Batboard

I have a need to monitor multiple channels simultaneously -- right now, two UHF channels and one VHF, but soon it will be three or four UHF and two or three VHF -- and I'm looking for suggestions.

At the moment, I have three handheld scanners sitting on my table feeding their audio into the multiple soundcards in my "monitoring computer" where I log the audio using RecAll-PRO. (Used computers and soundcards are free, or close it, and a lot cheaper than a real digital logger and, for my purposes, it just has to work not hold up in court.)

My problem is that, having the scanners in close proximity to each other, they tend to lock each other up -- when one receives, they all "receive" since the scanners are relatively poorly shielded. They don't share antenna (the UHF scanners use their stock rubber duck antenna and the one on the simplex VHF channel uses a homebrew, long wire antenna) and plugging them into separate UPSes and AC circuits make no difference. The only solution so far has been to physically separate the receivers by 12-18".

That works okay for the three monitors (plus my one desktop scanner that actually scans instead of logging) but, if I'm going to add 3-4 more, I'm going to run out of desk space very quickly. So, I'm looking for suggestions.

Aluminum foil "straightjackets" to keep the "alien" oscillators out? Some mobile radios that are actually designed to work in RF unfriendly environments? I only need to receive here so "broken" radios that can't tx are okay but by the time I buy radios, two multicouplers, two antennas, power supplies, etc. that is going to get expensive.

Our desires many times outpace our pocketbooks. Our desires also outpace reallaity.

You have your answer in your own post. The "CHEAP" pocket scanners are talking to each others probably via the IF leakage. With a common IF in all those receivers, leakage of the local oscillator is going from one radio to the next.

The only solution to the multi radios talking to each other is get a better radio, use an antenna multi coupler and separate the radios. It may take all 3 of these solutions to make it all work.

The other issue that you haven't run into yet from the sounds of it, is that the radios do generate a signal from the receivers. This signal will actually block some frequecies from being able to be heard. Most scanners will list the "birdie frequencies in the user manual.

I can remember one interference problem a number of years ago where a scanner was jamming a local government system. At the time they were using carrier squelch. You could hear the carrier about a half mile from the scanner.

We tracked it down and knocked on the door of the house the carrier was coming from. The lady there had just got this new scanner from Radio Shack about 3 days ago. We asked her to shut it off and take it back to the store for another one.

Jim

Jim202 wrote:Our desires many times outpace our pocketbooks. Our desires also outpace reallaity.

Definately. That doesn't mean we can't try to find an affordable way of doing something. Might not be a perfect solution, but it might work.

As far as reality - that is only what hasn't been dreamed up yet.

Jim202 wrote:You have your answer in your own post. The "CHEAP" pocket scanners are talking to each others probably via the IF leakage. With a common IF in all those receivers, leakage of the local oscillator is going from one radio to the next.

The only solution to the multi radios talking to each other is get a better radio, use an antenna multi coupler and separate the radios. It may take all 3 of these solutions to make it all work.

I definately understand the problem. Just looking for any suggestions on solutions I might not have thought of yet.

In the alternative, anyone have leads on some (inexpensive) radios? They don't need to be able to transmit, just receive, so maybe something that someone decided is not worth the money to fix? I just need line-level audio from it.

George,

If you don't have to hear every freq at the same time, ie scanners would work, try eBay for some Pro 77 series scanners. 8 channels, VHF, UHF/VHF, VHF hi-lo/UHF. Get a wide band pre-amp and a 4 or 8 output splitter.

You'll have to watch for good deals on the splitter/amp. I just picked up an amp 10-1000 MHz for under $50. And you can get splitters for around $50-60 too. The scanners have been going for <$10. Put up a multi-band scanner antenna on the roof. With this equipment you'll be amazed at the difference.

If you have a multi-band scanner (Pro 2002 or such) you can "reverse" the splitter and have multiple antennas running to one radio.

It'll solve a bunch of problems - it's something you have thought about, and not too expensive a solution.


Just my 2 pesos worth.


Jack

Excellent advice, I agree.

once in a while my brick phone interferes with a Saber

jcobb wrote:If you don't have to hear every freq at the same time, ie scanners would work, try eBay for some Pro 77 series scanners.

Sorry if I wasn't clear. I am looking to monitor the various frequencies simultaneously. It's part of our no-budget, QA process for an EMS agency - being able to pull up all of the radio traffic from various agencies at a single incident.

Right now, I dedicate one scanner to each channel but am getting the local oscillators locking up adjacent scanners. So, I either need to shield them better, separate them (the solution I'm using now -- it just does not scale to 7 scanners in one room), or get better receivers.

Yeah well your just not going to be able to use such cheap radios.

I got 4 Sabers piled up on top of each other next to my bed, and
believe me they all receive simultaneously without any interference.

Also a bank of Spectra's that are wired together. Again, Works
Perfectly.

However I'm sure you'd like the same thing, but you will need to
spend a little more on the radios.

http://www.hamtronics.com/

Has Exactly what you need. And they're NASA Certified too.

Or like me a bank of Sabers and Spectras, or how about a
SpectraTAC receiver????? Now there's a good idea !!!!!
That's what I'd use for a lot of simultaneous receivers.

But again, It's GONNA cost you some dough......Use Ebay...cheaper.
but be prepared for a few busted radios......

I was never satisfied with the way even One scanner worked, let
alone 7.

God Bless You.


Dave

Coming off of the splitter - use 2 1/2 ft. lengths of coax - use a dedicated scanner (with multiple freqs for agility) for each freq - and rack mount them in metal racks with 1 ft air space between each radio vertically(with a shelf in between), and at least 3 ft horizontally. I think that would solve a lot of your problems.

There are some problems that can't be solved with bubblegum and baling wire. Metal between the radios will keep the RF birdie problem to a minimum between radios, and at least 2 1/2 ft coax between the splitter and the radios should help a lot.

But like Ricci said, the quality of the radio will determine a lot. If you can't spend the gelt, and need to use what you have or go on the cheap - at least get a splitter and shield the radios/separate them.


Jack

Yeah thats true. Lots of steel helps alot. If you shield them
well enough you just might get away with it.

I get away with Transmiting while recording, so Yes it's definitely
worth a shot. I should have mentioned the Rack mount Steel
Shielding thing. In Fact my Spectra's ARE mounted in a 19" Rack.

DOH! (See how stupid I am? I didn't mention the most important
thing, I took it for granted. )DOH!

Thanks Jack. Again.

No Ricci, you're not stupid. Let me tell you about stupid:

The reason I needed to get another amp was that along with my 3 RX monitors on VHF, I decided to hook up a TS440SAT to listen to some HF stuff. Using the VHF antenna was about the only option I had and I figured better than a coathanger, right?

So I added a short coax to the TS440SAT and hooked it to the splitter. I accidently hit the auto tune switch on the 440 while doing freq/vol adjust. Amp (between splitter and antenna) went instantly........

Everything went deaf.......

Oh, well. Stupid is as stupid does.



Jack

Here is a suitable splitter:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... gory=25425

First - thanks to everyone for their comments. Even if they don't seem like they help me, I do try to read them each a few times just in case they spark an idea.

Second - apologies if I sound like I'm trying to do the impossible without spending more than a dime. When I say I have "no budget" and am looking for an "inexpensive" way to do something, I don't mean to imply I'm not going to spend any money. Just that I'm not looking for the Cadillac solution when the Yugo will work. The ride might be a little bumpier but, if I still get there, that's all that counts.

Lastly, - re:

jcobb wrote:Coming off of the splitter - use 2 1/2 ft. lengths of coax - use a dedicated scanner (with multiple freqs for agility) for each freq - and rack mount them in metal racks with 1 ft air space between each radio vertically(with a shelf in between), and at least 3 ft horizontally. I think that would solve a lot of your problems.

Thanks, Jack. That's very helpful. While I have an EE degree which I've never used professionally (not something I'm interested in doing day-in, day-out -- I like computer systems more), I don't even pretend to be an RF engineer. So while I understand most of the theory, I rely on experts to guide me as well. Instinctively, I would have gone with the shortest cable runs I could from the antenna splitter to the radio to keep out signals entering via the coax.

The rack was something I was already thinking about, mostly to contain everything. But the metal to isolate things is a good idea too.

If a working two-channel UHF Maxtrac is currently going for $100+ on eBay, maybe I can find some Maxtracs/Radius mobiles, or other similarly sized commercial or amatuer radios, that can't transmit and don't cost as much since they are 'broken." I figure I could share a power supply between them and mount them in the rack to keep things neat, and between them and a few scanners, get away with that for the receivers.

Anyone know if a Keynote pager has a earphone jack? I know the Minitors do, though it isn't a regular sized jack. If the pager has a different IF frequency than the scanners, it should not lock them up and hopefull the computers and radios won't overload the pager's circuitry and it could be used as one of the receivers in the system with a homebrew battery eliminator. (Don't have one to try with - just an idea.)

If I'm careful with which radio is receiving what channel, I can probably get away with the motley assortment of receivers since most of the signals are coming off of strong repeaters so a good antenna isn't critical to this project. Only one or two are simplex channels where the antenna is important. It doesn't need to look pretty - just work.

George - Your thoughts are right on target.

Jack-
Ouch ! Stupid autotuners.......I'd just blame it on where they put
the switch.......It would make me feel slightly better.Maybe. I feel
your pain. I hate when Sh!t Blows up, But Ah It happens to the
best of us Occaisonally. I've been REAL Lucky for the past few years
or so......I hope it continues....So far I never blew up a 2-Way....So
far.....I'll burn out a power supply so fast, It surprises me HOW Fast. Especially those cheap Clone Computer/ E machine Power
Supplies....One SCSI Drive, and you instantly need a new PS, some-
times a new Drive as well, but that's not too bad the drives' are
under warrantee. Not the Powersupplies though.

George,

The reason I specifically mentioned the Rat Shack early Pro series was that they are crystal controlled, can be had cheap, and have metal enclosures. After that series, Rat Shack went with the plastic housings for both handheld and mobile/base series scanners.

The metal housing ones obviously have more shielding, and would help with your situation - particularly if you do have repeaters that help with the sensitivity/antenna issue.

It may sound strange and counter-intutitive, but it seems like less birdies and interference with a splitter than having the radios with all their antennas sticking up in the room. You have everything internal to the coax and contained.


Jack