mike wrote:

Gentlemen,

I work for a student transportation company using UHF radio
communications. While I have played around with CB radios several years
ago I have no experience with UHF.

Our system operates on either of 2 channels near 470MHz. Channel 1
transmits via a repeater located in the hills a few miles away, while
channel 2 is direct.

For most of the last school year we have operated on channel 2 as
channel 1 wasn't working. A company recently came out (not following
known company authorization proceedures), and apparently repaired a
faulty repeater. Our company was charged about $185.00 for parts and
over $600.00 for labor. The rate worked out to be $80.00 per hour over
7.5 hours. Not only does this seem a wee bit steep to me, but the
communications are still poor on channel 1.

Assuming that the repeater is fine now, the problem seems to be more
related to the individual busses. Over the course of time our mechanics
have swapped-out radios, mics, and probably antennas as well. Given the
nature of the problems and my previous (limited) experience with CB, my
suspicion is that the antennas on the busses need to be tuned.

I used to tune my CB antennas with an SWR meter and get good results. I
understand the basics enough to be able to do that and could probably
teach our mechanic as well. However, since I have no experience with
UHF I don't know if there's more to it with UHF over standard CB and if
there is more equipment required than an SWR meter. I am just having a
real difficult time paying $80.00 an hour for someone to do something I
used to do quite easily.

Mike

$80 per hour isn't a bad price if the work is good. UHF requires more
expensive instruments than CB, they amortize that in the labor costs --
in other words that $80 per hour is for the guy _plus_ the equipment.

Assuming the radios in the busses are in good shape (you could send them
out for servicing and alighnment/checking for much less than you could
have the guy come out and do it) you are left with antennas and cabling.
I wouldn't expect that it's _just_ the antennas - coax can be pretty
lossy at those frequencies, if it's been beaten up it'll show.

So get an SWR meter that'll work reliably at 470MHz, and try adjusting
some antennas. Try replacing coax as well, and if either fix seems to
work then keep it up.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:
$80 per hour isn't a bad price if the work is good. UHF requires more
expensive instruments than CB, they amortize that in the labor costs --
in other words that $80 per hour is for the guy _plus_ the equipment.

Thanks, Tim. I am familiar with such issues, although I've had no
reference points for this type of work. If that is the prevailing rate
for UHF work then I'll accept that.


Assuming the radios in the busses are in good shape (you could send them
out for servicing and alighnment/checking for much less than you could
have the guy come out and do it) you are left with antennas and cabling.
I wouldn't expect that it's _just_ the antennas - coax can be pretty
lossy at those frequencies, if it's been beaten up it'll show.

That's where I was headed with this. I have no desire to replace
qualified service companies or personel, rather, it seems worthwhile to
look into the feasibility of moving some of the more routine service
requirements in-house. If it's not practical for us to tackle the
antenna tuning/coax/connections ourselves, then we'll just have to deal
with that.


So get an SWR meter that'll work reliably at 470MHz, and try adjusting
some antennas. Try replacing coax as well, and if either fix seems to
work then keep it up.

Thanks. I was concerned about there being some differences in the
process that I was unaware of between CB and UHF. My limited
understanding of antennas leads me to think that the principals remain
the same and therefore the process should as well. Nevertheless, it
seemed appropriate to ask.

Mike

Thanks. I was concerned about there being some differences in the
process that I was unaware of between CB and UHF. My limited
understanding of antennas leads me to think that the principals remain
the same and therefore the process should as well. Nevertheless, it
seemed appropriate to ask.

Mike

The principal is the same, but remember you are dealing with frequencies
about 20 times higher so what you are use to will be multiplyed by 20. That
is if you were cutting off an inch at a time theh you only need to cut off
about 1/8 of an inch. Also make sure the SWR meter will work at the higher
frequency. One desinged for a higher frequency will work at a lower
frequency just fine if you can generate enough power for the pickup. One
for a lower frequency will not work on a higher frequency as the pickup will
start approaching a large portion of a wavelength. Also with lossey coax
(which most all are at 400 mhz, the swr will be masked so a 3:1 or so at the
antenna will show up as almost a perfect match at the transmitter end.