Antenna Issues- Confusing performance

[WRED210]

I have a confusing antenna issue. I've been listening to the Midwest regional net with a 5w handheld. I can pick it up with a nagoya whip on the handheld and even better with a mag mount antenna stuck up on the steel roof of my covered patio. I tried the same antenna on a pie pan mounted on a pole about 10 feet above the same steel roof, and nothing what so ever. Any idea why the same antenna on a pole in the same location would not allow reception?

[BoxCar]

Need a bigger pie pan as that is your ground plane. A small cookie sheet or pizza pan would be better. Ace Hardware sells small sheets of steel and you need one about 12" or more per side.

[WRED210]

It was actually a pizza pan, but a small one.  There is maybe only 5-6 inches surrounding the antenna. I also tried fiberglass antenna that is not "supposed" to need a ground plane.  Would an antenna like that still benefit from a ground plane even if they dsay it isn't necessary?

[KAF6045]

3 hours ago, WRED210 said:

It was actually a pizza pan, but a small one.  There is maybe only 5-6 inches surrounding the antenna. I also tried fiberglass antenna that is not "supposed" to need a ground plane.  Would an antenna like that still benefit from a ground plane even if they dsay it isn't necessary?

If it is a 1/2wave (dipole of some sort) you actually want to get it AWAY from the ground(plane) as ground reflections will affect the radiation pattern (sending some of your signal upwards rather than sideways).

The steel roof may also be a factor -- as it may look like an elevated "real" ground, like a steep mound on average terrain.

 

[WRED210]

Well.... I mounted the fiberglass 1/2 wave on a mast about 23 high (about 10 ft above garage roof), and not near that steel covered patio... and get zero reception. It tries to break squelch, but I hear nothing. The nagoya whip on the same HT gets some reception.  Could it be that this cheap amazon antenna is just junk?

[SteveShannon]

7 minutes ago, WRED210 said:

Well.... I mounted the fiberglass 1/2 wave on a mast about 23 high (about 10 ft above garage roof), and not near that steel covered patio... and get zero reception. It tries to break squelch, but I hear nothing. The nagoya whip on the same HT gets some reception.  Could it be that this cheap amazon antenna is just junk?

Try different things to see what works. For instance, put it near the steel patio roof. 

 

[WRED210]

Could it be the 35 ft of cheap rg58 coax?  Would that cause enough loss to lose reception?

[SteveShannon]

2 minutes ago, WRED210 said:

Could it be the 35 ft of cheap rg58 coax?  Would that cause enough loss to lose reception?

If there’s actually something wrong with it, such as a short between the center conductor and the shield, yes. Or if the center conductor is broken or disconnected from the radio or antenna. 
Those kinds of problems can be present in the antenna as well. 
Try a different cable. 
 

[WRED210]

I'll try a different cable and a shorter run of the same kind and see if that makes a difference.  Thanks for your input.

[SteveShannon]

6 minutes ago, WRED210 said:

I'll try a different cable and a shorter run of the same kind and see if that makes a difference.  Thanks for your input.

You really can rule out almost everything by swapping things out. It’s a quick and easy way to troubleshoot. 

[KAF6045]

1 hour ago, WRED210 said:

Could it be the 35 ft of cheap rg58 coax?  Would that cause enough loss to lose reception?

OUCH... 10dB loss per 100ft at 450MHz... Over 3dB for 35ft, not counting any losses at connectors.

How borderline are those attempted stations? If they are only a few s-units to begin with, you may have enough attenuation to fall below the receiver threshold. Don't think I'd use RG58 for anything over 10ft (automotive routing), and even then I'd probably limit it to <100MHz (ie: HF and 6m).

[WRED210]

Yeah, I thought I'd give the set up a try with what I had,  before I spent money on good cable.  I think we may have found the problem.

[KAF6045]

18 minutes ago, WRED210 said:

Yeah, I thought I'd give the set up a try with what I had,  before I spent money on good cable.  I think we may have found the problem.

An antenna analyzer would be a good thing to have -- many can test for open/short conditions in a cable (and, given velocity factor, may even be able to measure distance to fault [though that is frequency dependent as they calculate based upon phase -- one cycle of a wavelength; for a 35ft cable, that may mean testing at 7MHz).

However, most of those are in the >$200 range, which is more than a 50ft length of decent coax would cost (presuming common connectors at both ends -- the coax I bought for my 2m/70cm antenna ran $200 or so for 70ft, half of the cost was PL259 at one end and N-connector at the other [my window pass through has an N connector -- the 2ft jumper from window to radio with N->PL259 was near $90!]).

A nanoVNA v2 is a bit cheaper (the v1 is no longer sold by the originator, but there are many clones of it with questionable quality).

[SteveShannon]

I was wrong to focus on problems like shorts or opens.  KAF6045 is correct. With RG58 you lose half of your power every thirty feet.  Sometimes you can up for that by placing a decent quality antenna up in the air, but with a bad antenna, a bad cable, or a weak signal lack of quality will really bite you.

Borrowing a VNA from someone can tell you if you have the kind of problem I was overly fixated on before (opens and shorts), but won’t tell you if your antenna has lousy performance.  

If an HT with a Nagoya has good performance but an antenna up in the air doesn’t you have every right to be suspicious of both the antenna and the cable.  I’ll include a link to a website with performance charts for various cables.  Be sure to look at the frequency you’re using.  The closest frequency will probably be 450 MHz.  Because GMRS is slightly higher, the losses through cable at GMRS frequencies will be even worse, but not a lot.  Every 3dB loss means half of the remaining power, so 10.6 dB loss costs about 90% of the power.  That’s for 100 feet.  At 35 feet you lose over 3.7 dB so you probably lose 55% of the signal each direction. That’s substantial and enough to make it difficult to know if the antenna works or not.  Of course everything adds up. It helps to start with something you know works and then try one thing at a time to see where you can get some improvements.

Coax losses site I mentioned: https://www.w4rp.com/ref/coax.html

[WRED210]

I'm pretty new to this radio stuff (just using HT's on Jeep runs) so I didn't realize the losses would be so significant. I am trying to consistently reach a repeater around 35+ miles away. I was able to make a brief contact via the HT and Nagoya, so I figured I'd try and get another antenna up higher with the cable I had. I'll get some LMR-400 cable and elimate that from the equation. I've got a 20w radio arriving Friday, so I'll start over with new cable and go from there. Thank you both for your input and advice. It is very much appreciated.