Vertical Antenna question

[theonerick]

I'm quite new to Amateur Radio, so be kind if my questions are "dumb" please.

I have a TYT TH-9800 in my house, 50' of LMR-400 running to my roof, and then there's my antenna. I'm using 2m, talking mostly to repeaters.

I originally got an Ed Fong DBJ-1 antenna and it worked well enough, but after getting to know the local area, I wanted something with a little more reach.

I just purchased a Harvest Wireless X300 and mounted it where the DBJ-1 had been (vent pipe on my roof). I used to get SWR readings well under 2, but with this antenna I am getting up to just a bit over 3. The curious thing is, with this antenna my meter (Nissei RS-40) also reads higher power (e.g. it shows about 70 W on my radio's 50W setting).

On to my real question: When I use my multimeter on this new antenna, the vertical element (inside) has continuity with the radials and the outside of the SO-239. And nothing I can find has continuity with the center! This doesn't seem right to me. Is it?

I imagine my description will result in questions, but I would appreciate any help that anyone can provide.

Thanks,
Rick
W1RKR

 

[ZigZag747]

Rick,

I do not know anything about the internal makings of the "Harvest Wireless X300" antenna, I could not find anything on eham regarding this antenna, I imagine with 6.5db gain at 2m from a vertical omni that it is a collinear antenna. The short you detecting is probably the loading or matching network in the antenna design to get the antenna to match the 50ohm coax it was designed for. If you have a SWR meter that would best tell you whether or not this antenna if operating properly or an antenna analyzer would be best. You cant beat a collinear for vertical onmi directional gain, I have a simple 2m copper tubing SlimJim mounted on an 18ft painter pole secured to a 5ft galvanized pole buried 2ft in the ground. I can hit repeaters 50 miles away on 5 watts with S4 readings. 10 watts full quite into the repeater furthest away. Of course I live in the country so no urban attenuation.

 

[ko6jw_2]

Many issues to address

There are several issues here. Let's start with the simplest first.

The Fong antenna is basically a j-pole in a plastic pipe. It is (like all j-poles) a half-wave vertical and needs no ground radials. Depending in how you reference gain measurements it has roughly 3db gain. It is the type of antenna that will allow you to work local repeaters and nearby simplex contacts.

Your new antenna claims higher gain and would theoretically give you access to more distant repeaters because of a lower radiation angle.

It seems, however, that the new antenna is giving higher SWR readings than the j-pole. Since nothing has changed with the feed line or the radio, there may be something wrong with the antenna. One would expect a commercial 2 meter/ 440 antenna to be below 1.5:1 at the band center and below 2 across the bands.

One issue is the accuracy of your SWR meter. It is not a lab grade meter by any means. Perhaps another ham with a better meter could help you. Testing the transmitter into a dummy load would help to determine its power output.

The use of multimeters for testing antennas is very limited. They can test for shorts or opens in transmission lines, but these are DC measurements and have nothing to do with RF performance. Some types of j-poles will show a short at DC - depending on how the antenna is fed. At RF frequencies they are not short circuits.

With ham equipment - just like anything else - you get what you pay for. The influx of Chinese made equipment has gotten many people on the air, but reliability is a problem. Accurate (not necessarily expensive) test equipment is a must. You have to be able to trust measurements in order to track down problems.

 

[cmdrwill]

http://www.amazon.com/Harvest-Wireless-X300-Dual-Antenna/dp/B019LVCJSO

Looks like someone is doing a poor copy of the Diamond antenna. The specs are WAY over rated.

Even the Diamond antenna is not that good, way too many failures. I is just a small gauge steal wire with piss poor copper plating and poor solder joints.

From what you have found it is not as good as the Ed Fong antenna.



"9.0db Harvest X300 V Uhf 2m 440 Dual Band Base Antenna 6.5db Vhf 9.0db Uhf"

 

[theonerick]

Thanks all for the answers. That antenna did indeed get returned, but I'm learning a lot in the process so it wasn't a total waste.

 

[paulears]

Amazon technical equipment always seems to have copy and pasted specs that actually say nothing at all.

Even the commercial antennas, that cost maybe four or five times and amateur one seem to have pretty modest gains. At UHF 6dB over a dipole is probably the best you can do on a single pole. Higher gain ones being huge and needing support at both ends. So we're really looking at what? 4.5-6dB gain as a maximum (using proper dBd type measurements, not the dBi ones)

The real solution is simple more hight or swap them for beams. I hardly ever see people advocating beams any more. I had a crossed 8 element VHF beam a few years ago and it was excellent, and with a bit of careful parking, pretty good for local coverage too off the side of it. For airband, simple and wideband omnis are the choice of the pros - so surely should be the same for us? The reality for most people with space for just one aerial is a modest vertical of some kind and that really is it. Decent mechanical construction, decent cable and that's really it?

Lots of people chasing their tails all the time - asking which antenna is better than the one they have - and the spec differences are 1-1.5dB - is that really worth it?

 

[wb6uqa]

Make sure your watt meter is made for VHF. You could be getting false readings.