VK4WDM > 03-11-2017, 06:49 AM
VK3ALB > 03-11-2017, 07:40 AM
VK4ADC > 03-11-2017, 07:51 AM
VK4WDM > 03-11-2017, 07:57 AM
(03-11-2017, 07:40 AM)VK3ALB Wrote: Hi Wayne,
The G5RV was not meant to be an all band antenna and your experience shows that. That it's a Jr probably exacerbates the situation. At 10m you are limited for 80m and of course 160 for full sized antennas.
The WIA foundation manual describes a OCF dipole that will give reasonable performance on a number of bands. Don't forget height and radiation angle are related. Consider full sized wire loops and wire antennas supported by the ubiquitous squid pole. VK7JJ is a good place to start. A full length 40m 1/4 wave vertical is not unreasonable and a 30m vertical is definitely in scope. Drew Diamond describes a top loaded 160m vertical that is under 10m high. Ground radials for verticals are very important - investigate the option of buried versus elevated radials.
I don't understand how some commercial verticals claim good performance without a ground system. What science do they know that we don't? In my area we have one bloke who bought a Gap Titan antenna whilst the rest of us use wire antennas. He never hears anything on 40m while we can generally hear each other. That's a lot of money for no result.
I'd much rather spend a lot less money one or two antennas that work really well on single bands than hundreds of dollars on something that may perform the same or worse.
Antenna modelling is now within reach for all of us. Antennas can be easily evaluated right at your desk before before you start building.
A good antenna on 40m will keep you busy for a month of Sundays with digi modes even at this part of the solar cycle.
Now, if I remember correctly, you were the bloke that was addicted to wire antennas???
Addition:
I forgot to add that VK2OMD, VK5ZD and G8JNJ have written about the CHA-250. Looking at the specs of the TZ-V-4 I can't see why you'd spend that much money on something that you could probably replicate at home.
VK4WDM > 03-11-2017, 05:09 PM
VK4ADC > 03-11-2017, 07:26 PM
VK5ZD > 03-11-2017, 10:21 PM
(03-11-2017, 07:51 AM) Wrote: The CHA250 uses a large "power swallow" resistor plus a balun effect so that the returned SWR looks ok to the transmitter if the basic feed impedance of the active vertical section varies widely from anything acceptable."
There's no resistor in the CHA250, but it still doesn't work very well. It's easy enough to "roll your own" if you have a suitable vertical element.
If you want to spend some money then I'd go with a vertical sitting on an auto-tuner (e.g. EDX-2) with whatever ground radials you can manage.
73
Iain
VK4ADC > 04-11-2017, 07:16 AM
VK2CSW > 05-11-2017, 08:42 AM
VK4ADC > 05-11-2017, 10:21 AM
(05-11-2017, 08:42 AM)VK2CSW Wrote: Well, just to show my ignorance of antenna theory, I ask:
In the circuit diagram it shows that both 'sides' of the feed from the transmitter attach to the right-hand tube, which appears to be metal in the photo.
Why does this not simply present a short-circuit to the transmitter?
VK2CSW > 05-11-2017, 10:35 AM
VK4ADC > 05-11-2017, 03:59 PM
VK4WDM > 07-11-2017, 04:36 PM
VK4ADC > 07-11-2017, 07:17 PM
VK4ADC > 12-11-2017, 02:50 PM
VK5PJ > 16-11-2017, 01:39 PM
VK4WDM > 15-01-2018, 09:07 AM
(03-11-2017, 06:49 AM)VK4WDM Wrote: As people have noticed from previous posts I have a very restricted area for antennas and a height limit of 10m.Update on this. I ended up making an ally tube vertical 10M tall. The lower sections are double wall so it is self supporting but I will consider adding guys if wind sway gets too scary. I then added 12M of wire to the top that slopes down to a 5M mast on the corner of the block so I now have a sloping "inverted L." The wire length is solely based on the distance available. I have an earth stake but no radials as yet but plan to add some in the next few days.
My "Western HF10" dipole (G5RV jr with loading coils) is about all I can fit wire-wise and the current results are not good.
I have decided to use a rotating dipole for the higher bands but need a vertical for 30, 40, 80m (and 160m would be a real bonus).
So what are the options as I see them?
1. Turn the mast that is currently holding up the dipole into a non-resonate "mono-pole" over radials and maybe an auto-tuner at the base. I could add a horizontal wire to give extra length. Low cost option. Would also give me a vertical option on the higher bands. There are some commercially-produced ones, but how good is this type of antenna on the low bands?
2. A trapped vertical such as the Rippletech TZ-V-3L ( a bit over the height limit but who is going to notice) over radials. More expensive that option one but is the extra cost worthwhile for an antenna dedicated to these bands?
3. Comet CHA250 vertical. Would also give me a vertical option on the higher bands. Does not need radials. Expensive and the reviews are very mixed especially on its low band efficiency.
What say ye?
73
Wayne VK4WDM
VK3LU > 15-01-2018, 12:28 PM
VK4ADC > 16-01-2018, 08:21 AM