Diamond X30 hookup?

[SpaceForceCmdr]

I'm getting one of these to use as a base station antenna (even though I only have a Yaesu HT at the moment). I may put it outside at some point, but for now, it's going to be in my attic on the 2nd floor. I'm thinking I will just attach it to a tripod, and set it on the floor. From there, the line feeds downstairs and I will connect it to my HT, or maybe my SDR for listening. Is there anything else that I need to consider? It doesn't need to be grounded by wire or anything, does it?

 

[AK9R]

The X30 has an SO239-style connector so whatever cable you use will need a PL259 connector. Since your handheld doesn't use that style of connector, you'll probably need an adapter.

 

[SpaceForceCmdr]

Thanks! Forgot to mention, I bought some adapters as well, so should be good.

 

[MTS2000des]

All antennas should have a surge suppressor, such as a PolyPhaser in line- even ones in your attic, to protect connected equipment. This is of course, best practices. Keep in mind, feedline quality is paramount if you want to hear weak signals, especially on UHF/700/800. LMR400 is a minimum for anything over 25 feet. The other thing to consider is adding a short jumper to reduce strain on a portable antenna jack. Rigid cable like LMR can put a lot of stress combined with RF adapter to the tiny SMA jack on most radios.

 

[SpaceForceCmdr]

Right now, I've got RG58 running down from the antenna to my room. I think it's a 50' cable. I actually have 2 of these cables. One goes to my SDR from my MLA loop for listening, and the other comes from the X30 which I will mainly use with my FT60 HT. I've been using the HT to connect to local repeaters and listen in, and I just managed to make a few contacts using Echolink and Allstar. So, for these purposes, do you think it'd be worth switching the cables to LMR? If not, do you think the RG58 that I'm using now is too stiff for the HT connection? It seems doable, but a bit awkward.

At this point, I'm thinking about two things at the minimum--getting a short jumper cable (maybe 6ft?) and getting an external mic for the HT. The PTT button is OK, but I think the external mic would be more comfortable (and maybe provide better audio, too?) Any suggestions? Thanks

 

[popnokick]

The Diamond X30 is a dual band ham antenna for 2M and 70cm. So you needn't worry about cable losses in the 700 / 800 mHz range because that antenna is not going to do well there anyway. However, any use of RG58 for more than a typical mobile installation (20 feet or less) is a huge loss on VHF / UHF. At 50 feet of cable, RG58 loss is over 6db at 440 mHz and over 3 dB at 145 mHz. That's a huge amount of your transmitted and received signal. So yes, replace the RG58. LMR400 would drop that loss to a little over 1dB at 50 feet and 440mHz, and even better at 145 mHz. BTW - Not so much loss on HF for your SDR & MLA loop so you can leave that 50 ft run of RG58 in place.

 

[SpaceForceCmdr]

That's good to know, thanks! Since the HT is only 5 watts, I'm definitely looking to get all the ooomph out of it that I can, so I'll look into the LMR cable. What's the typical thin cable that's use for a jumper, and would adding that into the mix cause a significant loss?

 

[popnokick]

The formula goes like this for the physical diameter of coax cables: The thinner the cable the higher the signal loss. Howcum? Laws of physics. Look at any coax cable spec / loss / diameter table and you'll begin to get the idea. There are a slew of them online (stay with the ones from the major manufacturers (Andrew, Belden, Davis, Times, etc). There are also apps for your cellphone allowing quick lookups but again cross-check the data with mfr info.

 

[SpaceForceCmdr]

The LMR400 sounds great, but I see it's pricey. 50' would cost almost as much as my radio! It seems like I can hit my local repeaters as is, so not sure it would be very cost effective.

 

[AK9R]

It seems like I can hit my local repeaters as is...

"Hitting" a repeater and being able to carry on a conversation with another repeater user are two different things. You may be hitting the repeater, but your signal may still have low signal strength and be noisy to other repeater users.

Here's a suggested progression of coax types for a VHF/UHF home station: RG-58, RG-8X, LMR-240, RG-8, LMR-400. Each step up the progression comes with a higher cost.

There are several coax loss calculators on the Internet. For this discussion, I'm going to use the one at: Coax Loss Calculator | KV5R.COM

For all of these calculations, here is the power delivered to the antenna assuming 50 feet of coax, transmitting on 146 MHz at 5 watts with a 1.2:1 SWR, and ignoring the losses in connectors:

Cable	Power (watts)
RG-58C (Belden 8259)	2.3
RG-8X (Belden 9258)	3.1
Times LMR-240	3.5
RG-8 (Belden 8237)	3.8
Times LMR-400	4.2

Now, let's move to 446 MHz and use the same parameters:

Cable	Power (watts)
RG-58C (Belden 8259)	1.1
RG-8X (Belden 9258)	1.9
Times LMR-240	2.7
RG-8 (Belden 8237)	3.0
Times LMR-400	3.7

Coax loss is not a trivial thing. I wouldn't dismiss it.

 

[Ubbe]

Don't forget to include RG6. That calculator says, after using 1.5:1 in SWR when using a 75 ohm coax to a 50 ohm load, will result in 3,3W power at 146Mhz and 2,4W at 446MHz. And RG6 are even cheaper to buy than RG58. It's worth a try at 16$ for 50ft. 50' Feet, Black RG6 Coaxial Cable (Coax Cable) with Weather Proof Connectors, F81 / RF, Digital Coax - AV, Cable TV, Antenna, and Satellite, CL2 Rated, 50 Foot : Electronics (amazon.com)

/Ubbe

 

[AK9R]

That calculator says, after using 1.5:1 in SWR when using a 75 ohm coax to a 50 ohm load...

I'm curious, if you start with a transmitter expecting a 50 ohm load, transition to RG6, run a length of cable, then transition back to the 50 ohm load, how many SWR bumps do you get? Many years ago, there was a company making adapters that would allow you to connect common cable TV hardline, which is also 75 ohm, to common 50 ohm RF devices. These adapters handled the 75 ohm to 50 ohm transformation or vice versa.