WRYZ926 Posted October 16, 2023 Author Report Posted October 16, 2023 49 minutes ago, WRYZ927 said: Some great suggestions thrown out here so far. I really like the heli-tape and mag mount as far as the simple leave no trace theme goes that @SteveC7010 mentioned. If the roof is aluminum, and because I just love to over complicate simple things, one could place a magnet above the headliner to contain the mag mount on the roof. I'll toss something out of left field, if only to keep the creative juices flowing. Aftermarket/factory roof racks, in whole or part would give a possible mounting solution, especially if it could serve its intended purpose of carrying crap on the roof, in addition to a place to hang an antenna. The roof is steel so a magnetic mount will work. And I like the idea of some 3M tape to protect the paint. I have also considered a roof rack mount too. I just wonder how the ground plane is with an antenna mounted a cross bar. WRYZ927 1 Quote
WRQC527 Posted October 16, 2023 Report Posted October 16, 2023 Although I don't like mag mounts as a long-term solution, I have used them, and to prevent scratching I've placed a cheap plastic (not glass) tablet screen protector on the roof. WRYJ580 and WRYZ926 2 Quote
wayoverthere Posted October 16, 2023 Report Posted October 16, 2023 1 hour ago, WRQC527 said: Although I don't like mag mounts as a long-term solution, I have used them, and to prevent scratching I've placed a cheap plastic (not glass) tablet screen protector on the roof. I'll also suggest protecting the point where the cable turns the corner into the hatch. Been running mag mounts (1, 2 or 3) on my truck for the past 3 years or so, and you can see the "rub" where it turns to tuck in behind the door seal WRYZ926 and WRQC527 2 Quote
WRYZ926 Posted October 16, 2023 Author Report Posted October 16, 2023 1 minute ago, wayoverthere said: I'll also suggest protecting the point where the cable turns the corner into the hatch. Been running mag mounts (1, 2 or 3) on my truck for the past 3 years or so, and you can see the "rub" where it turns to tuck in behind the door seal That is the other main concern I have. Quote
wayoverthere Posted October 16, 2023 Report Posted October 16, 2023 (edited) 1 hour ago, WRYZ926 said: That is the other main concern I have. If you have some roof rack bars/rails, those may help with keeping the cable off the roof between the mount and tucking into the hatch. That may bring it back to a lip mount being the best option. This comet has a short section of thin cable to help with squeezing past the seal, and limits the amount of cable available outside to rub. Closer to the hinge also limits how much you need loose to allow range of movement with the hatch, but may complicate routing while leaving a drip loop. (I know...Always compromises somewhere) Back to mag mounts, though, I've largely used Midland mag mounts, have to check the brand on one other (edit: it's a Browning), along with a late 90's radio shack mag mount and cb antenna. Even with antennas up to 3 ft, comet 2x4sr or double 5/8 Browning, the only time I've had one come loose was when the whip directly and solidly hit something, like a good sized branch. Lots of light hits with no movement. I can't see something like a "hatpin" 1/4 wave having enough leverage to knock the mount loose, and is only 6" tall. On the hatch, you can likely get by with a 1/2 wave (which tend to be around 12-15" for 450-470 mhz) and still clear the garage. Edited October 16, 2023 by wayoverthere checked brand of mount WRUU653 and WRYZ926 2 Quote
WRYZ926 Posted October 16, 2023 Author Report Posted October 16, 2023 Thank you for the information @wayoverthere. And yes most things will be a compromise, especially since I do not want to drill any holes. The mount you linked looks like the best option as far as mounting on the lift gate. My Escape does have the factory roof rails but no cross bars. wayoverthere 1 Quote
WRYZ926 Posted October 20, 2023 Author Report Posted October 20, 2023 I have decided to go with a magnetic mount for now on the Escape. I will have to use a 15-16 inch tall antenna so I don't tear up anything pulling into the garage. Next question for the gurus. How far apart should I keep a 2m/70cm antenna and a GMRS Antenna while mounted on top of the Escape? wayoverthere 1 Quote
WRYU400 Posted October 20, 2023 Report Posted October 20, 2023 I would suggest 12” or more. Sent using Tapatalk WRYZ926 1 Quote
WRYZ926 Posted October 20, 2023 Author Report Posted October 20, 2023 @WRYU400 thank you for the information. WRYU400 1 Quote
SteveShannon Posted October 21, 2023 Report Posted October 21, 2023 5 hours ago, WRYU400 said: I would suggest 12” or more. Sent using Tapatalk That is based on the wavelength of GMRS. 2 meters has a wavelength that’s three times greater. The rule of thumb when trying to prevent antennas from affecting each other is at least 1/4 wavelengths of the longest wavelength antenna and avoid exact multiples of the wavelengths of the signals. So, to prevent the longest wavelength (2 meter) from affecting the GMRS antenna, you would want at least half a meter which is close to 20 inches. Quote
WRYU400 Posted October 21, 2023 Report Posted October 21, 2023 The highest band used designates the minimum distance. Ever stack yagis? This is what is done. The lower band antennas do not have adverse effects with higher band antennas. Sent using Tapatalk Quote
SteveShannon Posted October 21, 2023 Report Posted October 21, 2023 1 minute ago, WRYU400 said: The highest band used designates the minimum distance. Ever stack yagis? This is what is done. The lower band antennas do not have adverse effects with higher band antennas. Sent using Tapatalk Why wouldn’t the presence of the GMRS antenna element being 1 foot away as you recommend adversely affect the propagation of the 2 meter antenna? It will act as a reflector, right? Quote
WRYU400 Posted October 21, 2023 Report Posted October 21, 2023 Reflectors are physically longer than the driven element. Sent using Tapatalk Quote
SteveShannon Posted October 21, 2023 Report Posted October 21, 2023 But these are not Yagi antennas these are omnidirectional quarter wave antennas or 5/8 wave antennas. Everything I read states to keep them at least a quarter wave of the lowest frequency apart: https://forums.radioreference.com/threads/antenna-spacing-on-roof.206774/ and even when stacking Yagis they recommend some distance to avoid affecting the lower frequency: https://directivesystems.com/wp-content/uploads/sites/2/2014/04/Stacking-Dis-similar-Yagis.pdf wayoverthere 1 Quote
WRYU400 Posted October 21, 2023 Report Posted October 21, 2023 Here’s an example, You have a 6 meter yagi, 2m yagi and a 70cm yagi stacked on a mast. The 70cm yagi should be 1/2 wave @ 70cm from the 2m yagi. The 2m yagi should be 1/2 wave @ 2m from the 6m yagi. The lower band yagis will not “see” the higher bands. Same goes with mobile antennas. 70cm whip should be 1/2 wave @ 70cm from a 2m whip etc. Dual band whips are using the lowest operating band. Sent using Tapatalk Quote
SteveShannon Posted October 21, 2023 Report Posted October 21, 2023 Here’s another article that explains the difference between horizontal spacing and vertical spacing: https://www.repeater-builder.com/antenna/separation.html Quote
WRYU400 Posted October 21, 2023 Report Posted October 21, 2023 Fine bud, I won’t help anyone else that asks for it here. Y’all are toxic. Sent using Tapatalk Quote
BoxCar Posted October 21, 2023 Report Posted October 21, 2023 I'll weigh in on this on WRYU400's side. The critical antenna is always the higher frequency one. A quarter wavelength distance results in the longer antenna acting as a reflector increasing the signal lobe opposite the reflector. As the higher frequency antenna is not at a distance that would resonate with the lower frequency antenna it has minimal effect on the higher frequency antenna. The articles Mr. Shannon is referencing are focused on antennas in the same band. Quote
WRYZ926 Posted October 21, 2023 Author Report Posted October 21, 2023 Well I sure won't try to transmit on 70cm and GMRS at the same time with both antennas on the roof of a vehicle. I probably won't even tune to 70cm while the GRMS is on. They are close enough in frequencies to cause issues. I was more concerned about 2m an GMRS. ANd I do appreciate all the helpful input from everyone. So please do not turn this into a pissing contest. SteveShannon and WRUU653 2 Quote
SteveShannon Posted October 21, 2023 Report Posted October 21, 2023 16 minutes ago, BoxCar said: The articles Mr. Shannon is referencing are focused on antennas in the same band. They really are not. I was specifically looking for articles that reference different bands. Here’s an example from this one: https://directivesystems.com/wp-content/uploads/sites/2/2014/04/Stacking-Dis-similar-Yagis.pdf “So how do you arrive at a proper spacing number for different bands? If you are stacking two antennas on different bands, you must look at the stacking distance for each antenna and locate the antennas so neither aperture sees the other antenna aperture. Let's take an example. We wish to stack a DSFO144-12 along with a DS222-10RS on the same mast. The 144-12 stacking distance (h-plane) is 10 ft 8" while the DS222-10RS is 74" . Take half of the stacking distance for the lowest frequency antenna and you have the extent of the aperture boundary for that antenna. In this case it is 5 ft 4 inches, or 64". Do the same for the other antenna. The correct distance for zero interaction, then, is 64 plus 37 inches, or 101" total spacing. Simple enough. There is no way either antenna will be bothered by the other PERIOD!” I want to point out that the shouted word at the end is not my emphasis, but came from the article as written. But, the fact is there will be effects also from placement on the ground plane and because the antennas are mounted on magnetic bases they can alway be moved. But I definitely agree that this shouldn’t be a pissing contest but rather a reasonable discussion reflecting our understanding. Quote
WRYZ926 Posted October 21, 2023 Author Report Posted October 21, 2023 I knew from the get go that there can/will be an issue running 70cm and GMRS at the same time with antennas close together like on a roof of a vehicle. I do have a little more room with the Escape versus a sedan to space the antennas out a little. Right now I am mostly using 2m and GMRS occasionally. The use of GMRS will change now that others in our club are starting to get GMRS radios. We discussed looking into a GMRS repeater on the 900ft tower that the 2m and 70cm repeaters are on. SteveShannon 1 Quote
BoxCar Posted October 21, 2023 Report Posted October 21, 2023 Yes, there are effects from what I learned was a parasitic radiator. The amount of effect is determined by the percentage of a quarter wavelength distance between them. At a quarter wavelength the parasitic radiator will boost the signal from the transmitting antenna and at a half wavelength will have no effect. At 1/8 wavelength there will be maximum affect as the reflected wave will be in full opposition to the radiator. A simple visualization can be done by drawing a full wave on a piece of paper and then moving a mirror representing the second antenna along the X axis, You will have a visual representation of the affect of the two antennas. SteveShannon 1 Quote
WRQC527 Posted October 21, 2023 Report Posted October 21, 2023 This guy seems to have established proper spacing between antennas for different bands. WRYZ927, SteveShannon and WRPG745 1 2 Quote
WRWS738 Posted October 25, 2023 Report Posted October 25, 2023 On 10/14/2023 at 1:28 PM, WRYZ926 said: I have a 2023 Ford Escape and any looking for different options for antennas and also running cables into the passenger compartment. The one thing I will NOT do is drill any holes for a NMO mount. Thanks I used a Comet RS 720 NMO Medium duty lip mount for my Equinox antenna. I use it as a hood mount on the drivers side. Works well for me WRQC527 1 Quote
WRYZ926 Posted October 25, 2023 Author Report Posted October 25, 2023 I ended up buying a Midland MXT500 to use as a base station and put the included mag mount on my Escape. With the mount in the center of my roof, I was able to run the coax through the back hatch without any issues. That does leave the cable too short to put a radio on the dash. I might use that mount for a dual band radio with a detachable head unit and get another mag mount for my GMRS radio. There isn't a whole lot of space to mount radios in the Escape. I might go with the BTech GMRS-20V2. That way I only need to worry about the dual band head unit and two mic's. Quote
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