[HCARC] Amplifier

Sat Mar 3 20:05:17 EST 2018

Some other problems you may have with an amplifier are you may have 
problems with RF getting into other electronics in your and your 
neighbors houses, you may not meet the FCC levels for RF exposure 
especially on the higher HF and VHF/UHF bands, and you may have problems 
with your amplifier and/or tuner because your not getting all the power 
into the antenna.

The biggest problem with poor antennas close to a house is RF coupling 
into any conductive objects near the antenna such as house power wiring, 
any phone or cable wiring in your house whether you are using them or 
not, and things like metal gutters, fences or anything else near the 
house.  With an antenna close to other conductive objects, radiation is 
not the only way power can couple.  As you probably realize, antennas 
produce a far field or radiation field and near fields.  With something 
like a dipole or vertical the near fields are generally considered to be 
important out to a distance of 1/5 wavelength.  Power can couple either 
inductively or capacitively to conductive objects in this volume. This 
non-radiative coupling can upset the impedance matching to the antenna.  
If the antenna is not well matched to the transmission line you can also 
lose power if there are conductive objects near the transmission line.

The FCC has not been very concerned about RF exposure from 100 W 
transceivers and typical antennas in typical residential areas. If you 
run high power you will have to do an RF safety evaluation of your 
station and keep that with your station records.

Now for the tuner and amplifier problems, with an antenna with a weird 
and probably unbalanced impedance the tuner will have a difficult time 
matching the transmitter to the transmission line and antenna.  What 
happens with big mismatches, whether you can match or not, is the losses 
in the tuner go up.  This leads to higher voltages and currents in the 
tuner and everything that is lost in the tuner is converted to heat.  
The heat and higher voltages in particular will stress the components in 
the tuner and may lead to component failure.  If the tuner can't reach a 
matche4d condition then the Amplifier will not see the 50 Ohm load it 
wants and efficiency will go down and any power that doesn't go into the 
tuner adds to the losses in the amplifier which again leads to heat and 
higher voltages.  Oh, yes, I almost forgot, the built in tuners probably 
won't do the job and if you run high power the lower quality tuners 
(read MFJ) won't handle the job either.  Think about the big old tuners, 
both commercial and home brew, they used large wires and straps and the 
capacitors were rated for several kiloVolts.  There is a message there!

Now for some practical experience.  When I lived in Albuquerque I was in 
a no antennas housing area.  My antenna was a wire about 100 feet long 
and one end was about 10 ft off the off the ground and the other end was 
about a foot off the flat roof.  I tried several different wire lengths 
and configurations before I found a combination that worked.  The 
configurations that didn't work (1) set off the fire alarms in the 
house3, (2) disrupted the TV my wife was watching (3) interfered with 
her computer controlled sewing machine and (4) picked up QRN from every 
electric/electronic device in the house.  I was primarily using ~ 70 W 
output although I sometimes used a 100 W output transmitter.

I wouldn't plan on using high power and I would plan on spending quite a 
bit of time trying different configurations and locations for the 
antenna.  Is it worth it?  I worked all states on 40,30, and 20 and 46 
states and all continents on 80 m with that set up. Of course it was all 
on CW.  It wasn't a great set up but I did have a lot of fun.

Kerry

On 3/3/2018 5:21 PM, Gary J - N5BAA wrote:
> Watts out is watts out regardless of how they got there, but amps are 
> EXPENSIVE especially if used purely to force a signal out of an 
> antenna.. But why can't you get an efficient antenna up.  Dale Gaudier 
> has designed an Off Center Fed Dipole (OCFD) that has one leg approx 
> 11 ft long and the other approx 55 ft long.  With a 4:1 balun that he 
> teaches how to make as the middle connector and some wire and an "Ugly 
> balun" you get an antenna that is virtually invisible that operates 
> equally well flat topped and as an inverted V.  One major advantage is 
> that if you keep the 11 ft leg close to the shack your coax run is 
> short.  This antenna is resonant on all bands 6-40 meters without 
> using a tuner.  I fly one on 3 10 ft steel chain link fence top rail 
> poles with the stiffeners at each joint.  Mine has been up for 3+ 
> years merely wired to my BIG Vertical BBQ grill.  I have a piece of 
> rebar in the ground to keep the base in place and a pulley and halyard 
> for raising and lowering antennas.  I suspect Dale's antenna might 
> also work with long leg curved to fit the space available.  Tony Moore 
> who used to be in the club had his with short leg in the front yard 
> and the long leg running over his roof.
>
> FOR DALE:  Maybe it's time to have another presentation for newer hams 
> on this OCFD Antenna.  Would you consider putting one on for part of 
> the May or June presentations since the Field Day presentation can be 
> short which could be the case if people attend the FD Planning Meetings.
>
> 73,
>
> Gary J
> N5BAA
>
> -----Original Message----- From: sgriffin1 at windstream.net
> Sent: Saturday, March 3, 2018 4:03 PM
> To: Hcarc
> Subject: [HCARC] Amplifier
>
>
>
>
>
>
>
>    I know this may be a silly question but just real curious I do 
> understand that to get the best signal out you're supposed to have an 
> efficient antenna. But if you're not able to have an efficient antenna 
> because of the lot size And trees as it is at my qth would brute force 
> of an amplifier be the answer to help in making a contact.Thanks for 
> the opinionsWD5ENHSteve
> Happy Connecting.  Sent from my Sprint Phone.
>
>
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