[AT] radio

[Chris Britton]

I've built plenty of custom arial's to satisfy my shortwave listening and 
Ham station habits... I can think of a couple easy options for you.

Build a 1/2 wave dipole or yaggie ( with the ''driven element'' tuned to: ) 
tuned either for the center of the band, or a specific frequency... a 
favorite station for instance... Run 300ohm twin lead from the antenna down 
to the radio.. aligator clip one leg to the antenna, and the other leg to a 
ground common with the radio.

This makes for a great signal.  If you choose yaggie ( by the way.. think of 
the yaggie as a stereotypical 'tv' antenna ), you can buy el-cheapo tv 
antenna boosters that also boost fm.. ratschack sells them.. easy way to get 
5-10-20 db of gain plus the 3 or so from your antenna rig..  One thing 
though.. dipoles and yaggies are directional... dipole will have a 180' 
swing.. yaggie , depending on the number, and how you mount the reflectors 
will vary..

You could also do the coax style single wire antenna.. it will not pick up 
as well.. .. but won't be directional.  However, a trip to an auto store or 
ratschack and you can get a 'car radio' antenna booster... that and a 12v 
wall wart and a filter capacitor and you will get some cheap gain as well.

Easiest dipole or yaggie design for the home tinkerer is pvc pipe and zip 
cable.. make a big "T" out of pipe.. zip tie a section of wire across the 
top.  strip and wire the 2 wires together at each end,  use a weather 
resistant grease filled wire nut.  Then at the center of the "T", cut one of 
the wires, and hook one side toeach end of the 300 ohm twin lead...  A yagie 
is built the same way, as only the driven element is wired.  The rest of the 
elements are reflectors and are tuned for harmonics and lower/higher 
bands... U channel aluminum makes great reflectors, and can be zip tied to 
the pvc arms.. just cut to length with a hacksaw... none of these 
measurements has to be super duper precise... the rf input section on modern 
rf equipment is virtually bullet proof since pll has been around..

Sink a larger piece of pvc pipe in the ground, leaving 4' or so topside... 
outside your window, and use it as the sleave for your antenna mast to set 
in..   set your antenna mast in it.. perhaps att a 't' in the middle with a 
short 4" piece sticking out as a way to turn your mast to tune it... it will 
be quite directional.

Should be about a 30 minute 15$ fun project for just the antenna 
components.. I suspect an rf amp of either the 12vac or 12vdc varietey will 
double that cost.. Also.. if you like the dipole / ballanced line idea.. but 
want to go with coax for the use of an amt.. get a balun... that is.. an 
impeadance matcher.. the little thingy with an "F" tv connector on it, then 
the 300 ohm twin leads.. you can get them male or female.. also, ratschack 
sells the gm and common motorola car antenna adapter plugs to go from F to 
car radio styel, so whatever amp design you choose, it will work...

Ok.. now the magic... the formula for calculating antenna length based on 
freq.  This won't be precise, as this calc is rated for freq's up to 56mhz, 
however, it's one of those 'horseshoe issues, as I use this as my quick rule 
of thumb for basic fm antenna calcs...

462, divided by the freq in mhz.. thus for 88mhz, the low end of the band.. 
5.25' is the half wave size for the antenna.  Jump to 108 mhz on the top 
side, and you have 4.27'  If you wanted it int he middle of the band, .. 
4.71' .... however.. if you have a favorite station.. I'd tune it to that 
instead..

I've brushed over 95% of the real math and other technical important minutia 
for the sake of 'easy'....so for all the other rf , and EE people out there, 
keep that in mind when you fire off your comments..

de Ke4rrd

73's

Soundguy




> From: Greg Hass <gkhass at avci.net>
> Subject: [AT] Shop related - radio
> I like to listen to the radio when I'm working alone in the shop, which is
> 99% of the time.  However, being isolated in Michigan's Thumb, we are 70
> miles from any decent radio stations.  The local station leaves everything
> to be desired.  Thus, I wish to put an outdoor FM antenna on the roof of
> the shop with 75 ohm cable coming into the shop.  (I already have one of
> these on the house and it works great!)  The radio I have in the shop is a
> big portable with an extendable antenna, but it has no provision for
> external hookup.  For those members who are electronically blessed, I was
> wondering if there was a simple way to hook the cable to the existing
> radio.  I do not wish to go to a newer digital radio as this one is 
> rugged,
> has nice big buttons for my clumsy hands, and is wired into a
> switch-controlled outlet to make turning it on easy.  Any ideas would be
> appreciated.  This is sort of tractor-related as it helps me keep my 
> sanity
> when working on old equipment.
>
> Greg Hass
> Bad Axe, MI
> In the tip of Michigan's Thumb
> *********************************