TV PRE AMPS for AIRBAND

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TV PRE AMPS for AIRBAND

Postby Dawly » Thu Sep 12, 2019 1:28 pm

Hi,

I read on here that some people have had success with TV PRE AMPS for airband. Years ago someone tried an OPTIMA 4 way TV AMP and said it was in a different class compared to the rubbish results he had had with scanner preamps costing 10 times as much.

I've found an inline preamp and a coax line feed of 12V:

https://www.ebay.co.uk/p/Axing-SVS-2-02 ... 2211318333

https://www.amazon.co.uk/Labgear-PSUFC- ... th=1&psc=1


I like the idea that it is an affordable way of getting the amp right up on the antenna mast, unlike my Watson airband preamp that isn't designed to work up there.

Any suggestions or comments would be appreciated. Thanks. Adam (Dawlish)
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Re: TV PRE AMPS for AIRBAND

Postby radiostationx » Thu Sep 12, 2019 6:25 pm

I have axing amp plus psufc for adsb, works very well.

https://forum.planefinder.net/threads/a ... #post-4738

Not tried this on airband though.
The axing has a much better thick ally cast casing than the cheaper generic ones.
The labgear psufc is a neat little unit, tiny.

The issue may be that it will amplify the mush a lot and play hell with your squelch control Adam.

If your antenna is a shorted design, don't forget to insert a DC blocker (aka capacitor in an f connector casing) in line before the antenna.
The axing has pass through on the 12v dc by design to feed other things in the line.
The DC blocker will stop the DC reaching the short.

A short on the DC line from the labgear psu will make it go into protection mode with red led until the fault is cleared and it will show green led.
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Re: TV PRE AMPS for AIRBAND

Postby G4RMT » Thu Sep 12, 2019 6:45 pm

They're surprisingly good, especially when you just use them to make up for feeder loss, but the reality is that they're also capable of causing other problems. As they're wide band devices any string RF local to you will be boosted too, and how will your receiver's front end cope with that. For me, I have very strong local signals from BBC Radio Suffolk, that causes my reception of BBC Radio Norfolk which is weaker, to be compromised. Marine band suffers from a nasty pager system on 155MHz - which means my scanner reception gets suddenly noisy when the pager perks up. If you could use a filter to remove above and below hairband, these devices can be useful. I don't use the one I have because I get 'phantom' signals appearing on frequencies they really are not on! If you live in an RF sparse area, they're worth a go at the low prices they go for.
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Re: TV PRE AMPS for AIRBAND

Postby Dawly » Thu Sep 12, 2019 7:23 pm

Thank you both for the advice, especially concerning the dc signal on the axing amp. I used to live near a hospital and the pages were a right nuisance across air and especially marine band. So this preamp would have been bad there. But it's not a problem here. If I do decide to try it I will report my findings in this thread.
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Re: TV PRE AMPS for AIRBAND

Postby Dawly » Thu Sep 12, 2019 7:59 pm

radiostationx,

PS.....

How will I know if my antenna is a shorted design? I've got what I think is a colinear which I bought from Nevada years ago a short white stick with 4 short ground planes. It's a smaller version of the D777. Thks.
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Re: TV PRE AMPS for AIRBAND

Postby radiostationx » Thu Sep 12, 2019 10:24 pm

Hi Adam,
Most white sticks are open circuit and are a single wire of stacked phased 3/8 wave sections typically 3 or 4 sections.

The Diamond d-777 is open type I think .

Some of the white sticks are twin lead or coaxial of 3 and a half 1/8 wave phased sections stacked with shorted top, sometimes 4 and a half sections again with shorted top.

A multimeter set to buzzer/continuity test between shield and centre of the so-239 or N socket of your antenna will tell you if it a shorted type or not.

There is very little insertion loss for the DC blocker so you could install one anyway shorted antenna or not.

A quick very rough drawing of a 3 and a half section 1/4 wave co-linear made out of rig power lead/speaker wire the "short" is a wire link shown in yellow for the drawing. This lot can fit easy in a white tube. Not as easy to make as it may seem, very very small errors in cutting of section lengths can make antenna total rubbish.
Rig DC pwr lead has impedance of around 72-75 ohms it is very important that the sections are very straight with "no slacking" at all because this upsets the phasing.

Image

The more elements, the greater the gain but with airband a 5/8 wave 8 element colinear would be a very big antenna.
Very difficult to get right DIY because of differing velocity factors due to varying copper content/production specs. Easier to make with coax but not that much easier.
The gain comes with a caveat..these antennas are not wideband at all, similar bandwidth to j-pole and they do not have low noise floor..not on your nelly.
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Re: TV PRE AMPS for AIRBAND

Postby Dawly » Wed Oct 16, 2019 7:01 pm

Mike, not sure if I thanked you for this diagram and for the advice on the DC shorted design of my white stick.
So thank you! I'm not sure how to proceed antenna-wise. I've tried upgrading the coax to WD100 but am puzzled
why it didn't do anything to improve CIV or MIL airband. I managed to get a tiny kink in the WD100 but only the one
along it's 20 meter length. I went back to try the RG58CU and things were noticeably better. Did loads of research on kinks
but concluded mine was not so terrible a kink as to degrade the signal. Maybe I was wrong. It's hard to install after RG58.

If my main losses are on UHF then I am thinking about making a seperate UHF-only bicone that I saw on the FC forum, especially as I think the design is so cool!

Of topic but just to let you know I am going to have a bash at installing the replacement EL backlight on my PRO2005 this coming week.

I keep missing post replies on forums especially on my smartphone. I must forget to tick something. Sorry.
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Re: TV PRE AMPS for AIRBAND

Postby radiostationx » Wed Oct 16, 2019 8:39 pm

Hi Dawly,
Sounds like you have an issue with the run of Webro WF100, prime suspect would be connectors/connections.
The WF100 should give better performance than rg58 over 20m distance not worse.
Something isnt right.
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Re: TV PRE AMPS for AIRBAND

Postby Dawly » Thu Oct 17, 2019 6:37 pm

Could it have something to do with my running the cable (sorry I meant WF100!) alongside the RG58 for some of it's length?

Or that some of it was suspended in mid-air rather than tacked neatly along the wall like the RG58?
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Re: TV PRE AMPS for AIRBAND

Postby mark99 » Sat Nov 09, 2019 12:51 pm

I have used a 6 way optima preamp for the last 5 years.
It works faultlessly. no noise, no birdies, clean, powerful boost from 100 to 1000 mhz .
It can pull signals from white noise and compared to the dedicated on the market scanner preamps, it is completely in its own league.
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