Silly question

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Re: Silly question

by G0KZZ » Wed Oct 05, 2022 6:31 am

Could that signal on 154MHz be the local oscillator from one of your other rigs? What is the exact frequency of the signal?

My thinking is 154ish minus 10.7MHz-ish would be around 144MHz.

Just a thought, Mark...

Re: Silly question

by sidspop » Sun Oct 02, 2022 11:24 pm

Re-kindling the old thread.
I removed the V2000 thing and feeder, and replaced with a dual band antenna, around 6 ft tall. Not sure what it is.
I even splashed out on new feeder, Force Zero, which is very similar to the old H100. Decent compression plugs as well.
Still the same problem. I checked the old feeder by stuffing 20 watts up it, and getting 18.5 out the other end (Bird 43)
I am being heard, but I struggle to receive all but strong local stations. Signals that are lower than around s8 on meter come through with noise, not fully quieting. I have tried numerous radios, and two that seemed to work the best are TR9130, and Tr711E. Both of those have helical filters in the front end, and as such I am now tempted to think that my radio is being desensitized by a strong local signal. If I remove the antenna patch cable from switch box, and hold the pin with finger, I get a signal on 154 Mhz that is end scale, using me as an antenna. Some data transmission system, which must be very close by.
Wonder if that sounds feasible?

Re: Silly question

by M0HJO » Thu May 07, 2020 10:04 pm

I have also found the the dual band antennas work much better than the tri band ones.

I changed to dual band and a single ant for the other band.

Check the SWR on some of these tri bands, terrible.

Re: Silly question

by G0DJA » Sat Jan 04, 2020 1:07 pm

RG213 is reasonable on 144MHz, loss per 100 metres about 6.9dB, so your run of 12m means a loss of about 0.828dB. So, if you put 10 watts in at the bottom, you should get 8.26 Watts out at the top. Assuming a good match to the antenna, and I don't just mean what you read on a typical Amateur Radio VSWR meter...

The thing is, that loss is the same on the signal coming down the cable as well, which is why most stations use some form of mast head pre-amplifier, to overcome the losses on the received signal.

I'd always say that any form of "White stick" antenna, especially one that says it will do three bands, is going to be a compromise.

For general FM simplex contacts, or using repeaters, with the occasional unexpected "DX", your set up is OK. However, if you ever get seduced to the dark side of VHF/UHF DXing, you will rapidly come to realize that, for a little extra effort, a better antenna and a pre-amp will pay dividends.

Re: Silly question

by sidspop » Sat Jan 04, 2020 12:17 pm

Current feeder is RG213, for a run of 12 metres max. Can't remember exactly. Through the wall, up the outside of house to chimney.
For the costs involved I will just change the lot, no point messing about.
I have never been one for the final tenth of a dB, but what is up I expect to work, and this has highlighted the issue.
Will replace antenna with X700, and new feeder.

Re: Silly question

by G0DJA » Sat Jan 04, 2020 12:04 pm

M0XXQ wrote: Fri Jan 03, 2020 8:51 pm My money is on faulty coax, the reason behind my theory is power.
lets say you have one or several micro-fractures in the coaxial cable, on RX this is significant why? Because there isn't enough voltage to breakdown the air in the micro-fractures, however on TX lets say you're sticking 100W into an ideal match of 50 Ohms that will give you around 200V PP, more than enough to breakdown micr-fractures in cable.
Check and/or replace the coax and report back, I might be wrong but my gut is telling me its your feeder
It's a possibility, but in that case I'd put money on either a faulty connection, or water in the coax.

I have heard of microfractures on Echoflex cable, where there's a solid outer sheath round the braid, but only when people wind it up and unwind it again, as in a contest station, but they cured that by using a different type of cable. I've not had any problems with Echoflex15 permanently installed, used on 23cm, for many years. I've not heard of it happening with the more commonly used cables.

As an aside, what type of cable are you using. Even for 144MHz at least UR67 would be a minimum (I am breaking my own rule at the moment, feeding a small 70cm antenna with the thinner RG213 but I know it's going to be lossy, I just have not got round to running a length of UR67 yet. When I do, I expect to notice a difference, or else I'll know that length of UR67 is duff (I've had some of my cable over 20 years and I've not exactly been kind to it...)

I did hear people complain about the connectors on Echoflex15 having the centre conductor pulling out of the connector, but again I've not suffered this. Maybe because I didn't leave the weight of the cable pulling on the connector.

Re: Silly question

by sidspop » Sat Jan 04, 2020 11:07 am

M0XXQ wrote: Fri Jan 03, 2020 8:51 pm Okay lads, gonna throw this one out for the craic - My money is on faulty coax, the reason behind my theory is power.
lets say you have one or several micro-fractures in the coaxial cable, on RX this is significant why? Because there isn't enough voltage to breakdown the air in the micro-fractures, however on TX lets say you're sticking 100W into an ideal match of 50 Ohms that will give you around 200V PP, more than enough to breakdown micr-fractures in cable.
Check and/or replace the coax and report back, I might be wrong but my gut is telling me its your feeder.

Cheers

Rob.
That seems to be a sensible suggestion.
I had already decided to replace that antenna anyway, I never use 70cms and 6 metres will be redundant as I have a 5 ele to go up. I also have a few rolls of new feeder, so in terms of safety going up the roof I would rather change the antenna and feeder at the same time.
Doesn't give a definitive answer to question, however I could use the 'faulty' feeder as a connecting lead between sig gen and radio, and check what the performance is like on known signals.

Re: Silly question

by VK5TM » Fri Jan 03, 2020 11:56 pm

Have you thought of checking some of the remote receiver sites to see if you are actually getting out?

There is the Reverse Beacon network for digital modes, but you can use WebSDR's for voice modes, you can either wear headphones to listen to your own signal or inject a test tone for a short period (followed by your callsign and "testing" of course).

Re: Silly question

by M0XXQ » Fri Jan 03, 2020 8:51 pm

Okay lads, gonna throw this one out for the craic - My money is on faulty coax, the reason behind my theory is power.
lets say you have one or several micro-fractures in the coaxial cable, on RX this is significant why? Because there isn't enough voltage to breakdown the air in the micro-fractures, however on TX lets say you're sticking 100W into an ideal match of 50 Ohms that will give you around 200V PP, more than enough to breakdown micr-fractures in cable.
Check and/or replace the coax and report back, I might be wrong but my gut is telling me its your feeder.

Cheers

Rob.

Re: Silly question

by G0DJA » Fri Jan 03, 2020 5:27 pm

Those multiband "White stick" antennas are a bit of a compromise. Ignore the claimed gain figures, they are often optimistic and are often quoted in meaningless units like "XdB gain", compared to what, a piece of wet string? When you dig deeper, you often find that they quote the gain over an isotropic radiator (in dBi) which is a theoretical radiator that transmits a signal over a uniform spherical pattern. That gives them 2.15dB more gain to claim than from something compared to a dipole (dBd).

Your mates 3 element Yagi will have a gain of about 7.5 dBd. Your white stick is throwing the RF in all directions and, on looking the specification up I see that they have, indeed, used dBi for their gain claims. So, your V2000 has a real world gain of about 4.05 dBd on 144MHz, if you believe the claims of the manufacturer. That's the same as your mate using a V2000 as well, but doubling his power output. (7.5dBd - 4.05dBd = 3.42dB and every 3dB extra is the same as doubling the power output).

I wouldn't trust a rigs "S-meter" reading either, they often don't keep to the "6dB per S point" standard and especially when the needle goes past the 'S9' reading. One manufacturer often sets their S-meter readings to a different value to another. The ARRL used to test new radios and the discrepancies where sometimes quite large.

Again, I assume your mate is using his Yagi in vertical polarization? If not, then you can take another 1dBd or so off your gain figure for the vertical, although there's some debate about whether this actually happens when signals are being reflected and bent by propagation effects.

At 1st I thought you were saying that your mate could hear you, but you couldn't hear him, but you mention a station on the Isle of White. If we are talking about your mate hearing the guy on the IoW and you can't then that just adds another level of complexity. How far away are you from each other? Propagation can be very good in one spot, I've heard of people working Spain on 144MHz FM using handhelds from Cornwall when people at home, a few miles away, hear nothing even though they have, technically, a better set up. It can be really frustrating to see DX Cluster spots from a neighbour, only a few miles away, working long distances but you can't hear a thing but, one day, the boot is on the other foot and you are working long distance stuff and your neighbour is hearing nothing this time. It gets 'worse' the higher you go in frequency. The guys near the coast, using 23cm and above, often hear and work DX that we poor people further inland don't hear due to sea paths. Then, another day, a good duct throws signals down in the middle of the country, going over the heads of the guys on the coast...

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