It is currently Fri Oct 18, 2019 6:20 pm

Click the link below to visit the site sponsor

The Ham Radio Shop




Post new topic Reply to topic  [ 87 posts ]  Go to page 1, 2, 3, 4, 5, 6  Next
 Mobile HF operation... 
Advanced Member
User avatar

Joined: Sat Jul 21, 2007 9:37 am
Posts: 10633
Location: Manchester IO83TK
Feedback: 60 (100%)
Reply with quote
Post Re: Mobile HF operation...
Kev, WWW.K0BG.COM is as good a place to start as any BUT in my opinion can go a bit deep for the not too die hard mobile fan..

A "decent" mobile set up is not only just about bonding , sticking short hf antennas on a mag and tuning for low vswr ( although a popular way ) isnt the "correct" way especially for the lower bands.

The lower band antennas need first to be resonant and then to be matched to coax as the feedpoint Z at resonance will or should be below 50 ohm.. for example i think my /m antenna has or has a feed Z of about 20 ohms on 40m if my memory serves me correct ( i may be thinking of 20m though) and then i had to match that to 50 ohm feed.

Bonding is your friend :lol: my old Rover was stupid, i had EVERYTHING that would take a strap bonded using the braid from old coax.. i systematically started from the mount and worked my way forward. took 2 days but it was summer so it was just a chilled out affair.

My thought is you really do need a physical connection to the car body at some point near the mount, i have 2 mounts on my van 1 is a body mount on the rear quarter panel which is drilled and bolted on..

the second is a mag mount on the roof BUT with a short strap off the mag body to a shorted out body mount for a physical connection to the body..

i don't think bonding is "tuning" the car body as in a tuned earth/counterpoise as that would be pretty impossible i recon but more one of lowering the losses in the earth system.

billy

_________________
Voice is for CBers, amateur radio operators, the average citizen, and the military. In other words, voice is for everyone with a mouth. CW is for those who choose this newer mode of communication. Newer? Why yes. Voice has been around for a million years.


Sat Feb 12, 2011 4:41 pm
Profile Send private message WWW

 Mobile HF operation... 
Contributor 2018

Joined: Thu Aug 27, 2009 6:53 pm
Posts: 466
Location: Eastbourne
Feedback: 30 (100%)
Reply with quote
Post Re: Mobile HF operation...
I had trouble with location of antenna and bonding etc on my motorhome so had to build a magnetic loop thinking it would be a compromise . After A/B tests it shows to be equal to other center loded verticals through 20-10m .I just need to connect variable cap to the motor and put it on the roof out of sight then the Mrs will be happy. /P /M is the new black.

Ta Drew


Sat Feb 12, 2011 5:28 pm
Profile Send private message

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Wed Jan 27, 2010 8:56 pm
Posts: 2939
Location: IO92mg Northampton... Boz Wellox!
Feedback: 2 (100%)
Reply with quote
Post Re: Mobile HF operation...
Kev,I've just got back from Weymouth where I managed to combine a shopping trip with exactly 23 minutes of mobile DXing........female attention deficit disorder started to kick in at that point :roll: but I have been on the radio a bit much yesterday and first thing this morning so hey ho.

Anyway parking a good 100 metres back from the surf on chesil beach about 15:00 saw the first contact on 17 (can I say bloddy contests?) to an SV station at 59 and the next into N1YTN Glenn who was tickled by working a mobile station in what was a very crowded band....that was running a TS50/RM HLA 300V and the converted CB antenna with capacitance hat.

The antenna mount is a 3/8 stud through the Zafira roof with a quick release,earthing currently consists of one piece of RG213 braid 4" long from just behind the stud mount connecting to the rear door......er,that's it :oops:

Battery is a deep cycle Exide Maxxima 900 that lasts exactly three medium size overs without keeping the engine running as I've found out previously the hard way.....run the engine and everythings good apart from running the heater with the windows open to stop over heating the engine and myself.

Efficiency,yes I reckon I might be in the market for some of that as during the week 100 watts plus a beach should normally be enough :lol: .......ok I would like the beach really and to heck with the increase in efficiency.......few palm trees too would be even better. :twisted:

Who's going to spill the beans on tuning the counterpoise as I'm clueless and Billy how did you go about matching the coax please.....as in moving a tap on a coil ?

Cheers all and good idea to pool ideas Kev right up to the point where we're all slugging it out for the same rare station. :lol:

Cheers,Dave.


Sat Feb 12, 2011 5:47 pm
Profile Send private message

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Sat Jul 21, 2007 9:37 am
Posts: 10633
Location: Manchester IO83TK
Feedback: 60 (100%)
Reply with quote
Post Re: Mobile HF operation...
M0TNX wrote:
Cheers Billy..

I know Dave AKC tunes his bike frame, and his backpack frame, I'm pretty sure he tunes the earth of the car with an L/C network, I'm sure Stephen G7DIE will tell all when he reads this, and the results those two get /m are very good..


can't see why you'd need one. surely if using an L/C matching network you would simply use it at the base of the antenna and tune against whatever available ground was provided by car/bike etc. using 1 square foot of metal as a ground isn't suddenly going to perform like 30 square foot of metal because its been "tuned".. i could be wrong..

a bike frame is a bike frame and will never look like 5 bike frames to the antenna..

maybe they are using them to help "tune" the antenna and get a good match ? same way as you may tune an elevated radial or c/poise.



Dave,

i can do my antenna both ways, i have a tapped loading coil.. i can simply tap the coil for lowest vswr on any band OR i can tap for resonance .

i used an inductor shunt fed to match the feed Z to coax on my /m antenna. basically an inductor to ground from the feedpoint of the antenna.

the antenna at the moment is just used to tap for lowest vswr as iv not finished the /m set up yet.. my old car was finished but its since died and gone car heaven.. :lol:

billy

_________________
Voice is for CBers, amateur radio operators, the average citizen, and the military. In other words, voice is for everyone with a mouth. CW is for those who choose this newer mode of communication. Newer? Why yes. Voice has been around for a million years.


Sat Feb 12, 2011 7:25 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member

Joined: Sat Jan 22, 2011 6:16 pm
Posts: 820
Location: stoke on trent
Feedback: 0 (0%)
Reply with quote
Post Re: Mobile HF operation...
Here we go then

When I set up my mobile setup, I started with the antenna mount and worked back towards the radio, I felt that due to the fact of my vehicle being 15 yrs old (ford maverick 2.7td) I wasnt too bothered about not drilling the roof, so I popped a hole as central as possible remembering that the sunroof goes backwards!! then used a 3/8ths heavyduty mfj gumdrop for the mount, this was bolted through 5mm plate as well that measures 2ft by 2ft6inches as I wanted a firm base, from each corner I then fixed and ran a 16mm2 silicone coated 126 strands wire to the 4 corners of the roof grab handles and these were terminated at each handle, 4 in total, obviously to do this I had to take the roof panel down which wasnt hard and went back quite easily, I then entered a bonding session literally,

I have in total 68 x 16mm2 126 strand straps of various lengths from 3 inches to 6/7 inches fitted to the vehicle these go from front to back and every hinge and panel are individually bonded, and also the exhaust and due to the fact the vehicle is a 4x4 on a seperate chassis I linked the body to the chassis at each body mounting point and also re-bonded the engine, gearbox and each axle and anything else that I could think of.

I then turned my attention to the feed point for the radio, this is 125 amp cable directly from the battery each lead is fused indpendently .This is as direct a run as possible, Ive added an alternative feed point for the radio from a seperate set of anderson style 200 amp leads again independently fused, a sort of fly lead that I can attach to a second independent battery if I wish, (handy for longer periods of operating).

I added in a seperate earthing lead ( 16mm2 )from the seatbase runner fixings and this goes directly to the earthing point on the radio.

Due to the nature of how I operate, normally for a few hrs and atop of a hill, I ran a seperation kit from the main radio and fitted the radiohead in place on a consule that held cds/tapes which is in the centre consule just up from the gearstick this I feel is a safe place to fix a radio as I was quite aware of "better" places but they would of been dangerous if I was involved in a accident, so I took the softer option, I think this needs a lot of thought as you never know what may happen in the future, on the same consule I added a external old pye speaker similiar to what is used in the taixis and angled this towards the driving position.This works a treat and is very loud and I only run with the volume on no4 position, or you can soon get a headache hihi.

So after all that, which took about a week of steady work I was ready for the contacts to roll in, and as yet I have had good success, all stations worked have commented on how "strong/punchy" the signal is for a mobile and that theres no hum or interferance on the signal when the engines running,

Now I am moving onto the antenna as I feel that is the weak spot on the set up, maybe some folk wont go to this amount of trouble but for me it was worth doing. Whats the point of doing the job if your shouting your head off and no one can hear you due to your "poor set up"

Sorry for the long post, but Kev did ask hihi

Regards

Lyndon.

_________________
ELECRAFT K2 ICOM706MK2G X1M
Antennas now that's a different question all together...
Think string that is wet....


Sat Feb 12, 2011 8:50 pm
Profile Send private message YIM

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Sat Jul 21, 2007 9:37 am
Posts: 10633
Location: Manchester IO83TK
Feedback: 60 (100%)
Reply with quote
Post Re: Mobile HF operation...
now im not arguing ANYTHING here BUT all i can see him doing is "tuning" the bike via a tuning unit ( basically an artificial earth system) then relying on capacative coupling to the beach.. capacative coupling is exactly the same thing a magmount does stuck on your roof.. theres no physical connection. and the bike like a magmount has rubber between itself and the earth

all i see that doing is gaining maximum ground current on the bike frame, the same as people do using an artificial earth and a bit of wire at home .. he could tune the L/C unit for maximum ground current sat on his bike on a lump of concrete in the middle of town..

i don't think that system is as directly beneficial as simply being on the beach myself but as i say i could be wrong..

im more inclined to think its a matching thing as apposed to an efficiency thing..


billy

_________________
Voice is for CBers, amateur radio operators, the average citizen, and the military. In other words, voice is for everyone with a mouth. CW is for those who choose this newer mode of communication. Newer? Why yes. Voice has been around for a million years.


Sat Feb 12, 2011 8:55 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member

Joined: Sat Jan 22, 2011 6:16 pm
Posts: 820
Location: stoke on trent
Feedback: 0 (0%)
Reply with quote
Post Re: Mobile HF operation...
m0jha wrote:
now im not arguing ANYTHING here BUT all i can see him doing is "tuning" the bike via a tuning unit ( basically an artificial earth system) then relying on capacative coupling to the beach.. capacative coupling is exactly the same thing a magmount does stuck on your roof.. theres no physical connection.

all i see that doing is gaining maximum ground current on the bike frame, the same as people do using an artificial earth and a bit of wire at home .. he could tune the L/C unit for maximum ground current sat on his bike on a lump of concrete in the middle of town..

i don't think that system is as directly beneficial as simply being on the beach myself but as i say i could be wrong..

im more inclined to think its a matching thing as apposed to an efficiency thing..


billy


Billy, Im with you on this one, In this situation I cannot see any benefits other than youve listed, a bikeframes a bikeframe after all said and done, I can only think this may help with earthing the radio maybe as well,which may also help when the batteries are running down, the biggest gain in this situation has got to be the effects of being next to the sea itself, to be honest its one that I havent heard being used inland, although 10 folks will be on now sayin they use it hihi, but if its effects can be more plainly explained then I am willing to give it a try, but to be honest I think it will be of no benefit to me at all.

_________________
ELECRAFT K2 ICOM706MK2G X1M
Antennas now that's a different question all together...
Think string that is wet....


Sat Feb 12, 2011 9:06 pm
Profile Send private message YIM

 Mobile HF operation... 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5662
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: Mobile HF operation...
Here's another way of describing things:

Say that we have a ground plane antenna comprising a full-size quarter-wave vertical section sitting above 4 full-size quarter-wave horizontal radials; suppose it's all elevated a short distance above ground.

Step 1: shorten the vertical section, but add a base loading coil to maintain resonance. That ensures maximum current into the vertical.

Step 2: shorten the radials, but add a loading coil to each one to maintain resonance. That ensures maximum current into each individual radial.

Step 3: now remove the four radial loading coils, connect all four short radials together, and insert a single loading coil between that point and the coax braid to maintain resonance. That ensures maximum current into the radial system.

Step 4: now remove the two loading coils and replace them with a single loading coil connected between the vertical section and the junction of the four short radials. Adjust that single loading coil for system resonance, and use a link coupling around it to connect the coax; adjust the turns on the link coupling for a perfect 50 Ohm match. Alternatively tap the coax braid and centre conductor directly onto the loading coil; adjust the tap positions to achieve a match.

Nothing revolutionary there - just a steady progression of logical steps. But if we wanted to get all fancy we could say that at Step 3 we "tuned the radial system to resonance on the operating frequency, this effectively connected the radials into the soil by capacitive coupling"

I think Billy had it right when he said we are simply tuning the whole system to resonance - short vertical plus short radials. It can actually be done with a single loading coil - no need to have a separate one for the vertical and the radials (bike).

73,
Steve G3TXQ


Sat Feb 12, 2011 9:22 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member

Joined: Sat Jan 22, 2011 6:16 pm
Posts: 820
Location: stoke on trent
Feedback: 0 (0%)
Reply with quote
Post Re: Mobile HF operation...
Thanks Steve for putting us right with what the effects of adding this to the system makes.

Your thoughts on bonding would be appreciated

Regards

Lyndon

_________________
ELECRAFT K2 ICOM706MK2G X1M
Antennas now that's a different question all together...
Think string that is wet....


Sat Feb 12, 2011 9:34 pm
Profile Send private message YIM

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Mon Jan 04, 2010 8:23 pm
Posts: 4278
Location: Still by the sea, but sadly only IO83ls
Feedback: 17 (100%)
Reply with quote
Post Re: Mobile HF operation...
From what I've learnt so far, and from my experience, is best summed up by what Steve has said above :lol: the ground tuning unit cannot replace the acreage of metal required for a good ground plane at HF, what it can do it match the vehicle to the feed. I couldn't use my backpack kit without a counterpoise normally, however with the ground tuning unit that's all I use, the frame and the GTU, tune for maximum ground current and tx away. The GTU allows me to use the screwdriver multiband, and match the ground network, all from the comfort of my driving seat :wink:

Dave and I carried out some back to back tests with my new antenna last night, previously I'd been using my screwdriver antenna for mobile and static DX, when parked up I changed whips and installed a rather large cap hat, this worked really well, but was never as good as Dave's centre or top loaded antennas, I re-evaluated my needs for when parked up, if I'm going to the effort of changing whips and adding the cap hat, why not just change to something more efficient, this is why the centre loaded antenna was created. During our back to back tests, there was nothing in it with our antennas, Dave's was a bit longer and more top loaded, but our reports were almost identical with each station we contacted, we were parked within 100yds of each other, a bit too close really, but the only way to test the antennas. From this test I can see the improvements made in changing to a different antenna straight away, I'm usually down on all signal reports compared to Dave, so I know I'm heading in the right direction. The Screwdriver remains my default mobile antenna, for it's simplicity and convenience, but when I'm on the DX hunt, it's relegated to passenger.

One thing from all this that I can say, with absolute certainty, is that the sea makes a massive difference, just today I was out with the backpack kit by the sea, I worked California with relative ease, until the adjacent station fired up, and when someone tells me I'm 59 they usually follow this with how shocked they are, all but the hard nosed contester gives a mobile or pedestrian mobile :wink: a genuine report, even the rare DX stations give a genuine report. It's not always blow the windows out signal reports, some are low, but all are welcomed.
I have spoken to Gordon, WB9BCL, many times from the car, today he heard me above the European horde and pedestrian mobile, he didn't believe I was using 80w, he said he's spoken to mobile/portable stations before who've said they're on low power, but are using more like 800w, I had to describe the system I was using in order to validate it, I switched the amp off and went to 5w, still 57, so I pulled the power lead on the FT817 and worked purely from the nicads, that's 2.5w max for a 55 in Illinois, he and I were both surprised, a simple top loaded home brew antenna and 80w made me into a big gun :lol: you've just got to love the effect mother nature has when down by the beach.

One other thing I'm grateful of is my car and it's designers, it's silent on HF, I get zero noise from it when mobile, any interference is either atmospheric, other cars, or the hash from housing and industrial estates.

_________________
My online log

My videos


Sat Feb 12, 2011 9:40 pm
Profile Send private message WWW

 Mobile HF operation... 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5662
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: Mobile HF operation...
g7imo/qrp wrote:
Your thoughts on bonding would be appreciated


Let's take an extreme example of an 8ft vertical used on 160m. The radiation resistance of the vertical is about 0.1Ī©, so we better make sure that anywhere we have displacement currents flowing - the vehicle body - the path resistance is small compared to that value. That makes bonding seem like an "good idea" :)

73,
Steve G3TXQ


Sat Feb 12, 2011 9:49 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member

Joined: Sat Jan 22, 2011 6:16 pm
Posts: 820
Location: stoke on trent
Feedback: 0 (0%)
Reply with quote
Post Re: Mobile HF operation...
G7DIE------Thanks for the info and well done on your dx contacts, it certainly makes for good conversation on the bands and keeps us all inspired to do more.

G3TXQ Thanks Steve, at least all that work I did wasnt for nothing then, 160 mtrs mobile now thats the way to go, maybe when Ive cracked 40/ 80 mtrs thou first,give me about 5yrs and maybe we will give it a try hihi



Regards

Lyndon

_________________
ELECRAFT K2 ICOM706MK2G X1M
Antennas now that's a different question all together...
Think string that is wet....


Sat Feb 12, 2011 9:57 pm
Profile Send private message YIM

 Mobile HF operation... 
Moderator

Joined: Fri May 22, 2009 1:23 pm
Posts: 5662
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: Mobile HF operation...
G7DIE wrote:
One thing from all this that I can say, with absolute certainty, is that the sea makes a massive difference, just today I was out with the backpack kit by the sea, I worked California with relative ease, until the adjacent station fired up, and when someone tells me I'm 59 they usually follow this with how shocked they are, all but the hard nosed contester gives a mobile or pedestrian mobile :wink: a genuine report, even the rare DX stations give a genuine report. It's not always blow the windows out signal reports, some are low, but all are welcomed.


EZNEC predicts that at low take off angles the Gain of a vertical near salt water on 20m is somewhere between 7dB and 10dB higher than over soil, depending on the properties of the soil. Definitely a good place to be!

Steve G3TXQ


Sat Feb 12, 2011 10:05 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Mon Jan 04, 2010 8:23 pm
Posts: 4278
Location: Still by the sea, but sadly only IO83ls
Feedback: 17 (100%)
Reply with quote
Post Re: Mobile HF operation...
Thanks for working that out Steve, I had wondered just how much of an effect the salt had, I'm starting to notice the phenomenon that G4AKC has experienced for years, disbelief as to the PEP and the equipment being used. I'm hoping to be QRV on 40m tomorrow from about 06:30hrs, I'll be putting that 7-10db to good use :D

_________________
My online log

My videos


Sat Feb 12, 2011 11:08 pm
Profile Send private message WWW

 Mobile HF operation... 
Advanced Member
User avatar

Joined: Sat Jul 21, 2007 9:37 am
Posts: 10633
Location: Manchester IO83TK
Feedback: 60 (100%)
Reply with quote
Post Re: Mobile HF operation...
Even antennas like the miracle whip and ATX walkabout come alive on the beach.

_________________
Voice is for CBers, amateur radio operators, the average citizen, and the military. In other words, voice is for everyone with a mouth. CW is for those who choose this newer mode of communication. Newer? Why yes. Voice has been around for a million years.


Sat Feb 12, 2011 11:59 pm
Profile Send private message WWW
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 87 posts ]  Go to page 1, 2, 3, 4, 5, 6  Next


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.