Is 10-feet of rg174 the reason why I'm getting a poor signal?

[saioke]

So, I recently bought this yagi - https://www.amazon.com/dp/B00EC804SO?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1 hoping to get a better signal at a p25 site 8-9 miles away than my Tram 1089 mag antenna and I've been disappointed to find that on my SDR, the signal with the yagi aimed at the site is practically the same as it is with my Tram 1089 and this shouldn't be the case, right?

I'm using the same cable on this yagi as I am with the Tram (rg174, 10-feet). But, surely 10 feet of rg174 wouldn't cause such a degradation that this supposedly more powerful yagi aimed at a site would receive the same amount of signal? I know rg174 isn't a good option for higher frequencies but it's not like I'm using 25+ feet of the stuff.

I don't really want to buy a new type of cable if this isn't the issue, but maybe someone with a similar experience can confirm whether or not changing the rg174 to something like lmr240 will make a difference? Any other suggestions on improving the signal would be appreciated too.

 

[mmckenna]

10 feet of RG-174 at 855MHz has about 3dB loss.
3dB loss is half your signal.

Your yagi claims to have 8dBi of gain. That may or may not be accurate, and a Yagi claiming that much gain across that much spectrum may be stretching the truth a bit.

But, yeah, if you are using 10 feet of RG-174 on both antennas, and that little Tram having maybe a few dB of gain on 800MHz, it would seem that a 4 element Yagi should work a bit better.

Keep in mind that not all coax cable is equal, losses can vary from manufacturer to manufacturer. Adapters and extra connectors add a bit of loss.
There might also be issues with the receiver getting overloaded a bit, especially if there is nearby cellular towers.

A simple test would be to take both antennas to a completely different location in range of the same radio site and test again. Might be something local to you.

 

[saioke]

Thanks for your input, I appreciate it! I didn't think such a short run would significantly reduce the gain. So, my tram 1089 supposedly has a gain of 3dbi. Using 10 feet of rg174, wouldn't that mean that the antenna effectively has no gain? If that's the case, then yeah, I should definitely be getting better performance out of the yagi, even if the listing is a bit of a lie. However, testing other sites in the area, they also seem to come in the same as the Tram. So maybe it is cable related. The CC of the site is 774mhz, and the highest voice channel goes up to 858mhz.

The rg174 I'm using isn't even high quality stuff, it's cheap junk that I spent maybe $5 bucks on. So that could also be an issue I suppose. Afaik there's not really a cell tower nearby, but using SDR#, I can indeed see some cell tower stuff going on in the early 700mhz band, and above 870mhz or so. those signals don't appear to be overloading anything even with the gain maxed out so I think I'm good in that department.

I can't really take my setup with me anywhere so I can do some proper testing unfortunately, but I do plan on finding a way to hook an sdr up to my phone sometime. I may just buy some new coax for now and see what happens. Do you think LMR240 would be good enough for 10-15 feet? Amazon seems to have KMR240 and I've heard LMR and KMR are very similar in performance while KMR is cheaper (but a knockoff).

 

[RichardKramer]

Just curious; where do you have your antennas mounted that you are only using 10' of cable. I'm taking a guess that either they are inside a room or just outside a window. If they're inside, positioning them in different areas of the room may give a better or worse signal.
I have a UHF aircraft discone mounted on a 6' pipe and board for a base in the basement by a window with 15' of RG58 cable. I have it there so I can grab it and take it along to the local park where I mount it on a 35' telescoping mast with 75' of RG59 cable.
In the basement I can monitor the pirates on the UHF 245 - 270MHz FM satcom band clear enough to understand what they are saying; but if I move the antenna to either side of the window the signal is barely readable.

 

[saioke]

Just curious; where do you have your antennas mounted that you are only using 10' of cable. I'm taking a guess that either they are inside a room or just outside a window. If they're inside, positioning them in different areas of the room may give a better or worse signal.
I have a UHF aircraft discone mounted on a 6' pipe and board for a base in the basement by a window with 15' of RG58 cable. I have it there so I can grab it and take it along to the local park where I mount it on a 35' telescoping mast with 75' of RG59 cable.
In the basement I can monitor the pirates on the UHF 245 - 270MHz FM satcom band clear enough to understand what they are saying; but if I move the antenna to either side of the window the signal is barely readable.

Currently yes, both antennas are indoors. I had the Tram 1089 mounted to my roof previously, which only took an extra 5 feet or so to pull off. (Extra 5 foot rg174 cable). Indoors I'm just using the 10 foot cable. The Tram wasn't terrible or anything but every time it rained or the humidity was high, or fog, etc, the signal would drop so low that I couldn't pick up a thing. That's the main reason why I got the Yagi, to maybe remedy it a bit. That, and i don't really want to keep a magnetic antenna on my roof especially when winter is coming - that's just asking for rust.
Indoors, the signal isn't quite as good as it is outside but it's doable. I do plan on putting the yagi outside in the same area, so about 15 feet up, but I don't want to do that until I can figure out the cable situation. Indoors, I found the signal sweet spot to be in a closet. For some reason, the signal is much worse if I put the antenna in front of a window.

I do have a lot of rg58 in my garage, I may cut a portion of it and solder some sma connectors together and see if it performs any better before I order anything. Good idea with the discone setup, is it a big discone? I have the Tram 1410 discone set up on my roof for my main scanner but the SDR has replaced it for the most part because the SDR picks up much better, I think because the cable connected to the discone has degraded so much in the weather and frankly my discone is mounted high up, and I've grown a fear of heights so I don't even want to mess with it lol. But discones; those bad boys are particularly amazing for airband. I envy you that you can listen to pirates, I could never pick up anything like that around here.

 

[RichardKramer]

Thanks for your reply. Yes, indoor antennas can be a challenge. My radio shack is in the basement; I have a sweet spot to rx the Allentown wx on 162.4 here in the shack which lets me try different ducks for best rx. The discone is a bit smaller than the Radio Shack discone; it's actually a shipboard discone I bought from a friend. It's an AS-390/SRC; I also have the AT-197A/GR UHF military discone.
Glad to hear you found a good spot in the closet!!! If you would like to see what my UHF antennas look like; here is a link:

AS-390A/SRC - Shipboard Communication Antenna - RAMI

The AS-390A/SRC is an antenna designed for shipboard application operating at 225-400 MHz. RAMI is a leading antenna supplier for the US military.

www.rami.com

 

[saioke]

Thanks for your reply. Yes, indoor antennas can be a challenge. My radio shack is in the basement; I have a sweet spot to rx the Allentown wx on 162.4 here in the shack which lets me try different ducks for best rx. The discone is a bit smaller than the Radio Shack discone; it's actually a shipboard discone I bought from a friend. It's an AS-390/SRC; I also have the AT-197A/GR UHF military discone.
Glad to hear you found a good spot in the closet!!! If you would like to see what my UHF antennas look like; here is a link:

AS-390A/SRC - Shipboard Communication Antenna - RAMI

The AS-390A/SRC is an antenna designed for shipboard application operating at 225-400 MHz. RAMI is a leading antenna supplier for the US military.

www.rami.com

I was going to say, lugging around a discone the size of the Tram 1410 or a Diamond wouldn't be easy unless you disassemble it completely each time. That looks much more manageable. Never seen one quite like that.

Allentown, PA? I have family out in that direction. About an 8 hour drive. Crazy you can pick up even pirates in your area! In my area, I don't even hear any chatter other than a local ham net every Sunday at 147.105 but they only talk about their dinner. Can pick up plenty of chatter at 40/80meters with a MLA-30 antenna though.

 

[Echo4Thirty]

Thanks for your input, I appreciate it! I didn't think such a short run would significantly reduce the gain. So, my tram 1089 supposedly has a gain of 3dbi. Using 10 feet of rg174, wouldn't that mean that the antenna effectively has no gain? If that's the case, then yeah, I should definitely be getting better performance out of the yagi, even if the listing is a bit of a lie. However, testing other sites in the area, they also seem to come in the same as the Tram. So maybe it is cable related. The CC of the site is 774mhz, and the highest voice channel goes up to 858mhz.

The rg174 I'm using isn't even high quality stuff, it's cheap junk that I spent maybe $5 bucks on. So that could also be an issue I suppose. Afaik there's not really a cell tower nearby, but using SDR#, I can indeed see some cell tower stuff going on in the early 700mhz band, and above 870mhz or so. those signals don't appear to be overloading anything even with the gain maxed out so I think I'm good in that department.

I can't really take my setup with me anywhere so I can do some proper testing unfortunately, but I do plan on finding a way to hook an sdr up to my phone sometime. I may just buy some new coax for now and see what happens. Do you think LMR240 would be good enough for 10-15 feet? Amazon seems to have KMR240 and I've heard LMR and KMR are very similar in performance while KMR is cheaper (but a knockoff).

3dbi is referenced to a non-existant isotropic antenna and is higher "gain" than if it were referenced to an industry standard dipole. Typically isotropic is 2.15 dB higher than the dipole, so in reality your antennna is only gaining .85 db over a dipole or .85 dBd. Minus your feedline loss of 3db, your effective system gain (or loss in this case) is actually -2.5 db. In other words, the antenna is doing little to overcome the half signal loss you are experiencing due to the feedline. I also would question where they came up with 3dBi for a 4 el yagi. Something doest jive.

Manufacturers of antennas love to rate their stuff in dBi as it makes the numbers bigger and more appealing to marketing.

Upgrade your feedline and get that DB loss as low as possible. Also make sure your yagi really is pointing at the site.

 

[unitdelta]

You might have already done this, but use a multimeter and check “center to center for good continuity (also with wiggling the cable near the connectors) as well as center to ground, on each end of cable, while wiggling cable near the connectors. This might show a potential fault once the cable is installed.

 

[mmckenna]

RG-174 is pretty poor coax, even if you have good stuff. The only benefit is that it routes easily for temporary mag mount type installs. I don't think I've ever used it, and wouldn't intentionally use it.

RG-58 is going to be an improvement. Depending on exactly which RG-58 you have, which manufacturer, and how well you install the connectors, you may see about half the amount of loss compared to the 174.
If it's free and easy, give it a try.

The LMR-240 would be an improvement over the RG-58. I've never used the KMR stuff. For a short 15 foot run, the cost savings is probably minimal compared to the true Times Microwave LMR-240.

Getting the Yagi outside with better coax would be a good idea. Just make sure you properly waterproof your outdoor connections. Rain/fog should not impact performance greatly, and if you were seeing that with the Tram, something else is wrong.

 

[saioke]

RG-174 is pretty poor coax, even if you have good stuff. The only benefit is that it routes easily for temporary mag mount type installs. I don't think I've ever used it, and wouldn't intentionally use it.

RG-58 is going to be an improvement. Depending on exactly which RG-58 you have, which manufacturer, and how well you install the connectors, you may see about half the amount of loss compared to the 174.
If it's free and easy, give it a try.

The LMR-240 would be an improvement over the RG-58. I've never used the KMR stuff. For a short 15 foot run, the cost savings is probably minimal compared to the true Times Microwave LMR-240.

Getting the Yagi outside with better coax would be a good idea. Just make sure you properly waterproof your outdoor connections. Rain/fog should not impact performance greatly, and if you were seeing that with the Tram, something else is wrong.

You're right. I managed to cut about 6 feet of rg58 earlier and solder some sma connectors to it, and wow. The signal on the yagi is much better. Before, I had to run the gain on the SDR maxed at 49 and the signal was still weak. Now, it's at 42/43 without showing errors. It's not raining anymore but I've never seen the signal appear so strong, and this is still all indoors. If LMR240 will be more improvement, I may pick some up. This pretty much confirms the issue was poor coax. Can't believe coax would make such a big difference!

But yeah, rain always seemed to affect the Tram. I thought I waterproofed the connection to the roof pretty well by adding Vaseline to the connector and taping it all up with black tape, but I didn't waterproof where the antenna screws onto the base of the magnet, and maybe that's where it went wrong.

But, I also think the p25 site has issues in the weather because I find much of the traffic swaps over to a different nearby site whenever it rains. I've been told that the site isn't in an optimal location and isn't even on the peak of the tower like it should be, and is supposedly facing a different direction than the city for some reason.

 

[mmckenna]

You're right. I managed to cut about 6 feet of rg58 earlier and solder some sma connectors to it, and wow. The signal on the yagi is much better. Before, I had to run the gain on the SDR maxed at 49 and the signal was still weak. Now, it's at 42/43 without showing errors. It's not raining anymore but I've never seen the signal appear so strong, and this is still all indoors. If LMR240 will be more improvement, I may pick some up. This pretty much confirms the issue was poor coax. Can't believe coax would make such a big difference!

Coax can make a big difference in some cases. RG-174 is pretty bad. Like I said, its usefulness is pretty much for cheap mag mount antennas and allowing the coax to pass through weatherstripping. That, and maybe some short internal jumper type use. I'd never rely on it for anything.

As you found, just about anything is an improvement over 174.

RG-58 would be fine for a run of 15 feet if that's what you need to get your antenna outside. I run a lot of 800MHz gear at work and all the mobile antenna installations come with 17 feet of RG-58. I trim to length, but not uncommon for some installs to have 15 feet of coax and the radios work just fine. If the signal is strong and you are not showing any decode errors, throwing more coax at it isn't going to make a difference.

But yeah, rain always seemed to affect the Tram. I thought I waterproofed the connection to the roof pretty well by adding Vaseline to the connector and taping it all up with black tape, but I didn't waterproof where the antenna screws onto the base of the magnet, and maybe that's where it went wrong.

Rain should not impact a mobile antenna.

 

[saioke]

Just wanted to share these here:

This is rg58 with the yagi


And this is the rg174 with the yagi
Doesn't look like much visually but the difference is night and day. I see far less errors with the rg58 and I have the gain set to 43.4, instead of maxed at 49.6. I can drop the gain to 42 but I see an error pop every few seconds so I think 43 is the sweet spot, though I still see occasional errors whenever someone talks on say, a VC at 852mhz. Still, quite an improvement when the same VC frequency would likely error out completely on the Tram.

Sticking to rg58 may be what I will do, but I need to get some proper sma connectors before I even attempt to run it outside. Probably not good to cut the ends of an sma connector and just solder the wire ends to the rg58 like I did lol. Doing it that way, it's still using maybe less than a foot of rg174 running into the SDR.

As for the rain, yeah, I would think a mobile antenna was designed for the elements, but who knows. It's possible I could've gotten a defective antenna. I mean, the Tram 1089 isn't even that expensive, think I paid $15 for it. I don't see any rain in the forecast for the next couple of weeks but, whenever it rains again I will update about the performance of the yagi to see if it still craps out at the site. If it does, I'm pretty sure there's a major issue at that site.

Anyway, thanks again for the help!

 

[Ubbe]

The coax loss tables show 3dB loss for each 10ft of RG174 at 900MHz and RG58 1,5dB
RG174 are really only suitable for jumper cables. I use 2ft of RG174 cables to connect my scanners to splitters and 1ft between amplifier and splitter and filters and so on.

If you have an antenna below the tree tops then when it rains or even dense fog those trees will work as a RF shield, so it makes sense that your reception then gets worse. You will need to receive signals above the tree line to have less effect from rain. I actually get improved reception when it rains as the raindrops reflects the RF signal down to my place in a valley. The same happens if an airplane pass nearby.

/Ubbe

 

[saioke]

The coax loss tables show 3dB loss for each 10ft of RG174 at 900MHz and RG58 1,5dB
RG174 are really only suitable for jumper cables. I use 2ft of RG174 cables to connect my scanners to splitters and 1ft between amplifier and splitter and filters and so on.

If you have an antenna below the tree tops then when it rains or even dense fog those trees will work as a RF shield, so it makes sense that your reception then gets worse. You will need to receive signals above the tree line to have less effect from rain. I actually get improved reception when it rains as the raindrops reflects the RF signal down to my place in a valley. The same happens if an airplane pass nearby.

/Ubbe

1.5DB is still a significant drop isn't it? So maybe it would be best to go for LMR240. Couldn't imagine using LMR400 on such a short run anyways. You mentioned splitters, guessing you run a multicoupler to avoid further signal loss? I was looking into them to split my antenna for two separate devices but they're quite expensive and it would be cheaper just to buy another antenna for what I'd use it for lol.

Unfortunately yeah, there's trees everywhere; many surrounding a lake in a valley about 2-3 miles away that I have the yagi pointed towards. Also, a cemetery on a hill. There's tons of elevation all around and I could never hope to even get it above the tree lines - would probably have to be about 300-400 feet up.

I fly a DJI drone occasionally and in my area, my drone can't even really hit a mile in any direction before it will start to lose signal. It's fine whenever I'm in a open area without much interference. I took aerial photos of the graveyard area and all the trees I have to practically go through to hit the tower last fall. 400 feet up, still no p25 tower in sight. Elevation doesn't look as bad as it is in the air.

 

[mmckenna]

1.5DB is still a significant drop isn't it?

Depends on the application.

I run an 800MHz system and use RG-58 on mobile antenna installations. Not uncommon to have 10-12 feet of coax in a vehicle to connect an 800MHz antenna to the mobile radio. The overall system design supports that.

So maybe it would be best to go for LMR240. Couldn't imagine using LMR400 on such a short run anyways.

Loss for 15 feet of cable at 855MHz:
RG-174 = 4.5dB
RG-58 = 2dB
LMR-240 = 1.1dB
LMR-400 = 0.6dB

There is a couple of things to look at here...

Your RG-174 performed poorly.
Switching to RG-58 gave you a strong enough signal to the receiver to get excellent decoding.

LMR-240 isn't going to improve performance in the eyes of your receiver. If you are already getting good decoding from RG-58, LMR-240 isn't going to help for listening to that specific system.
It won't hurt, but you'll be adding a bit of cost with likely zero noticeable improvement in performance.

LMR-400 is overkill. Like the 240, you won't notice a difference if the RG-58 is providing a good signal.
LMR-400 is also quite stiff and difficult to route in a residential installation. It's about 1/2" diameter and will require a large hole to get inside. It's going to add cost.
Due to it's stiffness, it's not something you'd want to connect directly to an SDR that's plugged directly into your computer. You'd damage the antenna connector or USB port. You'd either need to add a short jumper of more flexible cable to take the strain off (now were back to higher loss cable) or you'd need to add a USB cable.

Added cost, more hassle, and if you are already getting good decode with RG-58, wasted money.

If you were running an omnidirectional antenna and trying to hear radio traffic from all over, and you had your antenna up much higher, LMR-400 might make more sense. But, from what you are saying and how you are using it, it's not going to improve anything.

Your money, your choice, but I think you'll not see payback on increasing the cable to LMR400.

You mentioned splitters, guessing you run a multicoupler to avoid further signal loss? I was looking into them to split my antenna for two separate devices but they're quite expensive and it would be cheaper just to buy another antenna for what I'd use it for lol.

Passive splitters introduce at least 3dB of loss.
You'd want an active splitter that would add amplification to overcome that loss.

For such a short run of cable and the low cost of the antenna, you would be saving money by going with a second antenna and second coax run.

Unfortunately yeah, there's trees everywhere; many surrounding a lake in a valley about 2-3 miles away that I have the yagi pointed towards. Also, a cemetery on a hill. There's tons of elevation all around and I could never hope to even get it above the tree lines - would probably have to be about 300-400 feet up.

Wet foliage will attenuate RF. That's different than rain getting on your antenna.
But it's not a brick wall that's going to block all RF.

Depending on where you are in relation to the system you are trying to listen to, this may not be an issue.
Public safety radio systems are very carefully designed to provide suitable radio coverage to it's users. That often means hand held radio worn on the hip providing useable coverage throughout the jurisdiction regardless of weather.
If you are inside the jurisdiction covered by this radio system, you should do just fine with an outdoor antenna pointed at the tower site.

Don't get hung up on Decibel numbers. Don't over engineer this. It really sounds like the RG-58 with the external antenna will work just fine. If you want to go up a notch, the LMR-240 would be an option. I would not recommend LMR-400.