Mobile Muddle

I knew there was a reason I didn’t have a radio in the car. I just couldn’t remember what it was. Now I remember. SWR. After getting out quite well the other day from the mobile I thought I would add the DX500 to it and get out a little bit better….wrong. I went down the local electronics bazaar (Glodok) and purchased cable, connectors, lugs, wire, terminal strips, heatshrink, a dummy load and even a small switching power supply I didn’t need because it was going cheap. Spent the evening making up the welding cable with 4 30A fuses right up by the battery, heat shrink over the ends of the connectors etc etc and out we go to run the leads into the car. As I did not check the installation before I made up the cables I was not aware that the Kia Carnival Diesel that I was going to install it in does not have any holes in the fire wall to run 2ea 3/4" hunks of welding cable thru. Buggar!
Buggar and double buggar! And worse. I was able to cut a small hole in the rubber where a cable loom entered the car and poked a couple of 6mm wires through. Doubled up it might be enough for a few hundred watts. Won’t run the DX1600 for sure. Quite a long run into the back seat and bolted the conctions together.
Stuck the wilson 5k on top anf fired up the 257 to check things our. Seemed all right. The antenna was working the same as the other day although it need to be shortened a bit. Resonant around 27095 so would like to bring it into the mid 40’s somewhere. Fired up the DX500 to check the car. The car FM radio came on went off then stayed on. Lights came on that shouldn’t. Things were not happy behind the dashboard. Seemed the Kia did not like the Amp and the Amp certainly didn’t like the Kia. The SWR was 3 or 4 to one with the amp in line and on. Funny. Check it without the amp. 1:1.
Bother. Brain wave time..check it with the dummy load. Put the dummy behind the amp and keyed 450 FM with no SWR at all. Cables are OK. 30W from the radio 1:1. 50W from the Amp and SWR hits the roof. Do we need to ground the mag mount? Run a counterpoise.? I would like some ideas. A tuner would fix the problem but all mine are too big. or too small.
If anybody reading this has some ideas I woiuld be glad to hear them. Wilson 5k is mag mount and situated on the top of the roof in the clear. Lead from radio to amp is RG58 and about 75cm long, lead from amp to SWR meter is RG/8 and about 50cm long and SWR meter to antenna is the coax that came with the wilson 5K. mag mount.
Grrrrr. Will be mobile tomorrow but not with the DX500.
Any suggestions appreciated and acknowledged.
THanks guys. There goes the convenience of the magmount! I have renamed this "mobile muddler"! Suits me better. One question though…Why didn’t the 30W cause the SWR to go haywire? The fifty watts from the amp certainly did. I will try it again with the ICOM 706 with whatever it puts out and see if it still happens. Then I will earth the AMP. That is the next easiest thing I guess.Whatever I do to ground the magnetic antenna base  I am losing the whole reason for using the magnet mount in the first place which is flexibility. If I am going to bind the Magnet in place with earth wires I may as well just jet a plate and afix it to the roof rack, which will probably need grounding to the chasis also. I am going to persevere with the magnet and see if I can work it out. The AM radio in the car came on by itself so there must have been a lot of RF getting into the system somewhere. Grounding the amp may be enough to let me run a couple of hundred watts. Don’t need a lot. Will let you know.
I just got a message from 35SD001 via DK Cluster. He said he had the same problem with the Wilson 5k.He changed to Wilson 1k and problem went away…..
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2 Responses to Mobile Muddle

  1. Unknown says:

    Hello,David remember I mentioned that MAG MOUNTS do not like high power, you would need to run a ground wire from the base of the mount.Better if it was boot or bonnet mount with an earth strap on boot or bonnet lid to body.If possible earth coaxial cable to same earth as near as possible at base of mount.Never very successful magmounts with this sort of high power as manegnetic mounts sit on top of paintwork, not earthed onto actual metal body part.Sometimes a good earth on amp to body does help but again if antenna mount earthing is poor………….high swr.Hope this still no change here still hanging on!

  2. ssl-100...aka mike says:

    hi dave i agree with aja the mag mount is a poor setup for high power and low power for that matter but thats open to debate ………… the old days when i use to run mobile high power i played with mag mount antennas and found my 600 watt pep setup on the old xa falcon (center of roof for antenna)… i had to put two braided earth strapps to the two front seat safety belt posts (the top bolts on the pillars).from them to the mag mount earth point within the mag mount .this required removing the nut under the pastic cover on the bottom of the mount.this pastic cover is easy replaced with the same pastic firm that kids use on thier school books .it worked for me no more vswr pobs.braid from "silver" rg213 works good for at least 600 pep.the strapp can be covered in heatshink in the colour of your choosingthese days but back then i could only get black (white car) so got rid of that idea fast.glen

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