Radioguy7268

Any desense is too much. I've run plenty of 4 cavity duplexers in the scenario you describe (adding a bandpass cavity to the receive side) with absolutely no measured desense at 50 watts. If you can hear desense, you're probably seeing at least 2dB of loss in the receive path. 2 dB doesn't sound like much, until you realize that 3dB better of receive sensitivity would double the coverage area of your system's portable talk in. I guess it's human nature, but people will always pick the 4 watt portable over the 2 watt, yet how many of them will spend the time & money to improve the receive side of their repeater to gain 3dB? The net effect is the same. Getting 3dB of receive improvement will make your 4 watt portable seem like it's suddenly putting out 8 watts.

I'd look at why your repeater doesn't receive as well as it should. If it can transmit out with full quieting to 15 miles at just 7 watts, then a 4 watt portable should talk back in from that distance. A good used band pass filter & a receive pre-amp would set you back less than $250. What's your effective receive sensitivity measured at the site? (how strong of a signal does your receiver system require before it opens the repeat audio path?) What's the noise floor? Do you have any desense when the repeater begins to transmit? Your idea of satellite receivers is worthwhile, but you're already seeing that it's limited due to the lack of frequency spacing and spectrum if you stick to GMRS.

I think there's confusion between an RF ground plane, and electrical grounding. For UHF/GMRS frequencies, a ground plane is required for best signal propagation when you're working with a 1/4 wave antenna. A longer 1/2 wave antenna does not normally require a ground plane. The ground plane is a counterpoise to the antenna's radiating element. The counterpoise (RF ground plane) is going to reflect signals that would otherwise be radiated down by the antenna. For plastic body vehicles - look for something like this to use as an RF ground plane: https://www.solidsignal.com/pview.asp?p=K332 - or just use a 1/2 wave antenna. The DC ground for a vehicular antenna is provided by the coaxial shielding braid. That's going to measure continuity to vehicle ground no matter what type of plastic you're mounting the antenna to... provided the radio chassis itself is actually grounded. I realize I'm being simplistic. That's where we need to start from when someone wants to "ground" their antenna.

I'll toss in another vote for used Kenwoods. or Motorolas. or Vertex. Used commercial/business radios are a great fit for GMRS if you can handle the programming side of things.

You didn't mention what you wanted to use your "base" antenna for, or how you wanted to mount it. At my house, I've got an inexpensive Ed Fong antenna that costs around $40 off eBay. I've got it strapped to a chimney mount. It's reasonably small & lightweight, the white PVC doesn't stick out in the neighborhood, and it covers both VHF and UHF frequencies - so when I want to hook up a VHF scanner for local fire & township events, it does the job for that also. For GMRS, I'm only using it for a UHF control station at my house, so it doesn't need to be anything special. It just needs to hit my repeater that sits 14 miles away, and it does that reliably and cleanly. I've had it up for 6+ years now, no issues.

I'd rather side mount a 1/4 wave antenna than use one of those hockey pucks up on the roof. I have a tour bus customer who insists on using those low profile hockey pucks because they think that they rip off too many masts, and the drivers won't look up to check if the antenna is still there before they start out on a trip. You know what they complain about now? Range.

Vertex are pretty decent little radios - especially if you get them for free. I haven't played with the EVX-351 itself, but I have programmed a few of the analog VX-351. The EVX series is capable of either analog (legal for GMRS) or DMR digital (not an approved format for GMRS). The more recent versions of Vertex radio software is narrowband only for US users. You need the international version of software if you want wideband capability (Wideband 25 Khz is used on most GMRS repeaters).

If you've already got the existing (and properly tuned) Celwave 6 cavity notch duplexer, I'd improve the situation by just putting a tuned bandpass cavity on the receive side. I've always been leery of running notch duplexers on any type of high power/high performance machine. When you're dealing with isolation figures less than 60 dB, every increase in transmit power is also an increase in noise on the receive side. One of my eye opening experiences in the early days of my radio career was watching an old-time tech turn DOWN the power on a repeater to increase the actual performance of the system. Suddenly, handheld portables on the edge of the system were now getting in cleanly - effectively increasing the usable range of the system. Also, make sure that your jumper cables between the repeater and duplexer are up to the task. I've seen lots of duplexers get blamed for poor performance, when it was really the old, cracked jumpers that were causing all the problems. I have used some of the 8 cavity notch duplexers for on-site repeaters running at 10 watts or less, and I've found them to be a good option. I've also seen a great variation in the tuning ability of different Chinese suppliers for their duplexers. If you're buying one that is supposed to be tuned, you better have a way to verify it.

Pretty good chance that the repeater owner knew about the issue that Midland users would have, and chose to purposefully split the codes anyway. It's considered to be a cheap and effective way to keep "lesser" radios off the system. I'd upgrade to a commercial radio, and sell off the Midland.

Those Dish TV antennas should have grounding on them (assuming they were professionally installed by a certified DISH installer). Check them out to see where they were grounded. Make sure you use a Polyphaser or similar surge protector down where your coaxial cable enters the building. You'll need to ground that also. The Laird FG series is a decent antenna for the money.

If you're just trying to hit a repeater, then you really don't need any more height than what you have. When you say that you want a "base antenna" - what do you intend to use it for? If you're in NYC, there's already quite a few GMRS repeaters already on the air with excellent coverage. If you're trying to put up your own repeater, I'd ask "Why?"

Better yet, look up "Kenwood mobile power cord" on EBay. Plenty available, most around $10 with cord & fuse.

In VERY general terms, more cavities = more isolation. Larger cavities generally have a better efficiency - ie: less loss through the duplexer for equivalent isolation achieved. As Berkinet mentioned, the higher quality duplexers involve a combination of bandpass and reject technology. Lower cost "notch" style duplexers are usually limited to 65 to 75 dB of isolation between transmit & receive. Notch duplexers suffer in high power use, and they won't filter out other nearby transmitters very well (They are designed to only "notch out" the transmit frequency of the machine they're used on). Good duplexers have high isolation, low loss, low noise, and can handle high power. They'll also use quality components, and will be built to handle large swings in temperature without de-tuning.

Quite honestly - this is the FCC's job, and they should be the ones enforcing the rules & cracking down on mass-marketers with misleading advertising. The FCC doesn't care, because if they did, they would have actually issued fines to some of the more blatant examples. When the FCC doesn't care, it kind of makes it pointless. What will you do? Threaten them with a non-existing enforcement action?

I'd agree - it sounds like morse code at a really fast word per minute rate, and set to a low deviation. If you play around with Audacity, you can probably slow it down & figure out the code. Are you hearing it at regular intervals?

Base stations transmit on the 462.xxx frequencies. Repeaters are just base stations that operate in duplex mode, simultaneously re-transmitting what they receive. Base stations transmitting on the 462.xxx main channels can transmit at 50 watts. A fixed station transmits most often through a repeater - and can transmit at 15 watts on a 467.xxx frequency (listening on the repeater's base output of 462.xxx) A fixed station can operate also on a 462.xxx frequency, but when it does that, it's more often referred to as a base station, and it is operating in simplex mode (not going through a repeater). When it transmits on the base 462.xxx frequency, then it can operate at 50 watts. I was always taught to call the lower side of a frequency pair the 'Base' frequency. The higher side of the frequency pair was referred to as the 'mobile transmit'. My understanding of the rules is mine, and mine alone. I'm not sure what the FCC means. I just know what seems to work.

The M1225 is a solid performer. If that price is for a complete working radio - with mic, bracket, and possibly even a power cord, you're doing all right. Pro's? Proven reliable, easy to program, simple interface. Good audio, 16 pin option connector (lots of standard accessories like external speakers, etc.) & Part 95 type accepted. Con's? The receiver can get overloaded in high RF environments (Mine used to break squelch on it's own if I drove up to a hillside transmitter we operated - near to 3 other towers loaded with transmitters). Only other con I can think of - Motorola stopped making them & they're no longer supported.

I wonder who gave them the "rights" to advertise it as a "Made in the USA" radio?? Seriously - just buy a used M1225 or TK-880 radio. Twice the performance at half the price.

If a Baofeng/Btech portable out-performed your $350 mobile setup, I think you're doing something seriously wrong. For less than $150 - you can buy a solid 40+ watt used mobile radio from one of the top 3 or 4 brands that will actually last, and it will sound good to boot. If you're really up against it - $25 and a cup of coffee will buy you basic GMRS programming at most any local radio shop if you supply them with your correct frequencies and codes. If you're putting a Baofeng mobile amp onto a Baofeng portable - you're using one noise generator to amplify another noise generator. It's really not good practice, not at all. There's plenty of viable Part 90 gear out there & available. Both portable & mobile units. Yes, if you do want "brand new" Part 95, you're going to be searching a long time, but open up your field of vision a little, and there's plenty of choices.

Spending the money to "meter" a mag mount antenna that you're going to use with a Midland GMRS radio is a waste of time, money & effort IMHO. Your problem is your gear. If you want to have success using a GMRS wide area repeater, you pretty much need to go with Wideband capable equipment. That rules out most of the Midland stuff. The good news is, for not much more than the cost of the MFJ883 meter, you can pick up a really nice used Motorola or Kenwood radio and have it custom programmed to the GMRS repeater(s) you want to work on. Good luck with it.

ORI = Open Repeater Initiative The idea that GMRS repeaters would be "Open" - and available for any licensed user. Usually goes hand in hand with the ubiquitous 141.3 Hz "Travel tone".

I'd say so. They realized that Cellular networks take weeks and months to repair, and the least populated areas are the last ones to have service restored. I had a guy who was buying up all the old UHF wideband radios I could find & shipping them down to Puerto Rico. He stopped buying stuff about 6 months ago, not sure if he found another source, or just saturated his market.

You also need to consider that even when a radio lists a valid Part 90/ Part 95 type acceptance number, once you go to look up that number, you find out that the type acceptance is for very odd emission designations, usually at a power level that is well below what the radio is capable of being programmed for. In short, if the radio is "type accepted" for Part 90 or 95 - but only for ultra narrow 4K0F1D emissions, with just 1.1 watts of power - is it still a type accepted radio when you program it for 25 kHz wideband at 4 watts?

Generally - a well designed (and implemented) system will use proper filtering and isolation, and won't have a problem playing nicely with other nearby transmitters. The farther away (in frequency) the two (three, or four, +) transmitters are, the less chance they'll cause any appreciable amount of intermod. There are intermod calculators available online - including one thru Radio Mobile. Plug in your frequencies, and they'll run the theoretical results. Any decent site manager will require that YOU mitigate any interference or intermod problems that your transmitter(s) create. Most operate on a "first in" basis - meaning the guy who was there first doesn't need to fix his system (assuming it was properly built), you need to fix yours so that it doesn't interfere with any other existing user. Once you're in and operating without causing problems, the onus shifts to the next guy coming in. If the site is owned by a company specializing in Vertical Real Estate, you're going to want to be sitting down before you get the price quote. A smaller company might be more willing to talk, but you're going to need to make a pretty strong case for what you plan to bring to the table that's a benefit to them (rather than just a benefit to you.)

That's about as close to a smoking gun as you're going to get from the FCC. They are aware that people are using surplus Part 90 equipment - and they don't intend to anything to stop that use. As others have mentioned, there's never been a single enforcement action by the FCC against anyone for using Part 90 equipment in Part 95. If you've been around the block with the FCC a few times, you begin to realize that many of the rules have been written after the fact.