mobile antenna

[Midnitemo]

Having just gone legit with my radio's I'm now looking to improve the portable performance further with a new antenna , I have already bought a diamond srh771 for my transceiver which claims a bit of extra gain(upto 2.15 db on 2m)every little helps but I am looking for something a little better specifically to use at work and whilst out camping , it must be compact , easy to deploy , good value and most importantly give me more performance , Harry mentioned a "slim jim" antenna which I really like the look of , it claims upto 6db of gain on 2m , if this is true then that would be a decent improvement but would I be contravening my licence with this boost of erp possibly beyond my allowable 10watt's? I fancy one of the ready made ones from the USA which roll up to store and come with the extra 10/15ft of coax on it(what kind of losses would the extra coax be subject to?) are there any other antenna out there that might fit the bill? my work needs are in the main quick to deploy/break as I'm not really meant to be on the radio as such and it needs to be stowed quick smart if anyone turns up unexpected.

[Lightspeed]

(26 June 2017, 04:01)Midnitemo Wrote: Having just gone legit with my radio's I'm now looking to improve the portable performance further with a new antenna , I have already bought a diamond srh771 for my transceiver which claims a bit of extra gain(upto 2.15 db on 2m)every little helps but I am looking for something a little better specifically to use at work and whilst out camping , it must be compact , easy to deploy , good value and most importantly give me more performance , Harry mentioned a "slim jim" antenna which I really like the look of , it claims upto 6db of gain on 2m , if this is true then that would be a decent improvement but would I be contravening my licence with this boost of erp possibly beyond my allowable 10watt's? I fancy one of the ready made ones from the USA which roll up to store and come with the extra 10/15ft of coax on it(what kind of losses would the extra coax be subject to?) are there any other antenna out there that might fit the bill? my work needs are in the main quick to deploy/break as I'm not really meant to be on the radio as such and it needs to be stowed quick smart if anyone turns up unexpected.

Hi Midnight,

Don't worry about the gain issue on antennas. MRP ( Max Radiated Power) is about the amount of energy in watts getting radiated by the antenna. The antenna system (feeder and radiator always attenuate power to a greater or lesser extent) so you could output a little more power than your 10w limit if you can calculate how much of the power is being lost before transmission.

Sorry to be a pedant, but are you looking for a mobile antenna ( one that fixes to a vehicle) or a portable antenna that you carry with you and are effectively stand-alone??

[Midnitemo]

It's both really, have just bought a Nagoya mag mount to try on the car/motorhome but i'm mostly interested in a better antenna for work when i'm on nights that is discreet and requires no tell tale wire guy cables, clamps or brackets that will give the game away to an observant manager , I followed up something HP said about a "slim jim" the pipe type ones weren't really that interesting as they were more of a permanent fitting thing but I did come across a little flexible one at around 2m in length and polycoated making it able to be rolled up into a very small bundle (bob friendly) and weighing only a few ounces , just wondered did anybody have any experience with the flexible type "slim jim" or can anyone point me at other option's i've yet to come across.

[CharlesHarris]

A magnetic mount works best on a car, but an improvised ground plane can almost always be found around the home or office, such as a metal filing cabinet, metal rubbish bin, baking sheet, rain gutter, refrigerator, window air conditioning unit, balcony railing or almost any other large metal object.

On boats, motorcycles, caravans or wooden balcony railings use a half-wave antenna, which gives unity gain without a ground plane. If you need to place an antenna on a caravan, camper shell, ambulance or other vehicle with nonmetallic body where a magnetic mount won’t "stick," use a suction cup mount such as the one shown here:

http://www.w5fc.org/pse_docs/KNOWLEDGE/qst_p56.pdf

[CharlesHarris]

Sorry, old link doesn't work.

Here are some for some commercially-made suction cup platforms for small UHF mobile magnetic mount antennas:

https://3gstore.com/product/1579_wilson-...tenna.html

https://antennagear.net/suction-cup-ante...ne-901118/

https://www.southwestantennas.com/antenn...r-1071-008

[Midnitemo]

My work location is only 20ft above sea level at the mouth of a fairly major river surrounded by hills on the three non seaward sides which rise too between 400 and 800ft I also have HT cables cutting across my location in an east to west direction passing at its closest around 75m away so you can see why the best possible antenna is needed.

[Lightspeed]

This weekend's going to be good for playing radio. Especially so on VHF as its both the VHF field day and the third VHF Backpackers competition

http://www.rsgbcc.org/cgi-bin/contest_ru...4backpack3

These two events are effectively emergency communications radio preparedness training.

If you have access to a VHF rig that has SSB capability you'll make LOADS of contacts and will be surprised how far your signal will get out even from a modest antenna. I use a vintage Yaesu FT290R (2.5w) for the backpackers competitions and usually can get contacts across the SE England, midlands and into the Continent from an operating spot at 600m ASL, near to Reading.

If you can get up onto a high-ish point, even with an FM hand-held there's a good chance of making interesting contacts. Read the link above to prepare the right information to exchange.

Antenna. I am VERY impressed with the performance of the Diamond Super Gainer 7900. This can be mounted to an appropriate mag-mount, and for portable use you could mount it on a telescopic pole, with suitable ground planes attached to the mount base.
The one I have has 1:1 SWR on both VHF and Ham bands, and surprisingly, also at PMR446 frequencies. On both UHF and VHF I can reliably open repeaters 80 miles away from me using an un-modded UV5r (4w)
http://www.diamondantenna.net/sg7900a.html

Home-made three element Yagi beams constructed of waste pipe and aluminium dowel fro major DIY stores also work surprisingly well. These are really easy to build. As a support glass fiber* telescopic roach poles work well and can be easily erected by strapping them to fence posts etc using a bungy cord. You'll need an SWR meter and patch cables to get this sort of antenna tuned.

J-Poles: My sadly departed father was a great fan of them, but I've never had great success. There are many on-line tutorials for making roll-up versions out of 400ohm ladder line.... but I've never succeeded in building one that tunes correctly. The idea is great, but the implementation somewhat more difficult. Maybe buying one ready made and tuned is a viable idea. Again the good old fiber glass* roach pole is a good support for this sort of antenna.

* Important that its Fibre glass NOTCarbon fiber! Anything longer than 3.5m is usable, but big is most definitely best in this instance.

[Lightspeed]

Your Op asked about coax losses. It all depends on the type of coax and the length used. There are data charts available for this.

For portable and mobile use, just keep the lengths as short as possible and you'll be fine.

BTW you'll find a pair of headphones a godsend when operating portable.

[Midnitemo]

Sounds good this weekend but I sadly I'm in work on days so I will just have to listen as I'm to busy to give my full concentration to the radio , like the high gainer , it says in the blurb at the bottom don't use a mag mount , what are the fittings on it? tis now on the want list! think i'll try one of the pre made slim jims from Nelson antennas in America reckon on about £30 unless I get hit for import duties.

[Lightspeed]

Its a pity that you're working all weekend as this will be the busiest VHF weekend of the year. 5. Aug and 3, Sept are dates for the last two backpacker competitions. If you can pick up a working Yaesy FT290R in time for either of those, I think you'll not be disappointed.
BTW as far as I'm concerned field days and back packer competitions are as near as you'll get in the here and now to genuine grid-down / bug-out radio communications, as the rules mean they have to be off-grid and in the case of the backpackers remotely located as well. Running delicate radio equipment in the great outdoors is a far cry from operating from a base station or the comfort of a motor vehicle.

Also check-out SOTA ( http://www.sota.org) there's lots of good practice to be had from getting involved with this. In fact it may be more to your liking as its an activity that takes place all week long and with a large contingent of VHF hand-held stations too.

My Super gainer has an SO259 connector on it. Sorry, I didn't notice that its not recommended for mag mounts. I've no idea why. Mine are used with fixed bases.

The American antenna is for sure makeable for a whole lot less money, but as you're starting out, getting stuff that you know works correctly from the get-go is the best way to go.