Re: [VHFcontesting] 6m, 2m, 70cm EME

[David Olean <k1whs@metrocast.net>]

Hello Ev

The ability of the tower mtd preamp to function in todays world is 
problematic when you are near the horizon. KA6U has had all sorts of 
trouble when near his home in the Tampa area. and that is with a lot of 
elevation on his antenna. The bad part is that with digital TV the rfi 
sounds like band noise so it can be there and you do not suspect 
anything!  KM0T has a 222 setup with two yagis and he cannot hear much 
at all. He has a FB TX signal, but cannot make many QSOs due to his 
receiver. I suspect TV station RFI. He is looking in to it.  It is just 
one of those things that you do not suspect. On 432 I have a home made 
cavity in front of my preamp. It has 0,2 dB loss but does have good 
selectivity. It is a 4" diameter copper pipe.  I had similar problems on 
222 MHz and ended up with a Tommy Henderson cavity preamp made with more 
copper plumbing parts!  I was getting hit from a CH11 TV station. It 
shows up as a slight increase in background noise and will easily mask 
any signals.
The problem with portable setups is that there can be a lack of time. 
That makes polarity selection of prime importance on 432. On 222 MHz is 
is a good choice as well.  On 144 you can probably live without polarity 
selection.   When I worked KB7Q on 432, I was able to hear him only by 
moving polarization. K4EME tried working KB7Q in Hawaii, with a much 
bigger setup and higher power but was never successful even with KB7Q 
able to change polarity. K4EME has a great setup, but is linear pol 
only.  If I were doing it, I think I would use two yagis on 432 with 100 
watts. An extra 2 dB is still simple but allows you to have fun when 
times are not optimum.
Dave

On 9/30/2024 7:00 AM, Ev Tupis via VHFcontesting wrote:
>   Hi Dave.  Thanks for the tip on the cavity filter.  I hadn't considered that.
> With the assumption that KB7Q was pointing at the horizon, I calculate out...
> 9wl antenna at +20 dBi450 watts = 56 dBmPolarization "anomoly) = -3dB (equal V 
> and H signal strength for you)
> Ground Gain +3dB
> Total approximate system ERP (coax loss unknown) for the QRP side = ~78 dBm
> This is quite an education for me.  Thanks, Dave!
> Ev, W2EV
>
>      On Sunday, September 29, 2024 at 07:26:32 PM EDT, David Olean 
> <k1whs@metrocast.net> wrote:
>   
>   Hello Ev
> I have been playing on 432 and 222 MHz of late. It seems that a power
> level of 100 watts will allow you some limited success on 432, but only
> with the most well equipped stations.  I would strongly suggest rapid
> polarity adjustments.  That is easy with a single long yagi.   The other
> suggestion would be to have a very good and selective front end. A big
> copper cavity in front of your preamp is probably needed if you are
> going to travel to different spots.  I can almost guarantee that strong
> digtal TV stations on the low end of the UHF TV band will kill most
> preamps. I have had serious trouble both on 222 and 432 that really
> compromised my hearing ability.  After the re packing of the UHF TV
> channels, there is probably a multi megawatt TV station nearby that will
> kill your 432 front end. The end result is that digital noise gets into
> the preamp and s/n ratios go South!
>
> I tried today with KB7Q who was portable in Hawaii. I have a mid level
> station and had a bunch of trouble due to poor EME conditions.  I used 4
> X 12 el with polarity rotation.  Gene had a single  long yagi  (9wl) and
> 450 watts.  Polarization was quite diffused much of the time, with V and
> H not being much different. It made Gene's signal very difficult to hear
> even with his 450 watts.  I am sure a better day would have been easier,
> but you have to realize that many days will be less than optimum.
>
> I think 432 is your best bet with low power.  I have tried 100 watt QSOs
> on 222, but success is fleeting. I have done it with my four big yagis,
> but it is barely possible. I am sure that 144 is even worse unless you
> are talking about 2 or 3 "super stations". Good luck.
>
> Dave K1WHS
>
>
> On 9/27/2024 7:47 AM, Ev Tupis via VHFcontesting wrote:
> > Of the 6, 2, and 70cm bands (those that are most likely to be in a modern HF+ radio), which 
> > band has been shown to support EME with the least overall ERP?  I'm thinking 
> > "portable EME" where it isn't possible to transport big antennas or a generator to 
> > have a kw amp. :-)
> >
> > Assume that this portable station would target QSOing with only the "top tier" 
> > of well equipped DX stations.
> >
> > I'd be interested in only recent experience rather than "back in the day". Also 
> > interested in both CW (human decode) and FTx (machine decode) modes.
> > How little power and antenna (ERP) has been successful in making EME contact(s) 
> > and on what band/mode?
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