I can’t find any UK stockist but here’s a supply in Italy but at €24 it’s a bit expensive and it’s a no-name.
RE: RH770 telescopic antenna
I have been using a homemade 2m dipole antenna similar to Andrew’s design (VK1AD) for some 5 years or so.
See Portable 2m 144 MHz Coaxial Dipole Antenna | Get out of the Radio Shack and Live Life
I call it a flowerpot antenna from original designs that I used.(worth a web search?) It uses coax braid as lower dipole element and a Diamond RH770 telescopic antenna as the upper element to give a half wave antenna and I mount it by 19mm PVC pipe connectors atop a 2 meter high 19mm water pipe mast which doubles as a walking pole when fitted with a bamboo bean stick inside it to stiffen it. It has seen many activations completed as a simple set-up with a FT270E 2m handie at 5 watts.
A couple of weeks ago whilst activating Tal-y-fan North Wales, the strong winds blew down the mast normally ‘bungied’ to a fence or trig point and damaged the BNC connection on the extension coax.
So I plugged the RH770 directly into the FT270E by-passing the mast and completed the activation with 9 chasers.
It has proved to be very reliable for me and I did choose the more expensive Diamond manufacturer.
I use a BNC to SMA adapter on the rig and no ground planes are required as it is a balanced dipole.
I carry two standard internal batteries for the FT270E but they seldom run down even on multiple activations.
I choose to activate mostly on VHF so that I do not carry too much load onto summits having a double heart condition. By the way my Heart Pacemaker was not disturbed at all by the closeness of the half wave antenna at arms length from it on the HT using 5 watts. You should make your own assessment on the wiseness of this operation if you have a similar heart condition and not rely on my say so that it is ok
I have found this type of set-up to be a simple and reliable one for 2m but as Andy mentioned take care to extend the telescopic section slowly and without bending it. I do not know if the copycat versions of RH770 are inferior to the Diamond in this respect, but I have had mine for more than 5 years use on the genuine article for about £22, so not bad?
Rob G0HRT
I’ve ended up with two RH770’s (don’t ask - long story): a Diamond one with BNC connector (attached to HT in photo) and a Chinese one with SMA. I consistently get excellent reports using either during SOTA activations.
As others have said, you would be unwise to walk around using an RH770 so deploy it at the summit once you’re stationary.
My Yaesu HT has a SMA-female so the BNC one needs a BNC-SMA adapter. I’ve seen the combination sway back & forth alarmingly in high winds (Lancashire in winter). The SMA one is mechanically more stable on the HT so I usually take it with me.
The Chinese one was about one-third of the cost of the UK-supplied Diamond one, although allegedly more fragile.
And do they all have stock Andy? Andrew 2E0IME is the one looking for a UK stockist with stock of the model with the correct SMA fitting.
73 Ed.
I use the Diamond SRH770S. It is 70cm long but much more flexible than the RH770. It is not retractable but that doesn’t seem to be an issue. Great gain. And light too because it is much thinner than the RH770. And it is coated black. I don’t think it strains the radio’s connection at all.
Hi all,
There is no such thing as a high gain telescopic whip. Hi gain on 2 m is circa 14 dBd, not possible as a HH whip.
Some rubber ducky short whips are so bad that when a quarter wave whip is substituted it seems as if more than 10 dB gain has been achieved.
SMA connectors are not designed to take larger whips. A BNC will support a quarter wave readily but a 5/8 is pushing the friendship even though they are available from the usual firms…
If you want to use a longer whip some fairly flexible ones that are available on e-bay for a few dollars and provide significantly better performance than the original rubber duckies.
Telescopic whips are not low loss so a flat SWR curve can be expected. Great SWR bandwidth is an indication of low efficiency. You may think the convenience outweighs the loss and it can still be a lot better than the original rubber ducky.
A Slim Jim made from 300 ohm ribbon can be rolled up for transport and attached to a squid pole on site. I have built several using electrical conduit for a radome and find that a reasonable compromise for dx capability vs size. I use a second length of conduit as a short mast. It has a SMA connector on thin coax. 2.5 W FM on 2 m makes it easily to the radio horizon. Taking into account the coax loss the gain is around -1 to -2 dBd. It’s not a telescopic whip but it works so much better. No concerns over the ground plane for the on rig whip either.
If you look at https://vk3afw.wordpress.com/ you will find construction details of the Slim Jim I use.
73
Ron
VK3AFW.
Is that necessarily true? Bandwidth is related to the diameter of the radiator, the thicker the rod or wire the wider the bandwidth, but this can also be simulated by a cage. Cage dipoles are occasionally used to cover the whole of a wide band such as 80m without needing re-tuning, but does using a thicker radiator or simulating it with a cage reduce its efficiency?
I can confirm that the RH770 works extremely well with my Yaesu Handheld. High Gain it is not, as usual an inflated antenna gain claim, totally dishonest, but all the same they are good value for money from Chinese ebay sellers.
One thing though, if you stand the handheld up against a fence or a tree and it falls over the top section is guaranteed to break off, as the one lent to me by GI4ONL did. There is no way to repair such a cheap telescopic aerial - very thin metal used, hence the price. So I had to buy him a new one, but at around £6 it didn’t break the bank…
73 Phil
1 Like
Hi Brian,
We are talking about practical whip antennas on 2 m. It was not my expectation to be taken literally for every conceivable case. To put in every possibility would make my posts even more unacceptably pompous and boring. Assuming some context is reasonable is it not?
A cage quarter wave whip is not going to sit easily in my pack. But yes it could have a broader SWR bandwidth and it could be efficient. Can you name a manufacturer of such devices for 2 m?
There are multitudes of different designs that provide wide bandwidth and good efficiency. You could use a Disc-Cone antenna for a really wide bandwidth. It would put a big strain on an SMA connector and not offer much gain.
A telescoping whip is usually chrome plated (higher skin losses than copper), has sliding contacts (each adds some extra resistance) and relies on the transceiver case and the user’s hand and body for the counterpoise.
An external antenna such as the Slim Jim avoids these specific problems and shows up the average rubber ducky for what it is, a low efficiency antenna good for short range qso’s and one that poses less risk of poking someone in the eye than a big whip.
73
Ron
VK3AFW
Large SWR bandwidth means a low-Q antenna. You can get low Q by adding resistance, but you can also get it with large diameter elements: cage, bow-tie, etc. Large-diameter elements can be more efficient because they have a bigger surface, so less skin effect resistance.
Antennas like the Comet CHA-250B have a lossy balun, so those do trade efficiency for bandwidth.
wunder
Another excellent option is the Anli AL-800 for 2M/70CM - about 1M when fully extended. It has an SMA connector but I use it on my dual band HT with a BNC adapter. When extended it is too long for use on the trail but great once on a summit it works great.
Derek, WF4I
Well sorry Ron, it did look like a generalisation to me, but evidently not.
Anyway, in my case I unscrew the half wave whip from the mount on top of the car and use it with a PL259 - BNC adapter in the front antenna socket of my 817, and frankly although it works a treat I get nervous about the consequences of it toppling over. I have built a Slim Jim (and other antennas) but with the need for a pole and a feeder I think it and they were too much trouble. I have a handy for emergency use if I have a problem with the 817 (such as the occasion when it got too cold for the gel cell to work!) but with its barn door front end I would be wary of putting a more effective antenna on it!
Cheers all for the replys, I have a flowerpot antenna I have made also a slim Jim.
I think best idea seems a flowerpot on a 3m whip wedged between knees on a rocky summit or simular and a good flexi whip for when walking
Cheers
73 2E0FGX
Hi Matthew,
For some activations, I used diamond srh771 and also not original rh770, fixed to kx3 or th-f7.
Not original Rh770 was short lived, probably due to my fault… I’m ungraceful
My next purchase will be diamond srh770s, the right compromise: gain, manoeuvrability.
73
Roberto iw2obx