Using a scanner and 2m rig at same QTH

What's the best way to use a sensitive scanner like the Pro-106 and a Ham transceiver in the same household with close-by antennas or in a vehicle without blowing up the scanner? Is it even possible? Would filters be required on the receive antenna to shunt the transmitter's RF to ground at the frequencies it transmits on?

What's the educated opinion on this?

Use the most separation between the antennas as possible, and expect that the scanner WILL desense some when transmitting. It takes roughly around 100 db or so (or more) to isolate a transmitter from a receiver enough so that the receiver ignores the transmitter. Any filters you use on the scanner will necessarily restrict the frequency range.

In a vehicle, you're not likely to get enough separation to avoid desense, but if you keep the antennas far enough a part, you can avoid damage. How far is far enough? As far as you can get. There really is no magic number.

I agree. My empirical opinion is that aside from some desense on the scanner(s) when transmitting, it's not a concern. I can't address your specific scanner model, but I've had all manner of base, mobile and handheld scanners, and they have peacefully coexisted with all manner of base, mobile and handheld ham radios (35 years' worth!) If you keep the antennas at some reasonable distance apart, say 10-20 feet at home, you should be OK. Mobile is a little different, but I do have 55 watts on one side of the roof and scanner antennas a few feet away with no ill effect.

At home I can get the transmitting 2m antenna either higher or further away (or both). The way I understand vertical dipoles and discone antennas their radiation pattern is pretty-well concentrated above the horizon or even with it. Would putting the 2m antenna at the top of a mast and the scanner's discone on a support arm a few feet down the mast provide enough isolation? My next option is about a 30 foot horizontal offset.

I know all about desense and intermod with the Pro-106 and the HomePatrol. I had to install a tunable notch filter to get rid of 158 MHZ pager interference already and it's a broad enough notch that if affects some of the 2m frequencies as well. I can't take out out of the antenna coax or I lose all VHF high stuff. Maybe a couple of better-quality narrower-notch filters which can be easily connected or disconnected as transmitter use varies...

Vertical separation is a lot more effective than horizontal. If you can get 10-15' separation between the two antennas that would be good.

ST-Bob said:

A... Would putting the 2m antenna at the top of a mast and the scanner's discone on a support arm a few feet down the mast provide enough isolation?

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It will likely provide enough isolation to avoid damage to the scanner, but desense will still be severe. You would REALLY have to work at it to avoid desense... like horizontal separation on the order of several hundred feet, or vertical separation on the order of 50 feet. And even that might not be enough when you're dealing with a scanner.

ST-Bob said:

My next option is about a 30 foot horizontal offset.

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Typically, in a home installation, you settle for whatever maximum amount of separation you can manage, and live with whatever amount of desense you end up with. Getting a low quality wide band receiver to completely ignore a transmitter co-located on the premises is probably out of reach without extraordinary effort and expense.

106 and 2 meter rig.

I have the Pro 197. Rigs are Kenwood V71A and a Icom 2200H for VHF/UHF and Kenwood 480HX for HF. HF may do something in a tiny way??? The V71A and the 2200H desenses it if I am running 25 watts and up. 2200H is hooked to a beam about 30 feet away and 20 foot higher. Only when the beam is point in the scanner antenna's direction does it do anything at all. Diamond X200A is about 20 feet away and about 15 foot higher. It does desense it to the point that when I am talking on it, I turn the scanner completely off. Don't want to take any chances. As others have said space between them is the key and at different heights. The 106's front end is about the same as the Pro 197. The pro 197 has a sensitive front end for sure.

2meter vs Scanner

I have a yeasu mobile and a scanner (BCD396XT) in the car. antennas are about 2(ish) feet away from each other I Had to do it this way, and i blew my scanner, uniden fixed it, but it was the 2meter that caused the damage.And I knew better but oh well! When i transmit on the ham i always disconnect the antenna from scanner to be safe ,yeah it's a P.I.T.A. But dont feel like damaging a $500 scanner again

Hmm. This is perplexing to me. My elmer and I just set this up this past weekend-


The Cushcraft is hooked to a Pro-106 and the discone is hooked to a Yaesu FT2600M. I haven't noticed any issues, but I haven't done a whole lot of transmitting either this week. My elmer uses this setup without issue. Thoughts?

I spoke with someone at the Salem, NH HRO store and he said there should be plans somewhere to make an RF-activated relay that can short the scanner's coax to ground when transmitting. I haven't been able to find one though. Anyone know where such a circuit design might be found?

Someone has blind faith in worm drive stainless steel hose clamps.

I think you would have been better off with some rigid conduit and either bolted the two pieces of tube together as opposed to using hose clamps with something that heavy and something that high up.

The bottom line is - not to listen to the input frequency you are transmitting on with the scanner.
Put a scanner antenna next to a two meters antenna and have the same band of frequencies programmed into the scanner and in time - no matter what you do - it will take out the front end in the scanner. So the best thing to do is to shut the scanner off while using the radios.

Whats wrong with worm drive hose clamps? They are extremely strong for their size and you could not generate enough force to break them as pictured in kadetklapp's post.

On every street corner in my town the traffic lights and signs that hang over several lanes are all held together with the same kind of hose clamp but just a larger diameter.
prcguy

Daniel_Boone said:

Someone has blind faith in worm drive stainless steel hose clamps.

I think you would have been better off with some rigid conduit and either bolted the two pieces of tube together as opposed to using hose clamps with something that heavy and something that high up.

The bottom line is - not to listen to the input frequency you are transmitting on with the scanner.
Put a scanner antenna next to a two meters antenna and have the same band of frequencies programmed into the scanner and in time - no matter what you do - it will take out the front end in the scanner. So the best thing to do is to shut the scanner off while using the radios.

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prcguy,
Nothings wrong with the use of hose clamps in the way they are being used. Consider the source.
- 'Doc

My answer to the OP's question would be to turn the scanner off when I had to transmit on the other radio. And if you wanted to go the trouble involved, put a relay in line with the scanner's power source and have the relay activated by the transmitter's PTT circuit; not particularly hard to do.

Ok, I use the scanner to monitor 800 MHz P25 hybrid only, and my two-meter rig is well, two meters. So I won't harm the scanner by being that far apart on the spectrum, right?

I was planning to get a 33cm rig soon. Sounds like I may want to put that antenna in a different location.

BTW, the hose clamps are working just fine.

It's not so much a matter of harming the scanner or "crosstalk" since that's not as likely as is annoying listeners on 2M with all the background noise so please turn off the scanner while you're on the air.

prcguy said:

Whats wrong with worm drive hose clamps? They are extremely strong for their size and you could not generate enough force to break them as pictured in kadetklapp's post.

Click to expand...

I think the only thing wrong with the application shown in the picture is that the side mount could rotate around the main mast in a heavy wind.

Otherwise, for a home location like that, hose clamps are pretty strong, and it's a clever, cheap way to go about it.

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You'd be surprised how many hose clamps (Andrew calls them "round member adaptors") are used on tall commercial towers.

Gee, this thread has really made an acute turn away from what I originally asked... Hose-clamps have nothing to do with the question of how to isolate the scanner from the 2m transmitter.

To reiterate: Is there a proven, effective way to keep the RF from a nearby transmitter on the same (or close-by) frequency from getting into and damaging a scanner in the same vehicle or home? I visualize an RF-activated relay which switches the scanner's feed coax's center conductor and its shield to ground to both prevent the scanner from blowing out and to prevent overly high voltages from appearing on the coax.

I'm considering making up a male-female RJ-8 jumper which splits off the PTT signal from the mic to do this but an RF-activated relay would seem to make more sense to me. With an RF-activated setup I'd never have to worry about forgetting to install the jumper between the mic and radio.

I'm sure that even with the antenna leads shorted to each other and to ground there would be the potential for feedback through the scanner from incidental RF getting into its innards but that's not the issue. I just don't want to fry my expensive HP-1 or Pro-106 while I'm out in the car and transmit without thinking about it without first turning the scanner(s) off.