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eHam Forums => Satellites => Topic started by: W2MDE on January 30, 2023, 10:44:45 AM

Title: Seeking Recommendation for Mast-Mount UHF LNA
Post by: W2MDE on January 30, 2023, 10:44:45 AM
I’m starting down the Satellite road and trying to do as much “homework” as possible. I would appreciate any input from experienced Satellite Ops regarding a good quality mast-mount UHF LNA. I already have an IC-9700 available for a rig, and am currently planning to acquire a VHF QFHA and a UHF QFHA from Antennas.us (a standard M2 LEO pack is not an option since I want to keep the XYL happy by keeping the footprint smaller). Given that, I would appreciate any thoughts and recommendations for a good quality UHF LNA:

1) Specific recommended mast-mount UHF LNA with T/R switching (max RF output of IC-9700 is 75W)?  I realize that best practice is to use much less than full output.
2) Should I also consider a separate mast-mount VHF LNA with T/R switching (max RF output of IC-9700 is 100W)?  As above, I realize that best practice is to use much less than full output.
3) Pros and cons regarding powering the LNA(s) from the IC-9700 versus feeding DC from a separate bias-T arrangement?  Can the 9700 power both UHF and VHF LNAs if I decide to get both? 
4) Based on your experience, are there any other word of wisdom or “gotchas” I should be aware of?
5) FYI: My QTH is mid-latitude (FN20), and my proposed feedlines are 75-ft of LMR400.

Thanks in advance for your time and guidance.
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: WA3SKN on January 30, 2023, 12:08:07 PM
Are you planning FM or SSB/CW operations?

-Mike.
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: W2MDE on January 30, 2023, 12:15:09 PM
Planning SSB/CW ops, Mike.

-Mitch
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: N4UFO on January 31, 2023, 05:55:52 AM
I have serious reservations about omni antennas and almost always recommend against them. I have known sat ops at the top of the leader boards that used a small yagi type antenna handheld or on a tripod sometimes from inside their home that performed better than omni antennas. That said, the problem is almost always receive. I used to have a joke... how do you know a sat op using omni antennas is on a pass? You hear a lot of "QRZ? Is someone calling me?!!" :)  In all seriousness, I would be reluctant to even try it without preamps and I just hope that you are satisfied with the results after going to all that expense and effort.


As to your questions,

1) Specific recommended mast-mount UHF LNA with T/R switching (max RF output of IC-9700 is 75W)?  I realize that best practice is to use much less than full output.

Most mast mount preamps I know of have been discontinued and what's left is likely very expensive. I used the ARR RF switched regular preamps inside a box I purchased and mounted to the mast. They are still available ($149.95 new, ~$100 used, if you can find them) and I coupled them with some MFJ-916Bs for filtering out third harmonic issues and out of bad overload. Catch is, 25 watt output limit. If you e-mail me, I can send you pictures.


2) Should I also consider a separate mast-mount VHF LNA with T/R switching (max RF output of IC-9700 is 100W)?  As above, I realize that best practice is to use much less than full output.

With an omni antenna, I would... you will likely need help hearing even the VHF downlinks.


3) Pros and cons regarding powering the LNA(s) from the IC-9700 versus feeding DC from a separate bias-T arrangement?  Can the 9700 power both UHF and VHF LNAs if I decide to get both?

I ran a length of three wire rotor cable hooked to a 12v supply with a switch to choose between the preamps... black was common ground.


4) Based on your experience, are there any other word of wisdom or “gotchas” I should be aware of?

Just not to expect too much from omni antennas. If I were you, before I spent all that money on preamps, feedline and expensive omni antennas, I would get a simple handheld antenna (buy or build) and just get on the birds and learn about them first. For that matter, you might also build some simple omni antennas from PVC and copper wire and compare them to a handheld yagi so you can see what the difference is like.


5) FYI: My QTH is mid-latitude (FN20), and my proposed feedlines are 75-ft of LMR400.

Probably good enough on the feedline, preamps will easily overcome that 1 & 2 dB loss. - What to tell you to expect from your QTH given your antenna choice, not sure. Normally, guys in the North East do great into Europe, but that means low horizon passes and I have no idea if those antennas can make those passes. I see your issue is with the XYL... (Sorry, I have no experience with that, my XYL couldn't care less and even got her license, N4ICY.) Usually the issue for guys is a lack of AZ-EL rotors and we convince them to use a cheap TV rotor and set a yagi at 15-20 degrees tilt. That usually works a whole lot better than an omni setup. In fact, I started out that way, with simple homebrew directional antennas and no preamps, and worked into EU and even Africa over the SSB birds at the time... but forget the one FM sat back then (SO-50), couldn't hear it's downlink without a fully aimed antenna.


Please take all this in the spirit it is offered. Don't want to discourage you, but also don't want you to have a hole in your pocket and then be doubly discouraged. What I would really like is for you to prove me wrong and get me to put up a set of those antennas here! But even if you did, I doubt that would happen. After selling off my AZ-EL setup that helped my earn the AMSAT Century and Gridmaster awards, I find myself cross country with a very different QTH... surrounded by trees (leaves are a big deal on UHF), a steep hill immediately behind my house and a horizon full of mountains. I tend to be more interested in portable ops these days. If I can find a spot to go without same. ;)

Hope this helps... 73, Kevin N4UFO

Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: W1VT on January 31, 2023, 06:04:37 AM
Path calculations typically assume a very low noise environment.  If your antenna is near a house or similar occupied structure it is unlikely you have that. On 70cm foliage can be an issue.  Not just from path loss, but black body radiation.  A tree is very warm compared to cold sky at 70 cm. I would do some listening to estimate the noise level to determine the best location to put the antennas.
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: W2MDE on January 31, 2023, 06:24:19 AM
Kevin (N4UFO),

Love your call ... awesome! I can't thank you enough for your very candid and thoughtful response.  I take it exactly in the spirit that it's offered, Kevin.  Your caution and pain points from experience are exactly what I'm looking for as part of my research.  Most every ham as the word "compromise" at the top of their vocabulary, and I suspect Satellite work combines art, science and voodoo more than most other operating environments, so I want to temper my expectations accordingly. The thoughtful guidance that you've provided helps me do just that.

You've given me a lot to chew on, and I truly appreciate your input on all the points you've covered.  Part of the fun of this hobby is doing the research, making decisions, and then finding out how good or bad they were ... all without breaking the bank.  Then rinse and repeat.  For me, education is as much a part of this hobby as actual operating time.

Again, my thanks to you, Kevin.  And yes, you're helping me immensely.  As I continue my homework, I may reach out to you privately if that's okay.

73,
Mitch
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: W2MDE on January 31, 2023, 07:52:34 AM
Thanks, Zach (W1VT) for the advice.  Noted. I'll gather some observational data from some portable locations, trying to balance noise and sky transparency versus coax run length.  There are definitely trees on the property I have to be mindful of. I appreciate your input, Zach.

73,
Mitch
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: N4UFO on January 31, 2023, 12:53:14 PM
Kevin (N4UFO),  Love your call ... awesome!

Again, my thanks to you, Kevin.  And yes, you're helping me immensely.  As I continue my homework, I may reach out to you privately if that's okay.

Yep, love the call... was very lucky to get it. BTW, the wife, N4ICY... she says, it's not that she is cold; if anyone asks why she looks worn out (at a hamfest) she can point to me and they will say, 'Oh... I - C- Y!'  ;D

You are very welcome! And of course... e-mail me, (perhaps we can chat by phone, even, if you want) and I can send you some pictures and links. I don't have any of my former home stuff on my QRZ page (just current HF stuff) but I have a secondary page about my roving adventures: https://www.qrz.com/db/N4UFO/P (https://www.qrz.com/db/N4UFO/P) I have quite a bit more roving gear now, just not all of it is hooked up yet. So many projects, so many distractions.  :)

73, Kevin N4UFO

Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: WA3SKN on January 31, 2023, 04:07:25 PM
I haven't been on the "birds" for awhile now.  I can say I have seen omni directionals with a ground plane with the radiator tilted 37 degrees work OK... but it does have limitations.  And the AZ/EL plans can get expensive.  The best compromise arrangement was 3 el yagis tilted up 30 degrees with a single rotator... more elements narrowed the pattern too much to work well.  And the antennas were Turnstiles, not true yagis. 

-Mike.
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: N4UFO on January 31, 2023, 07:51:06 PM
And the antennas were Turnstiles, not true yagis.
Texas potato mashers, maybe?
Title: Re: Seeking Recommendation for Mast-Mount UHF LNA
Post by: WA3SKN on February 03, 2023, 10:26:30 AM
Nope!  True handmade turnstiles with reflectors and directors and mounted at a 30 degree angle up, rotatable 360 degrees. And potato-mashers can work too, just less gain!

-Mike.