[SDS100 Antennas] Remtronix 843S vs 920S vs Stock: RSSI champ vs audio champ—why?

[Trilliumaire]

On my SDS100, the Remtronix 843S consistently shows higher RSSI on steady carriers/tones, but the Remtronix 920S consistently produces clearer voice on ~800 MHz P25. Looking for explanations and best practices to measure this properly.

Currently in an "RF Disadvantaged" area in the mountains but near-ish to Denver, but no line of sight. HD TV antennas don't even work here.

I used the SDS100 in "Search with Scan" set. Once I found a lock, I swapped between the 3 antennas: Stock, 920S, and Remtronix 843S.

The 843S is expected to be the best all-around, an the 920S is expected to better at ~800 MHz.

What I found is that the 843S had better RSSI on what appeared to be unmodulated CW tones as I scanned, across everything. But when scanning on modulated signals, say around 800 MHz, the 920S did better at pulling in more conversations clearly.

So what are your thoughts on CW tone / carrier RSSI measurements vs. real-world modulated signal experiences with different antennas?

My theory is that the 843S is letting in more junk, so the RSSI is higher, but the 920S acts as a filter, increases SNR, but reduces RSSI.

???

 

[trentbob]

On my SDS100, the Remtronix 843S consistently shows higher RSSI on steady carriers/tones, but the Remtronix 920S consistently produces clearer voice on ~800 MHz P25. Looking for explanations and best practices to measure this properly.

Currently in an "RF Disadvantaged" area in the mountains but near-ish to Denver, but no line of sight. HD TV antennas don't even work here.

I used the SDS100 in "Search with Scan" set. Once I found a lock, I swapped between the 3 antennas: Stock, 920S, and Remtronix 843S.

The 843S is expected to be the best all-around, an the 920S is expected to better at ~800 MHz.

What I found is that the 843S had better RSSI on what appeared to be unmodulated CW tones as I scanned, across everything. But when scanning on modulated signals, say around 800 MHz, the 920S did better at pulling in more conversations clearly.

So what are your thoughts on CW tone / carrier RSSI measurements vs. real-world modulated signal experiences with different antennas?

My theory is that the 843S is letting in more junk, so the RSSI is higher, but the 920S acts as a filter, increases SNR, but reduces RSSI.

???

Well the 920s is the old original Radio Shack RS 800 that was made by GRE and now REM. That has very high gain on 7-800 MHz, you're going to have less errors on simulcast systems and it's going to sound better. Better audio and modulation.

REM has made three versions BNC, SMA and SMA 100 and they are all going to perform the same. The sma100 has the O-ring to maintain the Integrity of the water resistance in the radio but doesn't affect reception. It's tuned for 7-800 MHz. It does okay on UHF but not so much on VHF High, very compromised reception, it'll pick stuff up but it's not optimal in VHF High.

The other antenna coverage is VHF High, UHF and 7- 800 MHz. There might be some fluctuation in your reception but it's wide coverage.

If you are in an RF challenged area, you very well might be letting in more junk.

Not sure what you listen to on a regular basis but there are more ways to judge reception than RSSI. Sometimes a better RSSI can simply be because of a noisier environment.

If you're listening to simulcast systems, a good indicator for reception on simulcast systems like a phase 2 tdma simulcast system your best indicators are error rate and noise.

I'm being basic here but really good reception is going to give you better audio and modulation, scratchy noisy analog frequencies that are not coming in well are going to provide terrible audio.

The audio itself on the SDS-100 has always been a bone of contention, some people like it and some people don't. Personally I think it sounds good but some say the speaker is too small and it sounds tintty.

 

[AB4BF]

Well the 920s is the old original Radio Shack RS 800 that was made by GRE and now REM. That has very high gain on 7-800 MHz, you're going to have less errors on simulcast systems and it's going to sound better. Better audio and modulation.

REM has made three versions BNC, SMA and SMA 100 and they are all going to perform the same. The sma100 has the O-ring to maintain the Integrity of the water resistance in the radio but doesn't affect reception. It's tuned for 7-800 MHz. It does okay on UHF but not so much on VHF High, very compromised reception, it'll pick stuff up but it's not optimal in VHF High.

The other antenna coverage is VHF High, UHF and 7- 800 MHz. There might be some fluctuation in your reception but it's wide coverage.

If you are in an RF challenged area, you very well might be letting in more junk.

Not sure what you listen to on a regular basis but there are more ways to judge reception than RSSI. Sometimes a better RSSI can simply be because of a noisier environment.

If you're listening to simulcast systems, a good indicator for reception on simulcast systems like a phase 2 tdma simulcast system your best indicators are error rate and noise.

I'm being basic here but really good reception is going to give you better audio and modulation, scratchy noisy analog frequencies that are not coming in well are going to provide terrible audio.

The audio itself on the SDS-100 has always been a bone of contention, some people like it and some people don't. Personally I think it sounds good but some say the speaker is too small and it sounds tintty.

Several years ago, I ordered a Comet antenna for my Wouxun HT and received a scanner antenna by mistake. It is a Comet SMA-W100RX, SMA-P, 25-1300MHz Scanner Antenna. Would something like this work on your SDS-100? It is an SMA male, 986 mm long double jointed, black, extendable, 200 mm when closed.

 

[Trilliumaire]

Since I need a measurement close to Eb/No or SNR, I found that on the SDS100 you can go into the "Customize" menu in the display and add "D-ERROR", which is a bit error rate for digital comms, presumably from the FEC applied to the transmission. If we get in the lower SNR/(Eb/No) regime, I would be able to see this measurement directly (since the FEC would kick in), and get a more rigorous measurement of the performance of these different antennas, without relying on some vague RSSI value.

I also enabled the "NOISE" measurement on the SDS100.

Between these two, I should get a serious delta comparison of these various antennas, at least in the parts of the spectrum these digital signals live.

 

[trentbob]

Several years ago, I ordered a Comet antenna for my Wouxun HT and received a scanner antenna by mistake. It is a Comet SMA-W100RX, SMA-P, 25-1300MHz Scanner Antenna. Would something like this work on your SDS-100? It is an SMA male, 986 mm long double jointed, black, extendable, 200 mm when closed.

I've noticed that normal SMA antennas not made for Chinese radios sometimes do work on the proprietary recessed antenna connection and sometimes they don't.. they don't go deep enough to make a connection. Chinese radios use the reverse SMA don't they?

For example, my go to antenna for my SDS 100 is the Watson w 801 which is impossible to find now and if you do it's out of stock but it's an excellent all around antenna with very good 7-800 reception and very good VHF High and UHF but the SMA model does not fit and does not make contact so I use the BNC with the adapter. It's a normal SMA connection not the reverse SMA that you would use on a Chinese radio, it just doesn't go deep enough to make contact.

If you're lucky enough to get a knowledgeable vendor they may be able to tell you or maybe somebody here will know but there's really no way to know which normal SMA is going to work or not.. any REM SMA connection will work even if it doesn't have the O-ring to maintain the radios water resistance.

It's almost as if you have to try it to know.. Maybe a more knowledgeable member will have that answer

 

[Trilliumaire]

Would something like this work on your SDS-100?

It might, but I really want to compare the deltas in performance, across whatever antenna I plug in.

So without getting other equipment, like a spectrum analyzer, and digging in hard into the guts of the SDS100, I just wanted a simple way to measure the performance across antennas directly on the device, without too much hassle.

I may have found a way, maybe. Not sure what the scanner community does for this as a general rule.

I am new to scanners, but not new to RF/Antennas or DSP/Comms.

 

[trentbob]

So the first picture is the SMA connection that will fit a SDS 100 providing the water resistance. Notice the extension that allows it to go deeper into the mounting portal.



This is the SMA connection for an antenna used on a Chinese radio and as you can see it would not work on an SDS 100.

 

[Trilliumaire]

Yes, that definitely won't work with Uniden (Yuniden Hôrudingusu) ...

A Japanese company making SDS100's out of [mostly] Vietnam.

 

[Ubbe]

Since I need a measurement close to Eb/No or SNR, I found that on the SDS100 you can go into the "Customize" menu in the display and add "D-ERROR", which is a bit error rate for digital comms, presumably from the FEC applied to the transmission. If we get in the lower SNR/(Eb/No) regime, I would be able to see this measurement directly (since the FEC would kick in), and get a more rigorous measurement of the performance of these different antennas, without relying on some vague RSSI value.

I also enabled the "NOISE" measurement on the SDS100.

Between these two, I should get a serious delta comparison of these various antennas, at least in the parts of the spectrum these digital signals live.

D-error for digital and Noise for analog transmissions but it treats any modulation as noise so must be quiet when reading the value, like when a repeater have a few seconds of hang time after a transmission ends. FEC are disabled during transmissions using Motorola RAS, as the scanner cannot handle the RAS key, but D-error measurements still works properly. But it is said that RAS only needs to disable FEC on voice frames in the scanner and other data frames can still be using FEC, so your assumption might still be correct.

/Ubbe