Amateur Radio Transceiver - Mobile Installation

[PanBiker]

As reported in another thread, I have just taken delivery of a dual band mobile antenna which I ordered last week. It turned up today. Well packed as you can see.



I bought a package deal that comprises the antenna itself, a boot or hatchback mount and a 5m lead assembly. After carefully unpacking:



The antenna is a Diamond SG7200 it will be 95cm long when assembled and is for dual band use, it covers 144MHz (2m) and 433MHz (70cm). A good trade off for length and antenna gain. It is a half wavelength long on 144MHz and gives 3dbi gain and 2 x 5/8 wavelengths on 433MHz with 6dbi gain. The antenna should tune with less than 1:5 SWR (Standing Wave Ratio) and can handle up to 150W of RF power. There is spring loaded articulated joint just above the loading coil base which allows you to tilt the antenna radiator to 90 degrees to cater for low barriers etc.



The antenna is shipped in two sections. When assembled the centre joint in the antenna allows you to adjust the length of the radiator for best SWR on the feeder.

The antenna mount is adjustable in two planes and is designed for attaching to a boot or hatchback vehicle. The latter in my case with our Hyundai i30 The vehicle has very few suitable mounting points, most of the hatch is actually glass but there is a small area above the rear window on the side edge of the hatch that should accept the mount and also still allow access without having to dismount the antenna.

The 5m 50 ohm coaxial lead is pre terminated with an S0239 socket at one end and and a PL259 plug at the other. The socket goes on the mount, the antenna has a mating PL239 connector at the base of the loading coil.

First job of the installation will be installing the antenna mount and finding a suitable route for the feeder cable from the back hatch to the front driver position. I'll post some more pictures as I progress the installation.

[Stanley]

Wonderfully arcane.

[plaques]

Sticky out aerials on cars seem to be a number one attraction for vandals. I would have thought that some kind of clip on arrangement may be safer. Don't ask me how, I'm against drilling holes into the bodywork of cars ever since I drilled through some hidden cables.
Do you have a blue tooth screen to plug into so that its completely hands free. You can tell by this question I don't know much about these things.

[Big Kev]

First job of the installation will be installing the antenna mount and finding a suitable route for the feeder cable from the back hatch to the front driver position. I'll post some more pictures as I progress the installation.

Not sure on the access, front and rear, your headlining has Ian. I fitted a rear facing dashcam in my old Audi estate, a couple of cable pulling rods slid nicely betetween the roof and headlining. The cables from the front facing camera fitted nicely under the front edge of the headlining and tucked under the windsreen post trim.

Let me know if you need to borrow some rods.

[PanBiker]

Thanks Kev. I have some very thin fibreglass rods which I saved from a pop up tent, they are quite good for pulling cables. I only have to come from the driver back quarter to the left of the driver seat. The transceiver is going to be mounted vertically on the side of the centre divider to the left of the seat.

Sticky out aerials on cars seem to be a number one attraction for vandals. I would have thought that some kind of clip on arrangement may be safer. Don't ask me how,

That ones easy Ken. The antenna screws off the mount, it also has a tilt mechanism built in for getting under barriers etc.

Do you have a blue tooth screen to plug into so that its completely hands free.

No and I don't need one. Many of the more expensive marques of transceivers do have those niceties but are beyond my pocket. Legally, if you hold an amateur radio licence you can use a hand mic while mobile. This exemption is because of the role of emergency communication provision by radio amateurs given in times of emergency or disaster. My car is automatic so I am not using my left hand for gear changing so it would be relatively easy to use a hand mic while mobile but I won't. Hand mic will be used when static.

If you have a look in the other thread, here you will see that I have a workaround for a hands free option. Last time I had mobile equipment in a car I had a latching PTT (push to talk) switch in the gearstick head, where you put that switch is always the hard bit. I have my eye on the rear window lock switch in the driver door. It has potential to be repurposed. Getting at the gubbins though can be a bit of a nightmare. I will talk about car firewalls in this thread later.

[Big Kev]

Thanks Kev. I have some very thin fibreglass rods which I saved from a pop up tent, they are quite good for pulling cables. I only have to come from the driver back quarter to the left of the driver seat. The transceiver is going to be mounted vertically on the side of the centre divider to the left of the seat.

[PanBiker]

If I cant easily lift the carpet in the back I may have to chop the PL259 plug off the lead so I only have cable to thread. I can soon pop another one back on but I would rather keep the nice pre terminated one if I can.

[Stanley]

"I'm against drilling holes into the bodywork of cars ever since I drilled through some hidden cables. "
Snap Ken. I once did that on a Ford Anglebox I was 'refurbishing'. Couldn't understand why I couldn't see through the windows, car full of smoke of course! Luckily I had a spare car so I robbed the wiring loom off that and fitted it to the other..... Those were the days.

[chinatyke]

Luckily I had a spare car...

In your treasure chest? "I knew it would come in useful one day".

[Stanley]

The 1960s equivalent China. I was given both of them as scrappers. I got a couple of years out of the one I revived until the chassis broke in two one day. Those were the days!

[PanBiker]

I have received more bits for the install today. All I need to complete the job, power connector and some dust/rain caps for the antenna mount. A note on the power connector, I couldn't find an equivalent type in the UK for a reasonable price. Like the antenna I sourced this direct from China at a third of the price of a similar item in the UK with free postage, speed pack again, took just a week.

[plaques]

f I cant easily lift the carpet in the back I may have to chop the PL259 plug off the lead so I only have cable to thread. I can soon pop another one back on but I would rather keep the nice pre terminated one if I can.

t may sound a bit drastic but have you thought of a couples of holes in the floor and some nice tight grommets to seal the cable ? Don't go near the door sill its generally full of wires.

[PanBiker]

Nope, bit drastic, I wont be drilling any holes in it. The cable only has to go less than a couple of metres. I'll investigate a route under the back seats. Being a hatch back they conveniently hinge, might be able to send it down into the spare tyre well. Not really had a full appraisal yet. Cars are considerably more airtight than they used to be which can be a pain when you want to introduce some more wiring.

[PanBiker]

So here are the bits that came today:

Rain/dust caps for the SO239 socket and a plug for the power feed from the accessory socket in the car.



A bit closer look at this plug, it's switched with a LED indicator and rated at 20A it also has an integral fuse in the tip which is rated at 10A. The transceiver draws about 8A on full power so a 100% overkill connector fused down to 10A is about right. I got a switched version so I don't have to keep plugging and unplugging the connector to isolate the supply.



Ideally the transceiver should be connected directly to the battery but the Hyundai i30 has a double skinned firewall from the engine bay which makes it a bit difficult getting extra cables through from the battery to the cab. I am registered on a Hyundai support forum and there is a way to do it but it entails jacking the nearside front wheel, taking it off and then removing the mudguard liner. This apparently reveals a removable grommet through into the lower engine bay. There is another grommet at the back passenger side of the wheel arch where you can get access to the wiring loom run in the door sill.

A lot of bother to say the least so I opted to get the power from the existing internal accessory socket. The car has both cigarette lighter socket and the higher rated accessory socket which is fused at 25A.

So on to the antenna mount and cabling. I had a good look round for a convenient route for the antenna cable and found one down behind the rear seat back, behind the seat belt fastener then under this trim which is under the rear driver side seat. Clipped at the door sill but only secured by two screws so easy to get the cable underneath. The front edge of this trim is more or less immediately behind the driver seat.



Not a lot of room above the rear window but just enough to accommodate the mount and be able to clamp to metal. The mount is secured by four hex headed grub screws on the inside edge of the mount.



I loose fitted the socket then tightened it off after dressing the cable where I wanted to bring them onto the side of the parcel shelf. I popped a cable tie on to tidy the run round the mount.



I avoided bringing the cable over the hatch seal at the top and brought it down level with the side of the parcel shelf before looping it over the rubber seal. Any rain ingression runs down the outer channel of the hatch seal. I put a self stick cable tie base up near the top to secure the cable where it will flex with the opening and closing of the hatch, the cable itself runs down a convenient seam down the hatch side just wide enough for the 4mm coax.



I used some plastic P clips to secure the cable along to the top of the rear seat. Stops the cable wandering into the liftable parcel shelf and keeps it neat and tidy.



Here is the cable entering the trim under the rear seat. I have run it behind the seat belt anchor so it doesn't interfere with the operation of the belt.



This is the other side of the trim just behind the driver seat, you can just see the cable exiting. Easy then to feed the cable behind the seat belt anchor then under the driver seat to emerge where I need it to the left of the seat. I chased any spare cable down to this end and coiled it under the driver seat.



Here is where I decided to site the transceiver. The seat is pushed back here so that I could mount the support bracket. I fed the power cable down behind the transceiver and between the lugs of the mount. Spare power cable is looped and stored under the seat. The power cable is fused at 10A at both ends of the run. I have installed some ring core ferrite chokes on the power lead to suppress any RFI or noise from the engine or electrics.



Here is the hatch mount with the antenna in place. I switched the transceiver to low power and tested the SWR on each band at around the calling channel frequencies of 2M and 70cms bands. The antenna was resonant on 2M (144MHz - 145.500MHz for test) with an SWR of 1:1 to 1, that is excellent and indicates minimum loss of power on the feed line. 70cms (433MHz - 433.500MHz for test) tested as 1:2 to 1 SWR, not much different and still well within acceptable ranges for transmission.



Looking at the images for this project tells me that I need to vacuum the inside of the car.

[Stanley]

Warm day for doing a tidy job.....

[PanBiker]

Indeed, I was knackered last night, a few bruises from routing around under the seats and stuff. Not ideal with it powered from the accessory socket as you get a bit of voltage drop despite the current capability of the circuit. Beggars cant be choosers though and I'm not doing the front wheel jacking and stripping trick, wrong side of the car anyway. I will use it with the hand mic at the moment but only when static.

I ran the car up onto the tops above Elslack yesterday afternoon to test the setup, more chance of catching a contact. No problem there I heard Kevin (M0XLT) in Gargrave and Ray (G6HMN) in Winewall and we had a chat. Phil, can't remember his callsign called in from Otley as well. All working well, end stopping signal reports from the local lads and reasonable enough from Otley. I did notice that I will probably need to fit an extension speaker, the transceiver has the output socket. Internal speaker although facing outwards where I have it mounted still gets a bit lost down in the footwell. I checked for ignition interference and that seems OK, transmitting doesn't effect the car electronics either. When driving I checked that there was no oscillation on the antenna at speed, OK up to 60mph on Thornton drag.

Next trick is to fit the hands free microphone system so I can use it while mobile, handy for local repeater use and when out and about. It needs another coat of thinking about. It's all about the PTT (push to talk) switch. I have the gubbins and I know it works. Its just sorting the best deployment method.

[Stanley]

Vastly impressed. I had a friend in the US who had a Volvo car with CB installed. He was convinced the car had superb road holding and also that he was a CB freak. It was an unnerving experience to be on a drive with him, squealing tyres on the corners while he shouted "Breaker Breaker into the hand held microphone. (I never heard him contact anyone..... Sad.)

[PanBiker]

Here is the hatch mount with the antenna in place. I switched the transceiver to low power and tested the SWR on each band at around the calling channel frequencies of 2M and 70cms bands. The antenna was resonant on 2M (144MHz - 145.500MHz for test) with an SWR of 1:1 to 1, that is excellent and indicates minimum loss of power on the feed line. 70cms (433MHz - 433.500MHz for test) tested as 1:2 to 1 SWR, not much different and still well within acceptable ranges for transmission.

A bit more of an explanation about SWR readings when setting up antennas. SWR is the short form for Standing Wave Ratio. The majority of antenna systems are connected using coaxial cable which is an unbalanced feed system. You have an inner solid or stranded conductor which is surrounded by a dielectric insulation material, this then has a woven or wrapped copper shield that surrounds the dielectric which is then encased in the outer PVC jacket.

The inner conductor is the current carrier and the outer shielding is normally connected to ground or the common line of the chassis. Because the feed line is unbalanced, when you apply an RF current through the inner conductor this will cause a countering reflected current on the outer shielding. This is what is referred to as the SWR. If you could see the current it would look like a sine wave running along the length of the feeder. The greater the amplitude of the wave the higher the SWR will be. As this is a countering current this will attenuate the strength of signal on the inner conductor. If the SWR is high it indicates that the antenna is not fully resonant at the frequency that you are testing it on. This is why you aim to adjust the antenna for the best match at the centre of the frequency band that you will be transmitting on.

On vertical whip type antennas you make the adjustments by varying the length of the whip. Multiband antennas like this one for 2M and 70cms can be adjusted in both sections of the design. Get the lowest SWR adjustment in the middle of the band and you get maximum power output from the transmitter to the antenna. The SWR on the feeder is frequency dependant so will increase at each side of the matching point. Antennas are designed to compensate for this in the bandwidth characteristics of their design.

Most vertical antennas are designed as wideband so the drift either side of the resonant frequency will be quite wide. It's a trade off in design between bandwidth and gain, a wideband antenna will not have the same gain but it will operate over a much wider frequency spread. A narrowband antenna will have more gain but as the name suggest a much smaller frequency spread. Directional Yagi antennas and multi element beams are usually narrowband as they are designed to concentrate the forward radiated signal and suppress the signal off the back of the beam.

I should mention balanced line feeders, these are often used to feed wire dipole type antennas and consists of spaced ladder line or pre formed ribbon conductor. Some antenna designs are half and half and may have both open wire feeder and a coaxial section. This does introduce another can of worms for impedance matching but it is not relevant to this mobile installation.

[PanBiker]

As reported in the home brew thread the mobile microphone system, (finally with a latching PB PTT switch) is ready for redeployment.