Newbie needs help with Midland MXT575

[SargeDiesel]

First, I just joined the forum and wanted to say hello.

Second, I just purchased and installed a Midland MXT575, here are the details/questions:

I just installed my MXT575, using a shortened 12' midland (MTXA24) nmo cable(by CoolTech) attached to a Midland MXTA26 antenna. I have it mounted to a CoolTech stainless steel nmo mount next to the am/fm antenna on the passenger side hood cowl panel of my JT(Jeep Gladiator). I did run the power and antenna cables next to each other(??) and zip tied them to the vehicles wiring harness(??).... When testing, on channel 01(low power), I had SWR readings of 1.01 / FW-W 2.94 / RW-W .000 , but when I tested on channel 20(high power) I had SWR readings of 1.62 / FW-W 27 / RW-W 1.51.  -   First, I do not understand why there is a difference in SWR  ?  I am happy with the readings, but feel @ High power they need to be better and achieve at least 1:5:1 or below.  Secondly why is the output wattage so low for a 50 Watt radio ? I have seen this radio tested on YouTube several times and on low power it was 5.00+ watts and on high 49.00+ watts. I thought I might need to test into a dummy load for an accurate test, but during the YouTube test, the readings were the same whether testing into the antenna or a dummy load. I would prefer not to have to spend the $ on a dummy load if it is not needed.  I did just read that Midland GMRS antennas are pre-tuned to center channel (does that mean channel 11 ?) I can retest on channel 11 and there is some adjustment built into the antenna to shorten the length into the base, maybe this may improve the SWR, but what could possibly be causing the difference in SWR between Low/High power and the overall low output power... Thank you for any help.

Antenna, Cable , mount bundle (CoolTech) - https://www.cooltechllc.com/2018-jeep-wrangler-jl/139-gladiatorwrangler-front-antenna-mount.html#/91-front_bracket_options-bracket_nmo_adapter_12_midland_coax_mxta26_6db_antenna

[SteveShannon]

On 8/19/2022 at 9:55 PM, SargeDiesel said:

First, I just joined the forum and wanted to say hello.

Second, I just purchased and installed a Midland MXT575, here are the details/questions:

I just installed my MXT575, using a shortened 12' midland (MTXA24) nmo cable(by CoolTech) attached to a Midland MXTA26 antenna. I have it mounted to a CoolTech stainless steel nmo mount next to the am/fm antenna on the passenger side hood cowl panel of my JT(Jeep Gladiator). I did run the power and antenna cables next to each other(??) and zip tied them to the vehicles wiring harness(??).... When testing, on channel 01(low power), I had SWR readings of 1.01 / FW-W 2.94 / RW-W .000 , but when I tested on channel 20(high power) I had SWR readings of 1.62 / FW-W 27 / RW-W 1.51.  -   First, I do not understand why there is a difference in SWR  ?  I am happy with the readings, but feel @ High power they need to be better and achieve at least 1:5:1 or below.  Secondly why is the output wattage so low for a 50 Watt radio ? I have seen this radio tested on YouTube several times and on low power it was 5.00+ watts and on high 49.00+ watts. I thought I might need to test into a dummy load for an accurate test, but during the YouTube test, the readings were the same whether testing into the antenna or a dummy load. I would prefer not to have to spend the $ on a dummy load if it is not needed.  I did just read that Midland GMRS antennas are pre-tuned to center channel (does that mean channel 11 ?) I can retest on channel 11 and there is some adjustment built into the antenna to shorten the length into the base, maybe this may improve the SWR, but what could possibly be causing the difference in SWR between Low/High power and the overall low output power... Thank you for any help.

Antenna, Cable , mount bundle (CoolTech) - https://www.cooltechllc.com/2018-jeep-wrangler-jl/139-gladiatorwrangler-front-antenna-mount.html#/91-front_bracket_options-bracket_nmo_adapter_12_midland_coax_mxta26_6db_antenna

1. For any given antenna, SWR changes with frequency.  A graph of SWR vs. frequency often looks like there’s a sharp dip at the resonant frequency. 

2. Where are you measuring the output power? A dummy load will appear to the transmitter like an antenna that has a very low SWR at every frequency.  Also, was your Jeep running and putting out 13.8 volts or were you on battery at a voltage of 12+ volts?  On battery power the output power will sag slightly. Or it might just have been the radio you received. Many things can affect output power: input power, antenna cable, antenna, ground plane, etc.

3. Pretuned to center channel probably means that it’s tuned to midway between the 462 (used for simplex communications) and 467 MHz (which you transmit to a repeater) frequencies of the band, or about 465 MHz.  

4. Tuning the antenna to have a lower SWR might get you more transmitted watts, but honestly a few watts isn’t detectable in actual use.   I recommend either leaving the antenna alone or tuning it to the frequency you transmit on most often.  A higher frequency means a shorter antenna element, but if you shorten it too much it’s hard to undo.

[SteveShannon]

11 minutes ago, SargeDiesel said:

Maybe my question should be:

1. How do I properly test a newly installed GMRS radio for SWR and to test max wattage output ?

2. Is running the antenna cable and power cable together ok ? Is having both of them following the same path (zip tied to it) as the wiring harness ok ?

 

 

 

1. Make sure you’re using test equipment that’s high quality and accurately calibrated and appropriate for the frequency and power level you’re using. Make sure you’re testing at the specified voltage (13.8!) and using power cables that won’t cause voltage drop. It might help to visit a local radio shop. 
2. That can depend on a lot of things. Is your power wiring noisy? How high quality is your coax? When it comes to antennas, everything affects everything and a noisy power cable parallel to the coax could cause problems. 

[SteveShannon]

7 minutes ago, SargeDiesel said:

I when I tested my power cable,  I  had the same voltage reading at the battery and the end plug (if this is what you are referring to)  but I  haven't tested it while actually keying the handset.... I  would have to figure how to do that.... lol

All of my hardware is from Midland ... maybe I have made a rookie mistake in assuming Midland products are high quality  ???

Im really not sure how to go about testing "noisy cables"... so your advice to visit a local shop is probably a good idea.... the search is on.

The greater the current the more the voltage drops. Transmitting would consume more current so it’s possible you see a drop when transmitting. A battery doesn’t put out the full voltage  that the alternator does, but testing with the engine off does get rid of the greatest source of RF noise under the hood . 
I think Midland stuff is probably as good as anything other than commercial radios. It’s certainly good enough.  As you progress you might decide you want something else, but for now just enjoy it. 
Chasing that last watt or two can make you crazy without really being too meaningful. I would just make sure that your radio works well enough to converse with the people you want and reach the repeaters in your neck of the woods. 
I would be a little concerned about electrical noise on the power line when the engine is running. I think that you’d hear it though. 
That radio shop technician will know much more than me. 
Best wishes!

[KAF6045]

18 hours ago, SargeDiesel said:

Maybe my question should be:

1. How do I properly test a newly installed GMRS radio for SWR ? What channel(s) should I use  ?

For completeness -- ALL channels... INCLUDING the repeater inputs since they are 5MHz up from the simplex frequencies. However, you could probably skip the interstitials (in the current numbering scheme: 1-7, limit to 5W ERP) as they fall midway between the main channels. That leaves the main simplex channels (15-22) and the repeater channels (which may appear as 23-30, or as 15-22 with some indicator of repeater mode: rp15, 15R, etc.).

If your primary usage will be via repeaters, having a low SWR on the repeater channels will be more desirable. If you will be using simplex and repeaters, you'll have to compromise. Try to match simplex 22 and repeater 15 in SWR (simplex 15 and repeater 22 will be the worst SWRs, since you are tuning to put the minimum SWR around 464/465MHz, which is not a GMRS frequency band on its own, but midway between simplex and repeater frequencies.

This is where a standalone antenna analyzer (or a VNA -- though I don't have experience with those yet; mine arrived today, with the power switch in the ON position, so the battery is extremely dead with NO battery included [I've never seen a "standard flat-top 18650" locally -- button top and worse, protection circuit on some], and I hope it will charge). One: these devices don't spew high power RF, running in microWatt levels. Two: they let you sweep the frequency range while watching a needle and/or LCD display of SWR so you can rapidly get an idea of where the min-SWR is, and what the <2.0 bandwidth covers (Antenna analyzers tend to use of rotary dial to manually sweep, VNAs normally do the sweep via programmed parameters, and display graphically).

 

18 hours ago, SargeDiesel said:

2.  How would I test to insure my radio is capable of outputting the advertised 50 watts of power ? (Hopefully using my current equipment)

You would 1: need a calibrated RF signal source to validate your power meter reading and 2: a reasonable dummy load for the power and frequency range (a 300W dummy load can only operate for half a minute at 300W before giving it a multiple minute cool-down; same unit is good for 3 minutes at 50W before cool-down. At less then 25W it can pretty much go on forever).

You probably won't see a full "advertised" power. Especially when that power level is also an FCC legal maximum output power (whereas the common 100W Amateur rig is not limited that way -- since 1500W is the legal max). Manufacturers may set the max to some level below the 50 (a few watts) just to ensure compliance with FCC regulations. There is also just unit to unit differences -- if the final check-out technician is having a bad day, they may not spend much time tweaking the final output levels and consider anything under 50W is good.

A few watts is insignificant. If I recall, to double the received signal strength (2 S-units on a meter?), one has to use something like 10X the power (I need to restudy my technical books. If a 5W signal brings up half the s-meter, going to 50W is likely to only tick one or two more dots on the uncalibrated LCD meters most units display.

I have a BTech GMRS-V2 -- advertised as 5W HT... My last test showed something between 2.5 and 3.5W. In contrast, my GMRS-V1 (a 2W design) showed around 2.5W.

18 hours ago, SargeDiesel said:

3. Is running the antenna cable and power cable together ok ?

The main feature of coax is that it is supposed to be shielded from outside electrical noise. The RF signal goes up the center conductor, and ideally tends to be balanced by the /inside/ of the braided shield (this is a much simplified description). Noise tends to be induced on the outside of the braided shield where is should be grounded out at the radio. Twin-lead has lower losses, but has to be kept a few inches away from any metal, much less something carrying electricity.

 

18 hours ago, SargeDiesel said:

4. Is having both the antenna cable  and power cable zip tied to the wiring harness ok ? Will it interfere with any of the other  vehicle electronics  ?

The zip-tie somewhat concerns me.. How TIGHT are they? You don't want to squeeze the coax and the inner insulator may deform, putting the shield closer to the center conductor... And that will become an impedance bump (SWR affect -- maybe small but...).

For my install, I bought some canisters (10ft lengths, at O'Reilly) of split-tubing plastic conduit. Press the cables in through the split, then use cable clamps or zip-ties to hold the conduit in place.

Icom ID-5100 transceiver installed in the under-bed well. The conduit has a few inches of antenna cable, power cables, external speaker cable, microphone cable, and control head cable.

The speaker, microphone, and control head cables split off at the driver's seat to go in to the central console (actually, I should double check. The speaker is mounted just behind console, but did I run control cables along central console, or with power cables and split off at the driver's kick panel?

Just to get more on topic -- those are the GMRS and CB (both mag-mount antennas) which run up the right side until passenger seat, then cross over to central console.

 

Edited August 22, 2022 by KAF6045
Correction on VNA battery

[KAF6045]

13 hours ago, SargeDiesel said:

I just installed my MXT575, using a shortened 12' midland (MTXA24) nmo cable(by CoolTech) attached to a Midland MXTA26 antenna. I have it mounted to a CoolTech stainless steel nmo mount next to the am/fm antenna on the passenger side hood cowl panel of my JT(Jeep Gladiator). I did run the power and antenna cables next to each other(??) and zip tied them to the vehicles wiring harness(??).... When testing, on channel 01(low power), I had SWR readings of 1.01 / FW-W 2.94 / RW-W .000 , but when I tested on channel 20(high power) I had SWR readings of 1.62 / FW-W 27 / RW-W 1.51.  -   First, I do not understand why there is a difference in SWR  ?  I am happy with the readings, but feel @ High power they need to be better and achieve at least 1:5:1 or below.  Secondly why is the output wattage so low for a 50 Watt radio ? I have seen this radio tested on YouTube several times and on low power it was 5.00+ watts and on high 49.00+ watts. I thought I might need to test into a dummy load for an accurate test, but during the YouTube test, the readings were the same whether testing into the antenna or a dummy load. I would prefer not to have to spend the $ on a dummy load if it is not needed.  I did just read that Midland GMRS antennas are pre-tuned to center channel (does that mean channel 11 ?) I can retest on channel 11 and there is some adjustment built into the antenna to shorten the length into the base, maybe this may improve the SWR, but what could possibly be causing the difference in SWR between Low/High power and the overall low output power... Thank you for any help.

 

Mounting an antenna next to another is not recommended (besides the potential of overloading the AM/FM receiver front-end) the parallel antennas will interact and may cause SWR detuning or an inadvertent directionality of the signal. I'd suggest at least a foot of distance, more would be better. On my rust-bucket Liberty, the mag-mount that came with my MXT115 is near the front of the roof (about where the headrests of the seats, centered), a mag-mount CB antenna is about 18" behind that, and two-three feet in front of the AM/FM antenna. The 2m/70cm antenna is a glass-mount on the left (to get it away from curb-side trees when parking) rear side window (best I could do, even though they say not to mount on tinted glass -- have you seen any car that doesn't have rear&side windows tinted in the last decades?).

SWR varies by frequency, and depending upon the antenna, the bandwidth for low SWR will also vary (high gain antennas often have narrower bandwidths, being more sensitive to matching frequency). Presuming channel 1 is 462.5625 and your channel 20 is 462.675, channel 6 would be the closest match for comparison -- also try low power on all that you test (for comparison; the meter may have differing sensitivity based on power). How calibrated is the meter; most consumer gear may not read "true". Also, the radio may have a "roll-back" circuit, in which it reduces output power until the reflected power is below some threshold (this is to preserve the output transistors -- if they are pushing out 50W and 5W is coming back in, the transistor is essentially running 55W). Or was your channel 20 actually the repeater mode, in which case it was 467.675MHz.

I'm a bit perplexed by your channel numbers. To my knowledge, the Midland mobiles DO NOT INCLUDE CHANNEL 11. In the 2017 FRS/GMRS reorganization, the channels are defined as:

• 1-7 GMRS interstitials -- 5W ERP FM on 462MHz. Note: interstitials refers to these channels being created /between/ the original GMRS main channels.
• 8-14 FRS (allowed on GMRS handhelds) 0.5W ERP NFM on 467MHz (467 is repeater input frequencies, which is why the power is so limited)
• 15-22 GMRS main simplex channels; 50W out FM on 462MHz
• 23-30 (aka RP15-RP22 or such name variations) GMRS duplex (repeater), 50W out FM transmit on 467MHz, receive on 462MHz.

Note that 1-7 are rated ERP (so are affected by antenna gain; if you have a 3dBd gain antenna, you'd have to limit the output power to <2.5 to stay within the ERP); main channels are transmitter output -- feel free to put up a 9dBd gain antenna for an effective ERP over 200W and closer to 500W!.

The "middle" if all you mean is simplex would be interstitial 4, or main 18&19 (4 is between those two). But that is only considering simplex on 462MHz.

You can't transmit on the middle if you try to cover both 462 and 467MHz (the "middle" would be around 464.500MHz). If you don't use repeaters, no problem (and you probably don't need to run on high power either, as low will match most upper-end hand-helds which may be what is being used in the field). If repeaters are a primary usage, you'd want to tune the antenna closer to 467MHz (but not so far as to make 462MHz unusable).

Otherwise -- having duplex RP15 and simplex 22 showing similar SWRs would optimize the antenna (though you may not like either SWR, and simplex 15/RP22 will be even worse).

The good news... You need to /shorten/ the antenna (though as I mentioned, maybe relocate it first before checking SWR). If the set-screws don't let you lower it enough, you can grind off a few millimeters at a time until you acceptable SWR readings.

 

[SargeDiesel]

23 hours ago, Sshannon said:

1. For any given antenna, SWR changes with frequency.  A graph of SWR vs. frequency often looks like there’s a sharp dip at the resonant frequency. 

2. Where are you measuring the output power? A dummy load will appear to the transmitter like an antenna that has a very low SWR at every frequency.  Also, was your Jeep running and putting out 13.8 volts or were you on battery at a voltage of 12+ volts?  On battery power the output power will sag slightly. Or it might just have been the radio you received. Many things can affect output power: input power, antenna cable, antenna, ground plane, etc.

3. Pretuned to center channel probably means that it’s tuned to midway between the 462 (used for simplex communications) and 467 MHz (which you transmit to a repeater) frequencies of the band, or about 465 MHz.  

4. Tuning the antenna to have a lower SWR might get you more transmitted watts, but honestly a few watts isn’t detectable in actual use.   I recommend either leaving the antenna alone or tuning it to the frequency you transmit on most often.  A higher frequency means a shorter antenna element, but if you shorten it too much it’s hard to undo.

Thank you for your response. 

When I was measuring,  I  had the radio connected to the meter and the meter connected to the antenna. 

The vehicle was turned off using only battery power. 

My concern was the radio was only putting out half its power,  I just want to make sure it is capable of putting out full power,  like all the others of the same model I have seen tested.

Thanks again for your help. 

[SargeDiesel]

Maybe my question should be:

1. How do I properly test a newly installed GMRS radio for SWR ? What channel(s) should I use  ?

2.  How would I test to insure my radio is capable of outputting the advertised 50 watts of power ? (Hopefully using my current equipment)

3. Is running the antenna cable and power cable together ok ?

4. Is having both the antenna cable  and power cable zip tied to the wiring harness ok ? Will it interfere with any of the other  vehicle electronics  ?

Thanks 

 

 

 

[SargeDiesel]

7 minutes ago, Sshannon said:

1. Make sure you’re using test equipment that’s high quality and accurately calibrated and appropriate for the frequency and power level you’re using. Make sure you’re testing at the specified voltage (13.8!) and using power cables that won’t cause voltage drop. It might help to visit a local radio shop. 
2. That can depend on a lot of things. Is your power wiring noisy? How high quality is your coax? When it comes to antennas, everything affects everything and a noisy power cable parallel to the coax could cause problems. 

I when I tested my power cable,  I  had the same voltage reading at the battery and the end plug (if this is what you are referring to)  but I  haven't tested it while actually keying the handset.... I  would have to figure how to do that.... lol

All of my hardware is from Midland ... maybe I have made a rookie mistake in assuming Midland products are high quality  ???

Im really not sure how to go about testing "noisy cables"... so your advice to visit a local shop is probably a good idea.... the search is on.

[SargeDiesel]

22 hours ago, KAF6045 said:

For completeness -- ALL channels... INCLUDING the repeater inputs since they are 5MHz up from the simplex frequencies. However, you could probably skip the interstitials (in the current numbering scheme: 1-7, limit to 5W ERP) as they fall midway between the main channels. That leaves the main simplex channels (15-22) and the repeater channels (which may appear as 23-30, or as 15-22 with some indicator of repeater mode: rp15, 15R, etc.).

If your primary usage will be via repeaters, having a low SWR on the repeater channels will be more desirable. If you will be using simplex and repeaters, you'll have to compromise. Try to match simplex 22 and repeater 15 in SWR (simplex 15 and repeater 22 will be the worst SWRs, since you are tuning to put the minimum SWR around 464/465MHz, which is not a GMRS frequency band on its own, but midway between simplex and repeater frequencies.

This is where a standalone antenna analyzer (or a VNA -- though I don't have experience with those yet; mine arrived today, with the power switch in the ON position, so the battery is extremely dead with NO battery included [I've never seen a "standard flat-top 18650" locally -- button top and worse, protection circuit on some], and I hope it will charge). One: these devices don't spew high power RF, running in microWatt levels. Two: they let you sweep the frequency range while watching a needle and/or LCD display of SWR so you can rapidly get an idea of where the min-SWR is, and what the <2.0 bandwidth covers (Antenna analyzers tend to use of rotary dial to manually sweep, VNAs normally do the sweep via programmed parameters, and display graphically).

 

You would 1: need a calibrated RF signal source to validate your power meter reading and 2: a reasonable dummy load for the power and frequency range (a 300W dummy load can only operate for half a minute at 300W before giving it a multiple minute cool-down; same unit is good for 3 minutes at 50W before cool-down. At less then 25W it can pretty much go on forever).

You probably won't see a full "advertised" power. Especially when that power level is also an FCC legal maximum output power (whereas the common 100W Amateur rig is not limited that way -- since 1500W is the legal max). Manufacturers may set the max to some level below the 50 (a few watts) just to ensure compliance with FCC regulations. There is also just unit to unit differences -- if the final check-out technician is having a bad day, they may not spend much time tweaking the final output levels and consider anything under 50W is good.

A few watts is insignificant. If I recall, to double the received signal strength (2 S-units on a meter?), one has to use something like 10X the power (I need to restudy my technical books. If a 5W signal brings up half the s-meter, going to 50W is likely to only tick one or two more dots on the uncalibrated LCD meters most units display.

I have a BTech GMRS-V2 -- advertised as 5W HT... My last test showed something between 2.5 and 3.5W. In contrast, my GMRS-V1 (a 2W design) showed around 2.5W.

The main feature of coax is that it is supposed to be shielded from outside electrical noise. The RF signal goes up the center conductor, and ideally tends to be balanced by the /inside/ of the braided shield (this is a much simplified description). Noise tends to be induced on the outside of the braided shield where is should be grounded out at the radio. Twin-lead has lower losses, but has to be kept a few inches away from any metal, much less something carrying electricity.

 

The zip-tie somewhat concerns me.. How TIGHT are they? You don't want to squeeze the coax and the inner insulator may deform, putting the shield closer to the center conductor... And that will become an impedance bump (SWR affect -- maybe small but...).

For my install, I bought some canisters (10ft lengths, at O'Reilly) of split-tubing plastic conduit. Press the cables in through the split, then use cable clamps or zip-ties to hold the conduit in place.

Icom ID-5100 transceiver installed in the under-bed well. The conduit has a few inches of antenna cable, power cables, external speaker cable, microphone cable, and control head cable.

The speaker, microphone, and control head cables split off at the driver's seat to go in to the central console (actually, I should double check. The speaker is mounted just behind console, but did I run control cables along central console, or with power cables and split off at the driver's kick panel?

Just to get more on topic -- those are the GMRS and CB (both mag-mount antennas) which run up the right side until passenger seat, then cross over to central console.

 

Thank you for your detailed,  simplified response. Your build is really nice and well thought out...nicely done sir !  I made some changes. 

I moved the antenna from the passenger side away from the am/fm antenna to the drivers side.   I did mount it in the same location.   I also I rerouted the antenna cable away from the power cable and wiring harness(I didnt have it zip-tied tight at all).  The funny thing was , I  got some increased wattage,  but I also got a much higher SWR.  Before the changes,  my SWR was barely out of "safe" range @ 1:6:1 at high power.  After the changes it varied between channels between 1:9:1 - 2:0:1.  This initially led me to believe I needed to tune the "pre-tuned" antenna.   I then switched out the whip antenna for a ghost antenna using the exact same setup,  and achieved a large gain in wattage from the previous 25/27 to 35/37 watts and an almost perfect SWR reading throughout the channels.   So I left it alone.  So instead of tuning the Midland MXTA26, I am considering purchasing the  Larsen NMO450CHW which is a " 1/2 wave collinear antenna,  advertised not to need a ground plane. I think this might suit me better than the Midland since it is a 5/8 wave and the Jeep Gladiator is already antenna challenged in finding a good mounting location. 

I do have a question I haven't asked yet......   concerning the design of the NMO mount, I  see in every setup, there is a nylon or plastic insert in the center hole of the mount where the brass threaded piece comes up from underneath into the center of the mount for the top plate to screw on....  I was thinking this was to isolate it from coming into contact with the mount..... IF THIS IS THE CASE, when you screw the top brass mounting plate down onto the mount, it has an O-RING on the underneath side, my ?? is, is the O-ring there to protect from weather  ? Or is it there to keep the plate from coming into contact with the top of the mount when screwed down tight. (functioning similar to the nylon/plastic insert) ?  Because if it is the later, and it is the keep the brass plate from grounding on the mount, this may be some of my troubles... I  tend to over tighten everything and upon changing locations of the mount, I  realized I had tightened it down so tight,  I collapsed the o-ring and the brass antenna adapter most likely was in contact with the mount.

I appreciate everyone's help !

[KAF6045]

Can't help on the NMO... Unless the ancient dual band amateur antenna and clamp-on mount I'd used on a Plymouth Laser RS Turbo, back in the 90s had one. The ATAS-100/120 (40m-70cm screwdriver)  I used on a Jeep Cherokee (99-last year, when it was totaled in a roll-over accident) was "UHF" (PL-259/SO-239) style. The rust-bucket I'm now driving has mag-mounts for GMRS and CB, and a Larsen window-glass mount with dual-band antenna that just has a small threaded post with O-ring that the whip screws down against. In this case, the O-ring is obviously a weather-shield keeping rain from corroding the threaded fitting when the antenna is on.

 

[gortex2]

The ORing is to keep water out of the NMO. Nothing more.

 

[SargeDiesel]

1 hour ago, gortex2 said:

The ORing is to keep water out of the NMO. Nothing more.

 

If the o-ring is only for weather/water, why is the center post of the cable isolated from the mount with the nylon/plastic insert in the center hole of the mount ?  Just for fitment  ? I thought it was so the cable didn't touch/ground on the mount.... but that wouldn't make any sense if the top mount screws down onto and touches the mount anyway... ???

[BoxCar]

The center post is connected to the center conductor of the coax and the shield or outer conductor of the coax is grounded through the mount.

[axorlov]

3 hours ago, SargeDiesel said:

If the o-ring is only for weather/water, why is the center post of the cable isolated from the mount with the nylon/plastic insert in the center hole of the mount

The usual NMO-mounted antenna is only a half of the antenna, the other half is a ground plane created by a conductive flat roof of the vehicle. The threads that are holding NMO antenna in place are connected to this ground plane, while the center pin in the NMO mount is connected to the whip of the NMO antenna (as was pointed out above). The O-ring is simply to keep water out of the connector (as was described above).

[SargeDiesel]

12 hours ago, axorlov said:

The usual NMO-mounted antenna is only a half of the antenna, the other half is a ground plane created by a conductive flat roof of the vehicle. 

I understand about the ground plane(GP),  I  just misunderstood the function of the nylon/plastic spacer you see in the center hole of most mounts.

My issue is the design of the Jeep, the hood is Aluminum and non magnetic,  no roof or trunk to speak of,  so most owners use a lip mount or where I have placed it, on  the side hood cowl... which doesn't provide an ideal GP.

Because of the lack of a good solid adequate GP surface, would the 1/2 wave antennas work better for me ?  When I switched from the 5/8 wave whip to the 5/8 Ghost(3.5"), I got much better test results,  but at a sacrifice of fars and half the dB. (From my understanding the ghost doesn't need as good of a GP as the whip, but both are 5/8 - so I really don't understand why)

 

I  read the Larsen NMO0450CHW is a 1/2 wave and does not necessarily need a GP and I would get more fars over the 3.5" ghost and gain my dB back.  Would this be a good choice for when I need more coverage over the shorter, less powerful ghost antenna  ?

[axorlov]

20 minutes ago, SargeDiesel said:

When I switched from the 5/8 wave whip to the 5/8 Ghost(3.5"), I got much better test results,  but at a sacrifice of fars and half the dB

3.5" antenna can't be 5/8. 5/8 wavelength on GMRS frequency is around 16". When you are saying you've got better test results, you mean better measured SWR? If yes, it just demonstrates that more power is absorbed by an inefficient antenna and not being radiated. Converted to heat. There is a device, called Dummy Load to test transmitters. It usually has perfect SWR 1:1 and designed to not radiate at all.

1/2 wavelength antenna does not need ground plane. 5/8 antenna needs ground plane to provide 3 dBd gain and correct flattened pattern, however, it will work without ground plane with reduced radiating efficiency, distorted pattern and higher SWR. You will have higher common mode current on your coax, but that might still be ok. Without ground plane it likely will be about equivalent to the 1/2 antenna with higher SWR.

 

P.S.

I just re-read the thread, it seems that your problem is low measured power. It could be that your power/SWR meter is to blame, or your antenna, or your cable. If you buy aforementioned dummy load rated for 100W and 500MHz, you can test your output power safely at two places: at the radio and at the antenna. Difference will show how much power is absorbed by the coax. Also, your SWR meter should be rated for at least 500MHz, CB meters do not work at these frequencies.

[SargeDiesel]

25 minutes ago, axorlov said:

3.5" antenna can't be 5/8. 5/8 wavelength on GMRS frequency is around 16

[SargeDiesel]

34 minutes ago, axorlov said:

I just re-read the thread, it seems that your problem is low measured power. It could be that your power/SWR meter is to blame, or your antenna, or your cable

I did get a significant increase in wattage when I switched antennas from the whip to the ghost.. approximately 10 watts or so.

ButI also tried a completely different antenna ( the small 6 inch that came packaged with the  MXT575) I placed it on a large pizza pan for the GP, if I remember correctly,  it was in the 30 watt range, but nowhere near the advertised 50 watts.  When I have seen theses tested on YouTube,  they are constantly - 48/49 watts. I  did test with the vehicle running. 

 

The meter is  cheap one, but I believe is fine for GMRS.  it is a Surecom-SW33 plus. Here are the specs:

Max Power: 0.1 - 100W
V.S.W.R.: 1.00*19.9
SWR Detection Sensitivity: 3W min.
Frequency Range: 125MHz-525MHz
In/Out Impedance: 50Ω
Interface: SMA Female
Accuracy: mean +/- 5%

[axorlov]

Marketers, who create such work for printed materials and web, often have no clue. It maybe a helical antenna (very like it is), it may have total length of the wire at around 5/8, but it is not 5/8 antenna.

[SargeDiesel]

2 minutes ago, axorlov said:

Marketers, who create such work for printed materials and web, often have no clue. It maybe a helical antenna (very like it is), it may have total length of the wire at around 5/8, but it is not 5/8 antenna.

Makes sense  , in my situation do you think the 1/2 wave whip would work better ? (In easy newbie terms ... lol)

Thanks for all of your help... new to this, most is starting to sink in... but some Im still grasping at.... hopefully it will come together. 

[axorlov]

2 minutes ago, SargeDiesel said:

Surecom-SW33 plus

Ah, the famous SW-33. I have one and it is garbage. I also have Diamond SX600. The SW-33 and SX600 mostly agree with each other when measuring on 2m, but SW-33 is way off with power and SWR measurements on 70cm and GMRS.

[axorlov]

2 minutes ago, SargeDiesel said:

in my situation do you think the 1/2 wave whip would work better

I would keep 5/8 whip, if I was you. Before getting other antenna, I would sort out measuring equipment.

[gortex2]

As I say over and over the ghost antenna is about as good as a dummy load. If your goal is to talk to a guy in front of you on simplex use it. If you need distance a 1/4 wave is a better choice. A quick search on this site will give you hundreds of posts with the differences between the ghost and the gain from Midland. There are also many posts on the JT/JL/JK/TJ antenna mounting solutions. 

[SargeDiesel]

43 minutes ago, gortex2 said:

As I say over and over the ghost antenna is about as good as a dummy load. If your goal is to talk to a guy in front of you on simplex use it. If you need distance a 1/4 wave is a better choice. A quick search on this site will give you hundreds of posts with the differences between the ghost and the gain from Midland. There are also many posts on the JT/JL/JK/TJ antenna mounting solutions. 

Thanks,  new to the forum and radio in general,  still  a lot to figure out,  thanks for the tip.

[Ian]

On 8/20/2022 at 1:50 PM, KAF6045 said:

Mounting an antenna next to another is not recommended (besides the potential of overloading the AM/FM receiver front-end) the parallel antennas will interact and may cause SWR detuning or an inadvertent directionality of the signal. I'd suggest at least a foot of distance, more would be better. On my rust-bucket Liberty, the mag-mount that came with my MXT115 is near the front of the roof (about where the headrests of the seats, centered), a mag-mount CB antenna is about 18" behind that, and two-three feet in front of the AM/FM antenna. The 2m/70cm antenna is a glass-mount on the left (to get it away from curb-side trees when parking) rear side window (best I could do, even though they say not to mount on tinted glass -- have you seen any car that doesn't have rear&side windows tinted in the last decades?).

 

Relevant to this, Sti-Co makes combined entertainment/2-way radios that hook into the car stereo and the UHF radio by way of a diplexer; this would prevent that exact problem.