Which VHF-Hi ONLY antenna or other solution?

[300ohm]

Yeah, I did a 24" holl_ands loop with a mesh reflector behind it, and it comes very close to the the AD C5. Its wide band, but the gain is only about 7 to 8 dbi. Optimizing a loop for a single channel isnt going to do much, as a loop is naturally wide band.

[holl_ands]

Didn't modeled the AD C5 exactly, but did model a Dual Loop as well as a Loop with a Screen Reflector:
http://imageevent.com/holl_ands/loops/looprefl
Loop/Screen appears to be close to optimum for Ch13 without mods:
On Ch13, Raw Gain is 7.9 dBi with F/B=F/R=15 dB (a much bigger Reflector might help a bit.....)

That 9-Element Yagi with a Folded Dipole looks like a typical (so-so) K7MEM design:
On Ch13, Raw Gain is about 13.4 dBi with F/B and F/R about 14 dB (+/- 1 dB).

You also might want to consider whether adjacent Ch12 is degrading reception and whether
an antenna sidelobe null is available to suppress Ch12 while maintaining good gain on Ch13.
TVFool signal level predictions don't indicate that this would be a problem (Analog can be
tolerated at more than 40 dB higher levels than Digital), but the power levels might not be
correct and/or the propagation loss to your location might be different due to terrain factors.
Also, some tuners have much less tolerance to adjacent channel interference than others.....

[balm]

thanks for those suggestions,

re. #12, i might just try usng a #13 CM "Jointnna" ,do yo think that might be appropriate formy intended use

is there room for optimization specifically on #13 (especially gain) with the 5 element swept dipole yagi

wrt f/b ratio, i always thought so long as there was virtually 0 or less gain on the back, that was sufficent for most situations...the 9 elemet yagi i believe gives a 14 bi f/b ratio, does a higher f/b ratio actually help that much more in my case

[300ohm]

i always thought so long as there was virtually 0 or less gain on the back, that was sufficent for most situations..

With strong enough signals, you can get stations with a very high negative gain antenna, like a paper clip, heh.

[balm]

has this fracarro been modeled here and optimized for a single channel yet, i assume its too large for practical purposes...

http://www.fracarro.com/internationa...deband_BLV.pdf

[300ohm]

Actually it looks pretty compact. No, it hasnt been modeled. Not enough details available.

[balm]

why do the pics for the "high performance band III wideband", BLV6F, in the "instruction", vs the "photo" links differ, they appear as different antennas??


is this enough to model on?

http://www.fracarro.com/internationa...258&Itemid=340

[300ohm]

I guess the instructions are for any general purpose yagi type they sell.

[balm]

when i modeled the BLV6F, the far field gain pattern runs out the backside, instead of the front, is this just a lack of info in the model, or does it take a lot more optimizing to find the correct dimensions, or am i using NEC wrong?

[300ohm]

Most likely you dont have the correct dimensions.

Post the NEC file.

[balm]

thank 300ohm, ive narrowed the evolvers values range on the variables, and it seems to be going te right way now....round 12 dbi gain

[balm]

can you explain in basic terms why/how the swept back active element in these yagis (K6STI) help improve gain and f/b, intuitively i would have thought sweeping it forward would help? , and can this swept back be applied to all different types of yagis?

http://imageevent.com/holl_ands/yagis/k6sti

[300ohm]

The gain and the f/b come from the interaction of the directors and reflectors to the driven element.
Sweeping back the DE normally broadens the beamwidth, which in this case it looks like it does.
Also sweeping back normally results in some loss of gain, but if done correctly its minimal.
Sweeping forward does the opposite, narrows the beam and increases gain, but if swept forward too much, undesirable sidelobes will appear.

and can this swept back be applied to all different types of yagis?

Yes, but the trick is to do so with a minimum loss of gain. In the above example, the directors and reflectors are carefully placed to minimize the loss.

[Choclab]

Hey, everyone. First post here, although I've read for years. I have to say, the Hoverman work is phenomenal, and many of you are outstanding craftsmen with your builds! I have an Antennacraft version that I bought a couple months ago, and I'm surprised at how well it works. But I'm sure it's satisfying to DIY one instead.

Was looking around because I have two VHF channels (8 and 9) that I'd love to get, and the K7MEM scaled for 8-10 that holl_ands posted looks perfect. I'm a little skittish because I threw together a yagi a couple of years ago, and it was a dismal failure. I didn't put the proper effort into it, most likely.

Any ideas for the boom on one of these other than wood? I see that the sim was run for a wood boom, but PVC would be so much lighter. Not sure how I'd attach the elements to the top of the round conduit, though... And after last time, I think it's important to be absolutely precise.

Maybe even better, has anyone build a mclapp or other bay-type scaled to VHF-Hi? I know it would be big, but this is just a fun DX-type project and at my location space isn't a concern.

Thanks.

[stampeder]

Choclab, stay away from plastics as booms - they're too flexible:

ABS, PVC, other plastics and Rubber for structural parts