CB problems - promising development!
I installed a Firestik No Ground Plane antenna and coax on my CB tonight. You must use an NGP coax with an NGP antenna. Preliminary tests in the garage are quite promising.
I installed an NGP 4' long antenna. Since it has a 3/8 -24 thread on it and the BRP has a 6 mm 1.0 thread I had to modify the mounting block. I turned the block end for end and drilled and tapped a 3/8 - 24 thread about 1/2 inch deep. I rotated the block 90° and drilled and tapped a new 6 mm 1.0 thread for the mounting bolt and a 4 mm .7 thread for the coax connector screw. I put these two holes in the same relative position with respect to the antenna thread as the OEM holes. This makes the brass block dual purpose in case for whatever reason I need to reinstall an OEM antenna. The blocks are priced at $49.99 which is why I did not take the easy way out and just drill and tap the existing antenna thread for the new one.
Running and stashing the 17' of coax wasn't a problem. I wrapped a bunch of it into a bow tie loop and put it under the left side rear access panel. You must use a bow tie loop, not a circular one. A circular loop mucks up the electromagnetic tuning of the coax. Then I crossed straight over to the other side through gaps in the plastic under the seat. For now I have it run to the front and connected to an SWR meter for tuning. The SWR jumper goes back to the CB unit.
In my testing and adjusting so far, in the garage, I have no feedback squeal. The SWR is about 1.8 for channel 1, 2.0 for channel 19, and 3 + for channel 40. I have to do more tuning outside where conditions are closer to actual usage.
I will do more testing and tuning today, Wednesday, 4/13, and see how good I can get the settings, how clear the transmission is, and what the range is. I'll post more info and some pics also. I forgot to take pics of the installation before I buttoned everything up but I'll get what I can.
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Sorry if I am teaching you to suck eggs
http://www.spyderlovers.com/forums/a...d=132117&stc=1
The coax length has to be a part of the frequency range, for CB the frequency is approx 11 metres so the coax should be half wave or full wave, so 17 ft equates to 5.182 metres, being half wave. Then you tune the antenna length after using an SWR meter to see what needs adjusting. As you have no real groundplane, they have used a fixed coax length to compensate.
An SWR over 3 will almost certainly blow your output transistor in the amp as the signal will feed back down the coax and straight into the output. Nasty.
Can you line under the bodywork where the antenna is mounted with tin foil and ground it? That will help making a groundplane to reflect the signal and may improve matters. As you probably know, the signal radiates along the whole length of the antenna, not the tip. It needs a groundplane to reflect a "ghost" signal. Therefore, a quarter wave antenna (about 2.5 metres) will have a radio wave leaving the antenna as a 2.5 metre wave and the groundplane will have a similar "ghost" or reflected image making the transmitter look like a half wave in total is leaving. This keeps the output amp happy and efficient. Bundling up 5 metres of coax will not help but is the only way to achieve what you want given the installation on a plastic body.
This is a common problem on boats, even though water is a fabulous groundplane, it is difficult to get it set up properly with a fibreglass hull. I have seen fibreglass cars having their whole roof lined with foil and the antenna mounted mid roof just to try and receive a commercial radio signal in MW.
Sorry if I am teaching you to suck eggs / telling you the bleeding obvious.
BTW I am licenced from ELF to EHF (2200 metres to 1mm) but nowadays I have a small handy that covers 2 meter amateur, 70 cm amateur as well as UK and US PMR bands all at 5 watts output. 5 watts gives 3 to 5 km range, so probably better for group rides? Certainly easier to install an antenna as a tuned antenna will be no bigger than 8 inches (helical wound). It cost USD 70 for two radios on eBay. I have checked these with a frequency analyser and they are extremely clean with little bleed.
Jeff G6BBN
http://www.thunderpole.co.uk/cb-radio-guide.html
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CB Squeal Seems to be solved
I finally had luck with the CB squeal. I'd read a bit about other riders changing headsets from J&M or EdSets to the BRP. I did that in June and it seemed to work Ok. Then when we went riding the squeal was back. I was going to change the BRP headset in the drivers helmet to the passenger plug but when I unplugged the passenger headset cord the squeal went away. WOW (it's an EdSet passenger cord, but see below). So I headed down to the baseball fields to check the SWR's. Last week I installed the Firestick NGP antenna and NGP coax cable.
Previous SWR's with the J&M antenna was Ch 1=2.9, Ch 40 = 2.7
Firestick SWR's Ch 1=1.6, Ch 10=1.3, Ch 20= 1.0, Ch 30=1.3, Ch 40=1.7 This translates to an increase in efficiency from 80% to 95%-100% by changing to the NGP antenna. http://www.firestik.com/Tech_Docs/SWRLOSS.htm
I don't know why the SWR gets better in the midpoint of the channel set??
So then to confirm the EdSet passenger cord interference I plug it back in and no squeal?? What the heck, I'm confused, but the CB works now
Here's how I ran the 17 feet of CB coax to keep it away from metal.
It goes across the back and loops in the space between the two chrome mounts of the tail lights. It crosses 2X then goes up to the antenna. On the right side it came from the CB and looped upward and over the top of the right saddlebag past the radio. The radio didn't seem to interfere with it, I was afraid it might.
More to come if the squeal rears it's ugly head again.