JLeikhim
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Posts posted by JLeikhim
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What the FCC is gonna do is refer to industrial standards, as they call out in the Part 95 top level personal radio service paragraphs. In practice, who makes a certified HT that does 8 watts on the main channels?
They don't and primarily it has to do with specific absorption rate. https://en.wikipedia.org/wiki/Specific_absorption_rate
The labs that certify this gear must ensure that your body does not get heated above a certain level when RF device is operated nearby. You might see a 6 watt VHF radio, but that is pretty much the limit.
an example cert.
https://fccid.io/AZ489FT7087/RF-Exposure-Info/SAR-Report-1-of-2-3054950
- mbrun, AdmiralCochrane and berkinet
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I would not quickly discount the interaction of any large magnet and a radio transceiver. Recently I read in a trade magazine of a company that makes Class D audio amplifiers for Public Address systems. These amplifier have ferrite chokes inside to decouple the high frequency components of the amplifier. Some of their customers were screwing these amplifiers to overhead speaker boxes in close proximity of the speaker magnet. They encountered all sorts of problems. These are common rare earth permanent magnets used for all sorts of things. In a speaker, they create a strong fixed field whether powered or not.
Ferrite chokes are used throughout modern radio transceivers and many are quite small. Others like used in the power amplifier are large but already operating under heavy current flow. Current flow can saturate the magnetic properties of the choke, or any iron transformer.
AC and DC current in a ferrite choke or transformer, creates a magnetic force. Whether it be electrically or magnetically coupled, the ferrite choke can become saturated to the point where it no longer becomes capable of absorbing or transforming electromagnetic energy. It wont be damaged if you remove the external magnet, but it can cause a malfunction and possibly a fault.
I would not place any powerful magnet on top of an electronic device.
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I think the best application is expanding coverage in a local area where the availability of high towers is limited or expanded coverage is required. If you have a commuter corridor and one repeater is insufficient, two or more can be linked. Interstate linking is more of a novelty.
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You might want to use some of the features in Google Earth to draw the paths using the line feature and then viewing the elevations.
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Are the workers on the farm all family? If so GMRS is fine. If you have non family members as employees, they will need own GMRS license to communicate on your repeater. Otherwise a business license is required.
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It seems a bit sketchy. It appears to be related to an indiegogo project called Power Talkie that was an FRS portable that required linking to a smartphone to communicate. A bunch of folks still waiting for those devices complaining on indiegogo.
I am sticking with commercial part 95 radios.
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OK I went to the link. From the discussion, it seems the RX bandwidth might be adjustable from the "Channel spacing" setting. However there is no indication that the TX modulation increases. It would be odd that Midland would be freely releasing software to violate the FCC type acceptance of this radio. If it works, then that is great. But Caveat Emptor".
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What Midland ought to do is concede that their narrow band radios are a mistake and release a new model that will properly do wide-band. Add 8 WB repeater pairs 23-30 . They could also do it through the menu and make the RP light flash when WB mode is selected. WB then could apply to all the GMRS channels, simplex or repeater.
The question is, do they have a WB filter in the RX path? If it is SDR then it is math unless it is burned into a chip. Then you have that pesky modulation fidelity to be optimized for 16K0F3E. Not sure they can properly do 11K0F3E now.
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Directly on the 467 MHz primaries. Listened with various receivers, none have AFC. Last time I saw AFC was on the Micor repeaters, I think. Hope none of those remain in operation...they would be almost 50 years old and sliding back and forth with all the FRS traffic.
Some of our users tried to be heard using the same DCS code, but you need to be very close to overcome a 1-5 watt radio in the next room.
G
I was managing some UHF community repeaters on the Sears Tower back in 1980's. We had interference arriving at the antenna and LNA way up on the top pylon. It had a distinctive tone with heartbeat. HP had marketed some medical telemetry on the UHF splinter channels and those were buried deep in hospitals . Those transmitters were less than 50 milliwatts. The solution was to defeat AFC.
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Here in the San Francisco Bay and Sacramento regions we have started hearing a "baby monitor" type devices using GMRS 462 and 467 MHz primary repeater frequencies, in nursing home settings (given the message content). We are aware of about twenty incidents of this over the past three months, but the rate of occurrence is rising. The most recent was strong enough to interfere with a CERT/Fire Council repeater out here.These typically operate during daylight periods, and appear to be continuously keyed for up to 12-16 hours at a time, although background noise, such as televisions, could be keeping them transmitting if set for VOX. They do not have time-out timers enabled. These change channels occasionally, but usually end up on 462.625, 462.725, 467.625 and 467.725 MHz. They use a D754 or a D734 DCS code.This kind of device was explicitly mentioned in past FCC GMRS rulings as it was feared that manufacturer's might use these channels for such things.Given most repeaters here in California are on 1500-4000 ft. mountains, continuous destructive interference will occur to our repeater inputs.I tried to DF the source of one of these last week, but it was found to be in San Francisco and we ran out of time. SF is a particularly difficult place to do this due to the density, hills and other sources. Thankfully these are constantly keyed. The device I was looking for was horizontally polarized, making it about 10-20 dB weaker when received on a vertical vehicle antenna. A Yagi in horizontal worked best.My goal was not to go after the user (they don't know better), but instead get a picture of the device, determine its manufacturer and model number, and establish who is selling it. As these may be used in nursing care facilities, they will likely have to bring the device out to us to be safe.Please let us know here if you hear these as we are trying to keep a list of the channels and codes in use so we can identify the specific radio model.This is clearly in violation of §95.1733(a)(10) and §95.1763© for GMRS, and §95.587(3) for FRS. It also appears to violate §95.533.
Are they showing up directly on the 467.xxx GMRS inputs or the 467.xxx5 FRS channels? Some repeaters having AFC will pull in an offset channel.
Until we figure this out, if the owners are not compliant. Rude sounds.... Oops clean up needed in bed 13!
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I would love to buy a new jeep but the lack of a metal roof has put me off.
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There is a very real engineering aspect to this in that narrow band radios and wide band radios are incompatible with each other.
They were never to co-exist. And legally, you can't tweak a narrow band radio to work better.
While "they might work", they are operating at widely different parameters. There will be over-modulation received in one case and noisy weak modulation in the reverse. If you are expecting tone or digital squelch to work, they may not work.
Add a narrow band mobile and wide band repeater to the mix and the repeater often won't respond. This is a common thread by folks new to GMRS. They can't activate the repeater.
While I like the design of the Midland radios, they are creating a debacle by marketing radios (to the unwary) that have implications for a repeater operator, and users, who hope to reap the entire benefit of GMRS's potential performance.
GMRS main channels are 50 watts TPO, and +/- 5.0 KHz deviation. Always has been.
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Despite what Midland Marketing would like the world to believe, by marketing non compliant radios, GMRS is wide band baby.
The modulation is +/- 5.0 KHz, the channel bandwidth is 20 KHz and the channel spacing is 25 KHz. Example 462.600 and 467.600 MHz. The exception are the GMRS interstitial channels at 467 MHz which are narrow band +/- 2.5 KHz, on 12.5 KHz channel spacing. Example 467.5875 MHz when used by GMRS radios.
All FRS interstitial channels 462 and 467 MHz are narrowband. Example 462.5875 and 467.5875 MHz when used with FRS radios.
Wide band is what the God of FM Radio Major Edwin Armstrong intended:
https://en.wikipedia.org/wiki/Edwin_Howard_Armstrong#Wide-band_FM_radio
Wideband is tremendously better than narrowband: 3 dB better which translates to much greater area reliability. If you have a narrowband radio trying to use a wideband repeater or simply talking directly, the loss is greater ~ 6 dB.
YOUR REPEATER SYSTEM WILL PERFORM MUCH BETTER IF ALL COMPLY WITH WIDEBAND AS INTENDED. THERE WAS NEVER AN FCC NARROW BAND MANDATE FOR GMRS NOR WILL THERE EVER BE AS FRS ALREADY OCCUPIES THE INTERSTITIALS.
See the maps wide vs narrow. Green good, yellow nope.
http://www.leikhim.com/page13.php
FCC Rules:
§ 95.1773 GMRS authorized bandwidths.
Each GMRS transmitter type must be designed
such that the occupied bandwidth does not exceed
the authorized bandwidth for the channels used.
Operation of GMRS stations must also be in
compliance with these requirements.
(a ) Main channels. The authorized bandwidth is
20 kHz for GMRS transmitters operating on any of
the 462 MHz main channels (see § 95.1763(a )) or
any of the 467 MHz main channels (see
§ 95.1763(c )).
(b ) Interstitial channels. The authorized
bandwidth is 20 kHz for GMRS transmitters
operating on any of the 462 MHz interstitial
channels (see § 95.1763(b )and is 12.5 kHz for
GMRS transmitters operating on any of the
467 MHz interstitial channels (see § 95.1763(d )).
(c ) Digital data transmissions. Digital data
transmissions are limited to the 462 MHz main
channels and interstitial channels in the 462 MHz
and 467 MHz bands.§ 95.1775 GMRS modulation requirements.
Each GMRS transmitter type must be designed to
satisfy the modulation requirements in this section.
Operation of GMRS stations must also be in
compliance with these requirements.
(a ) Main channels. The peak frequency deviation
for emissions to be transmitted on the main
channels must not exceed ± 5 kHz.
(b ) 462 MHz interstitial channels. The peak
frequency deviation for emissions to be transmitted
on the 462 MHz interstitial channels must not
exceed ± 5 kHz.
(c ) 467 MHz interstitial channels. The peak
frequency deviation for emissions to be transmittedon the 467 MHz interstitial channels must not
exceed ± 2.5 kHz, and the highest audio frequency
contributing substantially to modulation must not
exceed 3.125 kHz.
(d ) Overmodulation. Each GMRS transmitter
type, except for a mobile station transmitter type
with a transmitter power output of 2.5 W or less,
must automatically prevent a higher than normal
audio level from causing overmodulation.
(e ) Audio filter. Each GMRS transmitter type
must include audio frequency low pass filtering,
unless it complies with the applicable paragraphs
of § 95.1779 (without filtering).
(1) The filter must be between the modulation
limiter and the modulated stage of the transmitter.
(2) At any frequency (f in kHz) between 3 and
20 kHz, the filter must have an attenuation of at
least 60 log (f/3) dB more than the attenuation at
1 kHz. Above 20 kHz, it must have an attenuation
of at least 50 dB more than the attenuation at
1 kHz.- UHFJim, Radioguy7268, n4gix and 2 others
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I would be wary of that LNA. Assuming your duplexing and preselector is working properly to reject TX noise and carrier (TNRD) to the degree that the additional low noise is useable, i would install an attenuator after that LNA to remove excess gain before the receiver. You do have that preselector between the duplexer and LNA I assume?
Have you performed a duplex sensitivity (effective sensitivit) test into dummy load and antenna?
If you don't run this basic test, the repeater can be functionally deaf.
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Thanks. I thought something was odd. His website promoting all those linked repeaters while a year or so back he claimed his "legal staff" claimed linking GMRS is prohibited. At the time he was citing old rules. His so called legal staff apparently ignorant the rules had been rewritten 2 years ago.
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Many years back, before these CCR became the rage, it was a common complaint of ham users of Japanese handhelds that when replacing the factory supplied "rubber duckie" antenna with a 5/8 wave dipole or a base station antenna that the receiver sensitivity would erode.
This was quickly identified as being a combination of both poor RF front end selectivity and poor dynamic range and IMD .
It would be interesting to subject these CCR radios as well as known good commercial grade radios to the rigorous testing of TIA603D.
Lacking the complete facilities to do so, it occurred to me that a UHF TEM cell could be put to use to combine a desired signal (12dB SINAD reference) and undesired noise spectrum (rejection notched at desired) from an amplified noise diode generator to perform a Noise Power Ratio test of these various radios having integral antennas. This set up could be used to quantitatively measure radios and rank them on a dB scale of best to worst.
This setup would simulate the "real world" environment of powerful emitters in and out of band of the receiver.
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Anyone a member of this organization? Do you have a repeater linked? Thoughts. Feel free to PM me or e-mail, better. Thanks
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I usually avoid these sort of products because in my opinion Cheap Chinese Radios are usually a Low Parts Count hot mess with crappy receiver performance.
For some stupid reason this caught my eye. I am sure it will be disappointing. Should I buy one? Has anyone bought one opened it up and found the manufacturer went the extra mile in RX design, or should I let the fact that it has an FM 88-108 receiver built in confirm my misgivings?
Well here it is, probably not FCC certified . But it is kind of cool.
I am verklempt, talk amongst yourselves...
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OP Marc is correct ultimately that elevation is everything in this game.
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Going from 1 watt to 4-5 watts makes a fairly substantial difference (about 10dB more quieting; I'll test it later) when 1 watt is barely understandable, because the signal gets about 6-8dB stronger. Going from 25 to 40 watts is only a 2dB increase, the same as going from 1 watt to 1.6 watts. There are times when that 2dB advantage makes a difference, but it's so rare that it's not really worth it. FM sees a pretty strong rate of SNR improvement with carrier strength increase when it's close to or just above demodulation threshold, but once the signal reaches a good level of quieting there's almost no improvement that can be made using higher transmitter power.
[edit] Here's actual, on-air performance between low and high power near threshold.
Excellent demonstration. FM capture of the noise floor is pretty evident. Also when in multipath, there are significant nulls of signal strength where additional power is beneficial. TSB-88 parameters used in modeling coverage predictions account for signal strength in estimating coverage at a particular reliability and delivered audio quality thresholds. Viewed on a coverage contour, even small amounts of signal power reduction most definitely affects reliability and signal quality.
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When you mentioned rx diversity on a single tower, I immediately pictured Yagis pointed in different directions.
While you could do this. For example a sectorized array of antennas. However, I think the theoretical diversity gain would be better letting all antennas see the subscriber. A lot would depend on the topography being served and where portable and mobiles are expected to travel.
As I said, this is an experimental idea that I have. In fact the parts are in my lab right now, looking for an appropriate site to test from. I might try three corner reflectors approximating 120 degree sectors to compare. One important thing I want to try is a fourth omni antenna in horizontal polarization.
I need some funding and a rooftop!
Mobil mount dangerous?
in Technical Discussion
Posted
Probably OK. Just observe precautions.
Ground the radio properly and as close to the radio as possible. Do not share a ground with the airbag control box. Look for some other bolt directly to the body or chassis and use a proper lug and serrated washer.
Make sure the antenna is properly terminated at the radio with a connector that is properly soldered or professionally crimped. Use an NMO mount antenna on the roof.
Get power directly from the battery with the fuse inside the engine compartment. If you need switched power, use a relay in series with the DC power cable.
Route your wires away from airbag wiring and components. You can cross an airbag wire harness at 90 degrees, but don't run parallel with it.