

 

[spongella]

You may want to use an outdoor antenna for better results. I've got the same exact radio but have not heard much on low VHF. Our local fire company still uses lowband VHF at times but have not heard any activity lately. ko6jw_2 is right on the money, a telescoping whip will help if you want an antenna directly attached to the radio.

Among my array of scanner antennas I have a Comet BNC-W100RX that extends to 40 inches but I've yet to use it with the BC125AT, which in my opinion is a great analog scanner. Good luck, hope you find an antenna that works for you.

 

[prcguy]

Sensitivity is only one parameter that determines how good a receiver might be. Not long ago I had several amateur hand helds at a local park on the side of a big hill that looks over much of Los Angeles and Orange County, CA. I had a couple of Yaesu amateur hand helds and a Baofeng UV-5R.

While all radios received local repeaters fine I could hear distant stations on 2m simplex with the Yaesu hand helds but the same signals did not exist on the Baofeng. I used the same antenna on each radio in the same location with the same results, the Yaesu's were hearing things the Baofeng could not.

I later checked the sensitivity of each radio on a service monitor and found the Baofeng was very sensitive and better than .1uv where the Yaesu radios were less sensitive and closer to .15uv and .2uv, which is 6dB worse than .1uv. The Baofeng should have received noticeably better with those specs but on the service monitor there is only one signal going into the radio and with an antenna the receiver is hit with countless high level signals adding up to something the Baofeng could not deal with.

The problem lies with the ability of the Yaesu radios to work in a high RF environment without their front ends or mixers getting overloaded and the radio creating internal IMD which raises the noise floor and blanks out weaker signals. The Baofeng was operating beyond its capabilities in a high RF environment and this was using a rubber duckie antenna right on the radio. If I had used a large base station antenna at the same location the Baofeng would have been completely useless and the Yaesu's might have been pushed too far.

The point I'm trying to make here is sensitivity is not the only specification you should be concerned about and in some cases like shopping for an HF receiver its almost irrelevant.

 

[Bob1955]

I know that the antenna has a great effect on receive (RX) quality, but I am wondering if there are any differences between the receiver engine/module contained in the various scanner models. This question is specifically for portable/hand-held units.

Aside from specific features, like trunking and other enhanced digital capabilities, do the higher end scanners have better RX capabilities (e.g., are they more sensitive) than lower-end models or do they all use the same RX engine? The same question can be asked for RX sensitivity between brands such as Uniden versus Whistler?

Right now I am using a BC125AT and am struggling to monitor Low VHF (39-45 Mhz for CA CHP). I upgraded the antenna to a Diamond RH77CA (thanks to reading threads on RR) and it helped, but it's still not great. It then dawned on me that there may be more sensitive receivers out there, hence the question. For what I am monitoring the BC125AT is sufficient, but I would consider upgrading if there was a more sensitive/powerful receiver.

Would be interested to hear comments.

I have the same BC125AT with the Diamond RH77CA and low band is awesome. FYI

 

[iMONITOR]

The point I'm trying to make here is sensitivity is not the only specification you should be concerned about and in some cases like shopping for an HF receiver its almost irrelevant.

Bob Grove of Monitoring Times spoke of this often! He discussed the importance of "Selectivity" and how much it was left out of the specifications of most scanner radios.

 

[zz0468]

What I've observed with low end consumer receivers such as scanners and CCR's is that, while they have decent sensitivity specs, the synthesizer phase noise is horrendous. A noisy local oscillator superimposes it's noise on the received signal at the IF output of the mixer.

The end result is a receiver that might be able to discern a weak signal, but will never fully quiet in FM mode. In digital modes, the BER will begin to deteriorate while the signal is still pretty strong. Couple that with poor overload resistance and you end up with a radio that, no matter how expensive it was, sounds cheap. A .3 uv signal in a scanner might break squelch on a scanner, but on a commercial radio it's actually usable.

Motorola builds the VCOs on ceramic substrates, and makes lots of other efforts to keep synthesizer noise as low as possible. Things like low noise regulators and electronic "super filters" like what Motorola does on some radios makes the LO extremely clean.

I've heard the old timers in the scanner community complain that the old crystal scanners sounded better and were more sensitive. Local oscillator phase noise is the reason.

 

[AA6IO]

My experience in Los Angeles with all handheld scanners, including the BC125AT, is that indeed the Radio Shack telescoping antenna is far superior to my RH77CAs for CHP reception. Look around for a RS Center center loaded telescoping antenna (not so easy to find these days), extend it out to near maximum (26.25 inches), and you'll hear the difference on CHP frequencies.

 

[Ubbe]

The noise comes from the jitter a phased locked loop produces in a synthesised scanner and has nothing to do with ceramic substrates.
If the VCO has to act quickly to be able to scan frequenceis at a fast rate it will have to have little filtering of the steer voltage to the VCO and will have a high noise level. If you can reduce the scan speed you can insert better filters to reduce the noise. Communication receivers often scan very slow due to the high filtering to get a cleaner audio. The jitter noise will also be detected by the squelch and makes it work less effective and some scanners filter out the noise by making the audio more muffled cutting out all high frequencies from the audio to the speaker.

/Ubbe

 

[zz0468]

The noise comes from the jitter a phased locked loop produces in a synthesised scanner and has nothing to do with ceramic substrates.

Sure it does. You can have the best loop filter in the world, and ruin it with a noisy VCO. Want it really clean? You have to work at it everywhere, including the DC power, and especially the VCO.

 

[Ubbe]

My understanding are that the majority of noise in a modern scanner comes from the dirty steering voltage to the VCO that then will act as an FM modulated white noise generator. Other noise sources are much lower in level. An old crystal scanner are usually superquiet with a saturated RF signal although it has the cheapest quality components you can imagine. The best professional two-way radios I dealth with had an optocoupler that would connect extra capacitance to the VCO steering voltage as soon as the channel scanning process was stopped. I used those $4000 radios as reference monitors as they had almost zero addition of own noise to a monitored signal.

/Ubbe