Antenna transmatch

[KC2UGV]

Ok, so I'm browsing for an antenna transmatch now. However, at near $100, my wife would shoot me if I bought one, since i just spend $375 on a radio+power supply (But, I did get a sweet D104 mic).

So, the question is: Until I buy a transmatch, how do I go about tuning my antenna, short of antenna for each band (Not all that adverse to it however, if it's the case).

I only ask, because I have no analyzer right now, so I can't really analyze my antenna system (It's a dipole, sorta. In the attic, like this:

       ^  <-- Feedpoint
     /    \
    |     |
    |     |
    |     |

It's "cut" for 20M, since I figure that would work as a eight wave on 80, quarter wave on 40, and a full wave on 10.

I'm only running very low power into the antenna currently, since I have no clue what the SWR or Impedances for each of the bands really are. I figure I wont cook my radio on low power.

So, how can I do a down-and-dirty tuner? Or some other trick that I don't know about? Or, would multiple antennas be the best bet? Am I being overly concerned about it?

[w3bny]

Honestly,

Ask to borrow one till you can afford to find/buy/build one. Unless your running a full bucket, you can find pretty good <200w tuners for pretty cheap.

As for plans, ARRL has some great home built plans

[X-Rated]

Wow. you are into some heavy duty stuff. Like when you want to use the 20M antenna for 80M, you will need to tune that and you will need to know a lot of stuff and specifically. Small changes like sneezing and differences in leg offsets will be pretty tremendous.

When you cut a regular dipole, the Q of that circuit is pretty low. Therefore it will tune over a relatively large range. When you cut an antenna short, you can make up for it with loading components and tuning stubs to offset the stray reactances. But the tuning range suffers because the Q of the antenna is high when properly tuned. Hitting it by accident will be difficult at best.

If you just want to drive it and find out what you can do, then go for it and run 5W. Your 840 should work pretty safely mismatched at 5W.

I have an MFJ 969. A lot of people badmouth MFJ tuners and rightly so. But this one is pretty good. You can sometimes find them for a little over $100. You really need a tuner.

[KG4CGC]

I have not built one yet but they look to be pretty easy to build. Use heavy duty parts all around. No need for fancy roller inductors.

[X-Rated]

I have not built one yet but they look to be pretty easy to build. Use heavy duty parts all around. No need for fancy roller inductors.

I built a tuner when I was a kid and it worked pretty good. I did bump it a few times and suffered RF burns. That was so much fun. I need to do that again.

[KG4CGC]

I have not built one yet but they look to be pretty easy to build. Use heavy duty parts all around. No need for fancy roller inductors.

I built a tuner when I was a kid and it worked pretty good. I did bump it a few times and suffered RF burns. That was so much fun. I need to do that again.

I'm sure that bumping furthered your education. Yes, as adults, we understand the importance of electrical safety in our everyday lives.
I'm just thankful that you are still around to express the importance of possibly shielding the unit. :angel

[KC2UGV]

I have not built one yet but they look to be pretty easy to build. Use heavy duty parts all around. No need for fancy roller inductors.

Well, I was thinking the building wouldn't be too hard. I've seen some designs online to look at. Are the variable air caps really close tolerance?

For example, if I build a butterfly and don't test the capacitance and do a "best guess", it should still work as long as I tune for "least noise", or no?

[KG4CGC]

I have not built one yet but they look to be pretty easy to build. Use heavy duty parts all around. No need for fancy roller inductors.

Well, I was thinking the building wouldn't be too hard. I've seen some designs online to look at. Are the variable air caps really close tolerance?

For example, if I build a butterfly and don't test the capacitance and do a "best guess", it should still work as long as I tune for "least noise", or no?

Use it with a VESWAR meter at low power and before keying tune for most noise.
SWR meter and most noise.

[N8YX]

What size attic?

If large enough, consider running a loop all the way around it, then build separate - switchable - matching networks for each band you wish to cover. Remotely activate each when you wish to change bands,

[w3bny]

Or just run Echolink and Hamsphere...