JIM M75 Preamp and the SDS-200

[Vulcanccit]

So I bought this in 2017 when I had a HomePatrol II:

Jim M75 Pre-Amplifier | Scanner Master

Jim M75 Pre-Amplifier

www.scannermaster.com

Now with my SDS-200 which I find is much more sensitive, especially in the air bands, I am wondering if putting this preamp on the SDS-200 would help any? I mean I am hearing, what I think, tons of stuff, I live in Memphis and I am hearing Unicom channels and planes down in Tupelo which is about 90 miles away, and some planes coming in clear over in Little Rock, AK...but I do not want to introduce any noise or artifacts. I am hearing all of the ems/police channels all around Memphis as well.

Curious what your all have seen with this device on your systems?

I will probably try it later tonight or tomorrow for grins, but wanted to see what all you folks might have experienced.

My antenna is the Diamond RH77CA, mounted outside and up about 15-20' using LMR-240 cable.

 

[a417]

Sounds like you're already hearing a ton, and I'm not sure how much more you expect to gain by using a preamp. If you "don't want to introduce any noise or artifact" then I wouldn't bother with the preamp, there are issues that can crop up with too much signal.

Give it a go, but you will probably find you don't need it.

 

[marksmith]

I agree. Too much signal can create lots of issues. Amplification does not Increase the signal, it just amplifies it. If it isn't there before amplification, it is unlikely it will be there after amplification. Especially with something like a digital SDS radio.

 

[Vulcanccit]

Yes on the HomePatrol II it just seemed to make the noise louder... so yes, it might of also made the signal (or really the modulated portion of the signal stronger/louder) the noise was also louder drowning it out, What I fear on the EMS/Police bands where the signal already is strong I could see it doing some front end overloading, or maybe even introduce some birdies... Right now, with the shielded ethernet and the antenna outside, the only interference I have is on 130.0000 even without ethernet or an antenna, that frequency breaks the squelch on the aviation band...it is listed as Delta Ramps 1 & 3 or something like that so I have it on avoid. With that JRE I could see it making a mess...so I will aboart this though and move on. Thank you all for your input! however feel free to chime in on the thread as you see fit . I love this forum!

 

[Ubbe]

SDS scanners already have a preamp built in. You would probably gain more if you could improve your antenna situation. That's a handheld antenna that requires the scanner working as counterpoise. Now you have no groundplane and staple the antenna to the wall will detune it. Try to get a base antenna GP kit and set the antenna clear of anything else above the roof line. That would probably improve reception more than any preamp.

/Ubbe

 

[bob550]

I agree with @Ubbe. Using an outdoor antenna mounted high as possible is your best option, not only for capturing clearer signals, but also for reducing home-based RFI. A dipole mounted on a 5' mast attached to an eave mount bracket is one way to go. Just make sure your antenna is properly grounded per local electrical codes.

 

[Vulcanccit]

SDS scanners already have a preamp built in. You would probably gain more if you could improve your antenna situation. That's a handheld antenna that requires the scanner working as counterpoise. Now you have no groundplane and staple the antenna to the wall will detune it. Try to get a base antenna GP kit and set the antenna clear of anything else above the roof line. That would probably improve reception more than any preamp.

/Ubbe

Such as the Diamond Discone? The Antenna is attached only with those plastic cable tacks, nothing metal other than the small nail. I do want to update the antenna and get it above the roof line but I have already spent more than I quoted my my wife lol, I need to reset a bit then go to the next phase .

 

[bob550]

but I have already spent more than I quoted my my wife

Spouse Rule #1: always over-quote, and under-spend!

 

[Vulcanccit]

Spouse Rule #1: always over-quote, and under-spend!

yes I should of known that after 39 years of marriage and also working in the radio broadcast business, that rule is what I use there, should of done it here lol

 

[Vulcanccit]

SDS scanners already have a preamp built in. You would probably gain more if you could improve your antenna situation. That's a handheld antenna that requires the scanner working as counterpoise. Now you have no groundplane and staple the antenna to the wall will detune it. Try to get a base antenna GP kit and set the antenna clear of anything else above the roof line. That would probably improve reception more than any preamp.

/Ubbe

I just re-read this so they have a kit to create ground plane for that little diamond antenna? Back in my early ham days I remember running like hundred pieces of wire making ground radials blanketing my parents room top lol, not sure why they allowed me to do such a thing hahahaha

 

[Ubbe]

I just re-read this so they have a kit to create ground plane for that little diamond antenna?

There should be a universal kit that is just a metal ring that the antennas connector fit into and fastened with a couple of screws. Then it's 4 metal rods going out horizontally from that ring. But with much less cost you could extend the coax and route behind that board to the top of the roof and then use your current cable tacks but only at the bottom of the antenna and let that middle coil reach above the roof line. You already had such a great reception that just having the antenna up in free air without touching too much of the wood work would be sufficient at a very low cost. The bottom of the antenna are low impedance and not so sensitive to be in contact with wood as the top of antenna are.

/Ubbe

 

[Vulcanccit]

There should be a universal kit that is just a metal ring that the antennas connector fit into and fastened with a couple of screws. Then it's 4 metal rods going out horizontally from that ring. But with much less cost you could extend the coax and route behind that board to the top of the roof and then use your current cable tacks but only at the bottom of the antenna and let that middle coil reach above the roof line. You already had such a great reception that just having the antenna up in free air without touching too much of the wood work would be sufficient at a very low cost. The bottom of the antenna are low impedance and not so sensitive to be in contact with wood as the top of antenna are.

/Ubbe

part of my issue is I am not sure I have a ladder tall enough to get me any higher.. I did want the base to be above the roof line but I was on the last step to go as high as I did... My wife refused to watch me do all of this because she didn't want me to fall hahah my son is taller so maybe he can get up there (also without mom watching.). My other thought was to attach the antenna to a 5 foot or so PVC pipe... then mount the pipe about where the antenna is ...then I can reach that point but the antenna would be taller... I could fish the coax thru the pipe and it should look just as clean...I have plenty of coax...50' worth, so I would say I have a good 15-20 feet more . I can hear my wife now..."what's wrong with how you have it?" lol.

 

[Ubbe]

My other thought was to attach the antenna to a 5 foot or so PVC pipe... then mount the pipe about where the antenna is ...

That's a good solution but will require much more sturdy fastener to the wall, but you'll probably have that figured out. And don't forget to water proof the connectors with some sealant vulcanization tape. It looked as if the connectors where naked.

/Ubbe

 

[Vulcanccit]

That's a good solution but will require much more sturdy fastener to the wall, but you'll probably have that figured out. And don't forget to water proof the connectors with some sealant vulcanization tape. It looked as if the connectors where naked.

/Ubbe

No I had it triple wrapped with Scotch 33 but ill probably redo it with that other scotch , the rubber stuff, along with the 33... I didn't get too fancy as I am not sure if this was my final install... I have a vacation coming up early June and I hope to do more... I think you all should come out and help and ill cook steaks! "Honey, about 53 people from the Radio Reference forum are coming over for a bit..... im cooking steaks" hahahah

 

[N9JIG]

The best place for an external preamp is at the antenna, placing it at the radio is less effective and amplifies any noise gathered thru the coax.

I think what you will find with the M75 in place at either end is an increase in the noise floor. This will require your squelch to need to be raised.

You might be happier raising the antenna higher if possible.

All that said, try it and see what happens. If it doesn't increase your overall results you can always remove it.