connectors for RFS 158-50 anyone?

[VK2KRR]

Gday

Would anyone have or know where I can get 2 x female N connectors for RFS cellflex 158-50 cable ??

I know I can get them through the old VK Discount cables, but it could take a few weeks and fairly expensive.

If anyone would like me to actually be able to hear them on 23cm greater than a 4x1 during the coming field day, I need the connectors to set up a RX only line with pre-amp. So please ask around see if anyone knows of any. Thanks.

[VK3HZ]

Hi Leigh,

Is your preamp at the antenna or in the shack?

Regards,
Dave

[VK2KRR]

It will be at the antenna.

[VK2OMD]

It will be at the antenna.

There is no doubt that reducing the loss of the feedline from the preamp to the receiver improves your receive capability (S/N on a weak signal)... but the difference might be just tenths of a dB for terrestrial paths.

So if you don't get the connectors, try whatever you have, even RG213 should not be far down on the 1 5/8" cable in terms of received S/N.

The article Effective use of a Low Noise Amplifier on VHF/UHF discusses the issue and contains a link to a tool for evaluating the impact of different configurations.

Owen

[VK3HZ]

Yes, the receive performance is going to be set by the front end of the preamp. (BTW - You should aim for very low loss between the preamp and the antenna). However, the preamp will have 25 or 30dB of gain. So any loss (within reason) in the coax from the preamp to the IC-910H will have a negligible effect on things. Using RG213 instead of that huge stuff you have will make about 0.05dB difference by my guesstimation - you wouldn't detect the difference.

In fact, if you read some of Owen's stuff, putting attenuation in the line between the preamp and rig may possibly improve performance - the RG-213 will act just like a 4dB attenuator.

So, I reckon you'd be much better spending your money on a length of RG-213 and connectors (probably total cost much less than just the Cellflex connectors) and keep the Cellflex for a 13cm Tx line or something.

Regards,
Dave.

[VK2OMD]

... you wouldn't detect the difference.

For typical installations, that is pretty right.

Click on the pic for a full size view.

Above is a G/T model for a typical configuration on 1296, using 30m LMR400 between LNA and transceiver. The losses in the line are calculated at VSWR=2, LNA's optimised for noise figure usually have poor input VSWR. Note the G/T figure, it is -6.2dB/K.

Changing the feedline to LDF7-50 (similar to the Cellflex 158) doesn't change the G/T figure enough to change the rounded answer of -6.2dB/K... so less than 0.1dB improvement in G/T, which means less than 0.1dB improvement in S/N.

Now what about doing the unthinkable, using RG213? Well, that is enough to change the rounded answer to -6.4dB/K, so which means a 0.2dB degradation in S/N.

Of course, the numbers depend on the scenario, and I gave a link above to the article and tools to plug in your own scenario.

Thinking laterally for a moment, what about RG6 at $0.30/m? It comes in at G/T=-6.3dB, which means a 0.1dB degradation in S/N... but it is probably better than that as the VSWR on the RG6 is probably a little lower (again related to the input impedance of a noise figure optimised FET LNA).

There is no doubt that Cellflex 158-50 is better, but I am with David, there is doubt that you will pick the difference.

Owen

[VK2JDS]

Hi Owen, its a single stage vk5eme preamp with the input loop optimised as best as possible. I was assuming it would be connected onto good cable due to the length required to go across the ground and up Leighs tower to the dish.
73's de Dave jds

[VK2OMD]

Hi Owen, its a single stage vk5eme preamp with the input loop optimised as best as possible. I was assuming it would be connected onto good cable due to the length required to go across the ground and up Leighs tower to the dish.
73's de Dave jds

Hi Dave,

I hear frequent debate on whether gain is more important or NF.

As you know by now:

• if gain is high enough, S/N is not very sensitive to changes in gain; and
• if NF is low enough, S/N is not very sensitive to changes in NF.

There are no Rules Of Thumb, you have to run the numbers, and the G/T spreadsheet provides a calculation framework.

Sure, if you have a preamp with low gain, the noise due to line loss to the transceiver AND the transceiver's own noise make a larger contribution to the system noise temperature.

You can think of it as David suggested, subtract the line loss from the LNA gain to obtain an effective Stage 1 gain in the cascade.

The results with a NF=0.6dB, G=21dB LNA will be different to the example that I gave. I don't know anything else about Leigh's configuration, but running the numbers on my earlier example, but with the EME103 single stage LNA specs begs the question why build the single stage preamp?

It probably won't surprise you after your own experience that in the example scenario, 30m of RG213 and a 33dB gain LNA has the same G/T (same S/N) as the Cellflex 158-50 and 21dB gain LNA.

But... one can talk about examples forever, the only thing they show is that Rules Of Thumb don't solve the problem, the solution is in the parameters of the specific scenario.

Owen

[VK2OMD]

Leigh,

I see someone advertising connectors for LDF7-50 real cheap on VKHAM. Do they suit Cellflex 158-50?

Owen

[VK2KRR]

Good question

[VK2XSO]

The Andrew Heliax ones are close. But they won't fix exactly. I've not had the chance to try terminate one on the other before. You may be able to get away with it for ham use.

I've been keeping an eye out for connecters for you Leigh, but have not been able to find these specific connectors being recovered or on their way to the scrap yard. I just cut of a 78-50 connector and though I'd check what it was you were looking for.

[VK2JDS]

This morning i repaired a male-male 6" short run of the flexi version of ldf4-50, the connector had been branded with an optus mobile tag, and was bought from scrap at blue mountains field day.
The interesting part is the back section of the connector was a sleeve which could take all sorts of heliaxes.
Once you solder on the centre pin and trim the outer copper back a bit the heliax pushes through the back part and lodges firmly into the connector with the centre pin correctly spaced. Then heat the back part of the outer shell of the connector and some of the heliax copper-outer carefully with oxy-camping-gas mix (or oxy-acetylene if you have it) and quickly run some solder into the gap and its done!
seems the critical bit is the centre pin, you can adapt or braze on outer rings to match the heliax size you have , then just fit a centre pin, push the heliax through till its the right spacing then solder the copper sleeve to the brazed-on jacket. if you get the idea.
so easy!
73's de Dave

[VK2KRR]

G'day
Thanks for the responses.

Ive just found out that the existing cable I am using is actually 158-50, not LDF 7-50. So I'll climb up in the roof in a moment and check for the part number on the connector.

[VK3BA]

G'day Leigh, I've just emailed you the RFS Cellflex spec sheets I've had for a while. If we can confirm it's exactly what you've got, I can put the word around again to see what turns up.

Cheers,

[VK2KRR]

OK the part number of the existing connector is ...............

RFS-NF-LCF-158-072D

Need 2

[VK2OMD]

Good question

Google is your friend!!!

From http://www.rfsworld.com/index.php?p=70&l=1#question_35.

Q:Are RFS coaxial cables and connectors compatible with Andrew cables and connectors?

A: Our CELLFLEX® "LCF" (formerly FLC) foam cables and connectors are compatible with Andrew Heliax "LDF" foam cables ½ inch, 7/8 inch, 1-1/4 and 1-5/8 inch sizes only. Our Superflex 1/4 inch and ½ inch is compatible with the Superflex Andrew cable.

It doesn't quite say that Andrews connectors go on their cable, but does say that their connectors go on Andrews cable... so it is likely that they are compatible.

Owen

[VK2KRR]

Owen

Apparantly LDF750 connectors will fit. Do u know who was selling them on VKHAM and if they were still on there?

[VK2OMD]

Owen

Apparantly LDF750 connectors will fit. Do u know who was selling them on VKHAM and if they were still on there?

The advert was fresh on 9/1 when I posted about it. My guess is that if it isn't there now, they were sold. Someone else might have acted more quickly, since IIRC they were pretty cheap.

Owen

[VK2KRR]

Ive luckily landed some Andrews L7PNF connectors here already. Older style LDF 7-50 connectors.
Should do the job, will give it a go if the temperature ever cools down.

[VK5PJ]

Owen and Leigh,
the gent in question (Ken) VK3ZER had connectors for ANDREW Heliax cable but had end of roll cable from "Huber & Suhner" which were not compatible.

I had ordered two 40 metre lengths from him and was about to send the money when he told me it was NOT Andrew cable at all and the Andrew connectors he had did NOT fit

I enquired with Huber & Suhner about connectors, yes min order is 500 as they have to have than many to fire up the manufacturing people... so my request for 4 connectors would not cut the mustard... they flatly refused to tell me the price of a connector, so I am guessing its way more than I can afford.

I have a phone number if its needed for Ken 3ZER, email me if you need it (OpInfo has my email)

Owen

Apparantly LDF750 connectors will fit. Do u know who was selling them on VKHAM and if they were still on there?

The advert was fresh on 9/1 when I posted about it. My guess is that if it isn't there now, they were sold. Someone else might have acted more quickly, since IIRC they were pretty cheap.

Owen