Moved antenna higher, receive seems worse

[bkspear]

All,
I have a dual band Diamond x50 antenna I originally had mounted on the side of my house. This weekend I installed an roof eave mount and mast to raise the antenna so it is alot higher than it was before. I thought this would improve my reception, but I seem to have worse reception on a couple stations than before. I am using the same cable and radio. Any ideas? Thanks.

 

[suwanneecomm]

depending on where you are located the best i could come up with is possibly being in a rf shadow (think mountain / building) now by changing elevation..maybe??

 

[byndhlptom]

poor reception

disconnecting, moving, and reconnecting cable damaged/comprimised the cable or connector(s)......

moving antenna damaged it (check swr).....

moving antenna moved it closer to a rf noise source......

$.02

 

[wb6uqa]

I had a 2 meter beam and every 10 feet higher was a new world.

 

[bkspear]

Thanks for all the replies so far. I'll try to address some of them. I did not even have to disconnect and reconnect my coax to the antenna. The existing cable was long enough so I removed the antenna from where it was attached , leaving it connected, then attached the antenna to a mast post, then raised it up on the roof eave mount. It is now 15-20 ft higher than it was before, which now pretty clears my roof line and chimney. I guess its possible the antenna is now in a "noise" spot, but how would I test for this? Would a SWR meter show me this? Does SWR matter on just receiving and not transmitting? Thanks.

 

[wyShack]

Another possibility is that the higher antenna is dealing with more interference from other things. Your antenna may now 'see' a high powered paging transmitter and AGC back the gain. this is often an issue with people who monitor aviation communications when their receive antenna 'get a whiff' of a nearby FM radio transmitter. -the AGC (automatic gain circuit) usually is everything in the RF pass band -not just the frequency tuned to. Today's wide band receivers are more susceptible to this than older radios which tended to have a tighter 'front end'. Handhelds often show this as they are designed to be used with the 'rubber duck' and not a antenna up and out in the clear.

If you have a switchable preamplifier or Attenuator, you may want to try different settings-in today's world selectivity more often than sensitivity determines ability to receive. Maximum signal to noise ratio is often not at the point of max gain.

73

 

[ab3a]

Check your transmission line from the antenna to your receiver. Make sure that when you remove it from the antenna that it's not shorted. Short out the far end of the cable and make sure that you read a reasonably low resistance through the cable. Then, make sure it is not kinked somewhere. This is especially the case some of the lower loss cables such as Belden 9913.

By the way, if you're using cheap coax such as RG-58 or RG-8X for distances longer than 50 feet, please stop. Change it out for something better. No, Really! It will make a very significant difference.

You might even want to get your hands on a watt meter and a dummy load. put the watt-meter between the radio and the terminated transmission line. Measure how much power you're putting in. Then take that watt meter and go to the far end of the cable, and measure between there and the dummy load. You will see a lower number commensurate with the amount of loss your transmission line has.

Next, take the dummy load off and measure how much reflected power your antenna has Right At the Antenna. This will tell you exactly how bad the antenna return loss is.

The problem is that, particularly at UHF frequencies, you can measure return loss at your radio and it will look good. What you may not realize is that your transmission line has losses too and you're measuring through those losses. In extreme cases, you could even have a dead short at he end of the line and you might not see much reflected power.

Finally, did you reinstall that connector shield properly at the base of the antenna? Did you seal that connector properly? Water gets in to antenna connectors in really subtle ways. You have to protect that connector and keep it dry.

Do all those things and I'm sure your antenna will give you years of good performance.

 

[popnokick]

Good advice from ab3a. You need to thoroughly check out the coax and connectors before you start chasing whether or not you moved into a "dead spot" or high interference area with the antenna. Another thought: You can very inexpensively acquire a simple spectrum analyzer / receiver; for about $25-35 including pigtail coax adapter you can buy a USB RTL-SDR stick receiver. And you will not need a transmitter or SWR meter for any of this. Install one of the free software programs on your laptop that turns the USB RTL-SDR stick into a VHF/UHF wideband receiver with waterfall display (HDSDR, SDR#, etc.) and plug it into your laptop. Connect to the end of the coax that is in the house. Take note of noise levels, signal levels, and take screen shots. Now head up to the roof with a good quality (9913, LMR400, etc.) short coax jumper and your laptop with the RTL-SDR setup. Disconnect the long coax from the rooftop antenna and replace it with the shorter coax jumper to your SDR laptop receiver. Launch the SDR software and take the same readings on the same channels and bands you did when in the house. Are the signal and noise levels for what you want to hear better, the same, or worse? If much better, then you likely have a coax problem in that long run - whether type of cable, connectors, moisture, short/open, etc. Are signals & noise levels about the same? Then probably not your coax, and you can start investigating the (possibly) high noise levels that you'll be able to see in the waterfall on the SDR software.

 

[bkspear]

Some more things to note. I am re-using the same coax before I raised the antenna, along with the same radio. I do have a rtl-sdr dongle and I'll connect it to the antenna to see if I can receive the stations that I was able to before the antenna move. Thanks!

 

[WA8ZTZ]

Assuming that nothing got damaged during the move, check several things:

Did the noise level increase after the move? If so, you moved closer to a noise source. Sometimes power line related but at VHF/UHF more likely rf from TV antenna or cable.

You may be experiencing desens from a strong nearby station (not necessarily in the same frequency range as your RX, think FM broadcast station). This can be tough to track down without a spectrum analyzer.

You may be in a shadow of something, try moving the antenna several feet and see what happens.

Just be absolutely certain your coax and antenna are healthy before you go off chasing ghosts.

 

[majoco]

old mast grounded, new mast not?

 

[KevinC]

Maybe I missed it...what radio is this antenna attached to?

 

[wb6uqa]

The best way to listen for noise is a AM receiver. Fm blocks noise. On VHF and UHF get the best coax you can afford . Keep antenna away from other metal. Check SWR.

 

[bkspear]

Some more info for the replies. This is a new mast/pole that I havent used before, but, I am reusing the same antenna and cable, never disconnected the cable for the install. I am using the same radio as before, Baofeng. I will attempt to attach a photo of the mount and pole with the antenna attached. I will be fixing the cable that is currently hanging down. Another thing I found is connecting the coax to my RTL-SDR dongle and running SDR# software, if I turn up the gain I can receive the frequencies that I was able to before. Without the gain, the noise floor is around -50-60 and too weak too receive the stations. Thanks!

 

[Ronaldski]

These are for scanners but look at tips 2,3,4,7 and especially 11
Reception FAQ's

 

[mmckenna]

Some more info for the replies. This is a new mast/pole that I havent used before, but, I am reusing the same antenna and cable, never disconnected the cable for the install. I am using the same radio as before, Baofeng. I will attempt to attach a photo of the mount and pole with the antenna attached. I will be fixing the cable that is currently hanging down. Another thing I found is connecting the coax to my RTL-SDR dongle and running SDR# software, if I turn up the gain I can receive the frequencies that I was able to before. Without the gain, the noise floor is around -50-60 and too weak too receive the stations. Thanks!

Looking at that photo I'd be willing to bet that the additional strain on the coax from being hung like that is your likely source of trouble.
RF connectors are not designed to be "load bearing" like that. While it may not seem like much, the crimp on connectors (or even a poorly soldered connector) will separate under the strain. Could be the physical movement of being raised/moved around caused it to fail.

I'd pull the coax cable down and check it completely, maybe even consider replacing it. When you reinstall it, make sure there is good strain relief.

 

[chief21]

I am using the same radio as before, Baofeng.

That might be the biggest issue. Generally speaking, Baofeng receivers are VERY sensitive, but not terribly selective, and do not necessarily do well on larger antennas. By raising your antenna, you might be inadvertently overloading the receiver in the Baofeng. If you have (or can borrow) a different radio (preferably one with a tighter front end - a mobile, perhaps), connect it to the antenna and see what the difference might be.

John AC4JK

 

[WA8ZTZ]

You have received some good tips... my guess at this point would be overload/desens or, judging from the pic, bad coax connector at the antenna due to too much strain on the connector from the weight of the coax.

btw, looks like the mast may not be grounded, you need to ground the mast for lightning protection
(it may also help receive as it will drain static off of the mast/antenna)

 

[robertmac]

In the classes you took for your ham license, did they discuss proper antenna installation? Has it rained since you raised the antenna. Did you notice any change before after it rained?

 

[wb6uqa]

Tape coax to mast. Hanging coax puts a lot of stress on connection.