Cutting down Scantenna

[fredg]

I actually have an old Channel Master Monitenna but it is very close to the same as a Scantenna.

I have repaired it a few times now and am getting ready to fix it again and I had a thought...

As all I monitor is VHF/UHF (VHF high) why not cut the antenna down for just those frequencies.

I swiped the reinforcement pic and modified it with what I might try and do. Before anyone jumps my case and tells me how stupid I am, note that this is with a 25 year old antenna that is already broken, I am not suggesting that this be done with a new antenna.... and I am asking because I do not know, so yes I am ignorant in this regard, so there I said it myself...

 

[ka5lqj]

Hmmmmm.....

Fred, GM,

First, I'm not going to call you, "stupid", because you certainly aren't and that's a really
harsh thing to say to anyone. All I can tell you is from looking at the "old" pic, it appears
there is some sort of "matching network" involved. Don't remove that. You might try
either cutting the elements off with a hacksaw and cover the top open ends to prevent
water from getting inside the elements and "shorting" them out. Then, try adjusting, if
possible, the matching network for better reception. OR....

You can take a female UHF connector (SO-239), solder (resin core) a suitable, say,
6½" wire to the "hot" side. Put a "hook" or even a "crimp ring" on the top. Now, take
4 wires, 7" long each and put a small crimp rin on both ends, that will allow 4-40 hardware to go through and "bolt" those to the "holes" in the SO-239. These become your
"ground plane". If you use 50 ohm coax, bend the ground "radials" down to a 45 degree angle. Then, it will match the 50 ohm cable. If you use RG-6 cable (72 ohm), leave the radials stick out straight, away from the connector. The ends of the radials, irregardless, should have some "eye protection" at the ends, just-in-case, LOL! Now take a piece of string and hang the antenna from a push-pin in the ceiling, voila'!

Now, unless you live quite some distance from the repeaters, etc, it should work. If you want a good "outdoor" antenna, may I suggest a "Slim Jim" antenna (Google is your Friend). That antenna has a lower "takeoff" angle, so you should hear stations farther out, unless you go to a yagi or quad beam antenna. Be sure you get any antenna as far up as possible, without having in become a "lightning magnet", LOL!

I use a "Slim Jim" here and have had great reception on VHF with it, as well as transmitting on 2 meter FM. Just be sure of your measurements, they really aren't critical as far as reception. An extra ½" might allow you to monitor down to the 406 mc band.

For the 800 mc "trunked band", I just use the BNC "whip" on the scanner. I can "copy" the Minden PD, 30 miles away, but never go over there. Longview, Tx is 60 miles west on 800 mcs. but I don't care to listen to them, LOL! The lower band (37 mcs and hi-band VHF do come in real well from over there though.

Just, "experiment". If it doesn't work, try something else.

Respectfully,
73,

Don/KA5-LQJ

 

[fredg]

Thanks for the detailed reply Don... my antenna actually does not have the thing you are calling the matching part... and I do not think it is a matching thing but rather the 800+MHz elements... but I could be wrong...

----------------
And it's Slackware Linux!!!! The REAL O/S!! ;-)

 

[rankin39]

You could cut the antenna down the way you pictured it, and it ought to work ok. However, the X shaped elements already make it broadbanded, the lowest freq. determined by the length of the X (i.e. it's already cut for high-band). It's just like a big "bow tie" antenna like the ones used for uhf TV. The way I cut mine down was simply to remove the center (long, low band) element entirely. Like you, mine had already partly broken and one of the low band elements was missing. You DO need a matching device with this antenna. It should have come with the antenna and should be one of those little baluns that you use with TV antennas when you feed them with coax. If yours got lost, you can get one cheap at radio shack or various other stores. Just ask for a TV balun.
Bob, w0nxn

 

[fredg]

Yes I have a Balun, I thought he was refering to the the stuff running through the horzonial center of the antenna, which my antenna does not have..

I think I understand what you are saying in reference to the X, but wouldn't it be more "tuned" if I have 19" and 6" elements? Making it more centered on 150-160 and 450-460...

Kind of the Dipole version of the RS 20-176 Groundplane

 

[fredg]

OK, so I cut my antenna down, I guess my question now is... on a fan dipole is there a hard fast rule as to the angle of seperation between the elements?

It would seem to me that I need to spread out my short angled elements now that they are shorter. I think I will check the angle on my 20-176 and make mine the same....

 

[fredg]

Here is a pic of my modified Monitenna now a VHF/UHF only. The long elements are 19.5 inches and the short elements are 6.5 inches. Looks like a baby Scantenna.... once it warms up (note snow on ground) I will mount it and see how/if it works...... (BTW my camera sucks)

I nipped and shaped the ends that I cut, turned out pretty good the ends are closed and it looks almost factory.

Despite how it looks in the pic the elements are the same size.... the pic throws it all off..