One antenna works and the other doesn't

[Flameout]

I was (and still am) using a mobile Nagoya UT-72g and although it works, it's very touchy as to it's position. I am using it inside my garage, on a vehicle and it needs to be in a very specific spot to hit the one repeater I'm using. If I move it even a foot, I can't hear the repeater, but in that one specific spot, it picks up great

I bought a GMRS specific Slim Jim, mounted on my roof, with a clear shot to that repeater, which is about 14 miles away and it will not pick up that same repeater at all. How can that mobile, inside my garage pick it up but the roof mounted one can't? Could it be that cable or maybe the connectors? I made a PVC "C" to hold the Slim Jim (I attached a photo - the other antenna in photo is my 2m/440 Comet GP-6) I think I may eventually just get a Comet CA-712EFC. The other photo is the view from my roof and that repeater is over in that direction

 

 

[PACNWComms]

Looks like some trees and possibly hills. Do you have a clear line of sight from the antenna to the repeater? The antenna in the garage may be lined up just right, while the roof mounted one may not be. Or possibly something is wrong with the antenna. Do you have a wattmeter to make sure power is getting out the roof mounted antenna? Another issue could be line loss, and the more coax you use, the more potential loss you may have. Which type of coax is being used with each antenna, length of coax, and type of connector, and adapters if used. 

[marcspaz]

The Comet antenna should be good to 470 MHz.  Have you tried using the Comet? 

 

Also, as mentioned above, some more info can help us help you.

 

What cable type and connectors are you using? 

How long is the cable run and is it all one piece? 

How many watts of output are at the radio? 

Did you test the antenna before you put it on the roof?

Depending on how long the cable is, you can get a false SWR reading at the radio... have you tested the SWR of the antenna? 

 

Two issues I see right off the bat, those two antennas are too close to one another for a few reasons. Also, PVC acts like a dielectric insulation, so we don't use PVC to hang antennas because it can change the frequency response of the antenna. The PVC at the top and bottom of the antenna, as well as along the side may be causing issues. I would recommend fiberglass rods, wood, or use an antenna analyzer to verify and set the antenna length to account for the capacitance created in the loop, introduced by the PVC.  I would be least likely to do the last option I listed because you will still be susceptible to drastic SWR changes with wet weather. 

[mbrun]

I was (and still am) using a mobile Nagoya UT-72g and although it works, it's very touchy as to it's position. I am using it inside my garage, on a vehicle and it needs to be in a very specific spot to hit the one repeater I'm using. If I move it even a foot, I can't hear the repeater, but in that one specific spot, it picks up great
I bought a GMRS specific Slim Jim, mounted on my roof, with a clear shot to that repeater, which is about 14 miles away and it will not pick up that same repeater at all. How can that mobile, inside my garage pick it up but the roof mounted one can't? Could it be that cable or maybe the connectors? I made a PVC "C" to hold the Slim Jim (I attached a photo - the other antenna in photo is my 2m/440 Comet GP-6) I think I may eventually just get a Comet CA-712EFC. The other photo is the view from my roof and that repeater is over in that direction
 
 

Your situation suggests that you may not have the “clear shot to that repeater” you suggest. 14 miles with truly a clear shot should result in very good strength (perhaps 40dB of more to spare), and with minimal effect from the environment. Given that pickup is touchy in the garage and that you are also having communications using the antenna on the roof, there are other factors that coming into play. These could very well be losses caused by many obstructions in the signal path and reflections caused by the environment. Changing the physical location (horizontally and/or vertically) may make a difference.

Marc makes some good suggestions. Heed them.
Always start your troubleshooting by making sure first that your antenna, then your complete antenna system, making sure both show they tuned correctly. You may wish to invest in and learn how to use a NanoVNA.

I concur that your antennas are too close together. Depending upon your operating power you could perhaps damage one radio while transmitting on the other, but this is a completely separate concern from what you brought up. For example, if your antennas are 3 feet apart, one antenna has a gain of 9dBi, one of 5dBi and assuming your amateur radio transmits at 100 watts on 70cm, the GMRS radio could see as much as 10 watts coming back in if my calculations are correct. If your radios cannot handle that in a sustained way you could experience a failure. Consider arraying your antennas vertically rather than horizontally if they are going to installed in close proximity so that you can benefit from the axial losses in their coverage patterns.

As far as additional troubleshooting is concerned. Consider getting on the roof and trying operation merely with a 5w HT at various locations to see which locations might exhibit stronger signals. It would be interesting for you to contrast the results against your chimney mounted GMRS antenna and perhaps there is some insight to be gained.

When you are operating in the fringe area of a repeater for what ever reason it is fringe, the smallest physical displacement of an antenna can make the difference between whether you receive or do not receive a signal.


Michael
WRHS965
KE8PLM

[Flameout]

Thanks for the tips and replies. The Slim Jim was purchased from N9TAX and has 16' of RG58, with a PL259 connector and that is connected to about 20' of LMR 195 right to the radio (also with PL259). That antenna is working fine on 2 other GMRS repeaters and also simplex. Just thought it was weird that it didn't pick up that one repeater when the indoor Nagoya picks it up great (if it is in the right location in the garage)

The Nagoya has 14' of RG58 and also with a PL259. My only watt meter is a SW-33 and I have that right at the radio. SWR on both antennas is good. Both below 1.5:1 but not sure how good that little meter actually is. 

When on of the roof antennas is being used, the other is not and it is actually not even connected to the radio. Will the close proximity still be a factor? I may try putting the Nagoya outside to see of that helps but I guess I need to find some metal to set it on. When the weather breaks, I'll get back on the roof and take the Slim Jim down for some further testing

[marcspaz]

Along with the power issues Micheal mentioned (causing damage by have the two antennas close), there is a chance you are building a two element vertical UHF beam and don't even realize it.

 

A full wave length of a GMRS signal is about 2 feet (61cm).  If the antennas are 2 feet apart or any correct segment of wave pattern within a couple of wavelengths, the passive vertical will act like a reflector and the slim jim will act like a driver... essentially creating a focused beam that hears better for a pattern 40 to 60 degrees forward and creates nulls (where you can't hear as well if at all) of about 40 to 60 degrees behind it.

 

So yeah, combine the possibility that you are fringe of the repeater making placement critical and you may have accidentally built a beam making it so it can't hear in the direction of the repeater, the terrain may be an issue and you are looking at almost 10 dB of line loss per hundred feet with both the LMR195 and the RG58, I'd say you need to make some changes.

 

Find a sweet spot on the roof using an HT (as mentioned above), ditch the PVC for fiberglass or wood, get 1 piece of LMR400 or better hooked up... you may make it work.

[Flameout]

Ok, the weather is kind of limiting what I can do, but I did buy a Comet CA-712EFC and although I can Rx ok with it, it is still very noisy and nowhere near as clear as the Nagoya that I mentioned above, that is inside my garage, on an old cookie sheet. I just don't get how that indoor mag mount antenna is outperforming the Comet?  I am using a 50' section of ABR Industries RG 8/U Type 50 ohm low loss coax for the Comet. In the photo with the comet, that roof is a metal roof, about 12' x 21', so could that be the problem? As soon as I get a chance, I will move the Comet to my house and away from that metal roof

[marcspaz]

If the antenna is higher than the roof line and at least a few feet away laterally, the roof should not have any impact.  I will say that you may be getting a bit of a shadowing in the garage, reducing the amount of RF noise you are exposing the antenna too and mimicking filtering.  I do this all the time in amateur radio on purpose.  I will use a 7MHz antenna to listen to 3.8MHz signals, because there is much less noise due to not being at the resonant frequency I want to hear.  Also, a higher gain antenna at a hire elevation is going to here more of everything, including noise.

 

It is going to be almost impossible to diagnose over the internet, but I would confirm your VSWR is good and then start looking at filtering the signal with a band-pass filter.

[mbrun]

Ok, the weather is kind of limiting what I can do, but I did buy a Comet CA-712EFC and although I can Rx ok with it, it is still very noisy and nowhere near as clear as the Nagoya that I mentioned above, that is inside my garage, on an old cookie sheet. I just don't get how that indoor mag mount antenna is outperforming the Comet?  I am using a 50' section of ABR Industries RG 8/U Type 50 ohm low loss coax for the Comet. In the photo with the comet, that roof is a metal roof, about 12' x 21', so could that be the problem? As soon as I get a chance, I will move the Comet to my house and away from that metal roof

I don’t believe that the the Nagoya is outperforming the Comet but I certainly acknowledge and accept what you are experiencing. RF is a weird animal.

What experience did you have when you used an HT while up on your roof and communicated with the subject repeater? What experience did you have when using your Nagoya antenna up on the roof at or near the same location as the Comet or the former slim jim?

A quick little story that occurred in the last 7 days. There is a 675 repeater in Wyoming, a suburb north of Cincinnati. It is used for the city-wide GMRS net weekly. I am on the fringe of that repeater and seldom participate because of poor signal quality in and out from my location. It is around 22 miles NW of me. Recently I was scanning the band, including scanning of repeater input frequencies, and suddenly I was listening to one side of a conversation from a guy actively using a different city repeater. Knowing him and what repeater he was on I reached out to him to ask his current location. He was about 3-5 miles further away in the same general direction as that 675 repeater; he was using his 50w mobile radio in the vehicle. I only heard him on input frequency for about a minute. What that suggested to me was that there were fewer obstructions between his antenna and mine for that mile or so stretch of roadway he was traveling than there is between the 675 repeater and me. The point of this being, location can be everything, even when that location is seems counter intuitive.

Since you know what the Nagoya performance is in the garage, what is like when it is located where the Comet is? Same? Better? Worse? Then a logical thing to ask is, what is the Comets performance in the garage when located at the location where the Nagoya works well?

Assuming all else is equal (same radio, same coax, same physical location, same SWR) the Comet should result in a stronger signal into the your radio, and into the repeater from your radio, from most locations where you compare the two antennas against one another. So ask yourself, what is technically different, if anything, other than location?

Isn’t radio fun?


Michael
WRHS965
KE8PLM

[marcspaz]

4 minutes ago, mbrun said:

Isn’t radio fun?

QFT!

[Flameout]

Thanks again for the tips. I'll see what I can do about filtering but might just need to wait for a break in the weather to make some outside adjustments. I never did get a chance to get up on my roof with an HT to try out, but will do that as soon as I possibly can. As for putting the Comet inside my garage, when I first got it, I did try it in here and really wasn't working very well. The antenna is just over 10' in length and my ceiling height is 10'.  Checking the SWR, using a MFJ-847, they are almost identical transmitting on 467.700 - the photos are the SWR on that frequency and on 462.700 both are 1.01 and 1.02

 

Yep, radio is fun!!  I would be much more frustrated without forums like this and help and tips from you guys!

[Flameout]

Just a little update on this antenna fiasco. Using the Comet, I was told my signal is great into the main repeater I was focusing on, but receiving on my end is all but non existent and the Nagoya is just the opposite. It is nothing but noise hitting the repeater, but I can receive from the repeater clear as day

I did notice when swapping out antennas that when I get the so-239 connector from the Comet cable within about an 1/8" of the radio, the receive audio is great, but as soon as I thread it onto the radio, it is garbage again. What does that mean?

[mbrun]

Just a little update on this antenna fiasco. Using the Comet, I was told my signal is great into the main repeater I was focusing on, but receiving on my end is all but non existent and the Nagoya is just the opposite. It is nothing but noise hitting the repeater, but I can receive from the repeater clear as day
I did notice when swapping out antennas that when I get the so-239 connector from the Comet cable within about an 1/8" of the radio, the receive audio is great, but as soon as I thread it onto the radio, it is garbage again. What does that mean?

To me, you are clearly on the fringe of that repeater. Seemingly no RF budget to spare. This means minor things can make the difference between getting into and not getting into the repeater, receiving and not receiving the repeater. I remain curious how things work when you use an HT and when using the Nagoya up on roof.

Moving on. I see a wire running laterally overhead through your yard in the photo. What is that? If that line is emitting some form of RFI, its proximity to your roof antenna could be causing just enough desense on the radio using that antenna. It could also explain the difference between results with antennas located at two different distances away from it.

Even if that wire or any connected electronics are not a noise source, it does have me questioning the presence of other sources of RFI that could be in closer proximity to your outdoor antenna than your antenna in the garage.

If the issue existed at my house some of the things I would be doing would be using a VNA to do more investigation of the antenna system, using the same radio for comparison of different antennas, comparing different antennas at the same physical location using the exact same feed-line, and I would be pulling out the spectrum analyzer to investigate RF background noise conditions in and around the antennal locations that have different Rx characteristics.

Hope there is a little nugget of inspiration in there.


Michael
WRHS965
KE8PLM

[marcspaz]

3 hours ago, Flameout said:

Just a little update on this antenna fiasco. Using the Comet, I was told my signal is great into the main repeater I was focusing on, but receiving on my end is all but non existent and the Nagoya is just the opposite. It is nothing but noise hitting the repeater, but I can receive from the repeater clear as day

I did notice when swapping out antennas that when I get the so-239 connector from the Comet cable within about an 1/8" of the radio, the receive audio is great, but as soon as I thread it onto the radio, it is garbage again. What does that mean?

 

I know the SWR and watt meter may not agree with this statement, but I would try this anyway.

 

Hook-up the Comet, put the tip (center lead) of the connector in the radio, but don't let any of the ground connection or collar touch the back of the radio.  If it hears fine, you need to test your transmission line.  I have experienced your symptoms many times over the years and found that there is a problem with the cable.  Typically a full or partial short circuit in the connector during assembly, but also occasionally in the coax itself. 

 

If you have an ohm meter, look for a short between the coax center and ground both while connected to the antenna and on its own.  Also see if you can find someone with an antenna and coax analyzer.

 

That said, don't discount anything mbrun stated.  That is all good info.  I personally would start with testing the cable so you know you're not chasing a ghost while using his troubleshooting recommendations. 

[Flameout]

Once again, more great tips. Thank you and I really do appreciate it. I learn a little more each day.

  I had a chance to play around a bit today (Still can't get up on the roof yet) and I checked the Comet/cable combo SWR and attached photos and everything seems good. I swapped out the coax anyhow. I lowered down the Comet, re attached the new coax, checked the radio and it was receiving a great signal from that repeater!  Ok, I figured I would go back outside and raise up the antenna another 5'. Did that and the radio was no longer picking up that repeater. I then realized that I needed to twist the antenna so that the 3 short radials were in a very specific position. I put a speaker in my windows, had the radio on loud and the Zello app open on my phone, in my pocket. When I heard anyone talking, I turned the antenna about 30 deg and sure enough it worked and the speaker was blasting audio. Does this make sense?

Oh, that other wire in the photo is my HF dipole antenna which is probably about 15' away. It's supposed to be a bit warmer tomorrow, so maybe I'll get a change to get onto the roof and do some tests

[mbrun]

@Flameout you’re making progress!

Regarding the direction of the radials. I have not experienced to my knowledge, nor read anything material that suggests a horizontal directional component based on radial direction. Does not mean there is not one. However, it is known that the quantity and downward angle of radials does have an effect on both the impedance and the vertical coverage pattern of the antenna.

Do keep in mind that when you see yourself rotating the radials that you are also indeed changing the physical location of the vertical component of the antenna as well, since to rotate the radials you rotate you typically have to rotate the whole assembly around the mast. So you are actually changing two things at once, not just one. While that small amount of movement may seem insignificant, you are working in UHF where the wavelengths are smaller and smaller changes have bigger effect than HF.


Michael
WRHS965
KE8PLM

[Flameout]

I got around to getting up onto the roof today. Took down my 2m/70cm and put the Comet 712 EFC in it's place. Nothing. Couldn't pick up the repeater at all but could hit it when transmitting, but no better than the lower spot that I had it previously mounted. Tried turning and raising it up and down but never once picked up the repeater (I did this all of this while there was traffic on the repeater)

The only time I could Rx was when holding it in my hand, tipped at about a 45 degree angle and kind of pointed in the direction of the repeater but I certainly can't mount it that way. Oh, and the HT didn't work at all either. I may do some more experimenting and will probably move it back to were it was, but would something like a directional Yagi work better?

[marcspaz]

I hate to say it, but sometimes a desired location just doesn't work, regardless of what you do. 

 

As an example, there is a repeater I like to talk on that is 35 miles from my VA home, in a North/North-West direction.  Due to terrain and atmospheric behavior, if I have my antenna smack in the middle of my driveway, I can work the repeater all day with 1 watt, receive full-quiet, and generally have a great path.

 

Well, if I move the exact same antenna, mast, tripod, etc., 2 feet in any direction, I can no longer hear the repeated and can't bring the repeater up, even with a full 50w.  With the antenna mounted on my home's roof, I can hear that repeater and talk on it, but I get poor audio reports and the receive signal is so low that my s-meter doesn't move.

 

It's starting to sound like you may be experiencing a similar issue.  Especially because you said if you hold it at an angle in your hand and point it in the repeater's direction.  It almost sounds like you are using a crude version troposcatter (oddly just discussing in another thread) to overcome whatever is blocking your signal path.

 

It sounds like its just time to pick a new location.

[Flameout]

Yeah, that makes a lot of sense and sure sounds like my situation. I put it back in it's original location and I'm receiving good, but my transmissions are a bit noisy.  I guess for now this will have to do. When warmer weather gets here, I'll experiment a bit more. Thanks again

[Flameout]

Oh, I'm sure you guys are sick of me, but a little update. I was receiving that specific repeater ok using that Wireman CQ-1000 coax, about a 30' run. I was hearing ok, but not great. Sometimes would be real clear than all of a sudden quite noisy, so I figured even better coax would help, so I bought some used Andrew Heliax 1/2" coax off of ebay https://www.ebay.com/itm/403458751305

It was listed at being 23' but was actually 26' so a little bonus. I ran it out to the Comet 712 EFC (That stuff is hard to work with!) Tested the SWR which was great, fired up the radio and it was worse than before. What is weird is I was attaching about a 16" piece of coax to the radio, with PL-259 on each end and all of a sudden the radio was picking up the repeater great, with no antenna. I connected that to the new 1/2" hardline and like magic I could no longer receive the repeater

Seems like if I just use the center of any of the coax and not thread the outer part on, it works but as soon as that outer part make contact, everything drops. I took down that antenna and I'm going to connect it to one of my HT's and just walk around the yard holding it to see if I can find a sweet spot and if that fails, I guess I just give up

[gman1971]

What you are experiencing might be receiver desense. Try adding a 10dB attenuator to the radio see if reception improves. You didn't specify what radio you were using.

G.

[gortex2]

Hooking the shield up should not kill your RX. You said you tested with a watt meter. Did you test at the antenna by chance ? If your receiving without the ground attached (Shield of the antenna) coverage must be ok in that area. Wondering if its actually an antenna issue. 

[Flameout]

I brought the antenna into my garage, attached about a 10' section of RG58AU that was lying around and then connected it to an HT. The repeater was active, so I was about to walk outside with radio/antenna combo when I hit a sweet spot in my garage. This is weird. I have the antenna leaning, from floor to ceiling and my Rx and Tx are great! Just as good or better than any of the 2m/440 repeaters I also use.  I attached a photo of the antenna in it's current position. It's not actually touching the truck and the tip is leaning against something on the ceiling, keeping it from falling. I'll probably leave it just as is is for a few days

So I guess it's nothing to do with coax (to an extent) or the antenna itself and must be with how the UHF wavelengths travel??

[gman1971]

If the antenna is fine, its most likely receiver desense. What radio are you using?

[Flameout]

14 hours ago, gman1971 said:

If the antenna is fine, its most likely receiver desense. What radio are you using?

Icom 2730, a Yaesu FT-70, Wouxun KG-UV9P, Wouxun KG-UV8H and a Wouxun 805G. They all seem to Rx about the same when connected to the Comet. I'm still pretty new at this so don't have much in the way of radios. 

[gman1971]

Can you try a 10dB attenuator on the comet when placed high?

 

G.