Hello all,
I’m presently using a 2 meter dipole for 2/70cms and a 2 meter 1/4 wave for mobile operation both are of course useless on 70cm although they do present a good match, do you have any simple designs for something that will at least work equally on both bands ?
Thanks all
Brad
Brad,
have you tried using them on 70cm? They may be better than you think.
In my mobile setup I used a 2m quarterwave whip on the car roof for 70cm and while it was no dx antenna it worked fine for local contacts. On a sota summit, I also used a 2m half wave dipole, not very straight but nominally horizontal polarisation and it did work on 70cm for a few contacts.
I’d try it, even just to establish a reference point.
73 Andrew vk1da
I have used them on 70cm but as most of the local repeaters (15 miles-ish) over bad terrain are marginal at best, with me just about getting in .If it is raining I can activate them but no one can hear me ,if its really bad rain I cannot even activate them. A dedicated 1/4 wave or 70 cms dipole helps quite a lot but I then lose 2 meters.It doesn’t help that I’m only using 1 or 0.5 watts ( solar powered battery charging) of course but I think with an antenna with a bit of gain and the better coax results would be better.
Fair enough…
There is no shortage of commercial antennas for 2+70 but they tend to be either mobile or base, not both. This is because the mobile antenna usually needs the car roof as a ground plane while the base usually has a built-in ground plane. For mobile an example is the Diamond SG-7500, which has significant gain on 70cm. I have a V-2000 as a white stick base antenna which covers 6/2/70, at 2.5m long its a bit impressive but boasts 8.4 dB gain on 70! If you want to construct a two band vertical one possibility is the PA0HMV antenna, described in “Backyard Antennas” by Peter Dodd, G3LDO, a book that I highly recommend!
Brad is your radio operation the 2025 version of Trivial Pursuit? I ask because you are getting poor results with how you operate and are changing anything but the items that are limiting performance.
You have said in many messages
you are trying to access repeaters on UHF over bad terrain
you are using antennas inside a loft
you are using very low powers for UHF
you were using rubbish coax (may now have been upgraded)
More power to your elbow for trying QRP and home brew antennas but UHF wont work very well in those circumstances. You don’t know how well your antennas work apart from the SWR. SWR is not an indication an antenna is radiating or radiating well. My dummy load has an SWR of 1.1:1 from 160m to 23cm but it’s a rubbish antenna.
For UHF you need an effective antenna, mounted high and in the clear, low loss coax for the run and sufficient power into the antenna to get enough signal out to overcome the free space path loss and the terrain path loss. This is not the case for 0.5W from a handy into an indoor antenna over a difficult path. You are wasting your time.
Your comment that you cannot be heard when it rains says your roof tiles/slates have high attenuation when wet. Having an antenna that doesn’t work when it’s wet in England is not viable because it’s wet most of the time.
You need an antenna that actually has been shown to work (homebrew or commercial) but something made from an internet design is unproven till you have proved it works compared with a known antenna.
You need to run sufficient power as well.
Otherwise you are not going to have any real success.
I understand your logic but that just doesn’t suit me, I don’t want to go out and buy myself the ultimate radio set up ( it defeats the object of Ham radio) move house to the top of a big hill and install an antenna farm on top of my house ( been there done that in the late 1980’s) with all my other hobbies and commitments I have little time to spend on top of Hills to get my radio kick so have to use it on my commute to work and whilst dog walking plus fairly occasionally at home when I have the time or inclination. ( not judging anyone that does any of these !) So my thing is to use cheap low power equipment and build everything I can, yes my radio setup is mediocre at best ( probably not even that good) It suits me to have antennas in the attic as it gives me easy access for experimentation.I am nearly there as regard what I need so just a little bit more gain and less loss will do the job. On 70 cm with the original set up a handheld was doing as good a job. The repeaters also vanish in the rain ( no roof tiles).
you are trying to access repeaters on UHF over bad terrain – unless I move my house, get the keeper to relocate the repeaters or use explosives and bull dozers to remove the hills and forestry I’m stuck with this !
you are using antennas inside a loft — as pointed out I don’t want an antenna farm and having the antennas in the attic means I have easy access to them.
you are using very low powers for UHF —- more fun ? I could of course just buy a massive amplifier or dump the radio entirely and use Echolink on my phone !
you were using rubbish coax (may now have been upgraded) Not yet but that will be done as soon as it arrives as well as the new antenna.
This is the path not the roof tiles as this happens from my handie and also mobile setup when parked outside my house.
You do seem a very angry chappy after all what do you care what I do.
Just to post my update, I am not at work today so along with doing some car maintenance, an oil change, a five mile causal walk in the forest with my dogs and finishing the tidy up of my allotment for winter. I have taken the 2 meter dipole apart and replaced the elements with ones cut for 70cms this is a great improvement but I have of course lost my 2 meter capability . I may get away with the coax change and something like the standard dual band flower pot antenna.
Two antennas, one switch. Problem solved.
There was a time in my youth when I lived in a council house and outside antennas were forbidden. My only choice was loft antennas, as Andy has pointed out that solution adds roof attenuation to all the other losses. My solution was to buy a (relatively) cheap TV antenna rotator and put a yagi in the loft space so that the gain of the yagi balanced out some of the losses. Since the loft is a protected environment I made the yagi out of stiff wire actually brass brazing wire) stapled to a length of wood. It took about an hour to build. Not an ideal solution but it got me contacts that could not be heard with a dipole!
PS: Antenna rotators are not cheap but one could perhaps salvage the rotator out of a dead microwave oven, or have a number of fixed el cheapo beams facing in different directions!
Maybe this Yagi (4-Element-2m-50Ohm-Yagi, Boom 100cm) that is DIY and works for both for 2m and 70cm would be something for you?
And with the rotor as suggested by Brian you could get the most out of reflections on hills and so on.
Or with a switch build 4 of them and switch depending on directions?
The rotator idea adds another project there are plenty of motors out there I could use I just need to work out a system to show me where it is pointing remotely 
shouldn’t be too hard. I had a long conversation on one of the 70 cm repeaters this evening on my £8.20 radio and off cut 70cm dipole with 500mw to a new ham who was using echolink on his phone, this was to a repeater that was very marginal on the 2 meter dipole.He was well impressed and on a budget, a sort of result as this little project was to show how cheap you can make it on air ! A lot of people are put off thinking it’s a rich mans hobby but like most hobbies it doesn’t have to be !
Yes.
Start with your 2m dipole. I’ll assume it is about 990mm long using 2mm wire for my model.
At the feedpoint, add two more wires 330mm long on either side, parallel to the 2m element and spaced 25mm on either side of it.
That’s it.
You can actually get by with just one wire, but the dimensions change a bit.
It’s actually a good match for 75 ohm coax, but 50 ohm stuff should work well enough. SWR(75) is 1.35 : 1 at 430 MHz, 1.03 : 1 at 437 MHz, and 1.16 : 1 at 440 MHz according to my model. On 2m, SWR(75) is 1.04 : 1 at 145 MHz and still only 1.3 : 1 at 148 MHz, so the only adjustment for IARU Region II should be to shorten the 440 MHz bars by an inch or so to shift it up to 445 MHz.
For mobile, I’ve used one of the commercial 2m quarter wave whips with the open coil in it to improve the pattern on 440. I haven’t tried making my own
For mounting beams in your attic, I’d strongly recommend the “Cheap Yagi” construction from WA5VJB:
(Sorry about the imperial units.) I’ve used this driven element construction on several yagis, from 121.5 MHz to 732 MHz. It has the advantage that the driven element is not split at the feedpoint, giving better mechanical stability when using wire, and no additional matching is required. 2m is close to the lower limit for 2mm copper wire, as the elements get wobbly, but it works quite well on 70cm.
In fact, this is the easiest construction method that I have found for UHF yagis.
I use my own dimensions (modeling tip: design the yagi for a feedpoint impedance of 12.5 ohms, as the half-folded driven steps up the impedance by a factor of 4, just like a folded dipole). I rotate the driven element around its axis so the short leg is in front of the longer one, and pass it through two holes in a piece of plastic water pipe. Then cut a notch in the pipe at the feedpoint, run the coax up through the boom, solder the shield to the back element and the center conductor to the front one. I leave the short end of the short element long enough so it passes through both sides of the boom for added stability.
Here are a couple examples:
A 95g 4-element hand-held yagi for 70cm. Driven element is copper for soldering, parasitic elements are aluminum wire (aluminium TIG welding rods are an excellent choice, and come in different sizes).
A longer 6-element version on a mast using standard water pipe fittings.
These antennas are so cheap and simple that, if you only need to hit repeaters in 2 or 3 directions, it often is easier to use multiple fixed antennas and switch among them rather than one on a rotator.
