Simple question; Intermod, how bad is it?

[videobruce]

This SDS200, just how bad is intermod on this receiver?
I'm talking about actually living IN a city, not 10 or 20 miles from the city limit where intermod probably doesn't exist no matter how bad the receiver is.

Over 50 years of battening with the problem, kit's only gotten worse wiyh all there 'digital' carriers blast what I'm tring to monitor on the UHF band. The only receiver I have ever owned where internmod is bearable is a Regency HX-1000. Past that, the RS Pro 2004 has been my 'workhorse' for the past 30 years, but it's keeps getting worse.

So, these 'digital' receivers are they any better than the older analog counterparts?

 

[MStep]

This SDS200, just how bad is intermod on this receiver?
I'm talking about actually living IN a city, not 10 or 20 miles from the city limit where intermod probably doesn't exist no matter how bad the receiver is.

Over 50 years of battening with the problem, kit's only gotten worse wiyh all there 'digital' carriers blast what I'm tring to monitor on the UHF band. The only receiver I have ever owned where internmod is bearable is a Regency HX-1000. Past that, the RS Pro 2004 has been my 'workhorse' for the past 30 years, but it's keeps getting worse.

So, these 'digital' receivers are they any better than the older analog counterparts?

Unfortunately, this is a question where "one size does not fit all". Incidentally, I also had an HX-1000 and I still have my RS 2004, although it is in storage. I am pretty close to the midtown Manhattan area (about one mile from The Empire State Building), BUT I can't get antennas topside so I pretty much use mag-mounts in my rear yard. In that admittedly limited configuration, I am not having any issues with intermod.

I know you will get answers from those more astute with the issue, but I would say overall that there have been improvements from the days of the 2004. There are so many different factors to consider that I think the only way you will find out is to actually try the SDS200 in your actual operating environment to experience the radio's capability.

In my experience, just one "sloppy" transmitter nearby can cause a host of problems with reception and overload which might cause or emulate intermod. You mention that your 2004 (which is indeed a "workhorse" of a receiver) and pretty advanced for its day. When you say the the intermod issue "keeps getting worse", I guess you have seen more and more transmitters on the air in your proximity in the last 30 years.

I'm also interested in hearing from those in major metropolitan areas whose antenna configurations are more considerable than my own. In my day, and I guess yours as well, we talked about receivers with "tight" or "loose" front-ends. Before I take another wack at running 9913 cable through my yard and up to the roof (not as easy as it used to be), I am also interested in what others have to say.

As I always mention, Amazon and Walmart have pretty liberal return policies, but I think, in the end, you will have to try it in your own environment to be the judge. Best of luck.

 

[Ubbe]

This SDS200, just how bad is intermod on this receiver?

The $0.75 receiver chip in the scanner are really bad when it comes to intermod and has a lot of internal mixing products, as most of the cheap SDR USB dongle receivers have. When a signal are received it can also be received at a 250KHz-350KHz distance just 15dB weaker in signal strength. The level and offset frequency varies with the filter settings and IFX but will always be there and occurs at multiple frequencies.

Those interferences doesn't appear on the exact frequency for the bandplan, they are a KHz or two at the side that makes the squelch harder to open but if you manually open the squelch fully you can hear them.

Interference test

/Ubbe

 

[jonwienke]

Ubbe is incorrect here, the SDS scanners have extensive pre-filters that the $30 SDR dongles do not, and therefore they handle intermod and adjacent channel interference significantly better than the dongles. They are more susceptible to interference than the x36 models, but in most cases filters or IFX solves the problem.

 

[videobruce]

Where I believed the problem was coming from was in the 424MHz portion that was just added a few years ago (so it seemed). I bought a couple of tunable filters (traps) to attempt to reduce these f'king 'digital' carriers, but found there are tons of other scattered all over the 452-460 portion so that was a waste. How can one ID a 'digital' carrier, even one that is not data, but voice in the jungle of dozens that 'sound' the same?

As to antennas, indoor or attic antennas don't even begin to make the grade for me since 90%+ of what I listen to are not high power 'repeaters'
that a short wire hanging out the back of the receiver would work. .

 

[videobruce]

I am pretty close to the midtown Manhattan area (about one mile from The Empire State Building), BUT I can't get antennas topside so I pretty much use mag-mounts in my rear yard. In that admittedly limited configuration, I am not having any issues with intermod.

I know you will get answers from those more astute with the issue, but I would say overall that there have been improvements from the days of the 2004.

When you say the the intermod issue "keeps getting worse", I guess you have seen more and more transmitters on the air in your proximity in the last 30 years.

Before I take another wack at running 9913 cable through my yard and up to the roof (not as easy as it used to be), I am also interested in what others have to say.

Amazing even with the limited antenna(s), I would bet that all those skyscrapers are blocking many of the xmitters.

AFA 'improvements', it would be likely adding 'features' (as usual) are where R&D $$ goes. The 2006 is worse (not by much thou) over the 2004. I have both, but looking to replace the 2006 with a 'digital' capable model.

Don't use 9913, it's old school. Go with Shireen RFC400 or Times Fiber LRC400. Same loss (far better than real old school RG8), ,but no 'moisture/condensation problems.

Not so much 'more xmitters' , more data/digital xmitters with their 200% audio levels (or so it seems) that knock you out of the chair.
When it was all audio, having two 'audio' carries break in was no where near as annoying as 'digital' intermod. Even pager interference 20+ years ago would be more welcome now.

 

[videobruce]

Is this SDS200 considered a SDR even thou it doesn't need a PC to operate other then initial programming (which shouldn't count)? Unless I'm missing something here.

I'm wondering, the fact this is a 'digital audio' receiver, does that in itself reduce (or should I say 'hide') some of this intermod from digital carriers??

 

[donc13]

Yes, it's at least partially an SDR exactly how much is software defined I don't know. It has a "PC" running it... It's built in.

 

[jonwienke]

Is this SDS200 considered a SDR even thou it doesn't need a PC to operate other then initial programming (which shouldn't count)? Unless I'm missing something here.

Yes, because it digitizes the RF signal, and demodulation is done with calculations performed on the digital RF data, rather than with analog circuitry.

I'm wondering, the fact this is a 'digital audio' receiver, does that in itself reduce (or should I say 'hide') some of this intermod from digital carriers??

Nope. That's a function of the modulation type, not the receiver design. AM has a very linear relationship between the RF s/n ratio and audio s/n. With FM, the audio s/n is more like the square of the RF s/n due to the capture effect. With digital, it's very close to binary--essentially zero relationship until the RF s/n gets bad enough to introduce decoding errors, and then audio goes from perfect to garbage with very little in between.

 

[videobruce]

Yes, it's at least partially an SDR exactly how much is software defined I don't know. It has a "PC" running it... It's built in.

Most electronics these days has some type of O/S running things, especially something like this, but that doesn't make it a "PC". Huge difference!

That's a function of the modulation type, not the receiver design. AM has a very linear relationship between the RF s/n ratio and audio s/n. With FM, the audio s/n is more like the square of the RF s/n due to the capture effect. With digital, it's very close to binary--essentially zero relationship until the RF s/n gets bad enough to introduce decoding errors, and then audio goes from perfect to garbage with very little in between.

Then as far as the 'intermod issue, there will be no difference based on just that ability over a pure (old school) analog reveiver.

 

[jonwienke]

Then as far as the 'intermod issue, there will be no difference based on just that ability over a pure (old school) analog reveiver.

Correct. It's all about front end filtering and proper gain staging to prevent the RF from clipping and generating spurious harmonics and mixing products, regardless of the receiver type.

 

[dlwtrunked]

This SDS200, just how bad is intermod on this receiver?
I'm talking about actually living IN a city, not 10 or 20 miles from the city limit where intermod probably doesn't exist no matter how bad the receiver is.

Over 50 years of battening with the problem, kit's only gotten worse wiyh all there 'digital' carriers blast what I'm tring to monitor on the UHF band. The only receiver I have ever owned where internmod is bearable is a Regency HX-1000. Past that, the RS Pro 2004 has been my 'workhorse' for the past 30 years, but it's keeps getting worse.

So, these 'digital' receivers are they any better than the older analog counterparts?

Actual true intermod can originate also from outside the receiver end or transmitter. Lose contacting metal near strong transmitters can generate intermod. I have also seen intermod generated in Connecticut where one transmitter's antenna was receiving another nearby transmitter and then intermod was generated in that transmitters circuit. Usually intermod is the result of an overloaded receiver but per above, it can be generated separate from the transmitter and receiver or inside the transmitter.

 

[donc13]

Most electronics these days has some type of O/S running things, especially something like this, but that doesn't make it a "PC". Huge difference!
Then as far as the 'intermod issue, there will be no difference based on just that ability over a pure (old school) analog reveiver.

"PC" stands for "Personal Computer" and in fact, your cell phone (smartphone) is a PC. But you knew that didn't you.

You want help, quit being snarky.

An SDR replaces hardware with software that is more flexible than the hardware. For example, you can change the IF without having to retune the whole front end.

NO SEPARATE personal computer of any form needed to do so.

 

[buddrousa]

If you take the time to learn and setup the SDS100/SDS200 scanner it will work in any city. The only Intermod problem I have run in to is a National Weather Service site 1/4 mile away when driving through the town. AND I did not take the time to adjust the scanner while I was driving.

 

[Ubbe]

I have also seen intermod generated in Connecticut where one transmitter's antenna was receiving another nearby transmitter and then intermod was generated in that transmitters circuit.

In my country it's mandatory to have a circulator installed to the transmitter at a site using multiple transmitters. Our FCC will not even start to handle a case without that in place.

/Ubbe

 

[blackbelter]

I live inside a mid size city and plenty of RF My SDS 200 with an RS 800 antenna monitoring a single P25 P2 behaves well . I must admit that monitoring the same system my Unication G5 is a much better performer and it’s my go to unit .

 

[dlwtrunked]

In my country it's mandatory to have a circulator installed to the transmitter at a site using multiple transmitters. Our FCC will not even start to handle a case without that in place.

/Ubbe

In the above case, the stations were about a mile (1.6 km) apart.
I spoke with the station by phone. They knew about the problem and were working on it. The problem did disappear after a few days.

 

[videobruce]

" circulator "??

 

[fxdscon]

" circulator "??

Circulator - Wikipedia

en.wikipedia.org

.

 

[Ubbe]

I've had other cases when badly designed receivers where overloaded and worked as diode mixers that created a third frequency that interfered to the system I was managing. You can't protect yourself from that and have to let the authorities do their investigation to find the source.

Another time a new broadcast FM high power station where introduced that where the most powerful station together with a second most powerful one at a 4Mhz difference in frequency that created havoc to all system using a 4MHz duplex split in VHF. Any kind of rusty bult or mix of aluminium and galvanized steel could create a diode mixer effect that interfered with those VHF systems and needed the FCC to pinpoint those sources. I can't even imagine what happens in badly designed receiver when it comes to intermod. Well, the link says it all when a SDS100 receiver are introduced to a single source of signal. Actual test with a single source of signal to a SDS100 receiver

/Ubbe