Curt Nixon wrote:

Good Morning All:

So, after this last week of ISS fun, I have the bug to upgrade into some simple satellite work. I will be confined to simple FM untill I can upgrade to all-mode rigs. My question is on coax and preamps.

I will use a pair of vertically polarized yagis to begin with. One for 144MHz and one on 70cm. I have some LMR 400 I got for the ISS project on 144 but it is so stiff, I didn't use it.

I built a simple "Arrow-style" antenna using the WA5VJB Cheap Yagi designs. One on 2m, one for 70cm, at right angles to each other, with an HB9ABX-design diplexer for the two. I use this handheld with my Kenwood TH-F7E HT and get into AO-51, SO-50 and AO-27 without any real difficult. Total time for construction about an hour ;-)

If you've got an antenna analyser or even just a good SWR meter, it will help a lot with getting the 2m part right. I didn't bother tuning the diplexer much for 70cm because the MFJ-259 antenna analyser I was using didn't cover UHF - so I just woke up a 70cm repeater on the other side of town and tuned until I could hear it best.

I find it hard to get into AO-51 when it's busy and people are hammering it with huge stacked arrays of antennas. When it's in QRP mode I get in no bother at all, with good reports from all over Europe. Not bad for an aerial build out of a bit of scrap wood, some brazing rods and a few feet of hydraulic pipe ;-)

Gordon

Curt,

I'll add my comments to those already given.

At 05:00 AM 10/25/2008, Curt Nixon wrote:

Good Morning All:

So, after this last week of ISS fun, I have the bug to upgrade into some simple satellite work. I will be confined to simple FM untill I can upgrade to all-mode rigs. My question is on coax and preamps.

I will use a pair of vertically polarized yagis to begin with. One for 144MHz and one on 70cm. I have some LMR 400 I got for the ISS project on 144 but it is so stiff, I didn't use it.

1. If you use LMR 400, do you add flexible sections at the antenna end

and in the shack, using LMR400UF? Or, should I just use all UF and forget the additional connections? The cost of the additional connectors (N) both in loss and $$ is probably advantage $ for UF. Not sure about the loss potential for adding two sets of interface connections.

I use LMR-400 with LMR-400UF jumpers to go around my az-el rotors. Losses in properly made connectors is negligible and the extra loss in a few feet of LMR-400UF is also negligible. It does cost you a few more connectors. BTW this is what I am using for the Rx side of me 2m-eme system. I do use N-female connectors one end of the jumper to eliminate having to insert a "barrel" adapter between two male connectors. N connectors are very good on all frequencies in use on satellites and have some wx-sealing properties (but one should still use two layers of electrical tape or coax seal or the like).

2. With a 5-7 element yagi on 144, is it really necessary to use low

loss coax as a opposed to 8x or 8x mini. Runs here are 35' if munted at 12' and 60' if mounted to roof tower at about 20'

35-ft of mini-8 (RG-8x) still is lossy so it is better to use low loss cable. The longer run it becomes more important. Realise that in transmit on 145-MHz you will lose RF power in the coax. If you only have a 5w HT that might become critical. If you have a 10 or 25 or 50w radio, you have power to throw away so on Tx the mini-8 would probably be fine.

3. On 70cm, I plan to add a mast preamp, but will use the yagi

"barefoot" to begin with. With a preamp at the antenna, is low loss coax still required or can the cost increment be put to better use in the preamp to begin with? The preamp of course also gives a convenient place for a connector interface from stiff to flexible if desired.

Once you have a preamp at the antenna, then RG-58 is adequate between the preamp and radio. If the preamp is used in the radio shack after a run of coax then low-loss cable will make a huge difference. But seriously, the preamp belongs at the antenna or you are throwing away most of the advantatge that the low noise figure provides.

Without a preamp low loss coax is important for the same reasons as given above about using the preamp in the shack. Using the LMR-400 would make a lot of difference on the UHF Rx side. Beyond a run of 75 or 100 feet maximum, you will do better with 1/2 or 7/8 inch hardline. This is another good reason to just mount the preamp at the antenna (you do not need "super" coax).

On my eme system Hardline is used on the Tx side to get my RF to the antennas with minimum loss. The preamp is mounted close the antenna so I run 150-feet of LMR-400 back to the receiver. EME requires much more attention to miniming losses and maximizing performance.

*********************************************************** 73, Ed - KL7UW BP40iq, 6m - 3cm 144-EME: FT-847, mgf-1801, 4x-xp20, 185w 1296-EME: DEMI-Xvtr, 0.30 dBNF, 4.9m dish, 60W http://www.kl7uw.com AK VHF-Up Group NA Rep. for DUBUS: [email protected] ***********************************************************