[VHFcontesting] Total newbie questions about 2m and 70cm antennas and receive filter

[James Duffey]

John - You ask some good questions. Here are my suggestions and opinions, not to be confused with absolute answers, but I hope they are some use to you. Others may have other answers.

> Realistically, I can probably only put up a dipole for 6m in the time I have.

A dipole is a good starter. It will be better than a loop, but not as good as a beam. The few dB difference between the loop and the dipole and the dipole and a beam are significant when the band begins to open, when it is closing and for those weak band openings that occur all too often. You might think of putting together a small Moxon, or use the PAR Stressed Moxon, which are not much more difficult to put up than a dipole and will be a big improvement. If not for June, then plan ahead for future contests.

> I have a 13 element 2m beam I can put up a few feet below my 5-band 20/17/15/12/10m quad.
> How far away from the quad does it need to be to work OK?

A half wavelength is probably good enough for temporary use. You will get some pattern degradation, but the gain should be pretty close to what it would be if isolated. That is between 3 and 4 feet. I stack closer than that on the rover and it is not deleterious. The higher frequency antenna will see the biggest effect, the lower antenna pretty much not at all. 

> How far from the 2m antenna does the 70cm antenna need to be if it's on the same mast?

Again, a half wavelength or greater on 70cm. That is 14 inches. Put it half way between he 2 meter Yagi and the quad and you should be OK.

> Could I put either antenna (or both?) right in the center of the HF quad so that it is firing through the quad's driven element? 

I think the 70cm Yagi would be OK there, but I wouldn't put the 2M antenna there.
 
> Do I also need some sort of omnidirectional antenna for either 2m and/or 70cm?

The 10dB or more you would give up to an omni antenna would not be too productive for those DX QSOes. When I am roving, the guys with single loops are good out to 50 miles or so and then tend to crap out; after that the guys with beams rule. I think that with a beam, you can hear the guys off the side of the beam as well as with a loop, and you can hear others working stations that you can't hear, so you know where to turn your beam to hear them. It isn't so bad. You might want to try a dipole, but I suspect that after awhile you won't use it much.   

> Seems to me that with such sharp directionality and high F/B ratio, my rotor is going to be VERY busy. Where can I get tips on what are the best directions to point when looking for contacts in the contest?

Well you work everyone in one direction and then go on. You move stations up in bands, so you only need to turn the beam once per station, not once per station per band. It is all simpler than it seems. Point the beam in the direction of the greatest VHF/UHF ham population. To start with, these are the large population centers near you. Near being within 200 to 300 miles. Look at last years line scores and see what stations in your neck of the woods were active. Point the beams in those directions. Concentrate on the high power stations and the guys with high scores and lots of bands in the listings first. Those guys will work hard to put you in the log on as many bands as you have. In pursuing them, you will hear lots of other stations. Work them as you hear them. Call CQ often.

With your 2M setup, you should be able to work reliably out to two grids or so from your location. Patience is the key. Draw a cirlw on the map, and point the beam towards last years winners.   

> In fact, is there some online reference for new VHF contesters that I can read to get some general pointers?

Shameless self promotion. It isn't online, but the beginner's VHF column in the Fall 2012 CQ VHF magazine has a good guide for first timers in VHF/UHF contesting. They will sell you a back issue.

> Radio questions:
> 
> Do I need to add a CW filter and an SSB filter to the radio? If so, what bandwidths are appropriate?

Radio answers:

I find a narrow CW filter useful to cut down noise on weak CW signals. The bandwidth is a matter of personal preference, I like a bit wider CW bandwidth, so I would say 500 Hz is fine. The stock SSB bandwidth should be OK. 

>   On HF, I might use 500 Hz or 300 Hz, and 2.3 or 2.0 KHz.  I don't know if the same applies on VHF.

Until you have some experience on VHF, use the filters you like on HF. The biggest advantage to the narrow filters on VHF/UHF is noise reduction, not QRM reduction. Operate with the stock filters or filters you are used to until you have some experience on VHF and UHF.

> Bonus question:
> 
> I think the rig does 100w on 6m, 50w on 2m, and 20w on 70cm if I recall correctly.  Is that going to be enough power to have fun, or am I going to get frustrated? 

Bonus Answer:

Yes, that is enough power to have fun. On 6M you will have lots of fun when the band is open. If you add a beam, you will have more fun when the band is opening and closing.

The key to successful VHF/UHF contesting is to be loud on two. Fifty Watts is a bit shy of being loud, but the beam will make up for a lot of the difference. Brick amplifiers in the 150 Watt to 200 Watt range are available used for about $1/Watt and are worth the jump in power over the 50 Watts in my opinion. That 5 to 6 dB difference over 50 Watts makes a much bigger difference on VHF/UHF than you would think from your HF experience. CW is also a useful tool if you are shy of power; on VHF/UHF cross mode contacts are quite acceptable, quite different than on HF, so if you call a station on SSB and they don't come back, call them on CW. It usually works. 

On the other hand, on 70cm 20W is a bit shy and again, a 100 Watt brick amplifier would help a lot. If you can't swing that, go to CW if you have hard times raising someone. Used VHF and UHF brick amplifiers are reasonably priced and fairly common. Try to borrow one if you can't afford to buy one.

> I am in a really good QTH btw, and an amplifier is really NOT in the budget at this time.

Well location is important, so you should do well. You also live in an area with high ham VHF/UHF population, so you should be able to work lots of people. 

To get an idea of what kind of coverage you can expect, look at the section on "Reliable VHF Coverage" in the ARRL Antenna Book. It is in Chapter 23 in my 2003 edition, but it is in more recent editions and in past editions as well. It has nomographs for determining your station capability, along with charts for path loss as a function of distance. The path loss as a function of distance charts are very interesting. After a steep initial rise in path loss due to line of site and diffraction, the curves flatten out, and 5 to 10 dB increase in station capability can easily result in a 100 to 150 mile increase in communication range. So, unlike HF, where we tend to poo-poo a 6 dB increase as only an S-unit, on VHF/UHF it can mean significant range increase. And more grids to work.

I hope this helps. Look for KK6MC/r in the contest. Hope for double skip. - Duffey KK6MC/r
--
KK6MC
James Duffey
Cedar Crest NM