VHF/UHF radio and antenna questions

[mmckenna]

To imagine gain think of it like a ballon sitting on a table. It’s pretty much round. Now push it down against the table with your hand and you see that it spreads out to the sides. That’s pretty much what gain does. Sometime that’s helpful, like when talking simplex across a flat desert. Sometimes it’s not helpful, like when trying to get into a repeater that is significantly higher than you are. I’ve found that something in the middle is usually the most practical.

That's an excellent visual example of how this works. I'm going to steal that for future use….

 

[ladn]

That's an excellent visual example of how this works. I'm going to steal that for future use….

Agreed, it's pretty evocative.

 

[K6GBW]

Evocative? Okay...I'll take that. I'm usually called something else!

 

[KY_Ham_64]

I was reading on the amateur radio part of Reddit about insulating connections, and some like to first put a layer of electrical tape over the connection, then the amalgamating tape, then another layer of electrical tape or two on top of that. Why would they do it that way? Is it because the amalgamating tape sticks too much to the cable and is hard to get off if it needs to be removed?

 

[K6GBW]

I was reading on the amateur radio part of Reddit about insulating connections, and some like to first put a layer of electrical tape over the connection, then the amalgamating tape, then another layer of electrical tape or two on top of that. Why would they do it that way? Is it because the amalgamating tape sticks too much to the cable and is hard to get off if it needs to be removed?

They do that because some brands of amalgamating tape leave a nasty gooey residue that is a nightmare to clean off, so the put the vinyl tape on to prevent that. The Coax Seal brand tape doesn't leave a gooey mess, that's one of the reasons I like it. It's easy to work with and as long as I've been using it, I've never had it fail on me. The vinyl tape on top is really just to weather protect the sealing tape.

 

[KY_Ham_64]

amalgamating tape

Is that this mastic tape I've read about?

I picked up some Temflex and Scotch 33+ yesterday at Lowe's, I'll be doing my tape up job when I get home.

Also what is this drip loop I hear about? Is that a loop in the cable when it comes off the antenna connection?

 

[mmckenna]

The tape on the connector first does make removal easier. On the commercial side, that's not always done as the process is to test before sealing and then it's rarely/never touched again. On the hobby side, swapping/reconfiguring antennas is more common, so ease of disassembly makes a lot of sense.

The Telewave document I linked to above is the way it's usually done on the commercial side. I think I said that I've taken down antennas that had been up since the early 1990's and the connectors all looked like new.

There's also some silicone based sealing tapes that are a bit easier to deal with. I've used that a few times, but it's only been over the last few years, so no idea what it'll look like in another 30 years.

The drip loop just gives the water a low point to drip off of so it doesn't follow the cable into the house/equipment. Pretty common to see this on telephone/cable TV installations outside the home. The cable will dip down below the hole, and then back up and into the house. That low point lets any water that follows the path drip off.

 

[mmckenna]

Here's said antenna from the early 90's. Installed by Motorola using the butyl rubber tape with nothing underneath. Perfectly sealed after 30 years, but a pain in the buttinsky to remove:

 

[KY_Ham_64]

Well, I got the connections all taped up on the X200, and mounted it to the 19' pole, and ran the cable in thru the nearest window to the radio. In the past I wasn't able to reach the Flemingsburg repeater which is only 20 miles from here but with about a 150' hill to our immediate west, that made contact near impossible. Well now not only can I hit it, I got a signal report on it. Reports on other reachable repeaters were stronger than before as well. So the pole obviously made the difference. SWR is still close to 1:1 on both bands.

Something my wife brought up I thought interesting. Right now the trees don't have their leaves on them yet, that usually is done by mid May. So I'm wondering if my results will get worse then. We don't get cell service here hardly at all. In the past we could only get a few texts, but nothing else, and that was only in the cold season without leaves on the trees. I know a cell signal is at a higher frequency, but I do wonder what will happen to VHF and UHF performance after May.

Here are a few pics of my setup. This will not be permanent but I just wanted to see how it performed.

 

[mmckenna]

Something my wife brought up I thought interesting. Right now the trees don't have their leaves on them yet, that usually is done by mid May. So I'm wondering if my results will get worse then. We don't get cell service here hardly at all. In the past we could only get a few texts, but nothing else, and that was only in the cold season without leaves on the trees. I know a cell signal is at a higher frequency, but I do wonder what will happen to VHF and UHF performance after May.

That can be an issue, but it really depends on a number of variables.

Frequency/wavelength. If the radio wave is similar to the length of the pine needle/leaves, especially when wet, then it can absorb some of the RF. Which shows the other variable:

Type of tree. Longer pine needles, when wet, can impact UHF to an extent. Shorter can impact 800MHz/Cellular. So, it really depends on your location, trees, frequency.

Usually VHF is not impacted significantly, and one of the reasons it's happy in forest service/wild land fire fighting use. Less attenuation, better in rolling hills.

So, sure, you may see some degradation in performance as the trees fill out, or if your antenna is above most of them, then not so much.

Here are a few pics of my setup. This will not be permanent but I just wanted to see how it performed.

Looks like a nice location.

When you do make it permanent, make sure you support the coax well along the mast. The weight of the coax constantly pulling on the connector is a common failure point.

 

[KY_Ham_64]

Ok thanks. I looked up the frequency of cell signals and it said around 700M-2GHz, so it may not matter as much in VHF but UHF might have some issues.

Will the metal of the pole mess with reception or transmission? Like creating some kind of parallel conductor inductive issue? Probably not the right way to state it, but the question remains.

Yeah, I think doing a loop just under the antenna connection point then tying it to the pole would help take off the stress at that point. I have some UV resistant tie wraps that I plan on using for this job.

Yes, it's very nice here, things are just starting to green up here. I have several fruit trees and some are starting to bloom, probably not a good thing in March but after the long cold winter we had, the trees are looking for any bit of warmth to bloom. Grass is starting to grow along with the wild onions. We put out some onion sets today, actually.

Anyways, skies open up more to the N-NE and SW because of the hills. I can reach a repeater north of Portsmouth, OH, which is at least 35 miles, but have trouble hitting one 20 miles west because of the hill directly behind us.

 

[mmckenna]

Ok thanks. I looked up the frequency of cell signals and it said around 700M-2GHz, so it may not matter as much in VHF but UHF might have some issues.

Will the metal of the pole mess with reception or transmission? Like creating some kind of parallel conductor inductive issue? Probably not the right way to state it, but the question remains.

No. the antenna is designed to be mounted on a mast like that.

Yeah, I think doing a loop just under the antenna connection point then tying it to the pole would help take off the stress at that point. I have some UV resistant tie wraps that I plan on using for this job.

Perfect. Loop isn't necessary, but won't hurt.
And you'd be surprised how many people don't know what a UV resistant tie wrap is, or why they should use them.

Yes, it's very nice here, things are just starting to green up here. I have several fruit trees and some are starting to bloom, probably not a good thing in March but after the long cold winter we had, the trees are looking for any bit of warmth to bloom. Grass is starting to grow along with the wild onions. We put out some onion sets today, actually.

I was at a conference at University of Cincinnati a few years back and flew out of the airport there in Kentucky. I had a few hours to spare and kind of cruised down south further into the state and it was quite beautiful.

Anyways, skies open up more to the N-NE and SW because of the hills. I can reach a repeater north of Portsmouth, OH, which is at least 35 miles, but have trouble hitting one 20 miles west because of the hill directly behind us.

Yeah, not much you can do about that, other than installing a really high tower, but that's a lot of work and money for one repeater.

 

[KY_Ham_64]

We had overcast/rainy conditions most of yesterday, I was able to hit a repeater about 30 miles east that I hadn't before. I guess it's the cloud cover that helps with that, helps refract the signal back towards the earth instead of it going into space? Will propagation also improve when the weather warms up? Guess that's what's called tropospheric ducting?

Was able to get into a net last night that I had struggled to in previous weeks. They said I had a good signal this time. Guess having your antenna 25ft up in the air helps with that.

 

[nd5y]

We had overcast/rainy conditions most of yesterday, I was able to hit a repeater about 30 miles east that I hadn't before. I guess it's the cloud cover that helps with that, helps refract the signal back towards the earth instead of it going into space?

Not just clouds. It happens when there is the temperature and/or humidity gradient changes sharply with altitude.
In my experience 30 miles is borderline too close to be affected by tropo propagation.

Will propagation also improve when the weather warms up?

Depends on where you are and the local climate.

Guess that's what's called tropospheric ducting?

Probably just local enhancement. Ducting usually only occurs over longer distances like hundreds of miles or more.

DXing Above 30 Mhz - The RadioReference Wiki

wiki.radioreference.com

 

[KY_Ham_64]

Participated in two 2m repeater nets last night, my regular one in Morehead, 16 miles distant; and one just north of Portsmouth, OH, just over 35 miles to the NE. The terrain really opens up in that direction, I was also able to get a response on a 70cm repeater near there as well. Really liking this new antenna setup.

 

[KY_Ham_64]

I have a question about grounding this antenna setup. I was thinking of getting some type of weatherproof enclosure and install it near the bottom of the pole to bring the coax into, with it going into a suppressor with that device attached to some kind of copper plate.

Then running the coax from the output of the suppressor up under the house up into my radio room (office).

From the copper plate, I'd attach my grounding conductor from there to the service ground point on the pole on the front side of the house. I have quite a bit of 10 AWG THWN, so could I use that as my conductor? Or does it have to be 6 AWG minimum?

Does this sound like a good grounding setup? Also, would the suppressor shunt any static electricity from the pole to ground in this configuration?

I guess I'd also need to connect the bottom of the pole itself somehow to the grounding plate as well?

 

[K6GBW]

Well, keep in mind what you are trying to do by grounding the coax. If you get hit by lightning you want that juice to scream down the coax and then into the earth...NOT into your house. So how big a wire you think can handle a couple of million volts? Go big.

Also, you don't have to have a direct hit to cause damage. About three years ago we had a strike on the street behind me. That put enough electricity in the air, picked up by my dipole, that it blew my poylyphaser. It died doing its job!

 

[KY_Ham_64]

So how big a wire you think can handle a couple of million volts? Go big.

If it's MV's, what difference does 6 or 10 AWG matter? I mean bigger would be better, yes. I have bare 6ga connecting the frames of my solar panels together, but that goes into a junction box which transitions to 10ga THHN which goes back to the service ground via 50 feet of conduit.

I was planning on getting a Polyphaser as my suppressor. I understand you can't measure any continuity from input to output as it has a capacitor in between. And it has a type of varistor that shunts higher voltages to ground. I wonder what kind of impact to your SWR one of these devices have.

 

[KY_Ham_64]

Saying all that, does my proposed setup sound like it meets applicable code?

 

[mmckenna]

I wonder what kind of impact to your SWR one of these devices have.

Negligible impact.

As for your installation idea, sounds good to me. You want the actual mast grounded as well as the coax shield and the Polyphaser. Big wire gives it a nice low resistance/low impedance path to ground. Code is around human safety, and that's your goal. Yes, in a direct strike everything is going to fuse open but at that point, it really doesn't matter.

The copper grounding plate is a common way of mounting the Polyphasers and then running one large grounding conductor to the rod.